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| author | Roger Frank <rfrank@pglaf.org> | 2025-10-15 04:44:49 -0700 |
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| committer | Roger Frank <rfrank@pglaf.org> | 2025-10-15 04:44:49 -0700 |
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diff --git a/14558-h/14558-h.htm b/14558-h/14558-h.htm new file mode 100644 index 0000000..210b84d --- /dev/null +++ b/14558-h/14558-h.htm @@ -0,0 +1,24682 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> + <meta name="generator" content= + "HTML Tidy for Windows (vers 1st August 2004), see www.w3.org" /> + + <title>The Project Gutenberg eBook of Darwinism, by Alfred Russel + Wallace.</title> +<style type="text/css"> +/*<![CDATA[ XML blockout */ +<!-- + p { margin-top: .75em; + text-align: justify; + margin-bottom: .75em; + } + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; + } + hr { width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; + } + + table {margin-left: auto; margin-right: auto;} + + body{margin-left: 10%; + margin-right: 10%; + } + + .linenum {position: absolute; top: auto; left: 4%;} /* poetry number */ + .blockquot{margin-left: 5%; margin-right: 10%; font-size: smaller;} + .pagenum {position: absolute; left: 92%; font-size: smaller; text-align: right;} /* page numbers */ + .sidenote {width: 20%; padding-bottom: .5em; padding-top: .5em; + padding-left: .5em; padding-right: .5em; margin-left: 1em; + float: right; clear: right; margin-top: 1em; + font-size: smaller; background: #eeeeee; border: dashed 1px;} + + .bb {border-bottom: solid 2px;} + .bl {border-left: solid 2px;} + .bt {border-top: solid 2px;} + .br {border-right: solid 2px;} + .bbox {border: solid 2px;} + + .center {text-align: center;} + .smcap {font-variant: small-caps;} + + .figcenter {margin: auto; text-align: center;} + + .figleft {float: left; clear: left; margin-left: 0; margin-bottom: 1em; margin-top: + 1em; margin-right: 1em; padding: 0; text-align: center;} + + .figright {float: right; clear: right; margin-left: 1em; margin-bottom: 1em; + margin-top: 1em; margin-right: 0; padding: 0; text-align: center;} + + .footnotes {border: dashed 1px; font-size: smaller; font-size: smaller;} + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + .footnote .label {position: absolute; right: 84%; text-align: right;} + .fnanchor {vertical-align: super; font-size: .8em; text-decoration: none;} + + .poem {margin-left:10%; margin-right:10%; text-align: left; font-size: smaller;} + .poem br {display: none;} + .poem .stanza {margin: 1em 0em 1em 0em;} + .poem span {display: block; margin: 0; padding-left: 3em; text-indent: -3em;} + .poem span.i2 {display: block; margin-left: 2em;} + .poem span.i4 {display: block; margin-left: 1em;} + // --> + /* XML end ]]>*/ +</style> +</head> + +<body> +<div>*** START OF THE PROJECT GUTENBERG EBOOK 14558 ***</div> + + <h1><a name="Page_-15" id="Page_-15"></a>DARWINISM</h1> + + <h2>AN EXPOSITION OF THE<br /> + THEORY OF NATURAL SELECTION<br /> + WITH SOME OF ITS APPLICATIONS</h2> + + <h3>BY</h3> + + <h2>ALFRED RUSSEL WALLACE<br /> + <span style='font-size: smaller;'>LL.D., F.L.S., ETC.</span></h2> + + <h4>WITH A PORTRAIT OF THE AUTHOR, MAP AND ILLUSTRATIONS</h4> + + <h5>MACMILLAN AND CO.<br /> + LONDON AND NEW YORK<br /> + 1889</h5> + <hr style='width: 45%;' /> + + <div class="figcenter" style="width: 298px;"> + <a name="frontispiece" id="frontispiece"></a> <img src= + "images/frontispiece.jpg" width="298" height="472" alt= + "Alfred R. Wallace" title="Alfred R. Wallace" /> <b>Alfred R. + Wallace</b> + </div> + <hr style='width: 45%;' /> + + <h2><a name="Page_-14" id="Page_-14"></a><a name= + "PREFACE_TO_SECOND_EDITION" id= + "PREFACE_TO_SECOND_EDITION"></a>PREFACE TO SECOND EDITION</h2> + + <p><a name="Page_-13" id="Page_-13"></a>The present edition is a + reprint of the first, with a few verbal corrections and the + alteration of some erroneous or doubtful statements. Of these + latter the following are the most important:—</p> + + <p><i>P.</i> <a href='#Page_30'>30</a>. The statement as to the + fulmar petrel, which Professor A. Newton assures me is erroneous, + has been modified.</p> + + <p><i>P.</i> <a href='#Page_34'>34</a>. A note is added as to + Darwin's statement about the missel and song-thrushes in + Scotland.</p> + + <p><i>P.</i> <a href='#Page_172'>172</a>. An error as to the + differently-coloured herds of cattle in the Falkland Islands, is + corrected.</p> + + <p><span style="margin-left: 2em;">PARKSTONE, DORSET</span><br /> + <span style="margin-left: 2em;"><i>August, + 1889</i>.</span><br /></p> + <hr style="width: 65%;" /> + + <h2><a name="Page_-12" id="Page_-12"></a><a name="Page_-11" id= + "Page_-11"></a><a name="PREFACE_TO_FIRST_EDITION" id= + "PREFACE_TO_FIRST_EDITION"></a>PREFACE TO FIRST EDITION</h2> + + <p>The present work treats the problem of the Origin of Species + on the same general lines as were adopted by Darwin; but from the + standpoint reached after nearly thirty years of discussion, with + an abundance of new facts and the advocacy of many new or old + theories.</p> + + <p>While not attempting to deal, even in outline, with the vast + subject of evolution in general, an endeavour has been made to + give such an account of the theory of Natural Selection as may + enable any intelligent reader to obtain a clear conception of + Darwin's work, and to understand something of the power and range + of his great principle.</p> + + <p>Darwin wrote for a generation which had not accepted + evolution, and which poured contempt on those who upheld the + derivation of species from species by any natural law of descent. + He did his work so well that "descent with modification" is now + universally accepted as the order of nature in the organic world; + and the rising generation of naturalists can hardly realise the + novelty of this idea, or that their fathers considered it a + scientific heresy to be condemned rather than seriously + discussed.</p> + + <p>The objections now made to Darwin's theory apply, solely, to + the particular means by which the change of species has been + brought about, not to the fact of that change. The objectors seek + to minimise the agency of natural selection and to subordinate it + to laws of variation, of use and disuse, of intelligence, and of + heredity. These views and objections are urged with much force + and more confidence, and for the<a name="Page_-10" id= + "Page_-10"></a> most part by the modern school of laboratory + naturalists, to whom the peculiarities and distinctions of + species, as such, their distribution and their affinities, have + little interest as compared with the problems of histology and + embryology, of physiology and morphology. Their work in these + departments is of the greatest interest and of the highest + importance, but it is not the kind of work which, by itself, + enables one to form a sound judgment on the questions involved in + the action of the law of natural selection. These rest mainly on + the external and vital relations of species to species in a state + of nature—on what has been well termed by Semper the + "physiology of organisms," rather than on the anatomy or + physiology of organs.</p> + <hr style='width: 45%;' /> + + <p>It has always been considered a weakness in Darwin's work that + he based his theory, primarily, on the evidence of variation in + domesticated animals and cultivated plants. I have endeavoured to + secure a firm foundation for the theory in the variations of + organisms in a state of nature; and as the exact amount and + precise character of these variations is of paramount importance + in the numerous problems that arise when we apply the theory to + explain the facts of nature, I have endeavoured, by means of a + series of diagrams, to exhibit to the eye the actual variations + as they are found to exist in a sufficient number of species. By + doing this, not only does the reader obtain a better and more + precise idea of variation than can be given by any number of + tabular statements or cases of extreme individual variation, but + we obtain a basis of fact by which to test the statements and + objections usually put forth on the subject of specific + variability; and it will be found that, throughout the work, I + have frequently to appeal to these diagrams and the facts they + illustrate, just as Darwin was accustomed to appeal to the facts + of variation among dogs and pigeons.</p> + + <p><a name="Page_-9" id="Page_-9"></a>I have also made what + appears to me an important change in the arrangement of the + subject. Instead of treating first the comparatively difficult + and unfamiliar details of variation, I commence with the Struggle + for Existence, which is really the fundamental phenomenon on + which natural selection depends, while the particular facts which + illustrate it are comparatively familiar and very interesting. It + has the further advantage that, after discussing variation and + the effects of artificial selection, we proceed at once to + explain how natural selection acts.</p> + + <p>Among the subjects of novelty or interest discussed in this + volume, and which have important bearings on the theory of + natural selection, are: (1) A proof that all <i>specific</i> + characters are (or once have been) either useful in themselves or + correlated with useful characters (Chap. VI); (2) a proof that + natural selection can, in certain cases, increase the sterility + of crosses (Chap. VII); (3) a fuller discussion of the colour + relations of animals, with additional facts and arguments on the + origin of sexual differences of colour (Chaps. VIII-X); (4) an + attempted solution of the difficulty presented by the occurrence + of both very simple and very complex modes of securing the + cross-fertilisation of plants (Chap. XI); (5) some fresh facts + and arguments on the wind-carriage of seeds, and its bearing on + the wide dispersal of many arctic and alpine plants (Chap. XII); + (6) some new illustrations of the non-heredity of acquired + characters, and a proof that the effects of use and disuse, even + if inherited, must be overpowered by natural selection (Chap. + XIV); and (7) a new argument as to the nature and origin of the + moral and intellectual faculties of man (Chap. XV).</p> + <hr style='width: 45%;' /> + + <p>Although I maintain, and even enforce, my differences from + some of Darwin's views, my whole work tends forcibly to + illustrate the overwhelming importance of Natural Selection over + all other agencies in the production of new species. <a name= + "Page_-8" id="Page_-8"></a>I thus take up Darwin's earlier + position, from which he somewhat receded in the later editions of + his works, on account of criticisms and objections which I have + endeavoured to show are unsound. Even in rejecting that phase of + sexual selection depending on female choice, I insist on the + greater efficacy of natural selection. This is pre-eminently the + Darwinian doctrine, and I therefore claim for my book the + position of being the advocate of pure Darwinism.</p> + + <p>I wish to express my obligation to Mr. Francis Darwin for + lending me some of his father's unused notes, and to many other + friends for facts or information, which have, I believe, been + acknowledged either in the text or footnotes. Mr. James Sime has + kindly read over the proofs and given me many useful suggestions; + and I have to thank Professor Meldola, Mr. Hemsley, and Mr. E.B. + Poulton for valuable notes or corrections in the later chapters + in which their special subjects are touched upon.</p> + + <p>GODALMING, <i>March 1889</i>.</p> + <hr style="width: 65%;" /> + + <h2><a name="Page_-7" id="Page_-7"></a>CONTENTS</h2> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#PREFACE_TO_SECOND_EDITION"><b>PREFACE TO SECOND + EDITION</b></a></p> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#PREFACE_TO_FIRST_EDITION"><b>PREFACE TO FIRST + EDITION</b></a></p> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#LIST_OF_ILLUSTRATIONS"><b>LIST OF + ILLUSTRATIONS</b></a></p> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_I"><b>CHAPTER I</b></a></p> + + <p style='font-weight:bold;'>WHAT ARE "SPECIES" AND WHAT IS MEANT + BY THEIR "ORIGIN"</p> + + <div class="blockquot"> + <p>Definition of species—Special creation—The early + transmutationists—Scientific opinion before + Darwin—The problem before Darwin—The change of + opinion effected by Darwin—The Darwinian + theory—Proposed mode of treatment of the subject</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_II"><b>CHAPTER II</b></a></p> + + <p style='font-weight:bold;'>THE STRUGGLE FOR EXISTENCE</p> + + <div class="blockquot"> + <p>Its importance—The struggle among plants—Among + animals—Illustrative cases—Succession of trees in + forests of Denmark—The struggle for existence on the + Pampas—Increase of organisms in a geometrical + ratio—Examples of rapid increase of animals—Rapid + increase and wide spread of plants—Great fertility not + essential to rapid increase—Struggle between closely + allied species most severe—The ethical aspect of the + struggle for existence</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_III"><b>CHAPTER III</b></a></p> + + <p style='font-weight:bold;'>THE VARIABILITY OF SPECIES IN A + STATE OF NATURE</p> + + <div class="blockquot"> + <p>Importance of variability—Popular ideas regarding + it—Variability of the lower animals—The variability + of insects—Variation among lizards<a name="Page_-6" id= + "Page_-6"></a>Variation among birds—Diagrams of + bird-variation—Number of varying + individuals—Variation in the mammalia—Variation in + internal organs—Variations in the skull—Variations + in the habits of animals—The variability of + plants—Species which vary little—Concluding + remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_IV"><b>CHAPTER IV</b></a></p> + + <p style='font-weight:bold;'>VARIATION OF DOMESTICATED ANIMALS + AND CULTIVATED PLANTS</p> + + <div class="blockquot"> + <p>The facts of variation and artificial selection—Proofs + of the generality of variation—Variations of apples and + melons—Variations of flowers—Variations of domestic + animals—Domestic + pigeons—Acclimatisation—Circumstances favourable to + selection by man—Conditions favourable to + variation—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_V"><b>CHAPTER V</b></a></p> + + <p style='font-weight:bold;'>NATURAL SELECTION BY VARIATION AND + SURVIVAL OF THE FITTEST</p> + + <div class="blockquot"> + <p>Effect of struggle for existence under unchanged + conditions—The effect under change of + conditions—Divergence of character—In + insects—In birds—In mammalia—Divergence leads + to a maximum of life in each area—Closely allied species + inhabit distinct areas—Adaptation to conditions at + various periods of life—The continued existence of low + forms of life—Extinction of low types among the higher + animals—Circumstances favourable to the origin of new + species—Probable origin of the dippers—The + importance of isolation—On the advance of organisation by + natural selection—Summary of the first five chapters</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_VI"><b>CHAPTER VI</b></a></p> + + <p style='font-weight:bold;'>DIFFICULTIES AND OBJECTIONS</p> + + <div class="blockquot"> + <p>Difficulty as to smallness of variations—As to the + right variations occurring when required—The beginnings + of important organs—The mammary glands—The eyes of + flatfish—Origin of the eye—Useless or non-adaptive + characters—Recent extension of the region of utility in + <a name="Page_-5" id="Page_-5"></a>plants—The same in + animals—Uses of tails—Of the horns of deer—Of + the scale-ornamentation of reptiles—Instability of + non-adaptive characters—Delboeuf's law—No + "specific" character proved to be useless—The swamping + effects of intercrossing—Isolation as preventing + intercrossing—Gulick on the effects of + isolation—Cases in which isolation is ineffective</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_VII"><b>CHAPTER VII</b></a></p> + + <p style='font-weight:bold;'>ON THE INFERTILITY OF CROSSES + BETWEEN DISTINCT SPECIES AND THE USUAL STERILITY OF THEIR HYBRID + OFFSPRING</p> + + <div class="blockquot"> + <p>Statement of the problem—Extreme susceptibility of the + reproductive functions—Reciprocal + crosses—Individual differences in respect to + cross-fertilisation—Dimorphism and trimorphism among + plants—Cases of the fertility of hybrids and of the + infertility of mongrels—The effects of close + interbreeding—Mr. Huth's objections—Fertile hybrids + among animals—Fertility of hybrids among + plants—Cases of sterility of mongrels—Parallelism + between crossing and change of conditions—Remarks on the + facts of hybridity—Sterility due to changed conditions + and usually correlated with other characters—Correlation + of colour with constitutional peculiarities—The isolation + of varieties by selective association—The influence of + natural selection upon sterility and + fertility—Physiological selection—Summary and + concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_VIII"><b>CHAPTER VIII</b></a></p> + + <p style='font-weight:bold;'>THE ORIGIN AND USES OF COLOUR IN + ANIMALS</p> + + <div class="blockquot"> + <p>The Darwinian theory threw new light on organic + colour—The problem to be solved—The constancy of + animal colour indicates utility—Colour and + environment—Arctic animals white—Exceptions prove + the rule—Desert, forest, nocturnal, and oceanic + animals—General theories of animal colour—Variable + protective colouring—Mr. Poulton's + experiments—Special or local colour + adaptations—Imitation of particular objects—How + they have been produced—Special protective colouring of + butterflies—Protective resemblance among marine + animals—Protection by terrifying enemies—Alluring + coloration—The coloration of birds' eggs—Colour as + a means of recognition—Summary of the preceding + exposition—Influence of locality or of climate on + colour—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a name="Page_-4" id="Page_-4"></a><a href= + "#CHAPTER_IX"><b>CHAPTER IX</b></a></p> + + <p style='font-weight:bold;'>WARNING COLORATION AND MIMICRY</p> + + <div class="blockquot"> + <p>The skunk as an example of warning coloration—Warning + colours among + insects—Butterflies—Caterpillars—Mimicry—How + mimicry has been produced—Heliconidae—Perfection of + the imitation—Other cases of mimicry among + Lepidoptera—Mimicry among protected groups—Its + explanation—Extension of the principle—Mimicry in + other orders of insects—Mimicry among the + vertebrata—Snakes—The rattlesnake and the + cobra—Mimicry among birds—Objections to the theory + of mimicry—Concluding remarks on warning colours and + mimicry</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_X"><b>CHAPTER X</b></a></p> + + <p style='font-weight:bold;'>COLOURS AND ORNAMENTS CHARACTERISTIC + OF SEX</p> + + <div class="blockquot"> + <p>Sex colours in the mollusca and crustacea—In + insects—In butterflies and moths—Probable causes of + these colours—Sexual selection as a supposed + cause—Sexual coloration of birds—Cause of dull + colours of female birds—Relation of sex colour to nesting + habits—Sexual colours of other vertebrates—Sexual + selection by the struggles of males—Sexual characters due + to natural selection—Decorative plumage of males and its + effect on the females—Display of decorative plumage by + the males—A theory of animal coloration—The origin + of accessory plumes—Development of accessory plumes and + their display—The effect of female preference will be + neutralised by natural selection—General laws of animal + coloration—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_XI"><b>CHAPTER XI</b></a></p> + + <p style='font-weight:bold;'>THE SPECIAL COLOURS OF PLANTS: THEIR + ORIGIN AND PURPOSE</p> + + <div class="blockquot"> + <p>The general colour relations of plants—Colours of + fruits—The meaning of nuts—Edible or attractive + fruits—The colours of flowers—Modes of securing + cross-fertilisation—The interpretation of the + facts—Summary <a name="Page_-3" id="Page_-3"></a>of + additional facts bearing on insect + fertilisation—Fertilisation of flowers by + birds—Self-fertilisation of flowers—Difficulties + and contradictions—Intercrossing not necessarily + advantageous—Supposed evil results of close + interbreeding—How the struggle for existence acts among + flowers—Flowers the product of insect + agency—Concluding remarks on colour in nature</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_XII"><b>CHAPTER XII</b></a></p> + + <p style='font-weight:bold;'>THE GEOGRAPHICAL DISTRIBUTION OF + ORGANISMS</p> + + <div class="blockquot"> + <p>The facts to be explained—The conditions which have + determined distribution—The permanence of + oceans—Oceanic and continental areas—Madagascar and + New Zealand—The teachings of the thousand-fathom + line—The distribution of marsupials—The + distribution of tapirs—Powers of dispersal as illustrated + by insular organisms—Birds and insects at + sea—Insects at great altitudes—The dispersal of + plants—Dispersal of seeds by the wind—Mineral + matter carried by the wind—Objections to the theory of + wind-dispersal answered—Explanation of north temperate + plants in the southern hemisphere—No proof of glaciation + in the tropics—Lower temperature not needed to explain + the facts—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_XIII"><b>CHAPTER XIII</b></a></p> + + <p style='font-weight:bold;'>THE GEOLOGICAL EVIDENCES OF + EVOLUTION</p> + + <div class="blockquot"> + <p>What we may expect—The number of known species of + extinct animals—Causes of the imperfection of the + geological record—Geological evidences of + evolution—Shells—Crocodiles—The rhinoceros + tribe—The pedigree of the horse tribe—Development + of deer's horns—Brain development—Local relations + of fossil and living animals—Cause of extinction of large + animals—Indications of general progress in plants and + animals—The progressive development of + plants—Possible cause of sudden late appearance of + exogens—Geological distribution of + insects—Geological succession of + vertebrata—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a name="Page_-2" id="Page_-2"></a><a href= + "#CHAPTER_XIV"><b>CHAPTER XIV</b></a></p> + + <p style='font-weight:bold;'>FUNDAMENTAL PROBLEMS IN RELATION TO + VARIATION AND HEREDITY</p> + + <div class="blockquot"> + <p>Fundamental difficulties and objections—Mr. Herbert + Spencer's factors of organic evolution—Disuse and effects + of withdrawal of natural selection—Supposed effects of + disuse among wild animals—Difficulty as to co-adaptation + of parts by variation and selection—Direct action of the + environment—The American school of + evolutionists—Origin of the feet of the + ungulates—Supposed action of animal + intelligence—Semper on the direct influence of the + environment—Professor Geddes's theory of variation in + plants—Objections to the theory—On the origin of + spines—Variation and selection overpower the effects of + use and disuse—Supposed action of the environment in + imitating variations—Weismann's theory of + heredity—The cause of variation—The non-heredity of + acquired characters—The theory of + instinct—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#CHAPTER_XV"><b>CHAPTER XV</b></a></p> + + <p style='font-weight:bold;'>DARWINISM APPLIED TO MAN</p> + + <div class="blockquot"> + <p>General identity of human and animal + structure—Rudiments and variations showing relation of + man to other mammals—The embryonic development of man and + other mammalia—Diseases common to man and the lower + animals—The animals most nearly allied to man—The + brains of man and apes—External differences of man and + apes—Summary of the animal characteristics of + man—The geological antiquity of man—The probable + birthplace of man—The origin of the moral and + intellectual nature of man—The argument from + continuity—The origin of the mathematical + faculty—The origin of the musical and artistic + faculties—Independent proof that these faculties have not + been developed by natural selection—The interpretation of + the facts—Concluding remarks</p> + </div> + + <p style='font-weight:bold; margin-top:1.5em'> + <a href="#INDEX"><b>INDEX</b></a></p> + <hr style="width: 65%;" /> + + <h2><a name="LIST_OF_ILLUSTRATIONS" id= + "LIST_OF_ILLUSTRATIONS"></a><a name="Page_-1" id= + "Page_-1"></a>LIST OF ILLUSTRATIONS</h2> + + <p><span style="margin-left: 2em;"><a href= + "#frontispiece">PORTRAIT OF AUTHOR</a></span><br /> + <span style="margin-left: 2em;">MAP SHOWING THE 1000-FATHOM + LINE</span><br /> + <span style="margin-left: 2em;"><a href="#fig01">1.</a> + DIAGRAM OF VARIATIONS OF LACERTA MURALIS</span><br /> + <span style="margin-left: 2em;"><a href="#fig02">2.</a> + " VARIATION OF LIZARDS</span><br /> + <span style="margin-left: 2em;"><a href="#fig03">3.</a> + " VARIATION OF WINGS AND TAIL OF + BIRDS</span><br /> + <span style="margin-left: 2em;"><a href="#fig04">4.</a> + " VARIATION OF DOLICHONYX + ORYZIVORUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig05">5.</a> + " VARIATION OF AGELAEUS + PHOENICEUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig06">6.</a> + " VARIATION OF CARDINALIS + VIRGINIANUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig07">7.</a> + " VARIATION OF TARSUS AND + TOES</span><br /> + <span style="margin-left: 2em;"><a href="#fig08">8.</a> + " VARIATION OF BIRDS IN LEYDEN + MUSEUM</span><br /> + <span style="margin-left: 2em;"><a href="#fig09">9.</a> + " VARIATION OF ICTERUS + BALTIMORE</span><br /> + <span style="margin-left: 2em;"><a href="#fig10">10.</a> + " VARIATION OF AGELAEUS + PHOENICEUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig11">11.</a> + " CURVES OF VARIATION</span><br /> + <span style="margin-left: 2em;"><a href="#fig12">12.</a> + " VARIATION OF CARDINALIS + VIRGINIANUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig13">13.</a> + " VARIATION OF SCIURUS + CAROLINENSIS</span><br /> + <span style="margin-left: 2em;"><a href="#fig14">14.</a> + " VARIATION OF SKULLS OF + WOLF</span><br /> + <span style="margin-left: 2em;"><a href="#fig15">15.</a> + " VARIATION OF SKULLS OF URSUS + LABIATUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig16">16.</a> + " VARIATION OF SKULLS OF SUS + CRISTATUS</span><br /> + <span style="margin-left: 2em;"><a href="#fig17">17.</a> PRIMULA + VERIS (Cowslip). From Darwin's <i>Forms of + Flowers</i></span><br /> + <span style="margin-left: 2em;"><a href="#fig18">18.</a> GAZELLA + SOEMMERRINGI (to show recognition marks)</span><br /> + <span style="margin-left: 2em;"><a href="#fig19">19.</a> + RECOGNITION MARKS OF AFRICAN PLOVERS</span><br /> + <span style="margin-left: 4em;">(from Seebohm's + <i>Charadriadae</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig20">20.</a> + RECOGNITION OF OEDICNEMUS VERMICULATUS AND OE. + SENEGALENSIS</span><br /> + <a name="Page_0" id="Page_0"></a> <span style= + "margin-left: 4em;">(from Seebohm's + <i>Charadriadae</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig21">21.</a> + RECOGNITION OF CURSORIUS CHALCOPTERUS AND C. + GALLICUS</span><br /> + <span style="margin-left: 4em;">(from Seebohm's + <i>Charadriadae</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig22">22.</a> + RECOGNITION OF SCOLOPAX MEGALA AND S. STENURA</span><br /> + <span style="margin-left: 4em;">(from Seebohm's + <i>Charadriadae</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig23">23.</a> METHONA + PSIDII AND LEPTALIS ORISE</span><br /> + <span style="margin-left: 2em;"><a href="#fig24">24.</a> + OPTHALMIS LINCEA AND ARTAXA SIMULANS</span><br /> + <span style="margin-left: 4em;">(from the Official <i>Narrative + of the Voyage of the Challenger</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig25">25.</a> WINGS OF + ITUNA ILIONE AND THYRIDIA MEGISTO</span><br /> + <span style="margin-left: 4em;">(from <i>Proceedings of the + Entomological Society</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig26">26.</a> MYGNIMIA + AVICULUS AND COLOBORHOMBUS FASCIATIPENNIS</span><br /> + <span style="margin-left: 2em;"><a href="#fig27">27.</a> + MIMICKING INSECTS FROM THE PHILIPPINES</span><br /> + <span style="margin-left: 4em;">(from Semper's <i>Animal + Life</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig28">28.</a> MALVA + SYLVESTRIS AND M. ROTUNDIFOLIA</span><br /> + <span style="margin-left: 4em;">(from Lubbock's <i>British Wild + Flowers in Relation to Insects</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig29">29.</a> LYTHRUM + SALICARIA, THREE FORMS OF</span><br /> + <span style="margin-left: 4em;">(from Lubbock's <i>British Wild + Flowers in Relation to Insects</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig30">30.</a> ORCHIS + PYRAMIDALIS (from Darwin's <i>Fertilisation of + Orchids</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig31">31.</a> + HUMMING-BIRD FERTILISING MARCGRAVIA NEPENTHOIDES</span><br /> + <span style="margin-left: 2em;"><a href="#fig32">32.</a> DIAGRAM + OF MEAN HEIGHT OF LAND AND DEPTH OF OCEANS</span><br /> + <span style="margin-left: 2em;"><a href="#fig33">33.</a> + GEOLOGICAL DEVELOPMENT OF THE HORSE TRIBE</span><br /> + <span style="margin-left: 4em;">(from Huxley's <i>American + Addresses</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig34">34.</a> DIAGRAM + ILLUSTRATING THE GEOLOGICAL DISTRIBUTION OF PLANTS</span><br /> + <span style="margin-left: 4em;">(from Ward's <i>Sketch of + Palaeobotany</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig35">35.</a> + TRANSFORMATION OF ARTEMIA SALINA TO A. MILHAUSENII</span><br /> + <span style="margin-left: 4em;">(from Semper's <i>Animal + Life</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig36">36.</a> + BRANCHIPUS STAGNALIS AND ARTEMIA SALINA</span><br /> + <span style="margin-left: 4em;">(from Semper's <i>Animal + Life</i>)</span><br /> + <span style="margin-left: 2em;"><a href="#fig37">37.</a> + CHIMPANZEE (TROGLODYTES NIGER)</span><br /></p> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_I" id="CHAPTER_I"></a><a name="Page_1" id= + "Page_1"></a>CHAPTER I</h2> + + <p style='font-weight:bold;'>WHAT ARE "SPECIES," AND WHAT IS + MEANT BY THEIR "ORIGIN"</p> + + <div class="blockquot"> + <p>Definition of species—Special creation—The early + Transmutationists—Scientific opinion before + Darwin—The problem before Darwin—The change of + opinion effected by Darwin—The Darwinian + theory—Proposed mode of treatment of the subject.</p> + </div> + + <p>The title of Mr. Darwin's great work is—<i>On the Origin + of Species by means of Natural Selection and the Preservation of + Favoured Races in the Struggle for Life</i>. In order to + appreciate fully the aim and object of this work, and the change + which it has effected not only in natural history but in many + other sciences, it is necessary to form a clear conception of the + meaning of the term "species," to know what was the general + belief regarding them at the time when Mr. Darwin's book first + appeared, and to understand what he meant, and what was generally + meant, by discovering their "origin." It is for want of this + preliminary knowledge that the majority of educated persons who + are not naturalists are so ready to accept the innumerable + objections, criticisms, and difficulties of its opponents as + proofs that the Darwinian theory is unsound, while it also + renders them unable to appreciate, or even to comprehend, the + vast change which that theory has effected in the whole mass of + thought and opinion on the great question of evolution.</p> + + <p>The term "species" was thus defined by the celebrated botanist + De Candolle: "A species is a collection of all the individuals + which resemble each other more than they resemble anything else, + which can by mutual fecundation <a name="Page_2" id= + "Page_2"></a>produce fertile individuals, and which reproduce + themselves by generation, in such a manner that we may from + analogy suppose them all to have sprung from one single + individual." And the zoologist Swainson gives a somewhat similar + definition: "A species, in the usual acceptation of the term, is + an animal which, in a state of nature, is distinguished by + certain peculiarities of form, size, colour, or other + circumstances, from another animal. It propagates, 'after its + kind,' individuals perfectly resembling the parent; its + peculiarities, therefore, are permanent."<a name="FNanchor_1_1" + id="FNanchor_1_1"></a><a href="#Footnote_1_1" class= + "fnanchor">[1]</a></p> + + <p>To illustrate these definitions we will take two common + English birds, the rook (Corvus frugilegus) and the crow (Corvus + corone). These are distinct <i>species</i>, because, in the first + place, they always differ from each other in certain slight + peculiarities of structure, form, and habits, and, in the second + place, because rooks always produce rooks, and crows produce + crows, and they do not interbreed. It was therefore concluded + that all the rooks in the world had descended from a single pair + of rooks, and the crows in like manner from a single pair of + crows, while it was considered impossible that crows could have + descended from rooks or <i>vice versâ</i>. The "origin" of + the first pair of each kind was a mystery. Similar remarks may be + applied to our two common plants, the sweet violet (Viola + odorata) and the dog violet (Viola canina). These also produce + their like and never produce each other or intermingle, and they + were therefore each supposed to have sprung from a single + individual whose "origin" was unknown. But besides the crow and + the rook there are about thirty other kinds of birds in various + parts of the world, all so much like our species that they + receive the common name of crows; and some of them differ less + from each other than does our crow from our rook. These are all + <i>species</i> of the genus Corvus, and were therefore believed + to have been always as distinct as they are now, neither more nor + less, and to have each descended from one pair of ancestral crows + of the same identical species, which themselves had an unknown + "origin." Of violets there are more than a hundred different + kinds in various parts of the world, all differing very slightly + from each other and forming distinct <a name="Page_3" id= + "Page_3"></a><i>species</i> of the genus Viola. But, as these + also each produce their like and do not intermingle, it was + believed that every one of them had always been as distinct from + all the others as it is now, that all the individuals of each + kind had descended from one ancestor, but that the "origin" of + these hundred slightly differing ancestors was unknown. In the + words of Sir John Herschel, quoted by Mr. Darwin, the origin of + such species was "the mystery of mysteries."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Early Transmutationists</i>.</p> + + <p>A few great naturalists, struck by the very slight difference + between many of these species, and the numerous links that exist + between the most different forms of animals and plants, and also + observing that a great many species do vary considerably in their + forms, colours, and habits, conceived the idea that they might be + all produced one from the other. The most eminent of these + writers was a great French naturalist, Lamarck, who published an + elaborate work, the <i>Philosophie Zoologique</i>, in which he + endeavoured to prove that all animals whatever are descended from + other species of animals. He attributed the change of species + chiefly to the effect of changes in the conditions of + life—such as climate, food, etc.—and especially to + the desires and efforts of the animals themselves to improve + their condition, leading to a modification of form or size in + certain parts, owing to the well-known physiological law that all + organs are strengthened by constant use, while they are weakened + or even completely lost by disuse. The arguments of Lamarck did + not, however, satisfy naturalists, and though a few adopted the + view that closely allied species had descended from each other, + the general belief of the educated public was, that each species + was a "special creation" quite independent of all others; while + the great body of naturalists equally held, that the change from + one species to another by any known law or cause was impossible, + and that the "origin of species" was an unsolved and probably + insoluble problem. The only other important work dealing with the + question was the celebrated <i>Vestiges of Creation</i>, + published anonymously, but now acknowledged to have been written + by the late Robert Chambers. In this work the action of general + laws was traced throughout the <a name="Page_4" id= + "Page_4"></a>universe as a system of growth and development, and + it was argued that the various species of animals and plants had + been produced in orderly succession from each other by the action + of unknown laws of development aided by the action of external + conditions. Although this work had a considerable effect in + influencing public opinion as to the extreme improbability of the + doctrine of the independent "special creation" of each species, + it had little effect upon naturalists, because it made no attempt + to grapple with the problem in detail, or to show in any single + case how the allied species of a genus could have arisen, and + have preserved their numerous slight and apparently purposeless + differences from each other. No clue whatever was afforded to a + law which should produce from any one species one or more + slightly differing but yet permanently distinct species, nor was + any reason given why such slight yet constant differences should + exist at all.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Scientific Opinion before Darwin.</i></p> + + <p>In order to show how little effect these writers had upon the + public mind, I will quote a few passages from the writings of Sir + Charles Lyell, as representing the opinions of the most advanced + thinkers in the period immediately preceding that of Darwin's + work. When recapitulating the facts and arguments in favour of + the invariability and permanence of species, he says: "The entire + variation from the original type which any given kind of change + can produce may usually be effected in a brief period of time, + after which no further deviation can be obtained by continuing to + alter the circumstances, though ever so gradually, indefinite + divergence either in the way of improvement or deterioration + being prevented, and the least possible excess beyond the defined + limits being fatal to the existence of the individual." In + another place he maintains that "varieties of some species may + differ more than other species do from each other without shaking + our confidence in the reality of species." He further adduces + certain facts in geology as being, in his opinion, "fatal to the + theory of progressive development," and he explains the fact that + there are so often distinct species in countries of similar + climate and vegetation by "<a name="Page_5" id= + "Page_5"></a>special creations" in each country; and these + conclusions were arrived at after a careful study of Lamarck's + work, a full abstract of which is given in the earlier editions + of the <i>Principles of Geology</i>.<a name="FNanchor_2_2" id= + "FNanchor_2_2"></a><a href="#Footnote_2_2" class= + "fnanchor">[2]</a></p> + + <p>Professor Agassiz, one of the greatest naturalists of the last + generation, went even further, and maintained not only that each + species was specially created, but that it was created in the + proportions and in the localities in which we now find it to + exist. The following extract from his very instructive book on + Lake Superior explains this view: "There are in animals peculiar + adaptations which are characteristic of their species, and which + cannot be supposed to have arisen from subordinate influences. + Those which live in shoals cannot be supposed to have been + created in single pairs. Those which are made to be the food of + others cannot have been created in the same proportions as those + which live upon them. Those which are everywhere found in + innumerable specimens must have been introduced in numbers + capable of maintaining their normal proportions to those which + live isolated and are comparatively and constantly fewer. For we + know that this harmony in the numerical proportions between + animals is one of the great laws of nature. The circumstance that + species occur within definite limits where no obstacles prevent + their wider distribution leads to the further inference that + these limits were assigned to them from the beginning, and so we + should come to the final conclusion that the order which prevails + throughout nature is intentional, that it is regulated by the + limits marked out on the first day of creation, and that it has + been maintained unchanged through ages with no other + modifications than those which the higher intellectual powers of + man enable him to impose on some few animals more closely + connected with him."<a name="FNanchor_3_3" id= + "FNanchor_3_3"></a><a href="#Footnote_3_3" class= + "fnanchor">[3]</a></p> + + <p>These opinions of some of the most eminent and influential + writers of the pre-Darwinian age seem to us, now, either + altogether obsolete or positively absurd; but they nevertheless + exhibit the mental condition of even the most advanced section of + scientific men on the problem of the <a name="Page_6" id= + "Page_6"></a>nature and origin of species. They render it clear + that, notwithstanding the vast knowledge and ingenious reasoning + of Lamarck, and the more general exposition of the subject by the + author of the <i>Vestiges of Creation</i>, the first step had not + been taken towards a satisfactory explanation of the derivation + of any one species from any other. Such eminent naturalists as + Geoffroy Saint Hilaire, Dean Herbert, Professor Grant, Von Buch, + and some others, had expressed their belief that species arose as + simple varieties, and that the species of each genus were all + descended from a common ancestor; but none of them gave a clue as + to the law or the method by which the change had been effected. + This was still "the great mystery." As to the further + question—how far this common descent could be carried; + whether distinct families, such as crows and thrushes, could + possibly have descended from each other; or, whether all birds, + including such widely distinct types as wrens, eagles, ostriches, + and ducks, could all be the modified descendants of a common + ancestor; or, still further, whether mammalia, birds, reptiles, + and fishes, could all have had a common origin;—these + questions had hardly come up for discussion at all, for it was + felt that, while the very first step along the road of + "transmutation of species" (as it was then called) had not been + made, it was quite useless to speculate as to how far it might be + possible to travel in the same direction, or where the road would + ultimately lead to.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Problem before Darwin</i>.</p> + + <p>It is clear, then, that what was understood by the "origin" or + the "transmutation" of species before Darwin's work appeared, was + the comparatively simple question whether the allied species of + each genus had or had not been derived from one another and, + remotely, from some common ancestor, by the ordinary method of + reproduction and by means of laws and conditions still in action + and capable of being thoroughly investigated. If any naturalist + had been asked at that day whether, supposing it to be clearly + shown that all the different species of each genus had been + derived from some one ancestral species, and that a full and + complete explanation were to be given of how each minute + difference in form, colour, or structure might have originated, + and how the <a name="Page_7" id="Page_7"></a>several + peculiarities of habit and of geographical distribution might + have been brought about—whether, if this were done, the + "origin of species" would be discovered, the great mystery + solved, he would undoubtedly have replied in the affirmative. He + would probably have added that he never expected any such + marvellous discovery to be made in his lifetime. But so much as + this assuredly Mr. Darwin has done, not only in the opinion of + his disciples and admirers, but by the admissions of those who + doubt the completeness of his explanations. For almost all their + objections and difficulties apply to those larger differences + which separate genera, families, and orders from each other, not + to those which separate one species from the species to which it + is most nearly allied, and from the remaining species of the same + genus. They adduce such difficulties as the first development of + the eye, or of the milk-producing glands of the mammalia; the + wonderful instincts of bees and of ants; the complex arrangements + for the fertilisation of orchids, and numerous other points of + structure or habit, as not being satisfactorily explained. But it + is evident that these peculiarities had their origin at a very + remote period of the earth's history, and no theory, however + complete, can do more than afford a probable conjecture as to how + they were produced. Our ignorance of the state of the earth's + surface and of the conditions of life at those remote periods is + very great; thousands of animals and plants must have existed of + which we have no record; while we are usually without any + information as to the habits and general life-history even of + those of which we possess some fragmentary remains; so that the + truest and most complete theory would not enable us to solve + <i>all</i> the difficult problems which the whole course of the + development of life upon our globe presents to us.</p> + + <p>What we may expect a true theory to do is to enable us to + comprehend and follow out in some detail those changes in the + form, structure, and relations of animals and plants which are + effected in short periods of time, geologically speaking, and + which are now going on around us. We may expect it to explain + satisfactorily most of the lesser and superficial differences + which distinguish one species from another. We may expect it to + throw light on the mutual relations of the <a name="Page_8" id= + "Page_8"></a>animals and plants which live together in any one + country, and to give some rational account of the phenomena + presented by their distribution in different parts of the world. + And, lastly, we may expect it to explain many difficulties and to + harmonise many incongruities in the excessively complex + affinities and relations of living things. All this the Darwinian + theory undoubtedly does. It shows us how, by means of some of the + most universal and ever-acting laws in nature, new species are + necessarily produced, while the old species become extinct; and + it enables us to understand how the continuous action of these + laws during the long periods with which geology makes us + acquainted is calculated to bring about those greater differences + presented by the distinct genera, families, and orders into which + all living things are classified by naturalists. The differences + which these present are all of the same <i>nature</i> as those + presented by the species of many large genera, but much greater + in <i>amount</i>; and they can all be explained by the action of + the same general laws and by the extinction of a larger or + smaller number of intermediate species. Whether the distinctions + between the higher groups termed Classes and Sub-kingdoms may be + accounted for in the same way is a much more difficult question. + The differences which separate the mammals, birds, reptiles, and + fishes from each other, though vast, yet seem of the same nature + as those which distinguish a mouse from an elephant or a swallow + from a goose. But the vertebrate animals, the mollusca, and the + insects, are so radically distinct in their whole organisation + and in the very plan of their structure, that objectors may not + unreasonably doubt whether they can all have been derived from a + common ancestor by means of the very same laws as have sufficed + for the differentiation of the various species of birds or of + reptiles.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Change of Opinion effected by Darwin</i>.</p> + + <p>The point I wish especially to urge is this. Before Darwin's + work appeared, the great majority of naturalists, and almost + without exception the whole literary and scientific world, held + firmly to the belief that <i>species</i> were realities, and had + not been derived from other species by any process accessible to + us; the different species of crow and of violet <a name="Page_9" + id="Page_9"></a>they are now, and to have originated by some + totally unknown process so far removed from ordinary reproduction + that it was usually spoken of as "special creation." There was, + then, no question of the origin of families, orders, and classes, + because the very first step of all, the "origin of species," was + believed to be an insoluble problem. But now this is all changed. + The whole scientific and literary world, even the whole educated + public, accepts, as a matter of common knowledge, the origin of + species from other allied species by the ordinary process of + natural birth. The idea of special creation or any altogether + exceptional mode of production is absolutely extinct! Yet more: + this is held also to apply to many higher groups as well as to + the species of a genus, and not even Mr. Darwin's severest + critics venture to suggest that the primeval bird, reptile, or + fish must have been "specially created." And this vast, this + totally unprecedented change in public opinion has been the + result of the work of one man, and was brought about in the short + space of twenty years! This is the answer to those who continue + to maintain that the "origin of species" is not yet discovered; + that there are still doubts and difficulties; that there are + divergencies of structure so great that we cannot understand how + they had their beginning. We may admit all this, just as we may + admit that there are enormous difficulties in the way of a + complete comprehension of the origin and nature of all the parts + of the solar system and of the stellar universe. But we claim for + Darwin that he is the Newton of natural history, and that, just + so surely as that the discovery and demonstration by Newton of + the law of gravitation established order in place of chaos and + laid a sure foundation for all future study of the starry + heavens, so surely has Darwin, by his discovery of the law of + natural selection and his demonstration of the great principle of + the preservation of useful variations in the struggle for life, + not only thrown a flood of light on the process of development of + the whole organic world, but also established a firm foundation + for all future study of nature.</p> + + <p>In order to show the view Darwin took of his own work, and + what it was that he alone claimed to have done, the concluding + passage of the introduction to the <i>Origin of</i> <a name= + "Page_10" id="Page_10"></a><i>Species</i> should be carefully + considered. It is as follows: "Although much remains obscure, and + will long remain obscure, I can entertain no doubt, after the + most deliberate and dispassionate judgment of which I am capable, + that the view which most naturalists until recently entertained + and which I formerly entertained—namely, that each species + has been independently created—is erroneous. I am fully + convinced that species are not immutable; but that those + belonging to what are called the same genera are lineal + descendants of some other and generally extinct species, in the + same manner as the acknowledged varieties of any one species are + the descendants of that species. Furthermore, I am convinced that + Natural Selection has been the most important, but not the + exclusive, means of modification."</p> + + <p>It should be especially noted that all which is here claimed + is now almost universally admitted, while the criticisms of + Darwin's works refer almost exclusively to those numerous + questions which, as he himself says, "will long remain + obscure."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Darwinian Theory</i>.</p> + + <p>As it will be necessary, in the following chapters, to set + forth a considerable body of facts in almost every department of + natural history, in order to establish the fundamental + propositions on which the theory of natural selection rests, I + propose to give a preliminary statement of what the theory really + is, in order that the reader may better appreciate the necessity + for discussing so many details, and may thus feel a more + enlightened interest in them. Many of the facts to be adduced are + so novel and so curious that they are sure to be appreciated by + every one who takes an interest in nature, but unless the need of + them is clearly seen it may be thought that time is being wasted + on mere curious details and strange facts which have little + bearing on the question at issue.</p> + + <p>The theory of natural selection rests on two main classes of + facts which apply to all organised beings without exception, and + which thus take rank as fundamental principles or laws. The first + is, the power of rapid multiplication in a geometrical + progression; the second, that the offspring always vary slightly + from the parents, though generally very closely resembling + <a name="Page_11" id="Page_11"></a>them. From the first fact or + law there follows, necessarily, a constant struggle for + existence; because, while the offspring always exceed the parents + in number, generally to an enormous extent, yet the total number + of living organisms in the world does not, and cannot, increase + year by year. Consequently every year, on the average, as many + die as are born, plants as well as animals; and the majority die + premature deaths. They kill each other in a thousand different + ways; they starve each other by some consuming the food that + others want; they are destroyed largely by the powers of + nature—by cold and heat, by rain and storm, by flood and + fire. There is thus a perpetual struggle among them which shall + live and which shall die; and this struggle is tremendously + severe, because so few can possibly remain alive—one in + five, one in ten, often only one in a hundred or even one in a + thousand.</p> + + <p>Then comes the question, Why do some live rather than others? + If all the individuals of each species were exactly alike in + every respect, we could only say it is a matter of chance. But + they are not alike. We find that they vary in many different + ways. Some are stronger, some swifter, some hardier in + constitution, some more cunning. An obscure colour may render + concealment more easy for some, keener sight may enable others to + discover prey or escape from an enemy better than their fellows. + Among plants the smallest differences may be useful or the + reverse. The earliest and strongest shoots may escape the slug; + their greater vigour may enable them to flower and seed earlier + in a wet autumn; plants best armed with spines or hairs may + escape being devoured; those whose flowers are most conspicuous + may be soonest fertilised by insects. We cannot doubt that, on + the whole, any beneficial variations will give the possessors of + it a greater probability of living through the tremendous ordeal + they have to undergo. There may be something left to chance, but + on the whole <i>the fittest will survive</i>.</p> + + <p>Then we have another important fact to consider, the principle + of heredity or transmission of variations. If we grow plants from + seed or breed any kind of animals year after year, consuming or + giving away all the increase we do not wish to keep just as they + come to hand, our plants or animals will continue much the same; + but if every year we <a name="Page_12" id="Page_12"></a>carefully + save the best seed to sow and the finest or brightest coloured + animals to breed from, we shall soon find that an improvement + will take place, and that the average quality of our stock will + be raised. This is the way in which all our fine garden fruits + and vegetables and flowers have been produced, as well as all our + splendid breeds of domestic animals; and they have thus become in + many cases so different from the wild races from which they + originally sprang as to be hardly recognisable as the same. It is + therefore proved that if any particular kind of variation is + preserved and bred from, the variation itself goes on increasing + in amount to an enormous extent; and the bearing of this on the + question of the origin of species is most important. For if in + each generation of a given animal or plant the fittest survive to + continue the breed, then whatever may be the special peculiarity + that causes "fitness" in the particular case, that peculiarity + will go on increasing and strengthening <i>so long as it is + useful to the species</i>. But the moment it has reached its + maximum of usefulness, and some other quality or modification + would help in the struggle, then the individuals which vary in + the new direction will survive; and thus a species may be + gradually modified, first in one direction, then in another, till + it differs from the original parent form as much as the greyhound + differs from any wild dog or the cauliflower from any wild plant. + But animals or plants which thus differ in a state of nature are + always classed as distinct species, and thus we see how, by the + continuous survival of the fittest or the preservation of + favoured races in the struggle for life, new species may be + originated.</p> + + <p>This self-acting process which, by means of a few easily + demonstrated groups of facts, brings about change in the organic + world, and keeps each species in harmony with the conditions of + its existence, will appear to some persons so clear and simple as + to need no further demonstration. But to the great majority of + naturalists and men of science endless difficulties and + objections arise, owing to the wonderful variety of animal and + vegetable forms, and the intricate relations of the different + species and groups of species with each other; and it was to + answer as many of these objections as possible, and to show that + the more we know of nature the more we <a name="Page_13" id= + "Page_13"></a>find it to harmonise with the development + hypothesis, that Darwin devoted the whole of his life to + collecting facts and making experiments, the record of a portion + of which he has given us in a series of twelve masterly + volumes.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Proposed Mode of Treatment of the Subject</i>.</p> + + <p>It is evidently of the most vital importance to any theory + that its foundations should be absolutely secure. It is therefore + necessary to show, by a wide and comprehensive array of facts, + that animals and plants <i>do</i> perpetually vary in the manner + and to the amount requisite; and that this takes place in wild + animals as well as in those which are domesticated. It is + necessary also to prove that all organisms <i>do</i> tend to + increase at the great rate alleged, and that this increase + actually occurs, under favourable conditions. We have to prove, + further, that variations of all kinds can be increased and + accumulated by selection; and that the struggle for existence to + the extent here indicated actually occurs in nature, and leads to + the continued preservation of favourable variations.</p> + + <p>These matters will be discussed in the four succeeding + chapters, though in a somewhat different order—the struggle + for existence and the power of rapid multiplication, which is its + cause, occupying the first place, as comprising those facts which + are the most fundamental and those which can be perfectly + explained without any reference to the less generally understood + facts of variation. These chapters will be followed by a + discussion of certain difficulties, and of the vexed question of + hybridity. Then will come a rather full account of the more + important of the complex relations of organisms to each other and + to the earth itself, which are either fully explained or greatly + elucidated by the theory. The concluding chapter will treat of + the origin of man and his relations to the lower animals.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href= + "#FNanchor_1_1"><span class="label">[1]</span></a> + <i>Geography and Classification of Animals</i>, p. 350.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href= + "#FNanchor_2_2"><span class="label">[2]</span></a> These + expressions occur in Chapter IX. of the earlier editions (to + the ninth) of the <i>Principles of Geology</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href= + "#FNanchor_3_3"><span class="label">[3]</span></a> L. + Agassiz, <i>Lake Superior</i>, p. 377.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_II" id="CHAPTER_II"></a><a name="Page_14" + id="Page_14"></a>CHAPTER II</h2> + + <p style='font-weight:bold;'>THE STRUGGLE FOR EXISTENCE</p> + + <div class="blockquot"> + <p>Its importance—The struggle among plants—Among + animals—Illustrative cases—Succession of trees in + forests of Denmark—The struggle for existence on the + Pampas—Increase of organisms in a geometrical + ratio—Examples of great powers of increase of + animals—Rapid increase and wide spread of + plants—Great fertility not essential to rapid + increase—Struggle between closely allied species most + severe—The ethical aspect of the struggle for + existence.</p> + </div> + + <p>There is perhaps no phenomenon of nature that is at once so + important, so universal; and so little understood, as the + struggle for existence continually going on among all organised + beings. To most persons nature appears calm, orderly, and + peaceful. They see the birds singing in the trees, the insects + hovering over the flowers, the squirrel climbing among the + tree-tops, and all living things in the possession of health and + vigour, and in the enjoyment of a sunny existence. But they do + not see, and hardly ever think of, the means by which this beauty + and harmony and enjoyment is brought about. They do not see the + constant and daily search after food, the failure to obtain which + means weakness or death; the constant effort to escape enemies; + the ever-recurring struggle against the forces of nature. This + daily and hourly struggle, this incessant warfare, is + nevertheless the very means by which much of the beauty and + harmony and enjoyment in nature is produced, and also affords one + of the most important elements in bringing about the origin of + species. We must, therefore, devote some time to the + consideration of its various aspects and of the many curious + phenomena to which it gives rise.</p> + + <p>It is a matter of common observation that if weeds are allowed + to grow unchecked in a garden they will soon destroy <a name= + "Page_15" id="Page_15"></a>a number of the flowers. It is not so + commonly known that if a garden is left to become altogether + wild, the weeds that first take possession of it, often covering + the whole surface of the ground with two or three different + kinds, will themselves be supplanted by others, so that in a few + years many of the original flowers and of the earliest weeds may + alike have disappeared. This is one of the very simplest cases of + the struggle for existence, resulting in the successive + displacement of one set of species by another; but the exact + causes of this displacement are by no means of such a simple + nature. All the plants concerned may be perfectly hardy, all may + grow freely from seed, yet when left alone for a number of years, + each set is in turn driven out by a succeeding set, till at the + end of a considerable period—a century or a few centuries + perhaps—hardly one of the plants which first monopolised + the ground would be found there.</p> + + <p>Another phenomenon of an analogous kind is presented by the + different behaviour of introduced wild plants or animals into + countries apparently quite as well suited to them as those which + they naturally inhabit. Agassiz, in his work on Lake Superior, + states that the roadside weeds of the northeastern United States, + to the number of 130 species, are all European, the native weeds + having disappeared westwards; and in New Zealand there are no + less than 250 species of naturalised European plants, more than + 100 species of which have spread widely over the country, often + displacing the native vegetation. On the other hand, of the many + hundreds of hardy plants which produce seed freely in our + gardens, very few ever run wild, and hardly any have become + common. Even attempts to naturalise suitable plants usually fail; + for A. de Candolle states that several botanists of Paris, + Geneva, and especially of Montpellier, have sown the seeds of + many hundreds of species of hardy exotic plants in what appeared + to be the most favourable situations, but that, in hardly a + single case, has any one of them become naturalised.<a name= + "FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" + class="fnanchor">[4]</a> Even a plant like the potato—so + widely cultivated, so hardy, and so well adapted to spread by + means of its many-eyed tubers—has not established itself in + a wild state in any part of Europe. It would be thought that + Australian plants would easily run <a name="Page_16" id= + "Page_16"></a>wild in New Zealand. But Sir Joseph Hooker informs + us that the late Mr. Bidwell habitually scattered Australian + seeds during his extensive travels in New Zealand, yet only two + or three Australian plants appear to have established themselves + in that country, and these only in cultivated or newly moved + soil.</p> + + <p>These few illustrations sufficiently show that all the plants + of a country are, as De Candolle says, at war with each other, + each one struggling to occupy ground at the expense of its + neighbour. But, besides this direct competition, there is one not + less powerful arising from the exposure of almost all plants to + destruction by animals. The buds are destroyed by birds, the + leaves by caterpillars, the seeds by weevils; some insects bore + into the trunk, others burrow in the twigs and leaves; slugs + devour the young seedlings and the tender shoots, wire-worms gnaw + the roots. Herbivorous mammals devour many species bodily, while + some uproot and devour the buried tubers.</p> + + <p>In animals, it is the eggs or the very young that suffer most + from their various enemies; in plants, the tender seedlings when + they first appear above the ground. To illustrate this latter + point Mr. Darwin cleared and dug a piece of ground three feet + long and two feet wide, and then marked all the seedlings of + weeds and other plants which came up, noting what became of them. + The total number was 357, and out of these no less than 295 were + destroyed by slugs and insects. The direct strife of plant with + plant is almost equally fatal when the stronger are allowed to + smother the weaker. When turf is mown or closely browsed by + animals, a number of strong and weak plants live together, + because none are allowed to grow much beyond the rest; but Mr. + Darwin found that when the plants which compose such turf are + allowed to grow up freely, the stronger kill the weaker. In a + plot of turf three feet by four, twenty distinct species of + plants were found to be growing, and no less than nine of these + perished altogether when the other species were allowed to grow + up to their full size.<a name="FNanchor_5_5" id= + "FNanchor_5_5"></a><a href="#Footnote_5_5" class= + "fnanchor">[5]</a></p> + + <p>But besides having to protect themselves against competing + plants and against destructive animals, there is a yet deadlier + <a name="Page_17" id="Page_17"></a>enemy in the forces of + inorganic nature. Each species can sustain a certain amount of + heat and cold, each requires a certain amount of moisture at the + right season, each wants a proper amount of light or of direct + sunshine, each needs certain elements in the soil; the failure of + a due proportion in these inorganic conditions causes weakness, + and thus leads to speedy death. The struggle for existence in + plants is, therefore, threefold in character and infinite in + complexity, and the result is seen in their curiously irregular + distribution over the face of the earth. Not only has each + country its distinct plants, but every valley, every hillside, + almost every hedgerow, has a different set of plants from its + adjacent valley, hillside, or hedgerow—if not always + different in the actual species yet very different in comparative + abundance, some which are rare in the one being common in the + other. Hence it happens that slight changes of conditions often + produce great changes in the flora of a country. Thus in 1740 and + the two following years the larva of a moth (Phalaena graminis) + committed such destruction in many of the meadows of Sweden that + the grass was greatly diminished in quantity, and many plants + which were before choked by the grass sprang up, and the ground + became variegated with a multitude of different species of + flowers. The introduction of goats into the island of St. Helena + led to the entire destruction of the native forests, consisting + of about a hundred distinct species of trees and shrubs, the + young plants being devoured by the goats as fast as they grew up. + The camel is a still greater enemy to woody vegetation than the + goat, and Mr. Marsh believes that forests would soon cover + considerable tracts of the Arabian and African deserts if the + goat and the camel were removed from them.<a name="FNanchor_6_6" + id="FNanchor_6_6"></a><a href="#Footnote_6_6" class= + "fnanchor">[6]</a> Even in many parts of our own country the + existence of trees is dependent on the absence of cattle. Mr. + Darwin observed, on some extensive heaths near Farnham, in + Surrey, a few clumps of old Scotch firs, but no young trees over + hundreds of acres. Some portions of the heath had, however, been + enclosed a few years before, and these enclosures were crowded + with young fir-trees growing too close together for all to live; + and these were not sown or planted, nothing having been done to + the ground beyond enclosing it <a name="Page_18" id= + "Page_18"></a>so as to keep out cattle. On ascertaining this, Mr. + Darwin was so much surprised that he searched among the heather + in the unenclosed parts, and there he found multitudes of little + trees and seedlings which had been perpetually browsed down by + the cattle. In one square yard, at a point about a hundred yards + from one of the old clumps of firs, he counted thirty-two little + trees, and one of them had twenty-six rings of growth, showing + that it had for many years tried to raise its head above the + stems of the heather and had failed. Yet this heath was very + extensive and very barren, and, as Mr. Darwin remarks, no one + would ever have imagined that cattle would have so closely and so + effectually searched it for food.</p> + + <p>In the case of animals, the competition and struggle are more + obvious. The vegetation of a given district can only support a + certain number of animals, and the different kinds of + plant-eaters will compete together for it. They will also have + insects for their competitors, and these insects will be kept + down by birds, which will thus assist the mammalia. But there + will also be carnivora destroying the herbivora; while small + rodents, like the lemming and some of the field-mice, often + destroy so much vegetation as materially to affect the food of + all the other groups of animals. Droughts, floods, severe + winters, storms and hurricanes will injure these in various + degrees, but no one species can be diminished in numbers without + the effect being felt in various complex ways by all the rest. A + few illustrations of this reciprocal action must be given.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Illustrative Cases of the Struggle for Life</i>.</p> + + <p>Sir Charles Lyell observes that if, by the attacks of seals or + other marine foes, salmon are reduced in numbers, the consequence + will be that otters, living far inland, will be deprived of food + and will then destroy many young birds or quadrupeds, so that the + increase of a marine animal may cause the destruction of many + land animals hundreds of miles away. Mr. Darwin carefully + observed the effects produced by planting a few hundred acres of + Scotch fir, in Staffordshire, on part of a very extensive heath + which had never been cultivated. After the planted portion was + about twenty-five years old he observed that the change in the + native vegetation <a name="Page_19" id="Page_19"></a>was greater + than is often seen in passing from one quite different soil to + another. Besides a great change in the proportional numbers of + the native heath-plants, twelve species which could not be found + on the heath flourished in the plantations. The effect on the + insect life must have been still greater, for six insectivorous + birds which were very common in the plantations were not to be + seen on the heath, which was, however, frequented by two or three + different species of insectivorous birds. It would have required + continued study for several years to determine all the + differences in the organic life of the two areas, but the facts + stated by Mr. Darwin are sufficient to show how great a change + may be effected by the introduction of a single kind of tree and + the keeping out of cattle.</p> + + <p>The next case I will give in Mr. Darwin's own words: "In + several parts of the world insects determine the existence of + cattle. Perhaps Paraguay offers the most curious instance of + this; for here neither cattle nor horses nor dogs have ever run + wild, though they swarm southward and northward in a feral state; + and Azara and Rengger have shown that this is caused by the + greater numbers, in Paraguay, of a certain fly which lays its + eggs in the navels of these animals when first born. The increase + of these flies, numerous as they are, must be habitually checked + by some means, probably by other parasitic insects. Hence, if + certain insectivorous birds were to decrease in Paraguay, the + parasitic insects would probably increase; and this would lessen + the number of the navel-frequenting flies—then cattle and + horses would become feral, and this would greatly alter (as + indeed I have observed in parts of South America) the vegetation: + this again would largely affect the insects, and this, as we have + just seen in Staffordshire, the insectivorous birds, and so + onward in ever-increasing circles of complexity. Not that under + nature the relations will ever be as simple as this. Battle + within battle must be continually recurring with varying success; + and yet in the long run the forces are so nicely balanced, that + the face of nature remains for a long time uniform, though + assuredly the merest trifle would give the victory to one organic + being over another."<a name="FNanchor_7_7" id= + "FNanchor_7_7"></a><a href="#Footnote_7_7" class= + "fnanchor">[7]</a></p> + + <p><a name="Page_20" id="Page_20"></a>Such cases as the above may + perhaps be thought exceptional, but there is good reason to + believe that they are by no means rare, but are illustrations of + what is going on in every part of the world, only it is very + difficult for us to trace out the complex reactions that are + everywhere occurring. The general impression of the ordinary + observer seems to be that wild animals and plants live peaceful + lives and have few troubles, each being exactly suited to its + place and surroundings, and therefore having no difficulty in + maintaining itself. Before showing that this view is, everywhere + and always, demonstrably untrue, we will consider one other case + of the complex relations of distinct organisms adduced by Mr. + Darwin, and often quoted for its striking and almost eccentric + character. It is now well known that many flowers require to be + fertilised by insects in order to produce seed, and this + fertilisation can, in some cases, only be effected by one + particular species of insect to which the flower has become + specially adapted. Two of our common plants, the wild + heart's-ease (Viola tricolor) and the red clover (Trifolium + pratense), are thus fertilised by humble-bees almost exclusively, + and if these insects are prevented from visiting the flowers, + they produce either no seed at all or exceedingly few. Now it is + known that field-mice destroy the combs and nests of humble-bees, + and Colonel Newman, who has paid great attention to these + insects, believes that more than two-thirds of all the + humble-bees' nests in England are thus destroyed. But the number + of mice depends a good deal on the number of cats; and the same + observer says that near villages and towns he has found the nests + of humble-bees more numerous than elsewhere, which he attributes + to the number of cats that destroy the mice. Hence it follows, + that the abundance of red clover and wild heart's-ease in a + district will depend on a good supply of cats to kill the mice, + which would otherwise destroy and keep down the humble-bees and + prevent them from fertilising the flowers. A chain of connection + has thus been found between such totally distinct organisms as + flesh-eating mammalia and sweet-smelling flowers, the abundance + or scarcity of the one closely corresponding to that of the + other!</p> + + <p>The following account of the struggle between trees in the + forests of Denmark, from the researches of M. Hansten-<a name= + "Page_21" id="Page_21"></a>Blangsted, strikingly illustrates our + subject.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href= + "#Footnote_8_8" class="fnanchor">[8]</a> The chief combatants are + the beech and the birch, the former being everywhere successful + in its invasions. Forests composed wholly of birch are now only + found in sterile, sandy tracts; everywhere else the trees are + mixed, and wherever the soil is favourable the beech rapidly + drives out the birch. The latter loses its branches at the touch + of the beech, and devotes all its strength to the upper part + where it towers above the beech. It may live long in this way, + but it succumbs ultimately in the fight—of old age if of + nothing else, for the life of the birch in Denmark is shorter + than that of the beech. The writer believes that light (or rather + shade) is the cause of the superiority of the latter, for it has + a greater development of its branches than the birch, which is + more open and thus allows the rays of the sun to pass through to + the soil below, while the tufted, bushy top of the beech + preserves a deep shade at its base. Hardly any young plants can + grow under the beech except its own shoots; and while the beech + can nourish under the shade of the birch, the latter dies + immediately under the beech. The birch has only been saved from + total extermination by the facts that it had possession of the + Danish forests long before the beech ever reached the country, + and that certain districts are unfavourable to the growth of the + latter. But wherever the soil has been enriched by the + decomposition of the leaves of the birch the battle begins. The + birch still flourishes on the borders of lakes and other marshy + places, where its enemy cannot exist. In the same way, in the + forests of Zeeland, the fir forests are disappearing before the + beech. Left to themselves, the firs are soon displaced by the + beech. The struggle between the latter and the oak is longer and + more stubborn, for the branches and foliage of the oak are + thicker, and offer much resistance to the passage of light. The + oak, also, has greater longevity; but, sooner or later, it too + succumbs, because it cannot develop in the shadow of the beech. + The earliest forests of Denmark were mainly composed of aspens, + with which the birch was apparently associated; gradually the + soil was raised, and the climate grew milder; then the fir came + and formed large forests. This tree ruled for centuries, and then + ceded the <a name="Page_22" id="Page_22"></a>first place to the + holm-oak, which is now giving way to the beech. Aspen, birch, + fir, oak, and beech appear to be the steps in the struggle for + the survival of the fittest among the forest-trees of + Denmark.</p> + + <p>It may be added that in the time of the Romans the beech was + the principal forest-tree of Denmark as it is now, while in the + much earlier bronze age, represented by the later remains found + in the peat bogs, there were no beech-trees, or very few, the oak + being the prevailing tree, while in the still earlier stone + period the fir was the most abundant. The beech is a tree + essentially of the temperate zone, having its northern limit + considerably southward of the oak, fir, birch, or aspen, and its + entrance into Denmark was no doubt due to the amelioration of the + climate after the glacial epoch had entirely passed away. We thus + see how changes of climate, which are continually occurring owing + either to cosmical or geographical causes, may initiate a + struggle among plants which may continue for thousands of years, + and which must profoundly modify the relations of the animal + world, since the very existence of innumerable insects, and even + of many birds and mammals, is dependent more or less completely + on certain species of plants.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Struggle for Existence on the Pampas</i>.</p> + + <p>Another illustration of the struggle for existence,in which + both plants and animals are implicated, is afforded by the pampas + of the southern part of South America. The absence of trees from + these vast plains has been imputed by Mr. Darwin to the supposed + inability of the tropical and sub-tropical forms of South America + to thrive on them, and there being no other source from which + they could obtain a supply; and that explanation was adopted by + such eminent botanists as Mr. Ball and Professor Asa Gray. This + explanation has always seemed to me unsatisfactory, because there + are ample forests both in the temperate regions of the Andes and + on the whole west coast down to Terra del Fuego; and it is + inconsistent with what we know of the rapid variation and + adaptation of species to new conditions. What seems a more + satisfactory explanation has been given by Mr. Edwin Clark, a + civil engineer, who resided nearly two years in the country and + <a name="Page_23" id="Page_23"></a>paid much attention to its + natural history. He says: "The peculiar characteristics of these + vast level plains which descend from the Andes to the great river + basin in unbroken monotony, are the absence of rivers or + water-storage, and the periodical occurrence of droughts, or + 'siccos,' in the summer months. These conditions determine the + singular character both of its flora and fauna.</p> + + <p>"The soil is naturally fertile and favourable for the growth + of trees, and they grow luxuriantly wherever they are protected. + The eucalyptus is covering large tracts wherever it is enclosed, + and willows, poplars, and the fig surround every estancia when + fenced in.</p> + + <p>"The open plains are covered with droves of horses and cattle, + and overrun by numberless wild rodents, the original tenants of + the pampas. During the long periods of drought, which are so + great a scourge to the country, these animals are starved by + thousands, destroying, in their efforts to live, every vestige of + vegetation. In one of these 'siccos,' at the time of my visit, no + less than 50,000 head of oxen and sheep and horses perished from + starvation and thirst, after tearing deep out of the soil every + trace of vegetation, including the wiry roots of the + pampas-grass. Under such circumstances the existence of an + unprotected tree is impossible. The only plants that hold their + own, in addition to the indestructible thistles, grasses, and + clover, are a little herbaceous oxalis, producing viviparous buds + of extraordinary vitality, a few poisonous species, such as the + hemlock, and a few tough, thorny dwarf-acacias and wiry rushes, + which even a starving rat refuses.</p> + + <p>"Although the cattle are a modern introduction, the numberless + indigenous rodents must always have effectually prevented the + introduction of any other species of plants; large tracts are + still honeycombed by the ubiquitous biscacho, a gigantic rabbit; + and numerous other rodents still exist, including rats and mice, + pampas-hares, and the great nutria and carpincho (capybara) on + the river banks."<a name="FNanchor_9_9" id= + "FNanchor_9_9"></a><a href="#Footnote_9_9" class= + "fnanchor">[9]</a></p> + + <p>Mr. Clark further remarks on the desperate struggle for + existence which characterises the bordering fertile zones, where + rivers and marshy plains permit a more luxuriant and varied + vegetable and animal life. After describing how the <a name= + "Page_24" id="Page_24"></a>river sometimes rose 30 feet in eight + hours, doing immense destruction, and the abundance of the larger + carnivora and large reptiles on its banks, he goes on: "But it + was among the flora that the principle of natural selection was + most prominently displayed. In such a district—overrun with + rodents and escaped cattle, subject to floods that carried away + whole islands of botany, and especially to droughts that dried up + the lakes and almost the river itself—no ordinary plant + could live, even on this rich and watered alluvial debris. The + only plants that escaped the cattle were such as were either + poisonous, or thorny, or resinous, or indestructibly tough. Hence + we had only a great development of solanums, talas, acacias, + euphorbias, and laurels. The buttercup is replaced by the little + poisonous yellow oxalis with its viviparous buds; the + passion-flowers, asclepiads, bignonias, convolvuluses, and + climbing leguminous plants escape both floods and cattle by + climbing the highest trees and towering overhead in a flood of + bloom. The ground plants are the portulacas, turneras, and + cenotheras, bitter and ephemeral, on the bare rock, and almost + independent of any other moisture than the heavy dews. The + pontederias, alismas, and plantago, with grasses and sedges, + derive protection from the deep and brilliant pools; and though + at first sight the 'monte' doubtless impresses the traveller as a + scene of the wildest confusion and ruin, yet, on closer + examination, we found it far more remarkable as a manifestation + of harmony and law, and a striking example of the marvellous + power which plants, like animals, possess, of adapting themselves + to the local peculiarities of their habitat, whether in the + fertile shades of the luxuriant 'monte' or on the arid, + parched-up plains of the treeless pampas."</p> + + <p>A curious example of the struggle between plants has been + communicated to me by Mr. John Ennis, a resident in New Zealand. + The English water-cress grows so luxuriantly in that country as + to completely choke up the rivers, sometimes leading to + disastrous floods, and necessitating great outlay to keep the + stream open. But a natural remedy has now been found in planting + willows on the banks. The roots of these trees penetrate the bed + of the stream in every direction, and the water-cress, unable to + obtain the requisite amount of nourishment, gradually + disappears.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_25" id="Page_25"></a><i>Increase of Organisms in a + Geometrical Ratio</i>.</p> + + <p>The facts which have now been adduced, sufficiently prove that + there is a continual competition, and struggle, and war going on + in nature, and that each species of animal and plant affects many + others in complex and often unexpected ways. We will now proceed + to show the fundamental cause of this struggle, and to prove that + it is ever acting over the whole field of nature, and that no + single species of animal or plant can possibly escape from it. + This results from the fact of the rapid increase, in a + geometrical ratio, of all the species of animals and plants. In + the lower orders this increase is especially rapid, a single + flesh-fly (Musca carnaria) producing 20,000 larvae, and these + growing so quickly that they reach their full size in five days; + hence the great Swedish naturalist, Linnaeus, asserted that a + dead horse would be devoured by three of these flies as quickly + as by a lion. Each of these larvae remains in the pupa state + about five or six days, so that each parent fly may be increased + ten thousand-fold in a fortnight. Supposing they went on + increasing at this rate during only three months of summer, there + would result one hundred millions of millions of millions for + each fly at the commencement of summer,—a number greater + probably than exists at any one time in the whole world. And this + is only one species, while there are thousands of other species + increasing also at an enormous rate; so that, if they were + unchecked, the whole atmosphere would be dense with flies, and + all animal food and much of animal life would be destroyed by + them. To prevent this tremendous increase there must be incessant + war against these insects, by insectivorous birds and reptiles as + well as by other insects, in the larva as well as in the perfect + state, by the action of the elements in the form of rain, hail, + or drought, and by other unknown causes; yet we see nothing of + this ever-present war, though by its means alone, perhaps, we are + saved from famine and pestilence.</p> + + <p>Let us now consider a less extreme and more familiar case. We + possess a considerable number of birds which, like the redbreast, + sparrow, the four common titmice, the thrush, and the blackbird, + stay with us all the year round These lay on an average six eggs, + but, as several of them have <a name="Page_26" id= + "Page_26"></a>two or more broods a year, ten will be below the + average of the year's increase. Such birds as these often live + from fifteen to twenty years in confinement, and we cannot + suppose them to live shorter lives in a state of nature, if + unmolested; but to avoid possible exaggeration we will take only + ten years as the average duration of their lives. Now, if we + start with a single pair, and these are allowed to live and + breed, unmolested, till they die at the end of ten + years,—as they might do if turned loose into a good-sized + island with ample vegetable and insect food, but no other + competing or destructive birds or quadrupeds—their numbers + would amount to more than twenty millions. But we know very well + that our bird population is no greater, on the average, now than + it was ten years ago. Year by year it may fluctuate a little + according as the winters are more or less severe, or from other + causes, but on the whole there is no increase. What, then, + becomes of the enormous surplus population annually produced? It + is evident they must all die or be killed, somehow; and as the + increase is, on the average, about five to one, it follows that, + if the average number of birds of all kinds in our islands is + taken at ten millions—and this is probably far under the + mark—then about fifty millions of birds, including eggs as + possible birds, must annually die or be destroyed. Yet we see + nothing, or almost nothing, of this tremendous slaughter of the + innocents going on all around us. In severe winters a few birds + are found dead, and a few feathers or mangled remains show us + where a wood-pigeon or some other bird has been destroyed by a + hawk, but no one would imagine that five times as many birds as + the total number in the country in early spring die every year. + No doubt a considerable proportion of these do not die here but + during or after migration to other countries, but others which + are bred in distant countries come here, and thus balance the + account. Again, as the average number of young produced is four + or five times that of the parents, we ought to have at least five + times as many birds in the country at the end of summer as at the + beginning, and there is certainly no such enormous disproportion + as this. The fact is, that the destruction commences, and is + probably most severe, with nestling birds, which are often killed + by heavy rains or blown away by severe storms, or left to die of + hunger if either of <a name="Page_27" id="Page_27"></a>the + parents is killed; while they offer a defenceless prey to + jackdaws, jays, and magpies, and not a few are ejected from their + nests by their foster-brothers the cuckoos. As soon as they are + fledged and begin to leave the nest great numbers are destroyed + by buzzards, sparrow-hawks, and shrikes. Of those which migrate + in autumn a considerable proportion are probably lost at sea or + otherwise destroyed before they reach a place of safety; while + those which remain with us are greatly thinned by cold and + starvation during severe winters. Exactly the same thing goes on + with every species of wild animal and plant from the lowest to + the highest. All breed at such a rate, that in a few years the + progeny of any one species would, if allowed to increase + unchecked, alone monopolise the land; but all alike are kept + within bounds by various destructive agencies, so that, though + the numbers of each may fluctuate, they can never permanently + increase except at the expense of some others, which must + proportionately decrease.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cases showing the Great Powers of Increase of Animals.</i></p> + + <p>As the facts now stated are the very foundation of the theory + we are considering, and the enormous increase and perpetual + destruction continually going on require to be kept ever present + in the mind, some direct evidence of actual cases of increase + must be adduced. That even the larger animals, which breed + comparatively slowly, increase enormously when placed under + favourable conditions in new countries, is shown by the rapid + spread of cattle and horses in America. Columbus, in his second + voyage, left a few black cattle at St. Domingo, and these ran + wild and increased so much that, twenty-seven years afterwards, + herds of from 4000 to 8000 head were not uncommon. Cattle were + afterwards taken from this island to Mexico and to other parts of + America, and in 1587, sixty-five years after the conquest of + Mexico, the Spaniards exported 64,350 hides from that country and + 35,444 from St. Domingo, an indication of the vast numbers of + these animals which must then have existed there, since those + captured and killed could have been only a small portion of the + whole. In the pampas of Buenos Ayres there were, at the end of + the last century, about twelve million cows and three million + horses, besides great numbers in all other parts <a name= + "Page_28" id="Page_28"></a>of America where open pastures offered + suitable conditions. Asses, about fifty years after their + introduction, ran wild and multiplied so amazingly in Quito, that + the Spanish traveller Ulloa describes them as being a nuisance. + They grazed together in great herds, defending themselves with + their mouths, and if a horse strayed among them they all fell + upon him and did not cease biting and kicking till they left him + dead. Hogs were turned out in St. Domingo by Columbus in 1493, + and the Spaniards took them to other places where they settled, + the result being, that in about half a century these animals were + found in great numbers over a large part of America, from 25° + north to 40° south latitude. More recently, in New Zealand, + pigs have multiplied so greatly in a wild state as to be a + serious nuisance and injury to agriculture. To give some idea of + their numbers, it is stated that in the province of Nelson there + were killed in twenty months 25,000 wild pigs.<a name= + "FNanchor_10_10" id="FNanchor_10_10"></a><a href= + "#Footnote_10_10" class="fnanchor">[10]</a> Now, in the case of + all these animals, we know that in their native countries, and + even in America at the present time, they do not increase at all + in numbers; therefore the whole normal increase must be kept + down, year by year, by natural or artificial means of + destruction.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Rapid Increase and Wide Spread of Plants</i>.</p> + + <p>In the case of plants, the power of increase is even greater + and its effects more distinctly visible. Hundreds of square miles + of the plains of La Plata are now covered with two or three + species of European thistle, often to the exclusion of almost + every other plant; but in the native countries of these thistles + they occupy, except in cultivated or waste ground, a very + subordinate part in the vegetation. Some American plants, like + the cotton-weed (Asclepias cuiussayica), have now become common + weeds over a large portion of the tropics. White clover + (Trifolium repens) spreads over all the temperate regions of the + world, and in New Zealand is exterminating many native species, + including even the native flax (Phormium <a name="Page_29" id= + "Page_29"></a>tenax), a large plant with iris-like leaves 5 or 6 + feet high. Mr. W.L. Travers has paid much attention to the + effects of introduced plants in New Zealand, and notes the + following species as being especially remarkable. The common + knotgrass (Polygonum aviculare) grows most luxuriantly, single + plants covering a space 4 or 5 feet in diameter, and sending + their roots 3 or 4 feet deep. A large sub-aquatic dock (Rumex + obtusifolius) abounds in every river-bed, even far up among the + mountains. The common sow-thistle (Sonchus oleraceus) grows all + over the country up to an elevation of 6000 feet. The water-cress + (Nasturtium officinale) grows with amazing vigour in many of the + rivers, forming stems 12 feet long and 3/4 inch in diameter, and + completely choking them up. It cost £300 a year to keep the + Avon at Christchurch free from it. The sorrel (Rumex acetosella) + covers hundreds of acres with a sheet of red. It forms a dense + mat, exterminating other plants, and preventing cultivation. It + can, however, be itself exterminated by sowing the ground with + red clover, which will also vanquish the Polygonum aviculare. The + most noxious weed in New Zealand appears, however, to be the + Hypochaeris radicata, a coarse yellow-flowered composite not + uncommon in our meadows and waste places. This has been + introduced with grass seeds from England, and is very + destructive. It is stated that excellent pasture was in three + years destroyed by this weed, which absolutely displaced every + other plant on the ground. It grows in every kind of soil, and is + said even to drive out the white clover, which is usually so + powerful in taking possession of the soil.</p> + + <p>In Australia another composite plant, called there the + Cape-weed (Cryptostemma calendulaceum), did much damage, and was + noticed by Baron Von Hugel in 1833 as "an unexterminable weed"; + but, after forty years' occupation, it was found to give way to + the dense herbage formed by lucerne and choice grasses.</p> + + <p>In Ceylon we are told by Mr. Thwaites, in his <i>Enumeration + of Ceylon Plants</i>, that a plant introduced into the island + less than fifty years ago is helping to alter the character of + the vegetation up to an elevation of 3000 feet. This is the + Lantana mixta, a verbenaceous plant introduced <a name="Page_30" + id="Page_30"></a>from the West Indies, which appears to have + found in Ceylon a soil and climate exactly suited to it. It now + covers thousands of acres with its dense masses of foliage, + taking complete possession of land where cultivation has been + neglected or abandoned, preventing the growth of any other + plants, and even destroying small trees, the tops of which its + subscandent stems are able to reach. The fruit of this plant is + so acceptable to frugivorous birds of all kinds that, through + their instrumentality, it is spreading rapidly, to the complete + exclusion of the indigenous vegetation where it becomes + established.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Great Fertility not essential to Rapid Increase</i>.</p> + + <p>The not uncommon circumstance of slow-breeding animals being + very numerous, shows that it is usually the amount of destruction + which an animal or plant is exposed to, not its rapid + multiplication, that determines its numbers in any country. The + passenger-pigeon (Ectopistes migratorius) is, or rather was, + excessively abundant in a certain area in North America, and its + enormous migrating flocks darkening the sky for hours have often + been described; yet this bird lays only two eggs. The fulmar + petrel exists in myriads at St. Kilda and other haunts of the + species, yet it lays only one egg. On the other hand the great + shrike, the tree-creeper, the nut-hatch, the nut-cracker, the + hoopoe, and many other birds, lay from four to six or seven eggs, + and yet are never abundant. So in plants, the abundance of a + species bears little or no relation to its seed-producing power. + Some of the grasses and sedges, the wild hyacinth, and many + buttercups occur in immense profusion over extensive areas, + although each plant produces comparatively few seeds; while + several species of bell-flowers, gentians, pinks, and mulleins, + and even some of the composite, which produce an abundance of + minute seeds, many of which are easily scattered by the wind, are + yet rare species that never spread beyond a very limited + area.</p> + + <p>The above-mentioned passenger-pigeon affords such an excellent + example of an enormous bird-population kept up by a comparatively + slow rate of increase, and in spite of its complete helplessness + and the great destruction which it suffers from its numerous + enemies, that the following account of one of its breeding-places + and migrations by the celebrated <a name="Page_31" id= + "Page_31"></a>American naturalist, Alexander Wilson, will be read + with interest:—</p> + + <p>"Not far from Shelbyville, in the State of Kentucky, about + five years ago, there was one of these breeding-places, which + stretched through the woods in nearly a north and south + direction, was several miles in breadth, and was said to be + upwards of 40 miles in extent. In this tract almost every tree + was furnished with nests wherever the branches could accommodate + them. The pigeons made their first appearance there about the + 10th of April, and left it altogether with their young before the + 25th of May. As soon as the young were fully grown and before + they left the nests, numerous parties of the inhabitants from all + parts of the adjacent country came with waggons, axes, beds, + cooking utensils, many of them accompanied by the greater part of + their families, and encamped for several days at this immense + nursery. Several of them informed me that the noise was so great + as to terrify their horses, and that it was difficult for one + person to hear another without bawling in his ear. The ground was + strewed with broken limbs of trees, eggs, and young squab + pigeons, which had been precipitated from above, and on which + herds of hogs were fattening. Hawks, buzzards, and eagles were + sailing about in great numbers, and seizing the squabs from the + nests at pleasure; while, from 20 feet upwards to the top of the + trees, the view through the woods presented a perpetual tumult of + crowding and fluttering multitudes of pigeons, their wings + roaring like thunder, mingled with the frequent crash of falling + timber; for now the axemen were at work cutting down those trees + that seemed most crowded with nests, and contrived to fell them + in such a manner, that in their descent they might bring down + several others; by which means the falling of one large tree + sometimes produced 200 squabs little inferior in size to the old + birds, and almost one heap of fat. On some single trees upwards + of a hundred nests were found, each containing one squab only; a + circumstance in the history of the bird not generally known to + naturalists.<a name="FNanchor_11_11" id= + "FNanchor_11_11"></a><a href="#Footnote_11_11" class= + "fnanchor">[11]</a> It was dangerous to walk <a name="Page_32" + id="Page_32"></a>under these flying and fluttering millions, from + the frequent fall of large branches, broken down by the weight of + the multitudes above, and which in their descent often destroyed + numbers of the birds themselves; while the clothes of those + engaged in traversing the woods were completely covered with the + excrements of the pigeons.</p> + + <p>"These circumstances were related to me by many of the most + respectable part of the community in that quarter, and were + confirmed in part by what I myself witnessed. I passed for + several miles through this same breeding-place, where every tree + was spotted with nests, the remains of those above described. In + many instances I counted upwards of ninety nests on a single + tree; but the pigeons had abandoned this place for another, 60 or + 80 miles off, towards Green River, where they were said at that + time to be equally numerous. From the great numbers that were + constantly passing over our heads to or from that quarter, I had + no doubt of the truth of this statement. The mast had been + chiefly consumed in Kentucky; and the pigeons, every morning a + little before sunrise, set out for the Indiana territory, the + nearest part of which was about sixty miles distant. Many of + these returned before ten o'clock, and the great body generally + appeared on their return a little after noon. I had left the + public road to visit the remains of the breeding-place near + Shelbyville, and was traversing the woods with my gun, on my way + to Frankfort, when about ten o'clock the pigeons which I had + observed flying the greater part of the morning northerly, began + to return in such immense numbers as I never before had + witnessed. Coming to an opening by the side of a creek, where I + had a more uninterrupted view, I was astonished at their + appearance: they were flying with great steadiness and rapidity, + at a height beyond gunshot, in several strata deep, and so close + together that, could shot have reached them, one discharge could + not have failed to bring down several individuals. From right to + left, as far as the eye could reach, the breadth of this vast + procession extended, seeming everywhere equally crowded. Curious + to determine how long this appearance would continue, I took out + my watch to note the time, and sat down to observe them. It was + then half-past one; I sat for more than an hour, but <a name= + "Page_33" id="Page_33"></a>instead of a diminution of this + prodigious procession, it seemed rather to increase, both in + numbers and rapidity; and anxious to reach Frankfort before + night, I rose and went on. About four o'clock in the afternoon I + crossed Kentucky River, at the town of Frankfort, at which time + the living torrent above my head seemed as numerous and as + extensive as ever. Long after this I observed them in large + bodies that continued to pass for six or eight minutes, and these + again were followed by other detached bodies, all moving in the + same south-east direction, till after six o'clock in the evening. + The great breadth of front which this mighty multitude preserved + would seem to intimate a corresponding breadth of their + breeding-place, which, by several gentlemen who had lately passed + through part of it, was stated to me at several miles."</p> + + <p>From these various observations, Wilson calculated that the + number of birds contained in the mass of pigeons which he saw on + this occasion was at least two thousand millions, while this was + only one of many similar aggregations known to exist in various + parts of the United States. The picture here given of these + defenceless birds, and their still more defenceless young, + exposed to the attacks of numerous rapacious enemies, brings + vividly before us one of the phases of the unceasing struggle for + existence ever going on; but when we consider the slow rate of + increase of these birds, and the enormous population they are + nevertheless able to maintain, we must be convinced that in the + case of the majority of birds which multiply far more rapidly, + and yet are never able to attain such numbers, the struggle + against their numerous enemies and against the adverse forces of + nature must be even more severe or more continuous.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Struggle for Life between, closely allied Animals and Plants + often the most severe.</i></p> + + <p>The struggle we have hitherto been considering has been mainly + that between an animal or plant and its direct enemies, whether + these enemies are other animals which devour it, or the forces of + nature which destroy it. But there is another kind of struggle + often going on at the same time between closely related species, + which almost always terminates in the destruction of one of them. + As an example of what is <a name="Page_34" id= + "Page_34"></a>meant, Darwin states that the recent increase of + the missel-thrush in parts of Scotland has caused the decrease of + the song-thrush.<a name="FNanchor_12_12" id= + "FNanchor_12_12"></a><a href="#Footnote_12_12" class= + "fnanchor">[12]</a> The black rat (Mus rattus) was the common rat + of Europe till, in the beginning of the eighteenth century, the + large brown rat (Mus decumanus) appeared on the Lower Volga, and + thence spread more or less rapidly till it overran all Europe, + and generally drove out the black rat, which in most parts is now + comparatively rare or quite extinct. This invading rat has now + been carried by commerce all over the world, and in New Zealand + has completely extirpated a native rat, which the Maoris allege + they brought with them from their home in the Pacific; and in the + same country a native fly is being supplanted by the European + house-fly. In Russia the small Asiatic cockroach has driven away + a larger native species; and in Australia the imported hive-bee + is exterminating the small stingless native bee.</p> + + <p>The reason why this kind of struggle goes on is apparent if we + consider that the allied species fill nearly the same place in + the economy of nature. They require nearly the same kind of food, + are exposed to the same enemies and the same dangers. Hence, if + one has ever so slight an advantage over the other in procuring + food or in avoiding danger, in its rapidity of multiplication or + its tenacity of life, it will increase more rapidly, and by that + very fact will cause the other to decrease and often become + altogether extinct. In some cases, no doubt, there is actual war + between the two, the stronger killing the weaker; but this is by + no means necessary, and there may be cases in which the weaker + species, physically, may prevail, by its power of more rapid + multiplication, its better withstanding vicissitudes of climates, + or its greater cunning in escaping the attacks of the common + enemies. The same principle is seen at work in the fact that + certain mountain varieties of sheep will starve out other + mountain varieties, so that the two cannot be kept together. In + plants the same thing occurs. If several distinct varieties of + wheat are sown together, and the mixed seed resown, some of the + varieties which best suit the soil and climate, or are naturally + the most fertile, will beat the others and so yield more seed, + and will consequently in a few years supplant the other + varieties.</p> + + <p><a name="Page_35" id="Page_35"></a>As an effect of this + principle, we seldom find closely allied species of animals or + plants living together, but often in distinct though adjacent + districts where the conditions of life are somewhat different. + Thus we may find cowslips (Primula veris) growing in a meadow, + and primroses (P. vulgaris) in an adjoining wood, each in + abundance, but not often intermingled. And for the same reason + the old turf of a pasture or heath consists of a great variety of + plants matted together, so much so that in a patch little more + than a yard square Mr. Darwin found twenty distinct species, + belonging to eighteen distinct genera and to eight natural + orders, thus showing their extreme diversity of organisation. For + the same reason a number of distinct grasses and clovers are sown + in order to make a good lawn instead of any one species; and the + quantity of hay produced has been found to be greater from a + variety of very distinct grasses than from any one species of + grass.</p> + + <p>It may be thought that forests are an exception to this rule, + since in the north-temperate and arctic regions we find extensive + forests of pines or of oaks. But these are, after all, + exceptional, and characterise those regions only where the + climate is little favourable to forest vegetation. In the + tropical and all the warm temperate parts of the earth, where + there is a sufficient supply of moisture, the forests present the + same variety of species as does the turf of our old pastures; and + in the equatorial virgin forests there is so great a variety of + forms, and they are so thoroughly intermingled, that the + traveller often finds it difficult to discover a second specimen + of any particular species which he has noticed. Even the forests + of the temperate zones, in all favourable situations, exhibit a + considerable variety of trees of distinct genera and families, + and it is only when we approach the outskirts of forest + vegetation, where either drought or winds or the severity of the + winter is adverse to the existence of most trees, that we find + extensive tracts monopolised by one or two species. Even Canada + has more than sixty different forest trees and the Eastern United + States a hundred and fifty; Europe is rather poor, containing + about eighty trees only; while the forests of Eastern Asia, + Japan, and Manchuria are exceedingly rich, about a hundred and + seventy species being already known. And in all these countries + the trees grow inter<a name="Page_36" id="Page_36"></a>mingled, + so that in every extensive forest we have a considerable variety, + as may be seen in the few remnants of our primitive woods in some + parts of Epping Forest and the New Forest.</p> + + <p>Among animals the same law prevails, though, owing to their + constant movements and power of concealment, it is not so readily + observed. As illustrations we may refer to the wolf, ranging over + Europe and Northern Asia, while the jackal inhabits Southern Asia + and Northern Africa; the tree-porcupines, of which there are two + closely allied species, one inhabiting the eastern, the other the + western half of North America; the common hare (Lepus timidus) in + Central and Southern Europe, while all Northern Europe is + inhabited by the variable hare (Lepus variabilis); the common jay + (Garrulus glandarius) inhabiting all Europe, while another + species (Garrulus Brandti) is found all across Asia from the + Urals to Japan; and many species of birds in the Eastern United + States are replaced by closely allied species in the west. Of + course there are also numbers of closely related species in the + same country, but it will almost always be found that they + frequent different stations and have somewhat different habits, + and so do not come into direct competition with each other; just + as closely allied plants may inhabit the same districts, when one + prefers meadows the other woods, one a chalky soil the other + sand, one a damp situation the other a dry one. With plants, + fixed as they are to the earth, we easily note these + peculiarities of station; but with wild animals, which we see + only on rare occasions, it requires close and long-continued + observation to detect the peculiarities in their mode of life + which may prevent all direct competition between closely allied + species dwelling in the same area.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Ethical Aspect of the Struggle for Existence</i>.</p> + + <p>Our exposition of the phenomena presented by the struggle for + existence may be fitly concluded by a few remarks on its ethical + aspect. Now that the war of nature is better known, it has been + dwelt upon by many writers as presenting so vast an amount of + cruelty and pain as to be revolting to our instincts of humanity, + while it has proved a stumbling-block in the way of those who + would fain believe in an all-wise and <a name="Page_37" id= + "Page_37"></a>benevolent ruler of the universe. Thus, a brilliant + writer says: "Pain, grief, disease, and death, are these the + inventions of a loving God? That no animal shall rise to + excellence except by being fatal to the life of others, is this + the law of a kind Creator? It is useless to say that pain has its + benevolence, that massacre has its mercy. Why is it so ordained + that bad should be the raw material of good? Pain is not the less + pain because it is useful; murder is not less murder because it + is conducive to development. Here is blood upon the hand still, + and all the perfumes of Arabia will not sweeten it."<a name= + "FNanchor_13_13" id="FNanchor_13_13"></a><a href= + "#Footnote_13_13" class="fnanchor">[13]</a></p> + + <p>Even so thoughtful a writer as Professor Huxley adopts similar + views. In a recent article on "The Struggle for Existence" he + speaks of the myriads of generations of herbivorous animals which + "have been tormented and devoured by carnivores"; of the + carnivores and herbivores alike "subject to all the miseries + incidental to old age, disease, and over-multiplication"; and of + the "more or less enduring suffering," which is the meed of both + vanquished and victor. And he concludes that, since thousands of + times a minute, were our ears sharp enough, we should hear sighs + and groans of pain like those heard by Dante at the gate of hell, + the world cannot be governed by what we call benevolence.<a name= + "FNanchor_14_14" id="FNanchor_14_14"></a><a href= + "#Footnote_14_14" class="fnanchor">[14]</a></p> + + <p>Now there is, I think, good reason to believe that all this is + greatly exaggerated; that the supposed "torments" and "miseries" + of animals have little real existence, but are the reflection of + the imagined sensations of cultivated men and women in similar + circumstances; and that the amount of actual suffering caused by + the struggle for existence among animals is altogether + insignificant. Let us, therefore, endeavour to ascertain what are + the real facts on which these tremendous accusations are + founded.</p> + + <p>In the first place, we must remember that animals are entirely + spared the pain we suffer in the anticipation of death—a + pain far greater, in most cases, than the reality. This leads, + probably, to an almost perpetual enjoyment of their lives; since + their constant watchfulness against danger, and even their actual + flight from an enemy, will be the enjoyable <a name="Page_38" id= + "Page_38"></a>exercise of the powers and faculties they possess, + unmixed with any serious dread. There is, in the next place, much + evidence to show that violent deaths, if not too prolonged, are + painless and easy; even in the case of man, whose nervous system + is in all probability much more susceptible to pain than that of + most animals. In all cases in which persons have escaped after + being seized by a lion or tiger, they declare that they suffered + little or no pain, physical or mental. A well-known instance is + that of Livingstone, who thus describes his sensations when + seized by a lion: "Starting and looking half round, I saw the + lion just in the act of springing on me. I was upon a little + height; he caught my shoulder as he sprang, and we both came to + the ground below together. Growling horribly close to my ear, he + shook me as a terrier-dog does a rat. The shock produced a stupor + similar to that which seems to be felt by a mouse after the first + shake of the cat. It causes a sort of dreaminess, <i>in which + there was no sense of pain or feeling of terror</i>, though I was + quite conscious of all that was happening. It was like what + patients partially under the influence of chloroform describe, + who see all the operation, but feel not the knife. This singular + condition was not the result of any mental process. The shake + annihilated fear, and allowed no sense of horror in looking round + at the beast."</p> + + <p>This absence of pain is not peculiar to those seized by wild + beasts, but is equally produced by any accident which causes a + general shock to the system. Mr. Whymper describes an accident to + himself during one of his preliminary explorations of the + Matterhorn, when he fell several hundred feet, bounding from rock + to rock, till fortunately embedded in a snow-drift near the edge + of a tremendous precipice. He declares that while falling and + feeling blow after blow, he neither lost consciousness nor + suffered pain, merely thinking, calmly, that a few more blows + would finish him. We have therefore a right to conclude, that + when death follows soon after any great shock it is as easy and + painless a death as possible; and this is certainly what happens + when an animal is seized by a beast of prey. For the enemy is one + which hunts for food, not for pleasure or excitement; and it is + doubtful whether any carnivorous animal in a state of nature + begins to seek after <a name="Page_39" id="Page_39"></a>prey till + driven to do so by hunger. When an animal is caught, therefore, + it is very soon devoured, and thus the first shock is followed by + an almost painless death. Neither do those which die of cold or + hunger suffer much. Cold is generally severest at night and has a + tendency to produce sleep and painless extinction. Hunger, on the + other hand, is hardly felt during periods of excitement, and when + food is scarce the excitement of seeking for it is at its + greatest. It is probable, also, that when hunger presses, most + animals will devour anything to stay their hunger, and will die + of gradual exhaustion and weakness not necessarily painful, if + they do not fall an earlier prey to some enemy or to + cold.<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href= + "#Footnote_15_15" class="fnanchor">[15]</a></p> + + <p>Now let us consider what are the enjoyments of the lives of + most animals. As a rule they come into existence at a time of + year when food is most plentiful and the climate most suitable, + that is in the spring of the temperate zone and at the + commencement of the dry season in the tropics. They grow + vigorously, being supplied with abundance of food; and when they + reach maturity their lives are a continual round of healthy + excitement and exercise, alternating with complete repose. The + daily search for the daily food employs all their faculties and + exercises every organ of their bodies, while this exercise leads + to the satisfaction of all their physical needs. In our own case, + we can give no more perfect definition of happiness, than this + exercise and this satisfaction; and we must therefore conclude + that animals, as a rule, enjoy all the happiness of which they + are capable. And this normal state of happiness is not alloyed, + as with us, by long periods—whole lives often—of + poverty or ill-health, and of the unsatisfied longing for + pleasures which others enjoy but to which we cannot attain. + Illness, and what answers to poverty in animals—continued + hunger—are quickly followed by unanticipated and almost + painless extinction. Where we err is, in giving to animals + feelings and emotions which they do not possess. To us the very + sight of blood and of torn or mangled limbs is painful, while the + idea of the suffering implied by it <a name="Page_40" id= + "Page_40"></a>is heartrending. We have a horror of all violent + and sudden death, because we think of the life full of promise + cut short, of hopes and expectations unfulfilled, and of the + grief of mourning relatives. But all this is quite out of place + in the case of animals, for whom a violent and a sudden death is + in every way the best. Thus the poet's picture of</p> + + <p><span style="margin-left: 2em;">"Nature red in tooth and + claw</span><br /> + <span style="margin-left: 4.5em;">With ravine"</span><br /></p> + + <p>is a picture the evil of which is read into it by our + imaginations, the reality being made up of full and happy lives, + usually terminated by the quickest and least painful of + deaths.</p> + + <p>On the whole, then, we conclude that the popular idea of the + struggle for existence entailing misery and pain on the animal + world is the very reverse of the truth. What it really brings + about, is, the maximum of life and of the enjoyment of life with + the minimum of suffering and pain. Given the necessity of death + and reproduction—and without these there could have been no + progressive development of the organic world,—and it is + difficult even to imagine a system by which a greater balance of + happiness could have been secured. And this view was evidently + that of Darwin himself, who thus concludes his chapter on the + struggle for existence: "When we reflect on this struggle, we may + console ourselves with the full belief that the war of nature is + not incessant, that no fear is felt, that death is generally + prompt, and that the vigorous, the healthy, and the happy survive + and multiply."</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href= + "#FNanchor_4_4"><span class="label">[4]</span></a> + <i>Géographic Botanique</i>, p. 798.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href= + "#FNanchor_5_5"><span class="label">[5]</span></a> <i>The + Origin of Species</i>, p. 53.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href= + "#FNanchor_6_6"><span class="label">[6]</span></a> <i>The + Earth as Modified by Human Action</i>, p. 51.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href= + "#FNanchor_7_7"><span class="label">[7]</span></a> <i>The + Origin of Species</i>, p. 56.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href= + "#FNanchor_8_8"><span class="label">[8]</span></a> See + <i>Nature</i>, vol. xxxi. p. 63.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href= + "#FNanchor_9_9"><span class="label">[9]</span></a> <i>A Visit + to South America</i>, 1878; also <i>Nature</i>, vol. xxxi. + pp. 263-339.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href= + "#FNanchor_10_10"><span class="label">[10]</span></a> Still + more remarkable is the increase of rabbits both in New + Zealand and Australia. No less than seven millions of + rabbit-skins have been exported from the former country in a + single year, their value being £67,000. In both + countries, sheep-runs have been greatly deteriorated in value + by the abundance of rabbits, which destroy the herbage; and + in some cases they have had to be abandoned altogether.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href= + "#FNanchor_11_11"><span class="label">[11]</span></a> Later + observers have proved that two eggs are laid and usually two + young produced, but it may be that in most cases only one of + these comes to maturity.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href= + "#FNanchor_12_12"><span class="label">[12]</span></a> + <i>Origin of Species</i>, p. 59. Professor A. Newton, + however, informs me that these species do not interfere with + one another in the way here stated.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href= + "#FNanchor_13_13"><span class="label">[13]</span></a> Winwood + Reade's <i>Martyrdom of Man,</i> p. 520.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href= + "#FNanchor_14_14"><span class="label">[14]</span></a> + <i>Nineteenth Century,</i> February 1888, pp. 162, 163.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href= + "#FNanchor_15_15"><span class="label">[15]</span></a> The + Kestrel, which usually feeds on mice, birds, and frogs, + sometimes stays its hunger with earthworms, as do some of the + American buzzards. The Honey-buzzard sometimes eats not only + earthworms and slugs, but even corn; and the Buteo borealis + of North America, whose usual food is small mammals and + birds, sometimes eats crayfish.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_III" id="CHAPTER_III"></a><a name="Page_41" + id="Page_41"></a>CHAPTER III</h2> + + <p style='font-weight:bold;'>THE VARIABILITY OF SPECIES IN A + STATE OF NATURE</p> + + <div class="blockquot"> + <p>Importance of variability—Popular ideas regarding + it—Variability of the lower animals—The variability + of insects—Variation among lizards—Variation among + birds—Diagrams of bird-variation—Number of varying + individuals—Variation in the mammalia—Variation in + internal organs—Variations in the skull—Variations + in the habits of Animals—The Variability of + plants—Species which vary little—Concluding + remarks.</p> + </div> + + <p>The foundation of the Darwinian theory is the variability of + species, and it is quite useless to attempt even to understand + that theory, much less to appreciate the completeness of the + proof of it, unless we first obtain a clear conception of the + nature and extent of this variability. The most frequent and the + most misleading of the objections to the efficacy of natural + selection arise from ignorance of this subject, an ignorance + shared by many naturalists, for it is only since Mr. Darwin has + taught us their importance that varieties have been + systematically collected and recorded; and even now very few + collectors or students bestow upon them the attention they + deserve. By the older naturalists, indeed, + varieties—especially if numerous, small, and of frequent + occurrence—were looked upon as an unmitigated nuisance, + because they rendered it almost impossible to give precise + definitions of species, then considered the chief end of + systematic natural history. Hence it was the custom to describe + what was supposed to be the "typical form" of species, and most + collectors were satisfied if they possessed this typical form in + their cabinets. Now, however, a collection is valued in + proportion as it contains illustrative specimens of all the + varieties that occur in each species, and in some cases these + <a name="Page_42" id="Page_42"></a>have been carefully described, + so that we possess a considerable mass of information on the + subject. Utilising this information we will now endeavour to give + some idea of the nature and extent of variation in the species of + animals and plants.</p> + + <p>It is very commonly objected that the widespread and constant + variability which is admitted to be a characteristic of + domesticated animals and cultivated plants is largely due to the + unnatural conditions of their existence, and that we have no + proof of any corresponding amount of variation occurring in a + state of nature. Wild animals and plants, it is said, are usually + stable, and when variations occur these are alleged to be small + in amount and to affect superficial characters only; or if larger + and more important, to occur so rarely as not to afford any aid + in the supposed formation of new species.</p> + + <p>This objection, as will be shown, is utterly unfounded; but as + it is one which goes to the very root of the problem, it is + necessary to enter at some length into the various proofs of + variation in a state of nature. This is the more necessary + because the materials collected by Mr. Darwin bearing on this + question have never been published, and comparatively few of them + have been cited in <i>The Origin of Species</i>; while a + considerable body of facts has been made known since the + publication of the last edition of that work.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variability of the Lower Animals</i>.</p> + + <p>Among the lowest and most ancient marine organisms are the + Foraminifera, little masses of living jelly, apparently + structureless, but which secrete beautiful shelly coverings, + often perfectly symmetrical, as varied in form as those of the + mollusca and far more complicated. These have been studied with + great care by many eminent naturalists, and the late Dr. W.B. + Carpenter in his great work—the <i>Introduction to the + Study of the Foraminifera</i>—thus refers to their + variability: "There is not a single species of plant or animal of + which the range of variation has been studied by the collocation + and comparison of so large a number of specimens as have passed + under the review of Messrs. Williamson, Parker, Rupert Jones, and + myself in our studies of the types of this group;" and he states + as the result of this extensive comparison of <a name="Page_43" + id="Page_43"></a>specimens: "The range of variation is so great + among the Foraminifera as to include not merely those + differential characters which have been usually accounted + <i>specific</i>, but also those upon which the greater part of + the <i>genera</i>, of this group have been founded, and even in + some instances those of its <i>orders</i>."<a name= + "FNanchor_16_16" id="FNanchor_16_16"></a><a href= + "#Footnote_16_16" class="fnanchor">[16]</a></p> + + <p>Coming now to a higher group—the Sea-Anemones—Mr. + P.H. Gosse and other writers on these creatures often refer to + variations in size, in the thickness and length of the tentacles, + the form of the disc and of the mouth, and the character of + surface of the column, while the colour varies enormously in a + great number of the species. Similar variations occur in all the + various groups of marine invertebrata, and in the great + sub-kingdom of the mollusca they are especially numerous. Thus, + Dr. S.P. Woodward states that many present a most perplexing + amount of variation, resulting (as he supposes) from supply of + food, variety of depth and of saltness of the water; but we know + that many variations are quite independent of such causes, and we + will now consider a few cases among the land-mollusca in which + they have been more carefully studied.</p> + + <p>In the small forest region of Oahu, one of the Sandwich + Islands, there have been found about 175 species of land-shells + represented by 700 or 800 varieties; and we are told by the Rev. + J.T. Gulick, who studied them carefully, that "we frequently find + a genus represented in several successive valleys by allied + species, sometimes feeding on the same, sometimes on different + plants. In every such case the valleys that are nearest to each + other furnish the most nearly allied forms; <i>and a full set of + the varieties of each species presents a minute gradation of + forms between the more divergent types found in the more widely + separated localities</i>."</p> + + <p>In most land-shells there is a considerable amount of + variation in colour, markings, size, form, and texture or + striation of the surface, even in specimens collected in the same + locality. Thus, a French author has enumerated no less than 198 + varieties of the common wood-snail (Helix nemoralis), while of + the equally common garden-snail (Helix hortensis) ninety + varieties have been described. Fresh-water shells are also + <a name="Page_44" id="Page_44"></a>subject to great variation, so + that there is much uncertainty as to the number of species; and + variations are especially frequent in the Planorbidae, which + exhibit many eccentric deviations from the usual form of the + species—deviations which must often affect the form of the + living animal. In Mr. Ingersoll's Report on the Recent Mollusca + of Colorado many of these extraordinary variations are referred + to, and it is stated that a shell (Helisonia trivolvis) abundant + in some small ponds and lakes, had scarcely two specimens alike, + and many of them closely resembled other and altogether distinct + species.<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href= + "#Footnote_17_17" class="fnanchor">[17]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Variability of Insects</i>.</p> + + <p>Among Insects there is a large amount of variation, though + very few entomologists devote themselves to its investigation. + Our first examples will be taken from the late Mr. T. Vernon + Wollaston's book, <i>On the Variation of Species</i>, and they + must be considered as indications of very widespread though + little noticed phenomena. He speaks of the curious little + carabideous beetles of the genus Notiophilus as being "extremely + unstable both in their sculpture and hue;" of the common Calathus + mollis as having "the hind wings at one time ample, at another + rudimentary, and at a third nearly obsolete;" and of the same + irregularity as to the wings being characteristic of many + Orthoptera and of the Homopterous Fulgoridae. Mr. Westwood in his + <i>Modern Classification of Insects</i> states that "the species + of Gerris, Hydrometra, and Velia are mostly found perfectly + apterous, though occasionally with full-sized wings."</p> + + <p>It is, however, among the Lepidoptera (butterflies and moths) + that the most numerous cases of variation have been observed, and + every good collection of these insects affords striking examples. + I will first adduce the testimony of Mr. Bates, who speaks of the + butterflies of the Amazon valley exhibiting innumerable local + varieties or races, while some species showed great individual + variability. Of the beautiful Mechanitis Polymnia he says, that + at Ega on the Upper Amazons, "it varies not only in general + colour and pattern, but also very considerably in the shape of + the wings, especially in the male sex." Again, at St. Paulo, + Ithomia</p> + + <p><a name="Page_45" id="Page_45"></a>Orolina exhibits four + distinct varieties, all occurring together, and these differ not + only in colour but in form, one variety being described as having + the fore wings much elongated in the male, while another is much + larger and has "the hind wings in the male different in shape." + Of Heliconius Numata Mr. Bates says: "This species is so variable + that it is difficult to find two examples exactly alike," while + "it varies in structure as well as in colours. The wings are + sometimes broader, sometimes narrower; and their edges are simple + in some examples and festooned in others." Of another species of + the same genus, H. melpomene, ten distinct varieties are + described all more or less connected by intermediate forms, and + four of these varieties were obtained at one locality, Serpa on + the north bank of the Amazon. Ceratina Ninonia is another of + these very unstable species exhibiting many local varieties which + are, however, incomplete and connected by intermediate forms; + while the several species of the genus Lycorea all vary to such + an extent as almost to link them together, so that Mr. Bates + thinks they might all fairly be considered as varieties of one + species only.</p> + + <p>Turning to the Eastern Hemisphere we have in Papilio Severus a + species which exhibits a large amount of simple variation, in the + presence or absence of a pale patch on the upper wings, in the + brown submarginal marks on the lower wings, in the form and + extent of the yellow band, and in the size of the specimens. The + most extreme forms, as well as the intermediate ones, are often + found in one locality and in company with each other. A small + butterfly (Terias hecabe) ranges over the whole of the Indian and + Malayan regions to Australia, and everywhere exhibits great + variations, many of which have been described as distinct + species; but a gentleman in Australia bred two of these distinct + forms (T. hecabe and T. Aesiope), with several intermediates, + from one batch of caterpillars found feeding together on the same + plant.<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href= + "#Footnote_18_18" class="fnanchor">[18]</a> It is therefore very + probable that a considerable number of supposed distinct species + are only individual varieties.</p> + + <p>Cases of variation similar to those now adduced among + butterflies might be increased indefinitely, but it is as well to + note that such important characters as the neuration of the + <a name="Page_46" id="Page_46"></a>wings, on which generic and + family distinctions are often established, are also subject to + variation. The Rev. R.P. Murray, in 1872, laid before the + Entomological Society examples of such variation in six species + of butterflies, and other cases have been since described. The + larvae of butterflies and moths are also very variable, and one + observer recorded in the <i>Proceedings of the Entomological + Society for</i> 1870 no less than sixteen varieties of the + caterpillar of the bedstraw hawk-moth (Deilephela galii).</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variation among Lizards</i>.</p> + + <p>Passing on from the lower animals to the vertebrata, we find + more abundant and more definite evidence as to the extent and + amount of individual variation. I will first give a case among + the Reptilia from some of Mr. Darwin's unpublished MSS., which + have been kindly lent me by Mr. Francis Darwin.</p> + + <p>"M. Milne Edwards (<i>Annales des Sci. Nat.</i>, I ser., tom. + xvi. p. 50) has given a curious table of measurements of fourteen + specimens of Lacerta muralis; and, taking the length of the head + as a standard, he finds the neck, trunk, tail, front and hind + legs, colour, and femoral pores, all varying wonderfully; and so + it is more or less with other species. So apparently trifling a + character as the scales on the head affording almost the only + constant characters."</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig01" id="fig01"></a> <img src="images/fig01.jpg" + width="400" height="645" alt= + "FIG. 1.—Variations of Lacerta muralis." title= + "FIG. 1.—Variations of Lacerta muralis." /> <b>FIG. + 1.—Variations of Lacerta muralis.</b> + </div> + + <div class="figcenter" style="width: 438px;"> + <a name="fig02" id="fig02"></a> <img src="images/fig02.jpg" + width="438" height="698" alt= + "FIG. 2.—Variation of Lizards." title= + "FIG. 2.—Variation of Lizards." /> <b>FIG. + 2.—Variation of Lizards.</b> + </div> + + <p>As the table of measurements above referred to would give no + clear conception of the nature and amount of the variation + without a laborious study and comparison of the figures, I have + endeavoured to find a method of presenting the facts to the eye, + so that they may be easily grasped and appreciated. In the + diagram opposite, the comparative variations of the different + organs of this species are given by means of variously bent + lines. The head is represented by a straight line because it + presented (apparently) no variation. The body is next given, the + specimens being arranged in the order of their size from No. 1, + the smallest, to No. 14, the largest, the actual lengths being + laid down from a base line at a suitable distance below, in this + case two inches below the centre, the mean length of the body of + the fourteen specimens being two inches. The respective lengths + of the neck, legs, and toe of <a name="Page_47" id= + "Page_47"></a><a name="Page_48" id="Page_48"></a><a name= + "Page_49" id="Page_49"></a>each specimen are then laid down in + the same manner at convenient distances apart for comparison; and + we see that their variations bear no definite relation to those + of the body, and not much to those of each other. With the + exception of No. 5, in which all the parts agree in being large, + there is a marked independence of each part, shown by the lines + often curving in opposite directions; which proves that in those + specimens one part is large while the other is small. The actual + amount of the variation is very great, ranging from one-sixth of + the mean length in the neck to considerably more than a fourth in + the hind leg, and this among only fourteen examples which happen + to be in a particular museum.</p> + + <p>To prove that this is not an isolated case, Professor Milne + Edwards also gives a table showing the amount of variation in the + museum specimens of six common species of lizards, also taking + the head as the standard, so that the comparative variation of + each part to the head is given. In the accompanying diagram (Fig. + 2) the variations are exhibited by means of lines of varying + length. It will be understood that, however much the specimens + varied in <i>size</i>, if they had kept the same + <i>proportions</i>, the variation line would have been in every + case reduced to a point, as in the neck of L. velox which + exhibits no variation. The different proportions of the variation + lines for each species may show a distinct mode of variation, or + may be merely due to the small and differing number of specimens; + for it is certain that whatever amount of variation occurs among + a few specimens will be greatly increased when a much larger + number of specimens are examined. That the amount of variation is + large, may be seen by comparing it with the actual length of the + head (given below the diagram) which was used as a standard in + determining the variation, but which itself seems not to have + varied.<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href= + "#Footnote_19_19" class="fnanchor">[19]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variation among Birds</i>.</p> + + <p>Coming now to the class of Birds, we find much more copious + evidence of variation. This is due partly to the fact that + Ornithology has perhaps a larger body of devotees than any other + branch of natural history (except entomology); to the moderate + size of the majority of birds; and to the circum<a name="Page_50" + id="Page_50"></a>stance that the form and dimensions of the + wings, tail, beak, and feet offer the best generic and specific + characters and can all be easily measured and compared. The most + systematic observations on the individual variation of birds have + been made by Mr. J.A. Allen, in his remarkable memoir: "On the + Mammals and Winter Birds of East Florida, with an examination of + certain assumed specific characters in Birds, and a sketch of the + Bird Faunae of Eastern North America," published in the + <i>Bulletin of the Museum of Comparative Zoology</i> at Harvard + College, Cambridge, Massachusetts, in 1871. In this work exact + measurements are given of all the chief external parts of a large + number of species of common American birds, from twenty to sixty + or more specimens of each species being measured, so that we are + able to determine with some precision the nature and extent of + the variation that usually occurs. Mr. Allen says: "The facts of + the case show that a variation of from 15 to 20 per cent in + general size, and an equal degree of variation in the relative + size of different parts, may be ordinarily expected among + specimens of the same species and sex, taken at the same + locality, while in some cases the variation is even greater than + this." He then goes on to show that each part varies to a + considerable extent independently of the other parts; so that + when the size varies, the proportions of all the parts vary, + often to a much greater amount. The wing and tail, for example, + besides varying in length, vary in the proportionate length of + each feather, and this causes their outline to vary considerably + in shape. The bill also varies in length, width, depth, and + curvature. The tarsus varies in length, as does each toe + separately and independently; and all this not to a minute degree + requiring very careful measurement to detect it at all, but to an + amount easily seen without any measurement, as it averages + one-sixth of the whole length and often reaches one-fourth. In + twelve species of common perching birds the wing varied (in from + twenty-five to thirty specimens) from 14 to 21 per cent of the + mean length, and the tail from 13.8 to 23.4 per cent. The + variation of the form of the wing can be very easily tested by + noting which feather is longest, which next in length, and so on, + the respective feathers being indicated by the numbers 1, 2, 3, + etc., com<a name="Page_51" id="Page_51"></a>mencing with the + outer one. As an example of the irregular variation constantly + met with, the following occurred among twenty-five specimens of + Dendroeca coronata. Numbers bracketed imply that the + corresponding feathers were of equal length.<a name= + "FNanchor_20_20" id="FNanchor_20_20"></a><a href= + "#Footnote_20_20" class="fnanchor">[20]</a></p> + + <pre> + RELATIVE LENGTHS OF PRIMARY WING FEATHERS OF + DENDROECA CORONATA. + ---------+-----------+----------+-----------+----------+---------- + Longest. | Second in | Third in | Fourth in | Fifth in | Sixth in + | Length. | Length. | Length. | Length. | Length. + ---------+-----------+----------+-----------+----------+---------- + 2 | 3 | 1 | 4 | 5 | 6 + 3 | 2 | 4 | 1 | 5 | 6 + | / 2 | | | | + 3 | { | 1 | 5 | 6 | 7 + | \ 4 | | | | + 2 \ | | | | | + } | 4 | 1 | 5 | 6 | 7 + 3 / | | | | | + 2 \ | | | | | + 1 | | | | | | + } | 5 | 6 | 7 | 8 | 9 + 3 | | | | | | + 4 / | | | | | + ---------+-----------+----------+-----------+----------+---------- + </pre> + + <p>Here we have five very distinct proportionate lengths of the + wing feathers, any one of which is often thought sufficient to + characterise a distinct species of bird; and though this is + rather an extreme case, Mr. Allen assures us that "the + comparison, extended in the table to only a few species, has been + carried to scores of others with similar results."</p> + + <p>Along with this variation in size and proportions there occurs + a large amount of variation in colour and markings. "The + difference in intensity of colour between the extremes of a + series of fifty or one hundred specimens of any species, + collected at a single locality, and nearly at the same season of + the year, is often as great as occurs between truly distinct + species." But there is also a great amount of individual + variability in the markings of the same species. Birds having the + plumage varied with streaks and spots differ exceedingly in + different individuals of the same species in respect to the size, + shape, and number of these marks, and in the general aspect of + the plumage resulting from such variations. "In the common + <a name="Page_52" id="Page_52"></a>song sparrow (Melospiza + melodia), the fox-coloured sparrow (Passerella iliaca), the swamp + sparrow (Melospiza palustris), the black and white creeper + (Mniotilta varia), the water-wagtail (Seiurus novaeboracencis), + in Turdus fuscescens and its allies, the difference in the size + of the streaks is often very considerable. In the song sparrow + they vary to such an extent that in some cases they are reduced + to narrow lines; in others so enlarged as to cover the greater + part of the breast and sides of the body, sometimes uniting on + the middle of the breast into a nearly continuous patch."</p> + + <p>Mr. Allen then goes on to particularise several species in + which such variations occur, giving cases in which two specimens + taken at the same place on the same day exhibited the two + extremes of coloration. Another set of variations is thus + described: "The white markings so common on the wings and tails + of birds, as the bars formed by the white tips of the greater + wing-coverts, the white patch occasionally present at the base of + the primary quills, or the white band crossing them, and the + white patch near the end of the outer tail-feathers are also + extremely liable to variation in respect to their extent and the + number of feathers to which, in the same species, these markings + extend." It is to be especially noted that all these varieties + are distinct from those which depend on season, on age, or on + sex, and that they are such as have in many other species been + considered to be of specific value.</p> + + <p>These variations of colour could not be presented to the eye + without a series of carefully engraved plates, but in order to + bring Mr. Allen's <i>measurements</i>, illustrating variations of + size and proportion, more clearly before the reader, I have + prepared a series of diagrams illustrating the more important + facts and their bearings on the Darwinian theory.</p> + + <p>The first of these is intended, mainly, to show the actual + amount of the variation, as it gives the true length of the wing + and tail in the extreme cases among thirty specimens of each of + three species. The shaded portion shows the minimum length, the + unshaded portion the additional length in the maximum. The point + to be specially noted here is, that in each of these common + species there is about the same amount of variation, and that it + is so great as to be obvious at a glance.</p> + + <div class="figcenter" style="width: 500px;"> + <a name="fig03" id="fig03"></a> <a name="Page_53" id= + "Page_53"></a><img src="images/fig03.jpg" width="500" height= + "328" alt="FIG. 3.—Variation of Wings and Tail." title= + "FIG. 3.—Variation of Wings and Tail." /> <b>FIG. + 3.—Variation of Wings and Tail.</b> + </div> + + <p><a name="Page_54" id="Page_54"></a>There is here no question + of "minute" or "infinitesimal" variation, which many people + suppose to be the only kind of variation that exists. It cannot + even be called small; yet from all the evidence we now possess it + seems to be the amount which characterises most of the common + species of birds.</p> + + <p>It may be said, however, that these are the extreme + variations, and only occur in one or two individuals, while the + great majority exhibit little or no difference. Other diagrams + will show that this is not the case; but even if it were so, it + would be no objection at all, because these are the extremes + among thirty specimens only. We may safely assume that these + thirty specimens, taken by chance, are not, in the case of all + these species, exceptional lots, and therefore we might expect at + least two similarly varying specimens in each additional thirty. + But the number of individuals, even in a very rare species, is + probably thirty thousand or more, and in a common species thirty, + or even three hundred, millions. Even one individual in each + thirty, varying to the amount shown in the diagram, would give at + least a million in the total population of any common bird, and + among this million many would vary much more than the extreme + among thirty only. We should thus have a vast body of individuals + varying to a large extent in the length of the wings and tail, + and offering ample material for the modification of these organs + by natural selection. We will now proceed to show that other + parts of the body vary, simultaneously, but independently, to an + equal amount.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig04" id="fig04"></a> <img src="images/fig04.jpg" + width="400" height="701" alt= + "FIG. 4.—Dolichonyx oryzivorus. 20 Males." title= + "FIG. 4.—Dolichonyx oryzivorus. 20 Males." /> <b>FIG. + 4.—Dolichonyx oryzivorus. 20 Males.</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig05" id="fig05"></a> <img src="images/fig05.jpg" + width="400" height="632" alt= + "FIG. 5.—Agelaeus phoeniceus. 40 Males." title= + "FIG. 5.—Agelaeus phoeniceus. 40 Males." /> <b>FIG. + 5.—Agelaeus phoeniceus. 40 Males.</b> + </div> + + <p>The first bird taken is the common Bob-o-link or Rice-bird + (Dolichonyx oryzivorus), and the Diagram, Fig. 4, exhibits the + variations of seven important characters in twenty male adult + specimens.<a name="FNanchor_21_21" id= + "FNanchor_21_21"></a><a href="#Footnote_21_21" class= + "fnanchor">[21]</a> These characters are—the lengths of the + body, wing, tail, tarsus, middle toe, outer toe, and hind toe, + being as many as can be conveniently exhibited in one diagram. + The length of the body is not given by Mr. Allen, but as it forms + a convenient standard of comparison, it has been obtained by + deducting the length of the tail from the total length of the + birds as given by him. The diagram has been constructed as + follows:—The twenty specimens are first arranged in a + series according to the body-lengths (which may be con<a name= + "Page_55" id="Page_55"></a><a name="Page_56" id= + "Page_56"></a><a name="Page_57" id="Page_57"></a>sidered to give + the size of the bird), from the shortest to the longest, and the + same number of vertical lines are drawn, numbered from one to + twenty. In this case (and wherever practicable) the body-length + is measured from the lower line of the diagram, so that the + actual length of the bird is exhibited as well as the actual + variations of length. These can be well estimated by means of the + horizontal line drawn at the mean between the two extremes, and + it will be seen that one-fifth of the total number of specimens + taken on either side exhibits a very large amount of variation, + which would of course be very much greater if a hundred or more + specimens were compared. The lengths of the wing, tail, and other + parts are then laid down, and the diagram thus exhibits at a + glance the comparative variation of these parts in every specimen + as well as the actual amount of variation in the twenty + specimens; and we are thus enabled to arrive at some important + conclusions.</p> + + <p>We note, first, that the variations of none of the parts + follow the variations of the body, but are sometimes almost in an + opposite direction. Thus the longest wing corresponds to a rather + small body, the longest tail to a medium body, while the longest + leg and toes belong to only a moderately large body. Again, even + related parts do not constantly vary together but present many + instances of independent variation, as shown by the want of + parallelism in their respective variation-lines. In No. 5 (see + Fig. 4) the wing is very long, the tail moderately so; while in + No. 6 the wing is much shorter while the tail is considerably + longer. The tarsus presents comparatively little variation; and + although the three toes may be said to vary in general together, + there are many divergencies; thus, in passing from No. 9 to No. + 10, the outer toe becomes longer, while the hind toe becomes + considerably shorter; while in Nos. 3 and 4 the middle toe varies + in an opposite way to the outer and the hind toes.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig06" id="fig06"></a> <img src="images/fig06.jpg" + width="400" height="667" alt= + "FIG. 6.—Cardinalis virginianus. 31 Males." title= + "FIG. 6.—Cardinalis virginianus. 31 Males." /> <b>FIG. + 6.—Cardinalis virginianus. 31 Males.</b> + </div> + + <p>In the next diagram (Fig. 5) we have the variations in forty + males of the Red-winged Blackbird (Agelaeus phoeniceus), and here + we see the same general features. One-fifth of the whole number + of specimens offer a large amount of variation either below or + above the mean; while the wings, tail, and head vary quite + independently of the body. The wing and tail too, <a name= + "Page_58" id="Page_58"></a><a name="Page_59" id= + "Page_59"></a>though showing some amount of correlated variation, + yet in no less than nine cases vary in opposite directions as + compared with the preceding species.</p> + + <p>The next diagram (Fig. 6), showing the variations of + thirty-one males of the Cardinal bird (Cardinalis virginianus), + exhibits these features much more strongly. The amount of + variation in proportion to the size of the bird is very much + greater; while the variations of the wing and tail not only have + no correspondence with that of the body but very little with each + other. In no less than twelve or thirteen instances they vary in + opposite directions, while even where they correspond in + direction the amount of the variation is often very + disproportionate.</p> + + <p>As the proportions of the tarsi and toes of birds have great + influence on their mode of life and habits and are often used as + specific or even generic characters, I have prepared a diagram + (Fig. 7) to show the variation in these parts only, among twenty + specimens of each of four species of birds, four or five of the + most variable alone being given. The extreme divergence of each + of the lines in a vertical direction shows the actual amount of + variation; and if we consider the small length of the toes of + these small birds, averaging about three-quarters of an inch, we + shall see that the variation is really very large; while the + diverging curves and angles show that each part varies, to a + great extent, independently. It is evident that if we compared + some thousands of individuals instead of only twenty, we should + have an amount of independent variation occurring each year which + would enable almost any modification of these important organs to + be rapidly effected.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig07" id="fig07"></a> <img src="images/fig07.jpg" + width="400" height="650" alt= + "FIG. 7.—Variation of Tarsus and Toes." title= + "FIG. 7.—Variation of Tarsus and Toes." /> <b>FIG. + 7.—Variation of Tarsus and Toes.</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig08" id="fig08"></a> <img src="images/fig08.jpg" + width="400" height="607" alt= + "FIG. 8.—Variation of Birds in Leyden Museum." title= + "FIG. 8.—Variation of Birds in Leyden Museum." /> <b>FIG. + 8.—Variation of Birds in Leyden Museum.</b> + </div> + + <p>In order to meet the objection that the large amount of + variability here shown depends chiefly on the observations of one + person and on the birds of a single country, I have examined + Professor Schlegel's Catalogue of the Birds in the Leyden Museum, + in which he usually gives the range of variation of the specimens + in the museum (which are commonly less than a dozen and rarely + over twenty) as regards some of their more important dimensions. + These fully support the statement of Mr. Allen, since they show + an equal amount of variability when the numbers compared are + <a name="Page_60" id="Page_60"></a><a name="Page_61" id= + "Page_61"></a><a name="Page_62" id="Page_62"></a>sufficient, + which, however, is not often the case. The accompanying diagram + exhibits the actual differences of size in five organs which + occur in five species taken almost at random from this catalogue. + Here, again, we perceive that the variation is decidedly large, + even among a very small number of specimens; while the facts all + show that there is no ground whatever for the common assumption + that natural species consist of individuals which are nearly all + alike, or that the variations which occur are "infinitesimal" or + even "small."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The proportionate Number of Individuals which present a + considerable amount of Variation.</i></p> + + <p>The notion that variation is a comparatively exceptional + phenomenon, and that in any case considerable variations occur + very rarely in proportion to the number of individuals which do + not vary, is so deeply rooted that it is necessary to show by + every possible method of illustration how completely opposed it + is to the facts of nature. I have therefore prepared some + diagrams in which each of the individual birds measured is + represented by a spot, placed at a proportionate distance, right + and left, from the median line accordingly as it varies in excess + or defect of the mean length as regards the particular part + compared. As the object in this set of diagrams is to show the + number of individuals which vary considerably in proportion to + those which vary little or not at all, the scale has been + enlarged in order to allow room for placing the spots without + overlapping each other.</p> + + <p>In the diagram opposite twenty males of Icterus Baltimore are + registered, so as to exhibit to the eye the proportionate number + of specimens which vary, to a greater or less amount, in the + length of the tail, wing, tarsus, middle toe, hind toe, and bill. + It will be noticed that there is usually no very great + accumulation of dots about the median line which shows the + average dimensions, but that a considerable number are spread at + varying distances on each side of it.</p> + + <p>In the next diagram (Fig. 10), showing the variation among + forty males of Agelaeeus phoeniceus, this approach to an equable + spreading of the variations is still more apparent; while in Fig. + 12, where fifty-eight specimens of Cardinalis <a name="Page_63" + id="Page_63"></a>virginianus are registered, we see a remarkable + spreading out of the spots, showing in some of the characters a + tendency to segregation into two or more groups of individuals, + each varying considerably from the mean.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig09" id="fig09"></a> <img src="images/fig09.jpg" + width="400" height="676" alt="FIG. 9" title="FIG. 9" /> <b>FIG. + 9</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig10" id="fig10"></a> <img src="images/fig10.jpg" + width="400" height="492" alt="FIG. 10." title="FIG. 10." /> + <b>FIG. 10.</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig11" id="fig11"></a> <img src="images/fig11.jpg" + width="400" height="80" alt="FIG. 11." title="FIG. 11." /> + <b>FIG. 11.</b> + </div> + + <p>In order fully to appreciate the teaching of these diagrams, + we must remember, that, whatever kind and amount of variations + are exhibited by the few specimens here compared, would be + greatly extended and brought into symmetrical form if large + numbers—thousands or millions—were subjected to the + same process of measurement and registration. We know, from the + general law which governs variations from a mean value, that with + increasing numbers the range <a name="Page_64" id= + "Page_64"></a>of variation of each part would increase also, at + first rather rapidly and then more slowly; while gaps and + irregularities would be gradually filled up, and at length the + distribution of the dots would indicate a tolerably regular curve + of double curvature like those shown in Fig. 11. The great + divergence <a name="Page_65" id="Page_65"></a>of the dots, when + even a few specimens are compared, shows that the curve, with + high numbers, would be a flat one like the lower curve in the + illustration here given. This being the case it would follow that + a very large proportion of the total number of individuals + constituting a species would diverge considerably from its + average condition as regards each part or organ; and as we know + from the previous diagrams of variation (Figs. 1 to 7) that each + part varies to a considerable extent, <i>independently</i>, the + materials constantly ready for natural selection to act upon are + abundant in quantity and very varied in kind. Almost any + combination of variations of distinct parts will be available, + where required; and this, as we shall see further on, obviates + one of the most weighty objections which have been urged against + the efficiency of natural selection in producing new species, + genera, and higher groups.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig12" id="fig12"></a> <img src="images/fig12.jpg" + width="400" height="287" alt="FIG. 12." title="FIG. 12." /> + <b>FIG. 12.</b> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variation in the Mammalia.</i></p> + + <p>Owing to the generally large size of this class of animals, + and the comparatively small number of naturalists who study them, + large series of specimens are only occasionally examined <a name= + "Page_66" id="Page_66"></a>and compared, and thus the materials + for determining the question of their variability in a state of + nature are comparatively scanty. The fact that our domestic + animals belonging to this group, especially dogs, present extreme + varieties not surpassed even by pigeons and poultry among birds, + renders it almost certain that an equal amount of variability + exists in the wild state; and this is confirmed by the example of + a species of squirrel (Sciurus carolinensis), of which sixteen + specimens, all males and all taken in Florida, were measured and + tabulated by Mr. Allen. The diagram here given shows, that, both + the general amount of the variation and the independent + variability of the several members of the body, accord completely + with the variations so common in the class of birds; while their + amount and their independence of each other are even greater than + usual.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variation in the Internal Organs of Animals.</i></p> + + <p>In case it should be objected that the cases of variation + hitherto adduced are in the external parts only, and that there + is no proof that the internal organs vary in the same manner, it + will be advisable to show that such varieties also occur. It is, + however, impossible to adduce the same amount of evidence in this + class of variation, because the great labour of dissecting large + numbers of specimens of the same species is rarely undertaken, + and we have to trust to the chance observations of anatomists + recorded in their regular course of study.</p> + + <p>It must, however, be noted that a very large proportion of the + variations already recorded in the external parts of animals + necessarily imply corresponding internal variations. When feet + and legs vary in size, it is because the bones vary; when the + head, body, limbs, and tail change their proportions, the bony + skeleton must also change; and even when the wing or tail + feathers of birds become longer or more numerous, there is sure + to be a corresponding change in the bones which support and the + muscles which move them. I will, however, give a few cases of + variations which have been directly observed.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig13" id="fig13"></a> <img src="images/fig13.jpg" + width="400" height="664" alt= + "FIG. 13.—Sciurus carolinensis. 32 specimens. Florida." + title= + "FIG. 13.—Sciurus carolinensis. 32 specimens. Florida." /> + <b>FIG. 13.—Sciurus carolinensis. 32 specimens. + Florida.</b> + </div> + + <p>Mr. Frank E. Beddard has kindly communicated to me some + remarkable variations he has observed in the internal <a name= + "Page_67" id="Page_67"></a><a name="Page_68" id= + "Page_68"></a>organs of a species of earthworm (Perionyx + excavatus). The normal characters of this species are—</p> + + <div class="blockquot"> + <p>Setae forming a complete row round each segment.</p> + + <p>Two pairs of spermathecae—spherical pouches without + diverticulae—in segments 8 and 9.</p> + + <p>Two pairs of testes in segments 11 and 12.</p> + + <p>Ovaries, a single pair in segment 13.</p> + + <p>Oviducts open by a common pore in the middle of segment + 14.</p> + + <p>Vasa deferentia open separately in segment 18, each + furnished at its termination with a large prostate gland.</p> + </div> + + <p>Between two and three hundred specimens were examined, and + among them thirteen specimens exhibited the following marked + variations:—</p> + + <div class="blockquot"> + <p>(1) The number of the spermathecae varied from two to three + or four pairs, their position also varying.</p> + + <p>(2) There were occasionally two pairs of ovaries, each with + its own oviduct; the external apertures of these varied in + position, being upon segments 13 and 14, 14 and 15, or 15 and + 16. Occasionally when there was only the normal single oviduct + pore present it varied in position, once occurring on the 10th, + and once on the 11th segment.</p> + + <p>(3) The male generative pores varied in position from + segments 14 to 20. In one instance there were two pairs instead + of the normal single pair, and in this case each of the four + apertures had its own prostate gland.</p> + </div> + + <p>Mr. Beddard remarks that all, or nearly all, the above + variations are found <i>normally</i> in other genera and + species.</p> + + <p>When we consider the enormous number of earthworms and the + comparatively very small number of individuals examined, we may + be sure, not only that such variations as these occur with + considerable frequency, but also that still more extraordinary + deviations from the normal structure may often exist.</p> + + <p>The next example is taken from Mr. Darwin's unpublished + MSS.</p> + + <div class="blockquot"> + <p>"In some species of Shrews (Sorex) and in some + field-mice<a name="Page_69" id="Page_69"></a> (Arvicola), the + Rev. L. Jenyns (<i>Ann. Nat. Hist.</i>, vol. vii. pp. 267, 272) + found the proportional length of the intestinal canal to vary + considerably. He found the same variability in the number of + the caudal vertebrae. In three specimens of an Arvicola he + found the gall-bladder having a very different degree of + development, and there is reason to believe it is sometimes + absent. Professor Owen has shown that this is the case with the + gall-bladder of the giraffe."</p> + </div> + + <p>Dr. Crisp (<i>Proc. Zool. Soc.</i>, 1862, p. 137) found the + gall-bladder present in some specimens of Cervus superciliaris + while absent in others; and he found it to be absent in three + giraffes which he dissected. A double gall-bladder was found in a + sheep, and in a small mammal preserved in the Hunterian Museum + there are three distinct gall-bladders.</p> + + <p>The length of the alimentary canal varies greatly. In three + adult giraffes described by Professor Owen it was from 124 to 136 + feet long; one dissected in France had this canal 211 feet long; + while Dr. Crisp measured one of the extraordinary length of 254 + feet, and similar variations are recorded in other + animals.<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href= + "#Footnote_22_22" class="fnanchor">[22]</a></p> + + <p>The number of ribs varies in many animals. Mr. St. George + Mivart says: "In the highest forms of the Primates, the number of + true ribs is seven, but in Hylobates there are sometimes eight + pairs. In Semnopithecus and Colobus there are generally seven, + but sometimes eight pairs of true ribs. In the Cebidae there are + generally seven or eight pairs, but in Ateles sometimes nine" + (<i>Proc. Zool. Soc.</i>, 1865, p. 568). In the same paper it is + stated that the number of dorsal vertebrae in man is normally + twelve, very rarely thirteen. In the Chimpanzee there are + normally thirteen dorsal vertebrae, but occasionally there are + fourteen or only twelve.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variations in the Skull.</i></p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig14" id="fig14"></a> <img src="images/fig14.jpg" + width="400" height="715" alt= + "FIG. 14.—Variation of Skull of Wolf. 10 specimens." + title= + "FIG. 14.—Variation of Skull of Wolf. 10 specimens." /> + <b>FIG. 14.—Variation of Skull of Wolf. 10 specimens.</b> + </div> + + <p>Among the nine adult male Orang-utans, collected by myself in + Borneo, the skulls differed remarkably in size and proportions. + The orbits varied in width and height, the cranial ridge was + either single or double, either much or little developed, and the + zygomatic aperture varied considerably in <a name="Page_70" id= + "Page_70"></a><a name="Page_71" id="Page_71"></a>size. I noted + particularly that these variations bore no necessary relation to + each other, so that a large temporal muscle and zygomatic + aperture might exist either with a large or a small cranium; and + thus was explained the curious difference between the + single-crested and the double-crested skulls, which had been + supposed to characterise distinct species. As an instance of the + amount of variation in the skulls of fully adult male orangs, I + found the width between the orbits externally to be only 4 inches + in one specimen and fully 5 inches in another.</p> + + <p>Exact measurements of large series of comparable skulls of the + mammalia are not easily found, but from those available I have + prepared three diagrams (Figs. 14, 15, and 16), in order to + exhibit the facts of variation in this very important organ. The + first shows the variation in ten specimens of the common wolf + (Canis lupus) from one district in North America, and we see that + it is not only large in amount, but that each part exhibits a + considerable independent variability.<a name="FNanchor_23_23" id= + "FNanchor_23_23"></a><a href="#Footnote_23_23" class= + "fnanchor">[23]</a></p> + + <p>In Diagram 15 we have the variations of eight skulls of the + Indian Honey-bear (Ursus labiatus), as tabulated by the late Dr. + J.E. Gray of the British Museum. For such a small number of + specimens the amount of variation is very large—from + one-eighth to one-fifth of the mean size,—while there are + an extraordinary number of instances of independent variability. + In Diagram 16 we have the length and width of twelve skulls of + adult males of the Indian wild boar (Sus cristatus), also given + by Dr. Gray, exhibiting in both sets of measurements a variation + of more than one-sixth, combined with a very considerable amount + of independent variability.<a name="FNanchor_24_24" id= + "FNanchor_24_24"></a><a href="#Footnote_24_24" class= + "fnanchor">[24]</a></p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig15" id="fig15"></a> <img src="images/fig15.jpg" + width="400" height="609" alt= + "FIG. 15.—Variation of 8 skulls (Ursus labiatus)." title= + "FIG. 15.—Variation of 8 skulls (Ursus labiatus)." /> + <b>FIG. 15.—Variation of 8 skulls (Ursus labiatus).</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig16" id="fig16"></a> <img src="images/fig16.jpg" + width="400" height="298" alt="FIG. 16." title="FIG. 16." /> + <b>FIG. 16.</b> + </div> + + <p>The few facts now given, as to variations of the internal + parts of animals, might be multiplied indefinitely by a search + through the voluminous writings of comparative anatomists. But + the evidence already adduced, taken in conjunction with the much + fuller evidence of variation in all external organs, leads us to + the conclusion that wherever variations are looked for among a + considerable number of individuals of the more <a name="Page_72" + id="Page_72"></a><a name="Page_73" id="Page_73"></a><a name= + "Page_74" id="Page_74"></a>common species they are sure to be + found; that they are everywhere of considerable amount, often + reaching 20 per cent of the size of the part implicated; and that + they are to a great extent independent of each other, and thus + afford almost any combination of variations that may be + needed.</p> + + <p>It must be particularly noticed that the whole series of + variation-diagrams here given (except the three which illustrate + the number of varying individuals) in every case represent the + actual amount of the variation, not on any reduced or enlarged + scale, but as it were life-size. Whatever number of inches or + decimals of an inch the species varies in any of its parts is + marked on the diagrams, so that with the help of an ordinary + divided rule or a pair of compasses the variation of the + different parts can be ascertained and compared just as if the + specimens themselves were before the reader, but with much + greater ease.</p> + + <p>In my lectures on the Darwinian theory in America and in this + country I used diagrams constructed on a different plan, equally + illustrating the large amount of independent variability, but + less simple and less intelligible. The present method is a + modification of that used by Mr. Francis Galton in his researches + on the theory of variability, the upper line (showing the + variability of the body) in Diagrams 4, 5, 6, and 13, being laid + down on the method he has used in his experiments with sweet-peas + and in pedigree moth-breeding.<a name="FNanchor_25_25" id= + "FNanchor_25_25"></a><a href="#Footnote_25_25" class= + "fnanchor">[25]</a> I believe, after much consideration, and many + tedious experiments in diagram-making, that no better method can + be adopted for bringing before the eye, both the amount and the + peculiar features of individual variability.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variations of the Habits of Animals.</i></p> + + <p>Closely connected with those variations of internal and + external structure which have been already described, are the + changes of habits which often occur in certain individuals or in + whole species, since these must necessarily depend upon some + corresponding change in the brain or in other parts of the + organism; and as these changes are of great importance in + relation to the theory of instinct, a few examples of them will + be now adduced.</p> + + <p><a name="Page_75" id="Page_75"></a>The Kea (Nestor notabilis) + is a curious parrot inhabiting the mountain ranges of the Middle + Island of New Zealand. It belongs to the family of Brush-tongued + parrots, and naturally feeds on the honey of flowers and the + insects which frequent them, together with such fruits or berries + as are found in the region. Till quite recently this comprised + its whole diet, but since the country it inhabits has become + occupied by Europeans it has developed a taste for a carnivorous + diet, with alarming results. It began by picking the sheepskins + hung out to dry or the meat in process of being cured. About 1868 + it was first observed to attack living sheep, which had + frequently been found with raw and bleeding wounds on their + backs. Since then it is stated that the bird actually burrows + into the living sheep, eating its way down to the kidneys, which + form its special delicacy. As a natural consequence, the bird is + being destroyed as rapidly as possible, and one of the rare and + curious members of the New Zealand fauna will no doubt shortly + cease to exist. The case affords a remarkable instance of how the + climbing feet and powerful hooked beak developed for one set of + purposes can be applied to another altogether different purpose, + and it also shows how little real stability there may be in what + appear to us the most fixed habits of life. A somewhat similar + change of diet has been recorded by the Duke of Argyll, in which + a goose, reared by a golden eagle, was taught by its + foster-parent to eat flesh, which it continued to do regularly + and apparently with great relish.<a name="FNanchor_26_26" id= + "FNanchor_26_26"></a><a href="#Footnote_26_26" class= + "fnanchor">[26]</a></p> + + <p>Change of habits appears to be often a result of imitation, of + which Mr. Tegetmeier gives some good examples. He states that if + pigeons are reared exclusively with small grain, as wheat or + barley, they will starve before eating beans. But when they are + thus starving, if a bean-eating pigeon is put among them, they + follow its example, and thereafter adopt the habit. So fowls + sometimes refuse to eat maize, but on seeing others eat it, they + do the same and become excessively fond of it. Many persons have + found that their yellow crocuses were eaten by sparrows, while + the blue, purple, and white coloured varieties were left + untouched; but Mr. Tegetmeier, who grows only these latter + colours, found that after <a name="Page_76" id="Page_76"></a>two + years the sparrows began to attack them, and thereafter destroyed + them quite as readily as the yellow ones; and he believes it was + merely because some bolder sparrow than the rest set the example. + On this subject Mr. Charles C. Abbott well remarks: "In studying + the habits of our American birds—and I suppose it is true + of birds everywhere—it must at all times be remembered that + there is less stability in the habits of birds than is usually + supposed; and no account of the habits of any one species will + exactly detail the various features of its habits as they really + are, in every portion of the territory it inhabits."<a name= + "FNanchor_27_27" id="FNanchor_27_27"></a><a href= + "#Footnote_27_27" class="fnanchor">[27]</a></p> + + <p>Mr. Charles Dixon has recorded a remarkable change in the mode + of nest-building of some common chaffinches which were taken to + New Zealand and turned out there. He says: "The cup of the nest + is small, loosely put together, apparently lined with feathers, + and the walls of the structure are prolonged for about 18 inches, + and hang loosely down the side of the supporting branch. The + whole structure bears some resemblance to the nests of the + hangnests (Icteridae), with the exception that the cavity is at + the top. Clearly these New Zealand chaffinches were at a loss for + a design when fabricating their nest. They had no standard to + work by, no nests of their own kind to copy, no older birds to + give them any instruction, and the result is the abnormal + structure I have just described."<a name="FNanchor_28_28" id= + "FNanchor_28_28"></a><a href="#Footnote_28_28" class= + "fnanchor">[28]</a></p> + + <p>These few examples are sufficient to show that both the habits + and instincts of animals are subject to variation; and had we a + sufficient number of detailed observations we should probably + find that these variations were as numerous, as diverse in + character, as large in amount, and as independent of each other + as those which we have seen to characterise their bodily + structure.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Variability of Plants.</i></p> + + <p>The variability of plants is notorious, being proved not only + by the endless variations which occur whenever a species is + largely grown by horticulturists, but also by the great + difficulty that is felt by botanists in determining the limits of + species in <a name="Page_77" id="Page_77"></a>many large genera. + As examples we may take the roses, the brambles, and the willows + as well illustrating this fact. In Mr. Baker's <i>Revision of the + British Roses</i> (published by the Linnean Society in 1863), he + includes under the single species, Rosa canina—the common + dog-rose—no less than twenty-eight named <i>varieties</i> + distinguished by more or less constant characters and often + confined to special localities, and to these are referred about + seventy of the <i>species</i> of British and continental + botanists. Of the genus Rubus or bramble, <i>five</i> British + species are given in Bentham's <i>Handbook of the British + Flora</i>, while in the fifth edition of Babington's <i>Manual of + British Botany</i>, published about the same time, no less than + <i>forty-five</i> species are described. Of willows (Salix) the + same two works enumerate <i>fifteen</i> and <i>thirty-one</i> + species respectively. The hawkweeds (Hieracium) are equally + puzzling, for while Mr. Bentham admits only seven British + species, Professor Babington describes no less than thirty-two, + besides several named varieties.</p> + + <p>A French botanist, Mons. A. Jordan, has collected numerous + forms of a common little plant, the spring whitlow-grass (Draba + verna); he has cultivated these for several successive years, and + declares that they preserve their peculiarities unchanged; he + also says that they each come true from seed, and thus possess + all the characteristics of true species. He has described no less + than fifty-two such species or permanent varieties, all found in + the south of France; and he urges botanists to follow his example + in collecting, describing, and cultivating all such varieties as + may occur in their respective districts. Now, as the plant is + very common almost all over Europe and ranges from North America + to the Himalayas, the number of similar forms over this wide area + would probably have to be reckoned by hundreds if not by + thousands.</p> + + <p>The class of facts now adduced must certainly be held to prove + that in many large genera and in some single species there is a + very large amount of variation, which renders it quite impossible + for experts to agree upon the limits of species. We will now + adduce a few striking cases of individual variation.</p> + + <p>The distinguished botanist, Alp. de Candolle, made a special + study of the oaks of the whole world, and has stated some + <a name="Page_78" id="Page_78"></a>remarkable facts as to their + variability. He declares that on the same branch of oak he has + noted the following variations: (1) In the length of the petiole, + as one to three; (2) in the form of the leaf, being either + elliptical or obovoid; (3) in the margin being entire, or + notched, or even pinnatifid; (4) in the extremity being acute or + blunt; (5) in the base being sharp, blunt, or cordate; (6) in the + surface being pubescent or smooth; (7) the perianth varies in + depth and lobing; (8) the stamens vary in number, independently; + (9) the anthers are mucronate or blunt; (10) the fruit stalks + vary greatly in length, often as one to three; (11) the number of + fruits varies; (12) the form of the base of the cup varies; (13) + the scales of the cup vary in form; (14) the proportions of the + acorns vary; (15) the times of the acorns ripening and falling + vary.</p> + + <p>Besides this, many species exhibit well-marked varieties which + have been described and named, and these are most numerous in the + best-known species. Our British oak (Quercus robur) has + twenty-eight varieties; Quercus Lusitanica has eleven; Quercus + calliprinos has ten; and Quercus coccifera eight.</p> + + <p>A most remarkable case of variation in the parts of a common + flower has been given by Dr. Hermann Müller. He examined two + hundred flowers of Myosurus minimus, among which he found + <i>thirty-five</i> different proportions of the sepals, petals, + and anthers, the first varying from four to seven, the second + from two to five, and the third from two to ten. Five sepals + occurred in one hundred and eighty-nine out of the two hundred, + but of these one hundred and five had three petals, forty-six had + four petals, and twenty-six had five petals; but in each of these + sets the anthers varied in number from three to eight, or from + two to nine. We have here an example of the same amount of + "independent variability" that, as we have seen, occurs in the + various dimensions of birds and mammals; and it may be taken as + an illustration of the kind and degree of variability that may be + expected to occur among small and little specialised + flowers.<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href= + "#Footnote_29_29" class="fnanchor">[29]</a></p> + + <p>In the common wind-flower (Anemone nemorosa) an almost equal + amount of variation occurs; and I have myself gathered <a name= + "Page_79" id="Page_79"></a>in one locality flowers varying from + 7/8 inch to 1-3/4 inch in diameter; the bracts varying from 1-1/2 + inch to 4 inches across; and the petaloid sepals either broad or + narrow, and varying in number from five to ten. Though generally + pure white on their upper surface, some specimens are a full + pink, while others have a decided bluish tinge.</p> + + <p>Mr. Darwin states that he carefully examined a large number of + plants of Geranium phaeum and G. pyrenaicum (not perhaps truly + British but frequently found wild), which had escaped from + cultivation, and had spread by seed in an open plantation; and he + declares that "the seedlings varied in almost every single + character, both in their flowers and foliage, to a degree which I + have never seen exceeded; yet they could not have been exposed to + any great change of their conditions."<a name="FNanchor_30_30" + id="FNanchor_30_30"></a><a href="#Footnote_30_30" class= + "fnanchor">[30]</a></p> + + <p>The following examples of variation in important parts of + plants were collected by Mr. Darwin and have been copied from his + unpublished MSS.:—</p> + + <p>"De Candolle (<i>Mem. Soc. Phys. de Genève</i>, tom. + ii. part ii. p. 217) states that Papaver bracteatum and P. + orientale present indifferently two sepals and four petals, or + three sepals and six petals, which is sufficiently rare with + other species of the genus."</p> + + <p>"In the Primulacae and in the great class to which this family + belongs the unilocular ovarium is free, but M. Dubury (<i>Mem. + Soc. Phys. de Genève</i>, tom. ii. p. 406) has often found + individuals in Cyclamen hederaefolium, in which the base of the + ovary was connected for a third part of its length with the + inferior part of the calyx."</p> + + <p>"M. Aug. St. Hilaire (Sur la Gynobase, <i>Mem. des Mus. + d'Hist. Nat.</i>, tom. x. p. 134), speaking of some bushes of the + Gomphia oleaefolia, which he at first thought formed a quite + distinct species, says: 'Voilà donc dans un même + individu des loges et un style qui se rattachent tantôt a + un axe vertical, et tantôt a un gynobase; donc celui-ci + n'est qu'un axe veritable; mais cet axe est deprimé au + lieu d'être vertical." He adds (p. 151), 'Does not all this + indicate that nature has tried, in a manner, in the family of + Rutaceae to produce from a single multilocular ovary, one-styled + and symmetrical, several unilocular ovaries, each with its own + style.' And he <a name="Page_80" id="Page_80"></a>subsequently + shows that, in Xanthoxylum monogynum, 'it often happens that on + the same plant, on the same panicle, we find flowers with one or + with two ovaries;' and that this is an important character is + shown by the Rutaceae (to which Xanthoxylum belongs), being + placed in a group of natural orders characterised by having a + solitary ovary."</p> + + <p>"De Candolle has divided the Cruciferae into five sub-orders + in accordance with the position of the radicle and cotyledons, + yet Mons. T. Gay (<i>Ann. des Scien. Nat.</i>, ser. i. tom. vii. + p. 389) found in sixteen seeds of Petrocallis Pyrenaica the form + of the embryo so uncertain that he could not tell whether it + ought to be placed in the sub-orders 'Pleurorhizée' or + 'Notor-hizée'; so again (p. 400) in Cochlearia saxatilis + M. Gay examined twenty-nine embryos, and of these sixteen were + vigorously 'pleurorhizées,' nine had characters + intermediate between pleuro-and notor-hizées, and four + were pure notor-hizées."</p> + + <p>"M. Raspail asserts (<i>Ann. des Scien. Nat.</i>, ser. i. tom. + v. p. 440) that a grass (Nostus Borbonicus) is so eminently + variable in its floral organisation, that the varieties might + serve to make a family with sufficiently numerous genera and + tribes—a remark which shows that important organs must be + here variable."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Species which vary little.</i></p> + + <p>The preceding statements, as to the great amount of variation + occurring in animals and plants, do not prove that all species + vary to the same extent, or even vary at all, but, merely, that a + considerable number of species in every class, order, and family + do so vary. It will have been observed that the examples of great + variability have all been taken from common species, or species + which have a wide range and are abundant in individuals. Now Mr. + Darwin concludes, from an elaborate examination of the floras and + faunas of several distinct regions, that common, wide ranging + species, as a rule, vary most, while those that are confined to + special districts and are therefore comparatively limited in + number of individuals vary least. By a similar comparison it is + shown that species of large genera vary more than species of + small genera. These facts explain, to some extent, why the + opinion has been so prevalent that variation is very limited in + amount and exceptional in character. For <a name="Page_81" id= + "Page_81"></a>naturalists of the old school, and all mere + collectors, were interested in species in proportion to their + rarity, and would often have in their collections a larger number + of specimens of a rare species than of a species that was very + common. Now as these rare species do really vary much less than + the common species, and in many cases hardly vary at all, it was + very natural that a belief in the fixity of species should + prevail. It is not, however, as we shall see presently, the rare, + but the common and widespread species which become the parents of + new forms, and thus the non-variability of any number of rare or + local species offers no difficulty whatever in the way of the + theory of evolution.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>We have now shown in some detail, at the risk of being + tedious, that individual variability is a general character of + all common and widespread species of animals or plants; and, + further, that this variability extends, so far as we know, to + every part and organ, whether external or internal, as well as to + every mental faculty. Yet more important is the fact that each + part or organ varies to a considerable extent independently of + other parts. Again, we have shown, by abundant evidence, that the + variation that occurs is very large in amount—usually + reaching 10 or 20, and sometimes even 25 per cent of the average + size of the varying part; while not one or two only, but from 5 + to 10 per cent of the specimens examined exhibit nearly as large + an amount of variation. These facts have been brought clearly + before the reader by means of numerous diagrams, drawn to scale + and exhibiting the actual variations in inches, so that there can + be no possibility of denying either their generality or their + amount. The importance of this full exposition of the subject + will be seen in future chapters, when we shall frequently have to + refer to the facts here set forth, especially when we deal with + the various theories of recent writers and the criticisms that + have been made of the Darwinian theory.</p> + + <p>A full exposition of the facts of variation among wild animals + and plants is the more necessary, because comparatively few of + them were published in Mr. Darwin's works, while the more + important have only been made known since <a name="Page_82" id= + "Page_82"></a>the last edition of <i>The Origin of Species</i> + was prepared; and it is clear that Mr. Darwin himself did not + fully recognise the enormous amount of variability that actually + exists. This is indicated by his frequent reference to the + extreme slowness of the changes for which variation furnishes the + materials, and also by his use of such expressions as the + following: "A variety when once formed must again, <i>perhaps + after a long interval of time</i>, vary or present individual + differences of the same favourable nature as before" + (<i>Origin</i>, p. 66). And again, after speaking of changed + conditions "affording a better chance of the occurrence of + favourable variations," he adds: "<i>Unless such occur natural + selection can do nothing</i>" (<i>Origin</i>, p. 64). These + expressions are hardly consistent with the fact of the constant + and large amount of variation, of every part, in all directions, + which evidently occurs in each generation of all the more + abundant species, and which must afford an ample supply of + favourable variations whenever required; and they have been + seized upon and exaggerated by some writers as proofs of the + extreme difficulties in the way of the theory. It is to show that + such difficulties do not exist, and in the full conviction that + an adequate knowledge of the facts of variation affords the only + sure foundation for the Darwinian theory of the origin of + species, that this chapter has been written.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_16_16" id="Footnote_16_16"></a><a href= + "#FNanchor_16_16"><span class="label">[16]</span></a> + <i>Foraminifera</i>, preface, p. x.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_17_17" id="Footnote_17_17"></a><a href= + "#FNanchor_17_17"><span class="label">[17]</span></a> + <i>United States Geological Survey of the Territories</i>, + 1874.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href= + "#FNanchor_18_18"><span class="label">[18]</span></a> + <i>Proceedings of the Entomological Society of London</i>, + 1875, p. vii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href= + "#FNanchor_19_19"><span class="label">[19]</span></a> <i>Ann. + des Sci. Nat.</i>, tom. xvi. p. 50.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_20_20" id="Footnote_20_20"></a><a href= + "#FNanchor_20_20"><span class="label">[20]</span></a> See + <i>Winter Birds of Florida</i>, p. 206, Table F.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_21_21" id="Footnote_21_21"></a><a href= + "#FNanchor_21_21"><span class="label">[21]</span></a> See + Table I, p. 211, of Allen's <i>Winter Birds of + Florida</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_22_22" id="Footnote_22_22"></a><a href= + "#FNanchor_22_22"><span class="label">[22]</span></a> + <i>Proc. Zool. Soc.</i>, 1864, p. 64.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_23_23" id="Footnote_23_23"></a><a href= + "#FNanchor_23_23"><span class="label">[23]</span></a> J.A. + Allen, on Geographical Variation among North American + Mammals, <i>Bull. U.S. Geol. and Geog. Survey</i>, vol. ii. + p. 314 (1876).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_24_24" id="Footnote_24_24"></a><a href= + "#FNanchor_24_24"><span class="label">[24]</span></a> + <i>Proc. Zool. Soc. Lond.</i>, 1864, p. 700, and 1868, p. + 28.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_25_25" id="Footnote_25_25"></a><a href= + "#FNanchor_25_25"><span class="label">[25]</span></a> See + <i>Trans. Entomological Society of London</i>, 1887, p. + 24.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_26_26" id="Footnote_26_26"></a><a href= + "#FNanchor_26_26"><span class="label">[26]</span></a> + <i>Nature</i>, vol. xix. p. 554.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_27_27" id="Footnote_27_27"></a><a href= + "#FNanchor_27_27"><span class="label">[27]</span></a> + <i>Nature</i>, vol. xvi. p. 163; and vol. xi. p. 227.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_28_28" id="Footnote_28_28"></a><a href= + "#FNanchor_28_28"><span class="label">[28]</span></a> + <i>Ibid.</i>, vol. xxxi. (1885), p. 533.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_29_29" id="Footnote_29_29"></a><a href= + "#FNanchor_29_29"><span class="label">[29]</span></a> + <i>Nature</i>, vol. xxvi. p. 81.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_30_30" id="Footnote_30_30"></a><a href= + "#FNanchor_30_30"><span class="label">[30]</span></a> + <i>Animals and Plants under Domestication</i>, vol. ii. p. + 258.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a><a name="Page_83" + id="Page_83"></a>CHAPTER IV</h2> + + <p style='font-weight:bold;'>VARIATION OF DOMESTICATED ANIMALS + AND CULTIVATED PLANTS</p> + + <div class="blockquot"> + <p>The facts of variation and artificial selection—Proofs + of the generality of variation—Variations of apples and + melons—Variations of flowers—Variations of domestic + animals—Domestic + pigeons—Acclimatisation—Circumstances favourable to + selection by man—Conditions favourable to + variation—Concluding remarks.</p> + </div> + + <p>Having so fully discussed variation under nature it will be + unnecessary to devote so much space to domesticated animals and + cultivated plants, especially as Mr. Darwin has published two + remarkable volumes on the subject where those who desire it may + obtain ample information. A general sketch of the more important + facts will, however, be given, for the purpose of showing how + closely they correspond with those described in the preceding + chapter, and also to point out the general principles which they + illustrate. It will also be necessary to explain how these + variations have been increased and accumulated by artificial + selection, since we are thereby better enabled to understand the + action of natural selection, to be discussed in the succeeding + chapter.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The facts of Variation and Artificial Selection.</i></p> + + <p>Every one knows that in each litter of kittens or of puppies + no two are alike. Even in the case in which several are exactly + alike in colours, other differences are always perceptible to + those who observe them closely. They will differ in size, in the + proportions of their bodies and limbs, in the length or texture + of their hairy covering, and notably in their disposition. They + each possess, too, an individual <a name="Page_84" id= + "Page_84"></a>countenance, almost as varied when closely studied + as that of a human being; not only can a shepherd distinguish + every sheep in his flock, but we all know that each kitten in the + successive families of our old favourite cat has a face of its + own, with an expression and individuality distinct from all its + brothers and sisters. Now this individual variability exists + among all creatures whatever, which we can closely observe, even + when the two parents are very much alike and have been matched in + order to preserve some special breed. The same thing occurs in + the vegetable kingdom. All plants raised from seed differ more or + less from each other. In every bed of flowers or of vegetables we + shall find, if we look closely, that there are countless small + differences, in the size, in the mode of growth, in the shape or + colour of the leaves, in the form, colour, or markings of the + flowers, or in the size, form, colour, or flavour of the fruit. + These differences are usually small, but are yet easily seen, and + in their extremes are very considerable; and they have this + important quality, that they have a tendency to be reproduced, + and thus by careful breeding any particular variation or group of + variations can be increased to an enormous + extent—apparently to any extent not incompatible with the + life, growth, and reproduction of the plant or animal.</p> + + <p>The way this is done is by artificial selection, and it is + very important to understand this process and its results. + Suppose we have a plant with a small edible seed, and we want to + increase the size of that seed. We grow as large a quantity of it + as possible, and when the crop is ripe we carefully choose a few + of the very largest seeds, or we may by means of a sieve sort out + a quantity of the largest seeds. Next year we sow only these + large seeds, taking care to give them suitable soil and manure, + and the result is found to be that the <i>average</i> size of the + seeds is larger than in the first crop, and that the largest + seeds are now somewhat larger and more numerous. Again sowing + these, we obtain a further slight increase of size, and in a very + few years we obtain a greatly improved race, which will always + produce larger seeds than the unimproved race, even if cultivated + without any special care. In this way all our fine sorts of + vegetables, fruits, and flowers have been obtained, all our + choice breeds <a name="Page_85" id="Page_85"></a>of cattle or of + poultry, our wonderful race-horses, and our endless varieties of + dogs. It is a very common but mistaken idea that this improvement + is due to crossing and feeding in the case of animals, and to + improved cultivation in the case of plants. Crossing is + occasionally used in order to obtain a combination of qualities + found in two distinct breeds, and also because it is found to + increase the constitutional vigour; but every breed possessing + any exceptional quality is the result of the selection of + variations occurring year after year and accumulated in the + manner just described. Purity of breed, with repeated selection + of the best varieties of that breed, is the foundation of all + improvement in our domestic animals and cultivated plants.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Proofs of the Generality of Variation.</i></p> + + <p>Another very common error is, that variation is the exception, + and rather a rare exception, and that it occurs only in one + direction at a time—that is, that only one or two of the + numerous possible modes of variation occur at the same time. The + experience of breeders and cultivators, however, proves that + variation is the rule instead of the exception, and that it + occurs, more or less, in almost every direction. This is shown by + the fact that different species of plants and animals have + required different <i>kinds</i> of modification to adapt them to + our use, and we have never failed to meet with variation <i>in + that particular direction</i>, so as to enable us to accumulate + it and so to produce ultimately a large amount of change in the + required direction. Our gardens furnish us with numberless + examples of this property of plants. In the cabbage and lettuce + we have found variation in the size and mode of growth of the + leaf, enabling us to produce by selection the almost innumerable + varieties, some with solid heads of foliage quite unlike any + plant in a state of nature, others with curiously wrinkled leaves + like the savoy, others of a deep purple colour used for pickling. + From the very same species as the cabbage (Brassica oleracea) + have arisen the broccoli and cauliflower, in which the leaves + have undergone little alteration, while the branching heads of + flowers grow into a compact mass forming one of our most delicate + vegetables. The brussels sprouts are another form of the same + plant, in <a name="Page_86" id="Page_86"></a>which the whole mode + of growth has been altered, numerous little heads of leaves being + produced on the stem. In other varieties the ribs of the leaves + are thickened so as to become themselves a culinary vegetable; + while, in the Kohlrabi, the stem grows into a turnip-like mass + just above ground. Now all these extraordinarily distinct plants + come from one original species which still grows wild on our + coasts; and it must have varied in all these directions, + otherwise variations could not have been accumulated to the + extent we now see them. The flowers and seeds of all these plants + have remained nearly stationary, because no attempt has been made + to accumulate the slight variations that no doubt occur in + them.</p> + + <p>If now we turn to another set of plants, the turnips, + radishes, carrots, and potatoes, we find that the roots or + underground tubers have been wonderfully enlarged and improved, + and also altered in shape and colour, while the stems, leaves, + flowers, and fruits have remained almost unchanged. In the + various kinds of peas and beans it is the pod or fruit and the + seed that has been subjected to selection, and therefore greatly + modified; and it is here very important to notice that while all + these plants have undergone cultivation in a great variety of + soils and climates, with different manures and under different + systems, yet the flowers have remained but little altered, those + of the broad bean, the scarlet-runner, and the garden-pea, being + nearly the same in all the varieties. This shows us how little + change is produced by mere cultivation, or even by variety of + soil and climate, if there is no <i>selection</i> to preserve and + accumulate the small variations that are continually occurring. + When, however, a great amount of modification has been effected + in one country, change to another country produces a decided + effect. Thus it has been found that some of the numerous + varieties of maize produced and cultivated in the United States + change considerably, not only in their size and colour, but even + in the shape of the seed when grown for a few successive years in + Germany.<a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href= + "#Footnote_31_31" class="fnanchor">[31]</a> In all our cultivated + fruit trees the fruits vary immensely in shape, size, colour, + flavour, time of ripening, and other qualities, while the leaves + and flowers usually differ so little that they are hardly + distinguishable except to a very close observer.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_87" id="Page_87"></a><i>Variations of Apples and of + Melons.</i></p> + + <p>The most remarkable varieties are afforded by the apple and + the melon, and some account of these will be given as + illustrating the effects of slight variations accumulated by + selection. All our apples are known to have descended from the + common crab of our hedges (Pyrus malus), and from this at least a + thousand distinct varieties have been produced. These differ + greatly in the size and form of the fruit, in its colour, and in + the texture of the skin. They further differ in the time of + ripening, in their flavour, and in their keeping properties; but + apple trees also differ in many other ways. The foliage of the + different varieties can often be distinguished by peculiarities + of form and colour, and it varies considerably in the time of its + appearance; in some hardly a leaf appears till the tree is in + full bloom, while others produce their leaves so early as almost + to hide the flowers. The flowers differ in size and colour, and + in one case in structure also, that of the St. Valery apple + having a double calyx with ten divisions, and fourteen styles + with oblique stigmas, but without stamens or corolla. The + flowers, therefore, have to be fertilised with the pollen from + other varieties in order to produce fruit. The pips or seeds + differ also in shape, size, and colour; some varieties are liable + to canker more than others, while the Winter Majetin and one or + two others have the strange constitutional peculiarity of never + being attacked by the mealy bug even when all the other trees in + the same orchard are infested with it.</p> + + <p>All the cucumbers and gourds vary immensely, but the melon + (Cucumis melo) exceeds them all. A French botanist, M. Naudin, + devoted six years to their study. He found that previous + botanists had described thirty distinct species, as they thought, + which were really only varieties of melons. They differ chiefly + in their fruits, but also very much in foliage and mode of + growth. Some melons are only as large as small plums, others + weigh as much as sixty-six pounds. One variety has a scarlet + fruit. Another is not more than an inch in diameter, but + sometimes more than a yard in length, twisting about in all + directions like a serpent. Some melons are exactly like + cucumbers; and an Algerian variety, when ripe, <a name="Page_88" + id="Page_88"></a>cracks and falls to pieces, just as occurs in a + wild gourd (C. momordica).<a name="FNanchor_32_32" id= + "FNanchor_32_32"></a><a href="#Footnote_32_32" class= + "fnanchor">[32]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variations of Flowers.</i></p> + + <p>Turning to flowers, we find that in the same genus as our + currant and gooseberry, which we have cultivated for their + fruits, there are some ornamental species, as the Ribes + sanguinea, and in these the flowers have been selected so as to + produce deep red, pink, or white varieties. When any particular + flower becomes fashionable and is grown in large quantities, + variations are always met with sufficient to produce great + varieties of tint or marking, as shown by our roses, auriculas, + and geraniums. When varied leaves are required, it is found that + a number of plants vary sufficiently in this direction also, and + we have zonal geraniums, variegated ivies, gold and silver marked + hollies, and many others.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variations of Domestic Animals.</i></p> + + <p>Coming now to our domesticated animals, we find still more + extraordinary cases; and it appears as if any special quality or + modification in an animal can be obtained if we only breed it in + sufficient quantity, watch carefully for the required variations, + and carry on selection with patience and skill for a sufficiently + long period. Thus, in sheep we have enormously increased the + wool, and have obtained the power of rapidly forming flesh and + fat; in cows we have increased the production of milk; in horses + we have obtained strength, endurance, or speed, and have greatly + modified size, form, and colour; in poultry we have secured + various colours of plumage, increase of size, and almost + perpetual egg-laying. But it is in dogs and pigeons that the most + marvellous changes have been effected, and these require our + special attention.</p> + + <p>Our various domestic dogs are believed to have originated from + several distinct wild species, because in every part of the world + the native dogs resemble some wild dogs or wolves of the same + country. Thus perhaps several species of wolves and jackals were + domesticated in very early times, and from breeds derived from + these, crossed and improved by selection, <a name="Page_89" id= + "Page_89"></a>our existing dogs have descended. But this + intermixture of distinct species will go a very little way in + accounting for the peculiarities of the different breeds of dogs, + many of which are totally unlike any wild animal. Such is the + case with greyhounds, bloodhounds, bulldogs, Blenheim spaniels, + terriers, pugs, turnspits, pointers, and many others; and these + differ so greatly in size, shape, colour, and habits, as well as + in the form and proportions of all the different parts of the + body, that it seems impossible that they could have descended + from any of the known wild dogs, wolves, or allied animals, none + of which differ nearly so much in size, form, and proportions. We + have here a remarkable proof that variation is not confined to + superficial characters—to the colour, hair, or external + appendages, when we see how the entire skeletons of such forms as + the greyhound and the bulldog have been gradually changed in + opposite directions till they are both completely unlike that of + any known wild animal, recent or extinct. These changes have been + the result of some thousands of years of domestication and + selection, different breeds being used and preserved for + different purposes; but some of the best breeds are known to have + been improved and perfected in modern times. About the middle of + the last century a new and improved kind of foxhound was + produced; the greyhound was also greatly improved at the end of + the last century, while the true bulldog was brought to + perfection about the same period. The Newfoundland dog has been + so much changed since it was first imported that it is now quite + unlike any existing native dog in that island.<a name= + "FNanchor_33_33" id="FNanchor_33_33"></a><a href= + "#Footnote_33_33" class="fnanchor">[33]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Domestic Pigeons.</i></p> + + <p>The most remarkable and instructive example of variation + produced by human selection is afforded by the various races and + breeds of domestic pigeons, not only because the variations + produced are often most extraordinary in amount and diverse in + character, but because in this case there is no doubt whatever + that all have been derived from one wild species, the common + rock-pigeon (Columba livia). As this is a very important point it + is well to state the evidence on which the belief is founded. The + wild rock-pigeon is of a slaty-blue <a name="Page_90" id= + "Page_90"></a>colour, the tail has a dark band across the end, + the wings have two black bands, and the outer tail-feathers are + edged with white at the base. No other wild pigeon in the world + has this combination of characters. Now in every one of the + domestic varieties, even the most extreme, all the above marks, + even to the white edging of the outer tail-feathers, are + sometimes found perfectly developed. When birds belonging to two + distinct breeds are crossed one or more times, neither of the + parents being blue, or having any of the above-named marks, the + mongrel offspring are very apt to acquire some of these + characters. Mr. Darwin gives instances which he observed himself. + He crossed some white fantails with some black barbs, and the + mongrels were black, brown, or mottled. He also crossed a barb + with a spot, which is a white bird with a red tail and red spot + on the forehead, and the mongrel offspring were dusky and + mottled. On now crossing these two sets of mongrels with each + other, he obtained a bird of a beautiful blue colour, with the + barred and white edged tail, and double-banded wings, so as + almost exactly to resemble a wild rock-pigeon. This bird was + descended in the second generation from a pure white and pure + black bird, both of which when unmixed breed their kind + remarkably true. These facts, well known to experienced + pigeon-fanciers, together with the habits of the birds, which all + like to nest in holes, or dovecots, not in trees like the great + majority of wild pigeons, have led to the general belief in the + single origin of all the different kinds.</p> + + <p>In order to afford some idea of the great differences which + exist among domesticated pigeons, it will be well to give a brief + abstract of Mr. Darwin's account of them. He divides them into + eleven distinct races, most of which have several sub-races.</p> + + <p>RACE I. <i>Pouters</i>.—These are especially + distinguished by the enormously enlarged crop, which can be so + inflated in some birds as almost to conceal the beak. They are + very long in the body and legs and stand almost upright, so as to + present a very distinct appearance. Their skeleton has become + modified, the ribs being broader and the vertebrae more numerous + than in other pigeons.</p> + + <p><a name="Page_91" id="Page_91"></a>RACE II. + <i>Carriers</i>.—These are large, long-necked birds, with a + long pointed beak, and the eyes surrounded with a naked + carunculated skin or wattle, which is also largely developed at + the base of the beak. The opening of the mouth is unusually wide. + There are several sub-races, one being called Dragons.</p> + + <p>RACE III. <i>Runts</i>.—These are very large-bodied, + long-beaked pigeons, with naked skin round the eyes. The wings + are usually very long, the legs long, and the feet large, and the + skin of the neck is often red. There are several sub-races, and + these differ very much, forming a series of links between the + wild rock-pigeon and the carrier.</p> + + <p>RACE IV. <i>Barbs</i>.—These are remarkable for their + very short and thick beak, so unlike that of most pigeons that + fanciers compare it with that of a bullfinch. They have also a + naked carunculated skin round the eyes, and the skin over the + nostrils swollen.</p> + + <p>RACE V. <i>Fantails</i>.—Short-bodied and rather + small-beaked pigeons, with an enormously developed tail, + consisting usually of from fourteen to forty feathers instead of + twelve, the regular number in all other pigeons, wild and tame. + The tail spreads out like a fan and is usually carried erect, and + the bird bends back its slender neck, so that in highly-bred + varieties the head touches the tail. The feet are small, and they + walk stiffly.</p> + + <p>RACE VI. <i>Turbits and Owls</i>.—These are + characterised by the feathers of the middle of neck and breast in + front spreading out irregularly so as to form a frill. The + Turbits also have a crest on the head, and both have the beak + exceedingly short.</p> + + <p>RACE VII. <i>Tumblers</i>.—These have a small body and + short beak, but they are specially distinguished by the singular + habit of tumbling over backwards during flight. One of the + sub-races, the Indian Lotan or Ground tumbler, if slightly shaken + and placed on the ground, will immediately begin tumbling head + over heels until taken up and soothed. If not taken up, some of + them will go on tumbling till they die. <a name="Page_92" id= + "Page_92"></a>Some English tumblers are almost equally + persistent. A writer, quoted by Mr. Darwin, says that these birds + generally begin to tumble almost as soon as they can fly; "at + three months old they tumble well, but still fly strong; at five + or six months they tumble excessively; and in the second year + they mostly give up flying, on account of their tumbling so much + and so close to the ground. Some fly round with the flock, + throwing a clean summersault every few yards till they are + obliged to settle from giddiness and exhaustion. These are called + Air-tumblers, and they commonly throw from twenty to thirty + summersaults in a minute, each clear and clean. I have one red + cock that I have on two or three occasions timed by my watch, and + counted forty summersaults in the minute. At first they throw a + single summersault, then it is double, till it becomes a + continuous roll, which puts an end to flying, for if they fly a + few yards over they go, and roll till they reach the ground. Thus + I had one kill herself, and another broke his leg. Many of them + turn over only a few inches from the ground, and will tumble two + or three times in flying across their loft. These are called + House-tumblers from tumbling in the house. The act of tumbling + seems to be one over which they have no control, an involuntary + movement which they seem to try to prevent. I have seen a bird + sometimes in his struggles fly a yard or two straight upwards, + the impulse forcing him backwards while he struggles to go + forwards."<a name="FNanchor_34_34" id= + "FNanchor_34_34"></a><a href="#Footnote_34_34" class= + "fnanchor">[34]</a></p> + + <p>The Short-faced tumblers are an improved sub-race which have + almost lost the power of tumbling, but are valued for possessing + some other characteristics in an extreme degree. They are very + small, have almost globular heads, and a very minute beak, so + that fanciers say the head of a perfect bird should resemble a + cherry with a barleycorn stuck in it. Some of these weigh less + than seven ounces, whereas the wild rock-pigeon weighs about + fourteen ounces. The feet, too, are very short and small, and the + middle toe has twelve or thirteen instead of fourteen or fifteen + scutellae. They have often only nine primary wing-feathers + instead of ten as in all other pigeons.</p> + + <p><a name="Page_93" id="Page_93"></a>RACE VIII. <i>Indian + Frill-back</i>.—In these birds the beak is very short, and + the feathers of the whole body are reversed or turn + backwards.</p> + + <p>RACE IX. <i>Jacobin</i>.—These curious birds have a hood + of feathers almost enclosing the head and meeting in front of the + neck. The wings and tail are unusually long.</p> + + <p>RACE X. <i>Trumpeter</i>.—Distinguished by a tuft of + feathers curling forwards over the beak, and the feet very much + feathered. They obtain their name from the peculiar voice unlike + that of any other pigeon. The coo is rapidly repeated, and is + continued for several minutes. The feet are covered with feathers + so large as often to appear like little wings.</p> + + <p>RACE XI. comprises <i>Laughers</i>, <i>Frill-backs</i>, + <i>Nuns</i>, <i>Spots</i>, <i>and Swallows</i>.—They are + all very like the common rock-pigeon, but have each some slight + peculiarity. The Laughers have a peculiar voice, supposed to + resemble a laugh. The Nuns are white, with the head, tail, and + primary wing-feathers black or red. The Spots are white, with the + tail and a spot on the forehead red. The Swallows are slender, + white in colour, with the head and wings of some darker + colour.</p> + + <p>Besides these races and sub-races a number of other kinds have + been described, and about one hundred and fifty varieties can be + distinguished. It is interesting to note that almost every part + of the bird, whose variations can be noted and selected, has led + to variations of a considerable extent, and many of these have + necessitated changes in the plumage and in the skeleton quite as + great as any that occur in the numerous distinct species of large + genera. The form of the skull and beak varies enormously, so that + the skulls of the Short-faced tumbler and some of the Carriers + differ more than any wild pigeons, even those classed in distinct + genera. The breadth and number of the ribs vary, as well as the + processes on them; the number of the vertebrae and the length of + the sternum also vary; and the perforations in the sternum vary + in size and shape. The oil gland varies in development, and is + sometimes absent. The number of the wing-feathers varies, and + those of the tail to an enormous extent. The proportions of the + leg and feet and the number <a name="Page_94" id="Page_94"></a>of + the scutellae also vary. The eggs also vary somewhat in size and + shape; and the amount of downy clothing on the young bird, when + first hatched, differs very considerably. Finally, the attitude + of the body, the manner of walking, the mode of flight, and the + voice, all exhibit modifications of the most remarkable + kind.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href= + "#Footnote_35_35" class="fnanchor">[35]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Acclimatisation</i>.</p> + + <p>A very important kind of variation is that constitutional + change termed acclimatisation, which enables any organism to + become gradually adapted to a different climate from the parent + stock. As closely allied species often inhabit different + countries possessing very different climates, we should expect to + find cases illustrating this change among our domesticated + animals and cultivated plants. A few examples will therefore be + adduced showing that such constitutional variation does + occur.</p> + + <p>Among animals the cases are not numerous, because no + systematic attempt has been made to select varieties for this + special quality. It has, however, been observed that, though no + European dogs thrive well in India, the Newfoundland dog, + originating from a severe climate, can hardly be kept alive. A + better case, perhaps, is furnished by merino sheep, which, when + imported directly from England, do not thrive, while those which + have been bred in the intermediate climate of the Cape of Good + Hope do much better. When geese were first introduced into + Bogota, they laid few eggs at long intervals, and few of the + young survived. By degrees, however, the fecundity improved, and + in about twenty years became equal to what it is in Europe. + According to Garcilaso, when fowls were first introduced into + Peru they were not fertile, whereas now they are as much so as in + Europe.</p> + + <p>Plants furnish much more important evidence. Our nurserymen + distinguish in their catalogues varieties of fruit-trees which + are more or less hardy, and this is especially the case in + America, where certain varieties only will stand the severe + climate of Canada. There is one variety of pear, the Forelle, + which both in England and France withstood frosts <a name= + "Page_95" id="Page_95"></a>that killed the flowers and buds of + all other kinds of pears. Wheat, which is grown over so large a + portion of the world, has become adapted to special climates. + Wheat imported from India and sown in good wheat soil in England + produced the most meagre ears; while wheat taken from France to + the West Indian Islands produced either wholly barren spikes or + spikes furnished with two or three miserable seeds, while West + Indian seed by its side yielded an enormous harvest. The orange + was very tender when first introduced into Italy, and continued + so as long as it was propagated by grafts, but when trees were + raised from seed many of these were found to be hardier, and the + orange is now perfectly acclimatised in Italy. Sweet-peas + (Lathyrus odoratus) imported from England to the Calcutta Botanic + Gardens produced few blossoms and no seed; those from France + flowered a little better, but still produced no seed, but plants + raised from seed brought from Darjeeling in the Himalayas, but + originally derived from England, flower and seed profusely in + Calcutta.<a name="FNanchor_36_36" id= + "FNanchor_36_36"></a><a href="#Footnote_36_36" class= + "fnanchor">[36]</a></p> + + <p>An observation by Mr. Darwin himself is perhaps even more + instructive. He says: "On 24th May 1864 there was a severe frost + in Kent, and two rows of scarlet runners (Phaseolus multiflorus) + in my garden, containing 390 plants of the same age and equally + exposed, were all blackened and killed except about a dozen + plants. In an adjoining row of Fulmer's dwarf bean (Phaseolus + vulgaris) one single plant escaped. A still more severe frost + occurred four days afterwards, and of the dozen plants which had + previously escaped only three survived; these were not taller or + more vigorous than the other young plants, but they escaped + completely, with not even the tips of their leaves browned. It + was impossible to behold these three plants, with their + blackened, withered, and dead brethren all around them, and not + see at a glance that they differed widely in their constitutional + power of resisting frost."</p> + + <p>The preceding sketch of the variation that occurs among + domestic animals and cultivated plants shows how wide it is in + range and how great in amount; and we have good reason to believe + that similar variation extends to all organised beings. In the + class of fishes, for example, we have one kind which has <a name= + "Page_96" id="Page_96"></a>been long domesticated in the East, + the gold and silver carps; and these present great variation, not + only of colour but in the form and structure of the fins and + other external organs. In like manner, the only domesticated + insects, hive bees and silkworm moths, present numbers of + remarkable varieties which have been produced by the selection of + chance variations just as in the case of plants and the higher + animals.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Circumstances favourable to Selection by Man.</i></p> + + <p>It may be supposed, that the systematic selection which has + been employed for the purpose of improving the races of animals + or plants useful to man is of comparatively recent origin, though + some of the different races are known to have been in existence + in very early times. But Mr. Darwin has pointed out, that + unconscious selection must have begun to produce an effect as + soon as plants were cultivated or animals domesticated by man. It + would have been very soon observed that animals and plants + produced their like, that seed of early wheat produced early + wheat, that the offspring of very swift dogs were also swift, and + as every one would try to have a good rather than a bad sort this + would necessarily lead to the slow but steady improvement of all + useful plants and animals subject to man's care. Soon there would + arise distinct breeds, owing to the varying uses to which the + animals and plants were put. Dogs would be wanted chiefly to hunt + one kind of game in one part of the country and another kind + elsewhere; for one purpose scent would be more important, for + another swiftness, for another strength and courage, for yet + another watchfulness and intelligence, and this would soon lead + to the formation of very distinct races. In the case of + vegetables and fruits, different varieties would be found to + succeed best in certain soils and climates; some might be + preferred on account of the quantity of food they produced, + others for their sweetness and tenderness, while others might be + more useful on account of their ripening at a particular season, + and thus again distinct varieties would be established. An + instance of unconscious selection leading to distinct results in + modern times is afforded by two flocks of Leicester sheep which + both originated from the same stock, and were then bred pure for + upwards of fifty years by two gentlemen, Mr. Buckley <a name= + "Page_97" id="Page_97"></a>and Mr. Burgess. Mr. Youatt, one of + the greatest authorities on breeding domestic animals, says: + "There is not a suspicion existing in the mind of any one at all + acquainted with the subject that the owner of either of them has + deviated in any one instance from the pure blood of Mr. + Bakewell's original flock, and yet the difference between the + sheep possessed by these two gentlemen is so great that they have + the appearance of being quite different varieties." In this case + there was no desire to deviate from the original breed, and the + difference must have arisen from some slight difference of taste + or judgment in selecting, each year, the parents for the next + year's stock, combined perhaps with some direct effect of the + slight differences of climate and soil on the two farms.</p> + + <p>Most of our domesticated animals and cultivated plants have + come to us from the earliest seats of civilisation in Western + Asia or Egypt, and have therefore been the subjects of human care + and selection for some thousands of years, the result being that, + in many cases, we do not know the wild stock from which they + originally sprang. The horse, the camel, and the common bull and + cow are nowhere found in a wild state, and they have all been + domesticated from remote antiquity. The original of the domestic + fowl is still wild in India and the Malay Islands, and it was + domesticated in India and China before 1400 B.C. It was + introduced into Europe about 600 B.C. Several distinct breeds + were known to the Romans about the commencement of the Christian + era, and they have since spread all over the civilised world and + been subjected to a vast amount of conscious and unconscious + selection, to many varieties of climate and to differences of + food; the result being seen in the wonderful diversity of breeds + which differ quite as remarkably as do the different races of + pigeons already described.</p> + + <p>In the vegetable kingdom, most of the cereals—wheat, + barley, etc.—are unknown as truly wild plants; and the same + is the case with many vegetables, for De Candolle states that out + of 157 useful cultivated plants thirty-two are quite unknown in a + wild state, and that forty more are of doubtful origin. It is not + improbable that most of these do exist wild, but they have been + so profoundly changed by thousands of years of cultivation as to + be quite unrecognisable. The <a name="Page_98" id= + "Page_98"></a>peach is unknown in a wild state, unless it is + derived from the common almond, on which point there is much + difference of opinion among botanists and horticulturists.</p> + + <p>The immense antiquity of most of our cultivated plants + sufficiently explains the apparent absence of such useful + productions in Australia and the Cape of Good Hope, + notwithstanding that they both possess an exceedingly rich and + varied flora. These countries having been, until a comparatively + recent period, inhabited only by uncivilised men, neither + cultivation nor selection has been carried on for a sufficiently + long time. In North America, however, where there was evidently a + very ancient if low form of civilisation, as indicated by the + remarkable mounds, earthworks, and other prehistoric remains, + maize was cultivated, though it was probably derived from Peru; + and the ancient civilisation of that country and of Mexico has + given rise to no fewer than thirty-three useful cultivated + plants.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Conditions favourable to the production of Variations.</i></p> + + <p>In order that plants and animals may be improved and modified + to any considerable extent, it is of course essential that + suitable variations should occur with tolerable frequency. There + seem to be three conditions which are especially favourable to + the production of variations: (1) That the particular species or + variety should be kept in very large numbers; (2) that it should + be spread over a wide area and thus subjected to a considerable + diversity of physical conditions; and (3) that it should be + occasionally crossed with some distinct but closely allied race. + The first of these conditions is perhaps the most important, the + chance of variations of any particular kind being increased in + proportion to the quantity of the original stock and of its + annual offspring. It has been remarked that only those breeders + who keep large flocks can effect much improvement; and it is for + the same reason that pigeons and fowls, which can be so easily + and rapidly increased, and which have been kept in such large + numbers by so great a number of persons, have produced such + strange and numerous varieties. In like manner, nurserymen who + grow fruit and flowers in large quantities have a great advantage + over private amateurs in the production of new varieties.</p> + + <p><a name="Page_99" id="Page_99"></a>Although I believe, for + reasons which will be given further on, that some amount of + variability is a constant and necessary property of all + organisms, yet there appears to be good evidence to show that + changed conditions of life tend to increase it, both by a direct + action on the organisation and by indirectly affecting the + reproductive system. Hence the extension of civilisation, by + favouring domestication under altered conditions, facilitates the + process of modification. Yet this change does not seem to be an + essential condition, for nowhere has the production of extreme + varieties of plants and flowers been carried farther than in + Japan, where careful selection continued for many generations + must have been the chief factor. The effect of occasional crosses + often results in a great amount of variation, but it also leads + to instability of character, and is therefore very little + employed in the production of fixed and well-marked races. For + this purpose, in fact, it has to be carefully avoided, as it is + only by isolation and pure breeding that any specially desired + qualities can be increased by selection. It is for this reason + that among savage peoples, whose animals run half wild, little + improvement takes place; and the difficulty of isolation also + explains why distinct and pure breeds of cats are so rarely met + with. The wide distribution of useful animals and plants from a + very remote epoch has, no doubt, been a powerful cause of + modification, because the particular breed first introduced into + each country has often been kept pure for many years, and has + also been subjected to slight differences of conditions. It will + also usually have been selected for a somewhat different purpose + in each locality, and thus very distinct races would soon + originate.</p> + + <p>The important physiological effects of crossing breeds or + strains, and the part this plays in the economy of nature, will + be explained in a future chapter.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>The examples of variation now adduced—and these might + have been almost indefinitely increased—will suffice to + show that there is hardly an organ or a quality in plants or + animals which has not been observed to vary; and further, that + whenever any of these variations have been useful to man he has + <a name="Page_100" id="Page_100"></a>been able to increase them + to a marvellous extent by the simple process of always preserving + the best varieties to breed from. Along with these larger + variations others of smaller amount occasionally appear, + sometimes in external, sometimes in internal characters, the very + bones of the skeleton often changing slightly in form, size, or + number; but as these secondary characters have been of no use to + man, and have not been specially selected by him, they have, + usually, not been developed to any great amount except when they + have been closely dependent on those external characters which he + has largely modified.</p> + + <p>As man has considered only utility to himself, or the + satisfaction of his love of beauty, of novelty, or merely of + something strange or amusing, the variations he has thus produced + have something of the character of monstrosities. Not only are + they often of no use to the animals or plants themselves, but + they are not unfrequently injurious to them. In the Tumbler + pigeons, for instance, the habit of tumbling is sometimes so + excessive as to injure or kill the bird; and many of our + highly-bred animals have such delicate constitutions that they + are very liable to disease, while their extreme peculiarities of + form or structure would often render them quite unfit to live in + a wild state. In plants, many of our double flowers, and some + fruits, have lost the power of producing seed, and the race can + thus be continued only by means of cuttings or grafts. This + peculiar character of domestic productions distinguishes them + broadly from wild species and varieties, which, as will be seen + by and by, are necessarily adapted in every part of their + organisation to the conditions under which they have to live. + Their importance for our present inquiry depends on their + demonstrating the occurrence of incessant slight variations in + all parts of an organism, with the transmission to the offspring + of the special characteristics of the parents; and also, that all + such slight variations are capable of being accumulated by + selection till they present very large and important divergencies + from the ancestral stock.</p> + + <p>We thus see, that the evidence as to variation afforded by + animals and plants under domestication strikingly accords with + that which we have proved to exist in a state of nature. <a name= + "Page_101" id="Page_101"></a>And it is not at all surprising that + it should be so, since all the species were in a state of nature + when first domesticated or cultivated by man, and whatever + variations occur must be due to purely natural causes. Moreover, + on comparing the variations which occur in any one generation of + domesticated animals with those which we know to occur in wild + animals, we find no evidence of greater individual variation in + the former than in the latter. The results of man's selection are + more striking to us because we have always considered the + varieties of each domestic animal to be essentially identical, + while those which we observe in a wild state are held to be + essentially diverse. The greyhound and the spaniel seem + wonderful, as varieties of one animal produced by man's + selection; while we think little of the diversities of the fox + and the wolf, or the horse and the zebra, because we have been + accustomed to look upon them as radically distinct animals, not + as the results of nature's selection of the varieties of a common + ancestor.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_31_31" id="Footnote_31_31"></a><a href= + "#FNanchor_31_31"><span class="label">[31]</span></a> Darwin, + <i>Animals and Plants under Domestication</i>, vol. i. p. + 322.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_32_32" id="Footnote_32_32"></a><a href= + "#FNanchor_32_32"><span class="label">[32]</span></a> These + facts are taken from Darwin's <i>Domesticated Animals and + Cultivated Plants</i>, vol. i. pp. 359, 360, 392-401; vol. + ii. pp. 231, 275, 330.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_33_33" id="Footnote_33_33"></a><a href= + "#FNanchor_33_33"><span class="label">[33]</span></a> See + Darwin's <i>Animals and Plants under Domestication</i>, vol. + i. pp. 40-42.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_34_34" id="Footnote_34_34"></a><a href= + "#FNanchor_34_34"><span class="label">[34]</span></a> Mr. + Brent in <i>Journal of Horticulture</i>, 1861, p. 76; quoted + by Darwin, <i>Animals and Plants under Domestication</i>, + vol. i. p. 151.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_35_35" id="Footnote_35_35"></a><a href= + "#FNanchor_35_35"><span class="label">[35]</span></a> This + account of domestic pigeons is greatly condensed from Mr. + Darwin's work already referred to.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_36_36" id="Footnote_36_36"></a><a href= + "#FNanchor_36_36"><span class="label">[36]</span></a> + <i>Animals and Plants under Domestication</i>, vol. ii. pp. + 307-311.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_V" id="CHAPTER_V"></a><a name="Page_102" id= + "Page_102"></a>CHAPTER V</h2> + + <p style='font-weight:bold;'>NATURAL SELECTION BY VARIATION AND + SURVIVAL OF THE FITTEST</p> + + <div class="blockquot"> + <p>Effect of struggle for existence under unchanged + conditions—The effect under change of + conditions—Divergence of character—In + insects—In birds—In mammalia—Divergence leads + to a maximum of life in each area—Closely allied species + inhabit distinct areas—Adaptation to conditions at + various periods of life—The continued existence of low + forms of life—Extinction of low types among the higher + animals—Circumstances favourable to the origin of new + species—Probable origin of the dippers—The + importance of isolation—On the advance of organisation by + natural selection—Summary of the first five chapters.</p> + </div> + + <p>In the preceding chapters we have accumulated a body of facts + and arguments which will enable us now to deal with the very core + of our subject—the formation of species by means of natural + selection. We have seen how tremendous is the struggle for + existence always going on in nature owing to the great powers of + increase of all organisms; we have ascertained the fact of + variability extending to every part and organ, each of which + varies simultaneously and for the most part independently; and we + have seen that this variability is both large in its amount in + proportion to the size of each part, and usually affects a + considerable proportion of the individuals in the large and + dominant species. And, lastly, we have seen how similar + variations, occurring in cultivated plants and domestic animals, + are capable of being perpetuated and accumulated by artificial + selection, till they have resulted in all the wonderful varieties + of our fruits, flowers, and vegetables, our domestic animals and + household pets, many of which differ from each other far more in + external characters, habits, and instincts than do species in + <a name="Page_103" id="Page_103"></a>a state of nature. We have + now to inquire whether there is any analogous process in nature, + by which wild animals and plants can be permanently modified and + new races or new species produced.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Effect of Struggle for Existence under Unchanged + Conditions.</i></p> + + <p>Let us first consider what will be the effect of the struggle + for existence upon the animals and plants which we see around us, + under conditions which do not perceptibly vary from year to year + or from century to century. We have seen that every species is + exposed to numerous and varied dangers throughout its entire + existence, and that it is only by means of the exact adaptation + of its organisation—including its instincts and + habits—to its surroundings that it is enabled to live till + it produces offspring which may take its place when it ceases to + exist. We have seen also that, of the whole annual increase only + a very small fraction survives; and though the survival in + individual cases may sometimes be due rather to accident than to + any real superiority, yet we cannot doubt that, in the long run, + those survive which are best fitted by their perfect organisation + to escape the dangers that surround them. This "survival of the + fittest" is what Darwin termed "natural selection," because it + leads to the same results in nature as are produced by man's + selection among domestic animals and cultivated plants. Its + primary effect will, clearly, be to keep each species in the most + perfect health and vigour, with every part of its organisation in + full harmony with the conditions of its existence. It prevents + any possible deterioration in the organic world, and produces + that appearance of exuberant life and enjoyment, of health and + beauty, that affords us so much pleasure, and which might lead a + superficial observer to suppose that peace and quietude reigned + throughout nature.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Effect under changed Conditions.</i></p> + + <p>But the very same process which, so long as conditions remain + substantially the same, secures the continuance of each species + of animal or plant in its full perfection, will usually, under + changed conditions, bring about whatever change of structure or + habits may be necessitated by them. The changed conditions to + which we refer are such as we know have occurred <a name= + "Page_104" id="Page_104"></a>throughout all geological time and + in every part of the world. Land and water have been continually + shifting their positions; some regions are undergoing subsidence + with diminution of area, others elevation with extension of area; + dry land has been converted into marshes, while marshes have been + drained or have even been elevated into plateaux. Climate too has + changed again and again, either through the elevation of + mountains in high latitudes leading to the accumulation of snow + and ice, or by a change in the direction of winds and ocean + currents produced by the subsidence or elevation of lands which + connected continents and divided oceans. Again, along with all + these changes have come not less important changes in the + distribution of species. Vegetation has been greatly modified by + changes of climate and of altitude; while every union of lands + before separated has led to extensive migrations of animals into + new countries, disturbing the balance that before existed among + its forms of life, leading to the extermination of some species + and the increase of others.</p> + + <p>When such physical changes as these have taken place, it is + evident that many species must either become modified or cease to + exist. When the vegetation has changed in character the + herbivorous animals must become able to live on new and perhaps + less nutritious food; while the change from a damp to a dry + climate may necessitate migration at certain periods to escape + destruction by drought. This will expose the species to new + dangers, and require special modifications of structure to meet + them. Greater swiftness, increased cunning, nocturnal habits, + change of colour, or the power of climbing trees and living for a + time on their foliage or fruit, may be the means adopted by + different species to bring themselves into harmony with the new + conditions; and by the continued survival of those individuals, + only, which varied sufficiently in the right direction, the + necessary modifications of structure or of function would be + brought about, just as surely as man has been able to breed the + greyhound to hunt by sight and the foxhound by scent, or has + produced from the same wild plant such distinct forms as the + cauliflower and the brussels sprouts.</p> + + <p>We will now consider the special characteristics of the + changes in species that are likely to be effected, and how far + they agree with what we observe in nature.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_105" id="Page_105"></a><i>Divergence of + Character.</i></p> + + <p>In species which have a wide range the struggle for existence + will often cause some individuals or groups of individuals to + adopt new habits in order to seize upon vacant places in nature + where the struggle is less severe. Some, living among extensive + marshes, may adopt a more aquatic mode of life; others, living + where forests abound, may become more arboreal. In either case we + cannot doubt that the changes of structure needed to adapt them + to their new habits would soon be brought about, because we know + that variations in all the external organs and all their separate + parts are very abundant and are also considerable in amount. That + such divergence of character has actually occurred we have some + direct evidence. Mr. Darwin informs us that in the Catskill + Mountains in the United States there are two varieties of wolves, + one with a light greyhound-like form which pursues deer, the + other more bulky with shorter legs, which more frequently attacks + sheep.<a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href= + "#Footnote_37_37" class="fnanchor">[37]</a> Another good example + is that of the insects in the island of Madeira, many of which + have either lost their wings or have had them so much reduced as + to be useless for flight, while the very same species on the + continent of Europe possess fully developed wings. In other cases + the wingless Madeira species are distinct from, but closely + allied to, winged species of Europe. The explanation of this + change is, that Madeira, like many oceanic islands in the + temperate zone, is much exposed to sudden gales of wind, and as + most of the fertile land is on the coast, insects which flew much + would be very liable to be blown out to sea and lost. Year after + year, therefore, those individuals which had shorter wings, or + which used them least, were preserved; and thus, in time, + terrestrial, wingless, or imperfectly winged races or species + have been produced. That this is the true explanation of this + singular fact is proved by much corroborative evidence. There are + some few flower-frequenting insects in Madeira to whom wings are + essential, and in these the wings are somewhat larger than in the + same species on the mainland. We thus see that there is no + general tendency to the abortion of wings in Madeira, but that it + is simply a case of adaptation to new conditions. Those insects + <a name="Page_106" id="Page_106"></a>to whom wings were not + absolutely essential escaped a serious danger by not using them, + and the wings therefore became reduced or were completely lost. + But when they were essential they were enlarged and strengthened, + so that the insect could battle against the winds and save itself + from destruction at sea. Many flying insects, not varying fast + enough, would be destroyed before they could establish + themselves, and thus we may explain the total absence from + Madeira of several whole families of winged insects which must + have had many opportunities of reaching the islands. Such are the + large groups of the tiger-beetles (Cicindelidae), the chafers + (Melolonthidae), the click-beetles (Elateridae), and many + others.</p> + + <p>But the most curious and striking confirmation of this portion + of Mr. Darwin's theory is afforded by the case of Kerguelen + Island. This island was visited by the <i>Transit of Venus</i> + expedition. It is one of the stormiest places on the globe, being + subject to almost perpetual gales, while, there being no wood, it + is almost entirely without shelter. The Rev. A.E. Eaton, an + experienced entomologist, was naturalist to the expedition, and + he assiduously collected the few insects that were to be found. + All were incapable of flight, and most of them entirely without + wings. They included a moth, several flies, and numerous beetles. + As these insects could hardly have reached the islands in a + wingless state, even if there were any other known land inhabited + by them—which there is not—we must assume that, like + the Madeiran insects, they were originally winged, and lost their + power of flight because its possession was injurious to them.</p> + + <p>It is no doubt due to the same cause that some butterflies on + small and exposed islands have their wings reduced in size, as is + strikingly the case with the small tortoise-shell butterfly + (Vanessa urticae) inhabiting the Isle of Man, which is only about + half the size of the same species in England or Ireland; and Mr. + Wollaston notes that Vanessa callirhoe—a closely allied + South European form of our red-admiral butterfly—is + permanently smaller in the small and bare island of Porto Santo + than in the larger and more wooded adjacent island of + Madeira.</p> + + <p>A very good example of comparatively recent divergence of + character, in accordance with new conditions of life, is afforded + by our red grouse. This bird, the Lagopus scoticus of <a name= + "Page_107" id="Page_107"></a>naturalists, is entirely confined to + the British Isles. It is, however, very closely allied to the + willow grouse (Lagopus albus), a bird which ranges all over + Europe, Northern Asia, and North America, but which, unlike our + species, changes to white in winter. No difference in form or + structure can be detected between the two birds, but as they + differ so decidedly in colour—our species being usually + rather darker in winter than in summer, while there are also + slight differences in the call-note and in habits,—the two + species are generally considered to be distinct. The differences, + however, are so clearly adaptations to changed conditions that we + can hardly doubt that, during the early part of the glacial + period, when our islands were united to the continent, our grouse + was identical with that of the rest of Europe. But when the cold + passed away and our islands became permanently separated from the + mainland, with a mild and equable climate and very little snow in + winter, the change to white at that season became hurtful, + rendering the birds more conspicuous instead of serving as a + means of concealment. The colour was, therefore, gradually + changed by the process of variation and natural selection; and as + the birds obtained ample shelter among the heather which clothes + so many of our moorlands, it became useful for them to assimilate + with its brown and dusky stems and withered flowers rather than + with the snow of the higher mountains. An interesting + confirmation of this change having really occurred is afforded by + the occasional occurrence in Scotland of birds with a + considerable amount of white in the winter plumage. This is + considered to be a case of reversion to the ancestral type, just + as the slaty colours and banded wings of the wild rock-pigeon + sometimes reappear in our fancy breeds of domestic + pigeons.<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href= + "#Footnote_38_38" class="fnanchor">[38]</a></p> + + <p>The principle of "divergence of character" pervades all nature + from the lowest groups to the highest, as may be well seen in the + class of birds. Among our native species we see it well marked in + the different species of titmice, pipits, and chats. The great + titmouse (Parus major) by its larger size and stronger bill is + adapted to feed on larger insects, and is even said sometimes to + kill small and weak birds. The smaller and weaker coal titmouse + (Parus ater) has adopted a <a name="Page_108" id= + "Page_108"></a>more vegetarian diet, eating seeds as well as + insects, and feeding on the ground as well as among trees. The + delicate little blue titmouse (Parus coeruleus), with its very + small bill, feeds on the minutest insects and grubs which it + extracts from crevices of bark and from the buds of fruit-trees. + The marsh titmouse, again (Parus palustris), has received its + name from the low and marshy localities it frequents; while the + crested titmouse (Parus cristatus) is a northern bird frequenting + especially pine forests, on the seeds of which trees it partially + feeds. Then, again, our three common pipits—the tree-pipit + (Anthus arboreus), the meadow-pipit (Anthus pratensis), and the + rock-pipit or sea-lark (Anthus obscurus) have each occupied a + distinct place in nature to which they have become specially + adapted, as indicated by the different form and size of the hind + toe and claw in each species. So, the stone-chat (Saxicola + rubicola), the whin-chat (S. rubetra), and the wheat-ear (S. + oenanthe) are more or less divergent forms of one type, with + modifications in the shape of the wing, feet, and bill adapting + them to slightly different modes of life. The whin-chat is the + smallest, and frequents furzy commons, fields, and lowlands, + feeding on worms, insects, small molluscs, and berries; the + stone-chat is next in size, and is especially active and lively, + frequenting heaths and uplands, and is a permanent resident with + us, the two other species being migrants; while the larger and + more conspicuous wheat-ear, besides feeding on grubs, beetles, + etc., is able to capture flying insects on the wing, something + after the manner of true flycatchers.</p> + + <p>These examples sufficiently indicate how divergence of + character has acted, and has led to the adaptation of numerous + allied species, each to a more or less special mode of life, with + the variety of food, of habits, and of enemies which must + necessarily accompany such diversity. And when we extend our + inquiries to higher groups we find the same indications of + divergence and special adaptation, often to a still more marked + extent. Thus we have the larger falcons, which prey upon birds, + while some of the smaller species, like the hobby (Falco + subbuteo), live largely on insects. The true falcons capture + their prey in the air, while the hawks usually seize it on or + near the ground, feeding on hares, rabbits, squirrels, grouse, + pigeons, and poultry. Kites and buzzards, on the <a name= + "Page_109" id="Page_109"></a>other hand, seize their prey upon + the ground, and the former feed largely on reptiles and offal as + well as on birds and quadrupeds. Others have adopted fish as + their chief food, and the osprey snatches its prey from the water + with as much facility as a gull or a petrel; while the South + American caracaras (Polyborus) have adopted the habits of + vultures and live altogether on carrion. In every great group + there is the same divergence of habits. There are ground-pigeons, + rock-pigeons, and wood-pigeons,—seed-eating pigeons and + fruit-eating pigeons; there are carrion-eating, insect-eating, + and fruit-eating crows. Even kingfishers are, some aquatic, some + terrestrial in their habits; some live on fish, some on insects, + some on reptiles. Lastly, among the primary divisions of birds we + find a purely terrestrial group—the Ratitae, including the + ostriches, cassowaries, etc.; other great groups, including the + ducks, cormorants, gulls, penguins, etc., are aquatic; while the + bulk of the Passerine birds are aerial and arboreal. The same + general facts can be detected in all other classes of animals. In + the mammalia, for example, we have in the common rat a fish-eater + and flesh-eater as well as a grain-eater, which has no doubt + helped to give it the power of spreading over the world and + driving away the native rats of other countries. Throughout the + Rodent tribe we find everywhere aquatic, terrestrial, and + arboreal forms. In the weasel and cat tribes some live more in + trees, others on the ground; squirrels have diverged into + terrestrial, arboreal, and flying species; and finally, in the + bats we have a truly aerial, and in the whales a truly aquatic + order of mammals. We thus see that, beginning with different + varieties of the same species, we have allied species, genera, + families, and orders, with similarly divergent habits, and + adaptations to different modes of life, indicating some general + principle in nature which has been operative in the development + of the organic world. But in order to be thus operative it must + be a generally useful principle, and Mr. Darwin has very clearly + shown us in what this utility consists.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Divergence leads to a Maximum of Organic Forms in each + Area.</i></p> + + <p>Divergence of character has a double purpose and use. In the + first place it enables a species which is being overcome <a name= + "Page_110" id="Page_110"></a>by rivals, or is in process of + extinction by enemies, to save itself by adopting new habits or + by occupying vacant places in nature. This is the immediate and + obvious effect of all the numerous examples of divergence of + character which we have pointed out. But there is another and + less obvious result, which is, that the greater the diversity in + the organisms inhabiting a country or district the greater will + be the total amount of life that can be supported there. Hence + the continued action of the struggle for existence will tend to + bring about more and more diversity in each area, which may be + shown to be the case by several kinds of evidence. As an example, + a piece of turf, three feet by four in size, was found by Mr. + Darwin to contain twenty species of plants, and these twenty + species belonged to eighteen genera and to eight orders, showing + how greatly they differed from each other. Farmers find that a + greater quantity of hay is obtained from ground sown with a + variety of genera of grasses, clover, etc., than from similar + land sown with one or two species only; and the same principle + applies to rotation of crops, plants differing very widely from + each other giving the best results. So, in small and uniform + islands, and in small ponds of fresh water, the plants and + insects, though few in number, are found to be wonderfully varied + in character.</p> + + <p>The same principle is seen in the naturalisation of plants and + animals by man's agency in distant lands, for the species that + thrive best and establish themselves permanently are not only + very varied among themselves but differ greatly from the native + inhabitants. Thus, in the Northern United States there are, + according to Dr. Asa Gray, 260 naturalised flowering plants which + belong to no less than 162 genera; and of these, 100 genera are + not natives of the United States. So, in Australia, the rabbit, + though totally unlike any native animal, has increased so much + that it probably outnumbers in individuals all the native mammals + of the country; and in New Zealand the rabbit and the pig have + equally multiplied. Darwin remarks that this "advantage of + diversification of structure in the inhabitants of the same + region is, in fact, the same as that of the physiological + division of labour in the organs of the same body. No + physiologist doubts that a <a name="Page_111" id= + "Page_111"></a>stomach adapted to digest vegetable matter alone, + or flesh alone, draws more nutriment from these substances. So, + in the general economy of any land, the more widely and perfectly + the animals and plants are diversified for different habits of + life, so will a greater number of individuals be capable of there + supporting themselves."<a name="FNanchor_39_39" id= + "FNanchor_39_39"></a><a href="#Footnote_39_39" class= + "fnanchor">[39]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The most closely allied Species inhabit distinct + Areas.</i></p> + + <p>One of the curious results of the general action of this + principle in nature is, that the most closely allied + species—those whose differences though often real and + important are hardly perceptible to any one but a + naturalist—are usually not found in the same but in widely + separated countries. Thus, the nearest allies to our European + golden plover are found in North America and East Asia; the + nearest ally of our European jay is found in Japan, although + there are several other species of jays in Western Asia and North + Africa; and though we have several species of titmice in England + they are not very closely allied to each other. The form most + akin to our blue tit is the azure tit of Central Asia (Parus + azureus); the Parus ledouci of Algeria is very near our coal tit, + and the Parus lugubris of South-Eastern Europe and Asia Minor is + nearest to our marsh tit. So, our four species of wild + pigeons—the ring-dove, stock-dove, rock-pigeon, and + turtle-dove—are not closely allied to each other, but each + of them belongs, according to some ornithologists, to a separate + genus or subgenus, and has its nearest relatives in distant parts + of Asia and Africa. In mammalia the same thing occurs. Each + mountain region of Europe and Asia has usually its own species of + wild sheep and goat, and sometimes of antelope and deer; so that + in each region there is found the greatest diversity in this + class of animals, while the closest allies inhabit quite distinct + and often distant areas. In plants we find the same phenomenon + prevalent. Distinct species of columbine are found in Central + Europe (Aguilegia vulgaris), in Eastern Europe, and Siberia (A. + glandulosa), in the Alps (A. Alpina), in the Pyrenees (A. + pyrenaiea), in the Greek mountains (A. ottonis), and in Corsica + (A. Bernardi), but rarely are two <a name="Page_112" id= + "Page_112"></a>species found in the same area. So, each part of + the world has its own peculiar forms of pines, firs, and cedars, + but the closely allied species or varieties are in almost every + case inhabitants of distinct areas. Examples are the deodar of + the Himalayas, the cedar of Lebanon, and that of North Africa, + all very closely allied but confined to distinct areas; and the + numerous closely allied species of true pine (genus Pinus), which + almost always inhabit different countries or occupy different + stations. We will now consider some other modes in which natural + selection will act, to adapt organisms to changed conditions.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Adaptation to Conditions at Various Periods of Life.</i></p> + + <p>It is found, that, in domestic animals and cultivated plants, + variations occurring at any one period of life reappear in the + offspring at the same period, and can be perpetuated and + increased by selection without modifying other parts of the + organisation. Thus, variations in the caterpillar or the cocoon + of the silkworm, in the eggs of poultry, and in the seeds or + young shoots of many culinary vegetables, have been accumulated + till those parts have become greatly modified and, for man's + purposes, improved. Owing to this fact it is easy for organisms + to become so modified as to avoid dangers that occur at any one + period of life. Thus it is that so many seeds have become adapted + to various modes of dissemination or protection. Some are winged, + or have down or hairs attached to them, so as to enable them to + be carried long distances in the air; others have curious hooks + and prickles, which cause them to be attached firmly to the fur + of mammals or the feathers of birds; while others are buried + within sweet or juicy and brightly coloured fruits, which are + seen and devoured by birds, the hard smooth seeds passing through + their bodies in a fit state for germination. In the struggle for + existence it must benefit a plant to have increased means of + dispersing its seeds, and of thus having young plants produced in + a greater variety of soils, aspects, and surroundings, with a + greater chance of some of them escaping their numerous enemies + and arriving at maturity. The various differences referred to + would, therefore, be brought about by variation and survival of + the fittest, just as surely as the length and quality <a name= + "Page_113" id="Page_113"></a>of cotton on the seed of the + cotton-plant have been increased by man's selection.</p> + + <p>The larvae of insects have thus been wonderfully modified in + order to escape the numerous enemies to whose attacks they are + exposed at this period of their existence. Their colours and + markings have become marvellously adapted to conceal them among + the foliage of the plant they live upon, and this colour often + changes completely after the last moult, when the creature has to + descend to the ground for its change to the pupa state, during + which period a brown instead of a green colour is protective. + Others have acquired curious attitudes and large ocelli, which + cause them to resemble the head of some reptile, or they have + curious horns or coloured ejectile processes which frighten away + enemies; while a great number have acquired secretions which + render them offensive to the taste of their enemies, and these + are always adorned with very conspicuous markings or brilliant + colours, which serve as a sign of inedibility and prevent their + being needlessly attacked. This, however, is a portion of the + very large subject of organic colour and marking, which will be + fully discussed and illustrated in a separate chapter.</p> + + <p>In this way every possible modification of an animal or plant, + whether in colour, form, structure, or habits, which would be + serviceable to it or to its progeny at any period of its + existence, may be readily brought about. There are some curious + organs which are used only once in a creature's life, but which + are yet essential to its existence, and thus have very much the + appearance of design by an intelligent designer. Such are, the + great jaws possessed by some insects, used exclusively for + opening the cocoon, and the hard tip to the beak of unhatched + birds used for breaking the eggshell. The increase in thickness + or hardness of the cocoons or the eggs being useful for + protection against enemies or to avoid accidents, it is probable + that the change has been very gradual, because it would be + constantly checked by the necessity for a corresponding change in + the young insects or birds enabling them to overcome the + additional obstacle of a tougher cocoon or a harder eggshell. As + we have seen, however, that every part of the organism appears to + be varying independently, at the same time, though to different + <a name="Page_114" id="Page_114"></a>amounts, there seems no + reason to believe that the necessity for two or more coincident + variations would prevent the required change from taking + place.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Continued Existence of Low Forms of Life.</i></p> + + <p>Since species are continually undergoing modifications giving + them some superiority over other species or enabling them to + occupy fresh places in nature, it may be asked—Why do any + low forms continue to exist? Why have they not long since been + improved and developed into higher forms? The answer, probably, + is, that these low forms occupy places in nature which cannot be + filled by higher forms, and that they have few or no competitors; + they therefore continue to exist. Thus, earthworms are adapted to + their mode of life better than they would be if more highly + organised. So, in the ocean, the minute foraminifera and + infusoria, and the larger sponges and corals, occupy places which + more highly developed creatures could not fill. They form, as it + were, the base of the great structure of animal life, on which + the next higher forms rest; and though in the course of ages they + may undergo some changes, and diversification of form and + structure, in accordance with changed conditions, their essential + nature has probably remained the same from the very dawn of life + on the earth. The low aquatic diatomaceae and confervae, together + with the lowest fungi and lichens, occupy a similar position in + the vegetable kingdom, filling places in nature which would be + left vacant if only highly organised plants existed. There is, + therefore, no motive power to destroy or seriously to modify + them; and they have thus probably persisted, under slightly + varying forms, through all geological time.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Extinction of Lower Types among the Higher Animals.</i></p> + + <p>So soon; however, as we approach the higher and more fully + developed groups, we see indications of the often repeated + extinction of lower by higher forms. This is shown by the great + gaps that separate the mammalia, birds, reptiles, and fishes from + each other; while the lowest forms of each are always few in + number and confined to limited areas. Such <a name="Page_115" id= + "Page_115"></a>are the lowest mammals—the echidna and + ornithorhynchus of Australia; the lowest birds—the apteryx + of New Zealand and the cassowaries of the New Guinea region; + while the lowest fish—the amphioxus or lancelet, is + completely isolated, and has apparently survived only by its + habit of burrowing in the sand. The great distinctness of the + carnivora, ruminants, rodents, whales, bats, and other orders of + mammalia; of the accipitres, pigeons, and parrots, among birds; + and of the beetles, bees, flies, and moths, among insects, all + indicate an enormous amount of extinction among the comparatively + low forms by which, on any theory of evolution, these higher and + more specialised groups must have been preceded.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Circumstances favourable to the Origin of New Species by + Natural Selection.</i></p> + + <p>We have already seen that, when there is no change in the + physical or organic conditions of a country, the effect of + natural selection is to keep all the species inhabiting it in a + state of perfect health and full development, and to preserve the + balance that already exists between the different groups of + organisms. But, whenever the physical or organic conditions + change, to however small an extent, some corresponding change + will be produced in the flora and fauna, since, considering the + severe struggle for existence and the complex relations of the + various organisms, it is hardly possible that the change should + not be beneficial to some species and hurtful to others. The most + common effect, therefore, will be that some species will increase + and others will diminish; and in cases where a species was + already small in numbers a further diminution might lead to + extinction. This would afford room for the increase of other + species, and thus a considerable readjustment of the proportions + of the several species might take place. When, however, the + change was of a more important character, directly affecting the + existence of many species so as to render it difficult for them + to maintain themselves without some considerable change in + structure or habits, that change would, in some cases, be brought + about by variation and natural selection, and thus new varieties + or new species might be formed. We have to consider, then, which + <a name="Page_116" id="Page_116"></a>are the species that would + be most likely to be so modified, while others, not becoming + modified, would succumb to the changed conditions and become + extinct.</p> + + <p>The most important condition of all is, undoubtedly, that + variations should occur of sufficient amount, of a sufficiently + diverse character, and in a large number of individuals, so as to + afford ample materials for natural selection to act upon; and + this, we have seen, does occur in most, if not in all, large, + wide-ranging, and dominant species. From some of these, + therefore, the new species adapted to the changed conditions + would usually be derived; and this would especially be the case + when the change of conditions was rather rapid, and when a + correspondingly rapid modification could alone save some species + from extinction. But when the change was very gradual, then even + less abundant and less widely distributed species might become + modified into new forms, more especially if the extinction of + many of the rarer species left vacant places in the economy of + nature.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Probable Origin of the Dippers.</i></p> + + <p>An excellent example of how a limited group of species has + been able to maintain itself by adaptation to one of these + "vacant places" in nature, is afforded by the curious little + birds called dippers or water-ouzels, forming the genus Cinclus + and the family Cinclidae of naturalists. These birds are + something like small thrushes, with very short wings and tail, + and very dense plumage. They frequent, exclusively, mountain + torrents in the northern hemisphere, and obtain their food + entirely in the water, consisting, as it does, of water-beetles, + caddis-worms and other insect-larvae, as well as numerous small + freshwater shells. These birds, although not far removed in + structure from thrushes and wrens, have the extraordinary power + of flying under water; for such, according to the best observers, + is their process of diving in search of their prey, their dense + and somewhat fibrous plumage retaining so much air that the water + is prevented from touching their bodies or even from wetting + their feathers to any great extent. Their powerful feet and long + curved claws enable them to hold on to stones at the bottom, and + thus to retain their position while picking up insects, shells, + <a name="Page_117" id="Page_117"></a>etc. As they frequent + chiefly the most rapid and boisterous torrents, among rocks, + waterfalls, and huge boulders, the water is never frozen over, + and they are thus able to live during the severest winters. Only + a very few species of dipper are known, all those of the old + world being so closely allied to our British bird that some + ornithologists consider them to be merely local races of one + species; while in North America and the northern Andes there are + two other species.</p> + + <p>Here then we have a bird, which, in its whole structure, shows + a close affinity to the smaller typical perching birds, but which + has departed from all its allies in its habits and mode of life, + and has secured for itself a place in nature where it has few + competitors and few enemies. We may well suppose, that, at some + remote period, a bird which was perhaps the common and more + generalised ancestor of most of our thrushes, warblers, wrens, + etc., had spread widely over the great northern continent, and + had given rise to numerous varieties adapted to special + conditions of life. Among these some took to feeding on the + borders of clear streams, picking out such larvae and molluscs as + they could reach in shallow water. When food became scarce they + would attempt to pick them out of deeper and deeper water, and + while doing this in cold weather many would become frozen and + starved. But any which possessed denser and more hairy plumage + than usual, which was able to keep out the water, would survive; + and thus a race would be formed which would depend more and more + on this kind of food. Then, following up the frozen streams into + the mountains, they would be able to live there during the + winter; and as such places afforded them much protection from + enemies and ample shelter for their nests and young, further + adaptations would occur, till the wonderful power of diving and + flying under water was acquired by a true land-bird.</p> + + <p>That such habits might be acquired under stress of need is + rendered highly probable by the facts stated by the well-known + American naturalist, Dr. Abbott. He says that "the water-thrushes + (Seiurus sp.) all wade in water, and often, seeing minute + mollusca on the bottom of the stream, plunge both head and neck + beneath the surface, so that often, for <a name="Page_118" id= + "Page_118"></a>several seconds, a large part of the body is + submerged. Now these birds still have the plumage pervious to + water, and so are liable to be drenched and sodden; but they have + also the faculty of giving these drenched feathers such a good + shaking that flight is practicable a moment after leaving the + water. Certainly the water-thrushes (Seiurus ludovicianus, S. + auricapillus, and S. noveboracensis) have taken many preliminary + steps to becoming as aquatic as the dipper; and the winter-wren, + and even the Maryland yellow-throat are not far behind."<a name= + "FNanchor_40_40" id="FNanchor_40_40"></a><a href= + "#Footnote_40_40" class="fnanchor">[40]</a></p> + + <p>Another curious example of the way in which species have been + modified to occupy new places in nature, is afforded by the + various animals which inhabit the water-vessels formed by the + leaves of many epiphytal species of Bromelia. Fritz Müller + has described a caddis-fly larva which lives among these leaves, + and which has been modified in the pupa state in accordance with + its surroundings. The pupae of caddis-flies inhabiting streams + have fringes of hair on the tarsi to enable them to reach the + surface on leaving their cases. But in the species inhabiting + bromelia leaves there is no need for swimming, and accordingly we + find the tarsi entirely bare. In the same plants are found + curious little Entomostraca, very abundant there but found + nowhere else. These form a new genus, but are most nearly allied + to Cythere, a marine type. It is believed that the transmission + of this species from one tree to another must be effected by the + young crustacea, which are very minute, clinging to beetles, many + of which, both terrestrial and aquatic, also inhabit the bromelia + leaves; and as some water-beetles are known to frequent the sea, + it is perhaps by these means that the first emigrants established + themselves in this strange new abode. Bromeliae are often very + abundant on trees growing on the water's edge, and this would + facilitate the transition from a marine to an arboreal habitat. + Fritz Müller has also found, among the bromelia leaves, a + small frog bearing its eggs on its back, and having some other + peculiarities of structure. Several beautiful little aquatic + plants of the genus Utricularia or bladder-wort also inhabit + bromelia leaves; and these send runners out to neighbouring + plants and thus spread themselves with great rapidity.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_119" id="Page_119"></a><i>The Importance of + Isolation.</i></p> + + <p>Isolation is no doubt an important aid to natural selection, + as shown by the fact that islands so often present a number of + peculiar species; and the same thing is seen on the two sides of + a great mountain range or on opposite coasts of a continent. The + importance of isolation is twofold. In the first place, it leads + to a body of individuals of each species being limited in their + range and thus subjected to uniform conditions for long spaces of + time. Both the direct action of the environment and the natural + selection of such varieties only as are suited to the conditions, + will, therefore, be able to produce their full effect. In the + second place, the process of change will not be interfered with + by intercrossing with other individuals which are becoming + adapted to somewhat different conditions in an adjacent area. But + this question of the swamping effects of intercrossing will be + considered in another chapter.</p> + + <p>Mr. Darwin was of opinion that, on the whole, the largeness of + the area occupied by a species was of more importance than + isolation, as a factor in the production of new species, and in + this I quite agree with him. It must, too, be remembered, that + isolation will often be produced in a continuous area whenever a + species becomes modified in accordance with varied conditions or + diverging habits. For example, a wide-ranging species may in the + northern and colder part of its area become modified in one + direction, and in the southern part in another direction; and + though for a long time an intermediate form may continue to exist + in the intervening area, this will be likely soon to die out, + both because its numbers will be small, and it will be more or + less pressed upon in varying seasons by the modified varieties, + each better able to endure extremes of climate. So, when one + portion of a terrestrial species takes to a more arboreal or to a + more aquatic mode of life, the change of habit itself leads to + the isolation of each portion. Again, as will be more fully + explained in a future chapter, any difference of habits or of + haunts usually leads to some modification of colour or marking, + as a means of concealment from enemies; and there is reason to + believe that this difference will be intensified by natural + selection as a means of identification <a name="Page_120" id= + "Page_120"></a>and recognition by members of the same variety or + incipient species. It has also been observed that each + differently coloured variety of wild animals, or of domesticated + animals which have run wild, keep together, and refuse to pair + with individuals of the other colours; and this must of itself + act to keep the races separate as completely as physical + isolation.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>On the Advance of Organisation by Natural Selection.</i></p> + + <p>As natural selection acts solely by the preservation of useful + variations, or those which are beneficial to the organism under + the conditions to which it is exposed, the result must + necessarily be that each species or group tends to become more + and more improved in relation to its conditions. Hence we should + expect that the larger groups in each class of animals and + plants—those which have persisted and have been abundant + throughout geological ages—would, almost necessarily, have + arrived at a high degree of organisation, both physical and + mental. Illustrations of this are to be seen everywhere. Among + mammalia we have the carnivora, which from Eocene times have been + becoming more and more specialised, till they have culminated in + the cat and dog tribes, which have reached a degree of perfection + both in structure and intelligence fully equal to that of any + other animals. In another line of development, the herbivora have + been specialised for living solely on vegetable food till they + have culminated in the sheep, the cattle, the deer, and the + antelopes. The horse tribe, commencing with an early four-toed + ancestor in the Eocene age, has increased in size and in perfect + adaptation of feet and teeth to a life on open plains, and has + reached its highest perfection in the horse, the ass, and the + zebra. In birds, also, we see an advance from the imperfect + tooth-billed and reptile-tailed birds of the secondary epoch, to + the wonderfully developed falcons, crows, and swallows of our + time. So, the ferns, lycopods, conifers, and monocotyledons of + the palaeozoic and mesozoic rocks, have developed into the + marvellous wealth of forms of the higher dicotyledons that now + adorn the earth.</p> + + <p>But this remarkable advance in the higher and larger groups + does not imply any universal law of progress in organisation, + because we have at the same time numerous examples (as has been + already pointed out) of the persistence of lowly organised + <a name="Page_121" id="Page_121"></a>forms, and also of absolute + degradation or degeneration. Serpents, for example, have been + developed from some lizard-like type which has lost its limbs; + and though this loss has enabled them to occupy fresh places in + nature and to increase and flourish to a marvellous extent, yet + it must be considered to be a retrogression rather than an + advance in organisation. The same remark will apply to the whale + tribe among mammals; to the blind amphibia and insects of the + great caverns; and among plants to the numerous cases in which + flowers, once specially adapted to be fertilised by insects, have + lost their gay corollas and their special adaptations, and have + become degraded into wind-fertilised forms. Such are our + plantains, our meadow burnet, and even, as some botanists + maintain, our rushes, sedges, and grasses. The causes which have + led to this degeneration will be discussed in a future chapter; + but the facts are undisputed, and they show us that although + variation and the struggle for existence may lead, on the whole, + to a continued advance of organisation; yet they also lead in + many cases to a retrogression, when such retrogression may aid in + the preservation of any form under new conditions. They also lead + to the persistence, with slight modifications, of numerous lowly + organised forms which are suited to places which higher forms + could not fully occupy, or to conditions under which they could + not exist. Such are the ocean depths, the soil of the earth, the + mud of rivers, deep caverns, subterranean waters, etc.; and it is + in such places as these, as well as in some oceanic islands which + competing higher forms have not been able to reach, that we find + many curious relics of an earlier world, which, in the free air + and sunlight and in the great continents, have long since been + driven out or exterminated by higher types.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Summary of the first Five Chapters.</i></p> + + <p>We have now passed in review, in more or less detail, the main + facts on which the theory of "the origin of species by means of + natural selection" is founded. In future chapters we shall have + to deal mainly with the application of the theory to explain the + varied and complex phenomena presented by the organic world; and, + also, to discuss some of the theories put forth by modern + writers, either as being more fundamental than <a name="Page_122" + id="Page_122"></a>that of Darwin or as supplementary to it. + Before doing this, however, it will be well briefly to summarise + the facts and arguments already set forth, because it is only by + a clear comprehension of these that the full importance of the + theory can be appreciated and its further applications + understood.</p> + + <p>The theory itself is exceedingly simple, and the facts on + which it rests—though excessively numerous individually, + and coextensive with the entire organic world—yet come + under a few simple and easily understood classes. These facts + are,—first, the enormous powers of increase in geometrical + progression possessed by all organisms, and the inevitable + struggle for existence among them; and, in the second place, the + occurrence of much individual variation combined with the + hereditary transmission of such variations. From these two great + classes of facts, which are universal and indisputable, there + necessarily arises, as Darwin termed it, the "preservation of + favoured races in the struggle for life," the continuous action + of which, under the ever-changing conditions both of the + inorganic and organic universe, necessarily leads to the + formation or development of new species.</p> + + <p>But, although this general statement is complete and + indisputable, yet to see its applications under all the complex + conditions that actually occur in nature, it is necessary always + to bear in mind the tremendous power and universality of the + agencies at work. We must never for an instant lose sight of the + fact of the enormously rapid increase of all organisms, which has + been illustrated by actual cases, given in our second chapter, no + less than by calculations of the results of unchecked increase + for a few years. Then, never forgetting that the animal and plant + population of any country is, on the whole, stationary, we must + be always trying to realise the ever-recurring destruction of the + enormous annual increase, and asking ourselves what determines, + in each individual case, the death of the many, the survival of + the few. We must think over all the causes of destruction to each + organism,—to the seed, the young shoot, the growing plant, + the full-grown tree, or shrub, or herb, and again the fruit and + seed; and among animals, to the egg or new-born young, to the + youthful, and to the adults. Then, we must always bear in mind + that what goes on in the case of the individual or family group + we may <a name="Page_123" id="Page_123"></a>observe or think of, + goes on also among the millions and scores of millions of + individuals which are comprised in almost every species; and must + get rid of the idea that <i>chance</i> determines which shall + live and which die. For, although in many individual cases death + may be due to chance rather than to any inferiority in those + which die first, yet we cannot possibly believe that this can be + the case on the large scale on which nature works. A plant, for + instance, cannot be increased unless there are suitable vacant + places its seeds can grow in, or stations where it can overcome + other less vigorous and healthy plants. The seeds of all plants, + by their varied modes of dispersal, may be said to be seeking out + such places in which to grow; and we cannot doubt that, in the + long run, those individuals whose seeds are the most numerous, + have the greatest powers of dispersal, and the greatest vigour of + growth, will leave more descendants than the individuals of the + same species which are inferior in all these respects, although + now and then some seed of an inferior individual may + <i>chance</i> to be carried to a spot where it can grow and + survive. The same rule will apply to every period of life and to + every danger to which plants or animals are exposed. The best + organised, or the most healthy, or the most active, or the best + protected, or the most intelligent, will inevitably, in the long + run, gain an advantage over those which are inferior in these + qualities; that is, <i>the fittest will survive</i>, the fittest + being, in each particular case, those which are superior in the + special qualities on which safety depends. At one period of life, + or to escape one kind of danger, concealment may be necessary; at + another time, to escape another danger, swiftness; at another, + intelligence or cunning; at another, the power to endure rain or + cold or hunger; and those which possess all these faculties in + the fullest perfection will generally survive.</p> + + <p>Having fully grasped these facts in all their fulness and in + their endless and complex results, we have next to consider the + phenomena of variation, discussed in the third and fourth + chapters; and it is here that perhaps the greatest difficulty + will be felt in appreciating the full importance of the evidence + as set forth. It has been so generally the practice to speak of + variation as something exceptional and comparatively + rare—as an abnormal deviation from the uniformity and + stability of the <a name="Page_124" id="Page_124"></a>characters + of a species—and so few even among naturalists have ever + compared, accurately, considerable numbers of individuals, that + the conception of variability as a general characteristic of all + dominant and widespread species, large in its amount and + affecting, not a few, but considerable masses of the individuals + which make up the species, will be to many entirely new. Equally + important is the fact that the variability extends to every organ + and every structure, external and internal; while perhaps most + important of all is the independent variability of these several + parts, each one varying without any constant or even usual + dependence on, or correlation with, other parts. No doubt there + is some such correlation in the differences that exist between + species and species—more developed wings usually + accompanying smaller feet and <i>vice versâ</i>—but + this is, generally, a useful adaptation which has been brought + about by natural selection, and does not apply to the individual + variability which occurs within the species.</p> + + <p>It is because these facts of variation are so important and so + little understood, that they have been discussed in what will + seem to some readers wearisome and unnecessary detail. Many + naturalists, however, will hold that even more evidence is + required; and more, to almost any amount, could easily have been + given. The character and variety of that already adduced will, + however, I trust, convince most readers that the facts are as + stated; while they have been drawn from a sufficiently wide area + to indicate a general principle throughout nature.</p> + + <p>If, now, we fully realise these facts of variation, along with + those of rapid multiplication and the struggle for existence, + most of the difficulties in the way of comprehending how species + have originated through natural selection will disappear. For + whenever, through changes of climate, or of altitude, or of the + nature of the soil, or of the area of the country, any species + are exposed to new dangers, and have to maintain themselves and + provide for the safety of their offspring under new and more + arduous conditions, then, in the variability of all parts, + organs, and structures, no less than of habits and intelligence, + we have the means of producing modifications which will certainly + bring the species into harmony with its <a name="Page_125" id= + "Page_125"></a>new conditions. And if we remember that all such + physical changes are slow and gradual in their operation, we + shall see that the amount of variation which we know occurs in + every new generation will be quite sufficient to enable + modification and adaptation to go on at the same rate. Mr. Darwin + was rather inclined to exaggerate the necessary slowness of the + action of natural selection; but with the knowledge we now + possess of the great amount and range of individual variation, + there seems no difficulty in an amount of change, quite + equivalent to that which usually distinguishes allied species, + sometimes taking place in less than a century, should any rapid + change of conditions necessitate an equally rapid adaptation. + This may often have occurred, either to immigrants into a new + land, or to residents whose country has been cut off by + subsidence from a larger and more varied area over which they had + formerly roamed. When no change of conditions occurs, species may + remain unchanged for very long periods, and thus produce that + appearance of stability of species which is even now often + adduced as an argument against evolution by natural selection, + but which is really quite in harmony with it.</p> + + <p>On the principles, and by the light of the facts, now briefly + summarised, we have been able, in the present chapter, to + indicate how natural selection acts, how divergence of character + is set up, how adaptation to conditions at various periods of + life has been effected, how it is that low forms of life continue + to exist, what kind of circumstances are most favourable to the + formation of new species, and, lastly, to what extent the advance + of organisation to higher types is produced by natural selection. + We will now pass on to consider some of the more important + objections and difficulties which have been advanced by eminent + naturalists.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_37_37" id="Footnote_37_37"></a><a href= + "#FNanchor_37_37"><span class="label">[37]</span></a> + <i>Origin of Species</i>, p. 71.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_38_38" id="Footnote_38_38"></a><a href= + "#FNanchor_38_38"><span class="label">[38]</span></a> + Yarrell's <i>British Birds</i>, fourth edition, vol. iii. p. + 77.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_39_39" id="Footnote_39_39"></a><a href= + "#FNanchor_39_39"><span class="label">[39]</span></a> + <i>Origin of Species</i>, p. 89.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_40_40" id="Footnote_40_40"></a><a href= + "#FNanchor_40_40"><span class="label">[40]</span></a> + <i>Nature</i>, vol. xxx. p. 30.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a><a name="Page_126" + id="Page_126"></a>CHAPTER VI</h2> + + <p style='font-weight:bold;'>DIFFICULTIES AND OBJECTIONS</p> + + <div class="blockquot"> + <p>Difficulty as to smallness of variations—As to the + right variations occurring when required—The beginnings + of important organs—The mammary glands—The eyes of + flatfish—Origin of the eye—Useless or non-adaptive + characters—Recent extension of the region of utility in + plants—The same in animals—Uses of tails—Of + the horns of deer—Of the scale-ornamentation of + reptiles—Instability of non-adaptive + characters—Delboeuf's law—No "specific" character + proved to be useless—The swamping effects of + intercrossing—Isolation as preventing + intercrossing—Gulick on the effects of + isolation—Cases in which isolation is ineffective.</p> + </div> + + <p>In the present chapter I propose to discuss the more obvious + and often repeated objections to Darwin's theory, and to show how + far they affect its character as a true and sufficient + explanation of the origin of species. The more recondite + difficulties, affecting such fundamental questions as the causes + and laws of variability, will be left for a future chapter, after + we have become better acquainted with the applications of the + theory to the more important adaptations and correlations of + animal and plant life.</p> + + <p>One of the earliest and most often repeated objections was, + that it was difficult "to imagine a reason why variations tending + in an infinitesimal degree in any special direction should be + preserved," or to believe that the complex adaptation of living + organisms could have been produced "by infinitesimal beginnings." + Now this term "infinitesimal," used by a well-known early critic + of the <i>Origin of Species</i>, was never made use of by Darwin + himself, who spoke only of variations being "slight," and of the + "small amount" of the variations that might be selected. Even in + using these terms he undoubtedly afforded <a name="Page_127" id= + "Page_127"></a>grounds for the objection above made, that such + small and slight variations could be of no real use, and would + not determine the survival of the individuals possessing them. We + have seen, however, in our third chapter, that even Darwin's + terms were hardly justified; and that the variability of many + important species is of considerable amount, and may very often + be properly described as large. As this is found to be the case + both in animals and plants, and in all their chief groups and + subdivisions, and also to apply to all the separate parts and + organs that have been compared, we must take it as proved that + the average <i>amount</i> of variability presents no difficulty + whatever in the way of the action of natural selection. It may be + here mentioned that, up to the time of the preparation of the + last edition of <i>The Origin of Species</i>, Darwin had not seen + the work of Mr. J.A. Allen of Harvard University (then only just + published), which gave us the first body of accurate comparisons + and measurements demonstrating this large amount of variability. + Since then evidence of this nature has been accumulating, and we + are, therefore, now in a far better position to appreciate the + facilities for natural selection, in this respect, than was Mr. + Darwin himself.</p> + + <p>Another objection of a similar nature is, that the chances are + immensely against the right variation or combination of + variations occurring just when required; and further, that no + variation can be perpetuated that is not accompanied by several + concomitant variations of dependent parts—greater length of + a wing in a bird, for example, would be of little use if + unaccompanied by increased volume or contractility of the muscles + which move it. This objection seemed a very strong one so long as + it was supposed that variations occurred singly and at + considerable intervals; but it ceases to have any weight now we + know that they occur simultaneously in various parts of the + organism, and also in a large proportion of the individuals which + make up the species. A considerable number of individuals will, + therefore, every year possess the required combination of + characters; and it may also be considered probable that when the + two characters are such that they always <i>act</i> together, + there will be such a correlation between them that they will + frequently <i>vary</i> together. But there is another + consideration that seems to show that this coincident <a name= + "Page_128" id="Page_128"></a>variation is not essential. All + animals in a state of nature are kept, by the constant struggle + for existence and the survival of the fittest, in such a state of + perfect health and usually superabundant vigour, that in all + ordinary circumstances they possess a surplus power in every + important organ—a surplus only drawn upon in cases of the + direst necessity when their very existence is at stake. It + follows, therefore, that <i>any</i> additional power given to one + of the component parts of an organ must be useful—an + increase, for example, either in the wing muscles or in the form + or length of the wing might give <i>some</i> increased powers of + flight; and thus alternate variations—in one generation in + the muscles, in another generation in the wing itself—might + be as effective in permanently improving the powers of flight as + coincident variations at longer intervals. On either supposition, + however, this objection appears to have little weight if we take + into consideration the large amount of coincident variability + that has been shown to exist.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Beginnings of Important Organs.</i></p> + + <p>We now come to an objection which has perhaps been more + frequently urged than any other, and which Darwin himself felt to + have much weight—the first beginnings of important organs, + such, for example, as wings, eyes, mammary glands, and numerous + other structures. It is urged, that it is almost impossible to + conceive how the first rudiments of these could have been of any + use, and, if not of use they could not have been preserved and + further developed by natural selection.</p> + + <p>Now, the first remark to be made on objections of this nature + is, that they are really outside the question of the origin of + all existing species from allied species not very far removed + from them, which is all that Darwin undertook to <i>prove</i> by + means of his theory. Organs and structures such as those above + mentioned all date back to a very remote past, when the world and + its inhabitants were both very different from what they are now. + To ask of a new theory that it shall reveal to us exactly what + took place in remote geological epochs, and how it took place, is + unreasonable. The most that should be asked is, that some + probable or possible mode of origination should be pointed out in + some at least of these <a name="Page_129" id= + "Page_129"></a>difficult cases, and this Mr. Darwin has done. One + or two of these may be briefly given here, but the whole series + should be carefully read by any one who wishes to see how many + curious facts and observations have been required in order to + elucidate them; whence we may conclude that further knowledge + will probably throw light on any difficulties that still + remain.<a name="FNanchor_41_41" id="FNanchor_41_41"></a><a href= + "#Footnote_41_41" class="fnanchor">[41]</a></p> + + <p>In the case of the mammary glands Mr. Darwin remarks that it + is admitted that the ancestral mammals were allied to the + marsupials. Now in the very earliest mammals, almost before they + really deserved that name, the young may have been nourished by a + fluid secreted by the interior surface of the marsupial sack, as + is believed to be the case with the fish (Hippocampus) whose eggs + are hatched within a somewhat similar sack. This being the case, + those individuals which secreted a more nutritious fluid, and + those whose young were able to obtain and swallow a more constant + supply by suction, would be more likely to live and come to a + healthy maturity, and would therefore be preserved by natural + selection.</p> + + <p>In another case which has been adduced as one of special + difficulty, a more complete explanation is given. Soles, turbots, + and other flatfish are, as is well known, unsymmetrical. They + live and move on their sides, the under side being usually + differently coloured from that which is kept uppermost. Now the + eyes of these fish are curiously distorted in order that both + eyes may be on the upper side, where alone they would be of any + use. It was objected by Mr. Mivart that a sudden transformation + of the eye from one side to the other was inconceivable, while, + if the transit were gradual the first step could be of no use, + since this would not remove the eye from the lower side. But, as + Mr. Darwin shows by reference to the researches of Malm and + others, the young of these fish are quite symmetrical, and during + their growth exhibit to us the whole process of change. This + begins by the fish (owing to the increasing depth of the body) + being unable to maintain the vertical position, so that it falls + on one side. It then twists the lower eye as much as possible + towards the upper side; and, the whole bony structure of the head + being at <a name="Page_130" id="Page_130"></a>this time soft and + flexible, the constant repetition of this effort causes the eye + gradually to move round the head till it comes to the upper side. + Now if we suppose this process, which in the young is completed + in a few days or weeks, to have been spread over thousands of + generations during the development of these fish, those usually + surviving whose eyes retained more and more of the position into + which the young fish tried to twist them, the change becomes + intelligible; though it still remains one of the most + extraordinary cases of degeneration, by which + symmetry—which is so universal a characteristic of the + higher animals—is lost, in order that the creature may be + adapted to a new mode of life, whereby it is enabled the better + to escape danger and continue its existence.</p> + + <p>The most difficult case of all, that of the eye—the + thought of which even to the last, Mr. Darwin says, "gave him a + cold shiver"—is nevertheless shown to be not + unintelligible; granting of course the sensitiveness to light of + some forms of nervous tissue. For he shows that there are, in + several of the lower animals, rudiments of eyes, consisting + merely of pigment cells covered with a translucent skin, which + may possibly serve to distinguish light from darkness, but + nothing more. Then we have an optic nerve and pigment cells; then + we find a hollow filled with gelatinous substance of a convex + form—the first rudiment of a lens. Many of the succeeding + steps are lost, as would necessarily be the case, owing to the + great advantage of each modification which gave increased + distinctness of vision, the creatures possessing it inevitably + surviving, while those below them became extinct. But we can well + understand how, after the first step was taken, every variation + tending to more complete vision would be preserved till we + reached the perfect eye of birds and mammals. Even this, as we + know, is not absolutely, but only relatively, perfect. Neither + the chromatic nor the spherical aberration is absolutely + corrected; while long-and short-sightedness, and the various + diseases and imperfections to which the eye is liable, may be + looked upon as relics of the imperfect condition from which the + eye has been raised by variation and natural selection.</p> + + <p>These few examples of difficulties as to the origin of + remarkable or complex organs must suffice here; but the reader + who wishes further information on the matter may study carefully + <a name="Page_131" id="Page_131"></a>the whole of the sixth and + seventh chapters of the last edition of <i>The Origin of + Species</i>, in which these and many other cases are discussed in + considerable detail.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Useless or non-adaptive Characters.</i></p> + + <p>Many naturalists seem to be of opinion that a considerable + number of the characters which distinguish species are of no + service whatever to their possessors, and therefore cannot have + been produced or increased by natural selection. Professors Bronn + and Broca have urged this objection on the continent. In America, + Dr. Cope, the well-known palaeontologist, has long since put + forth the same objection, declaring that non-adaptive characters + are as numerous as those which are adaptive; but he differs + completely from most who hold the same general opinion in + considering that they occur chiefly "in the characters of the + classes, orders, families, and other higher groups;" and the + objection, therefore, is quite distinct from that in which it is + urged that "specific characters" are mostly useless. More + recently, Professor G.J. Romanes has urged this difficulty in his + paper on "Physiological Selection" (<i>Journ. Linn. Soc.</i>, + vol. xix. pp. 338, 344). He says that the characters "which serve + to distinguish allied species are frequently, if not usually, of + a kind with which natural selection can have had nothing to do," + being without any utilitarian significance. Again he speaks of + "the enormous number," and further on of "the innumerable + multitude" of specific peculiarities which are useless; and he + finally declares that the question needs no further arguing, + "because in the later editions of his works Mr. Darwin freely + acknowledges that a large proportion of specific distinctions + must be conceded to be useless to the species presenting + them."</p> + + <p>I have looked in vain in Mr. Darwin's works to find any such + acknowledgment, and I think Mr. Romanes has not sufficiently + distinguished between "useless characters" and "useless specific + distinctions." On referring to all the passages indicated by him + I find that, in regard to specific characters, Mr. Darwin is very + cautious in admitting inutility. His most pronounced "admissions" + on this question are the following: "But when, from the nature of + the organism and of the conditions, modifications have been + induced which are <a name="Page_132" id= + "Page_132"></a>unimportant for the welfare of the species, they + may be, and apparently often have been, transmitted in nearly the + same state <i>to numerous, otherwise modified, descendants</i>" + (<i>Origin</i>, p. 175). The words I have here italicised clearly + show that such characters are usually not "specific," in the + sense that they are such as distinguish species from each other, + but are found in numerous allied species. Again: "Thus a large + yet undefined extension may safely be given to the direct and + indirect results of natural selection; but I now admit, after + reading the essay of Nägeli on plants, and the remarks by + various authors with respect to animals, more especially those + recently made by Professor Broca, that in the earlier editions of + my <i>Origin of Species</i> I perhaps attributed too much to the + action of natural selection or the survival of the fittest. I + have altered the fifth edition of the <i>Origin</i> so as to + confine my remarks to adaptive changes of structure, <i>but I am + convinced, from the light gained during even the last few years, + that very many structures which now appear to us useless, will + hereafter be proved to be useful, and will therefore come within + the range of natural selection</i>. Nevertheless I did not + formerly consider sufficiently the existence of structures which, + <i>as far as we can at present judge</i>, are neither beneficial + nor injurious; and this I believe to be one of the greatest + oversights as yet detected in my work." Now it is to be remarked + that neither in these passages nor in any of the other less + distinct expressions of opinion on this question, does Darwin + ever admit that "specific characters"—that is, the + particular characters which serve to distinguish one species from + another—are ever useless, much less that "a large + proportion of them" are so, as Mr. Romanes makes him "freely + acknowledge." On the other hand, in the passage which I have + italicised he strongly expresses his view that much of what we + suppose to be useless is due to our ignorance; and as I hold + myself that, as regards many of the supposed useless characters, + this is the true explanation, it may be well to give a brief + sketch of the progress of knowledge in transferring characters + from the one category to the other.</p> + + <p>We have only to go back a single generation, and not even the + most acute botanist could have suggested a reasonable use, for + each species of plant, of the infinitely varied forms, sizes, + <a name="Page_133" id="Page_133"></a>and colours of the flowers, + the shapes and arrangement of the leaves, and the numerous other + external characters of the whole plant. But since Mr. Darwin + showed that plants gained both in vigour and in fertility by + being crossed with other individuals of the same species, and + that this crossing was usually effected by insects which, in + search of nectar or pollen, carried the pollen from one plant to + the flowers of another plant, almost every detail is found to + have a purpose and a use. The shape, the size, and the colour of + the petals, even the streaks and spots with which they are + adorned, the position in which they stand, the movements of the + stamens and pistil at various times, especially at the period of, + and just after, fertilisation, have been proved to be strictly + adaptive in so many cases that botanists now believe that all the + external characters of flowers either are or have been of use to + the species.</p> + + <p>It has also been shown, by Kerner and other botanists, that + another set of characteristics have relation to the prevention of + ants, slugs, and other animals from reaching the flowers, because + these creatures would devour or injure them without effecting + fertilisation. The spines, hairs, or sticky glands on the stem or + flower-stalk, the curious hairs or processes shutting up the + flower, or sometimes even the extreme smoothness and polish of + the outside of the petals so that few insects can hang to the + part, have been shown to be related to the possible intrusion of + these "unbidden guests."<a name="FNanchor_42_42" id= + "FNanchor_42_42"></a><a href="#Footnote_42_42" class= + "fnanchor">[42]</a> And, still more recently, attempts have been + made by Grant Allen and Sir John Lubbock to account for the + innumerable forms, textures, and groupings of leaves, by their + relation to the needs of the plants themselves; and there can be + little doubt that these attempts will be ultimately successful. + Again, just as flowers have been adapted to secure fertilisation + or cross-fertilisation, fruits have been developed to assist in + the dispersal of seeds; and their forms, sizes, juices, and + colours can be shown to be specially adapted to secure such + dispersal by the agency of birds and mammals; while the same end + is secured in other <a name="Page_134" id="Page_134"></a>cases by + downy seeds to be wafted through the air, or by hooked or sticky + seed-vessels to be carried away, attached to skin, wool, or + feathers.</p> + + <p>Here, then, we have an enormous extension of the region of + utility in the vegetable kingdom, and one, moreover, which + includes almost all the specific characters of plants. For the + species of plants are usually characterised either by differences + in the form, size, and colour of the flowers, or of the fruits; + or, by peculiarities in the shape, size, dentation, or + arrangement of the leaves; or by peculiarities in the spines, + hairs, or down with which various parts of the plant are clothed. + In the case of plants it must certainly be admitted that + "specific" characters are pre-eminently adaptive; and though + there may be some which are not so, yet all those referred to by + Darwin as having been adduced by various botanists as useless, + either pertain to genera or higher groups, or are found in some + plants of a species only—that is, are individual variations + not specific characters.</p> + + <p>In the case of animals, the most recent wide extension of the + sphere of utility has been in the matter of their colours and + markings. It was of course always known that certain creatures + gained protection by their resemblance to their normal + surroundings, as in the case of white arctic animals, the yellow + or brown tints of those living in deserts, and the green hues of + many birds and insects surrounded by tropical vegetation. But of + late years these cases have been greatly increased both in number + and variety, especially in regard to those which closely imitate + special objects among which they live; and there are other kinds + of coloration which long appeared to have no use. Large numbers + of animals, more especially insects, are gaudily coloured, either + with vivid hues or with striking patterns, so as to be very + easily seen. Now it has been found, that in almost all these + cases the creatures possess some special quality which prevents + their being attacked by the enemies of their kind whenever the + peculiarity is known; and the brilliant or conspicuous colours or + markings serve as a warning or signal flag against attack. Large + numbers of insects thus coloured are nauseous and inedible; + others, like wasps and bees, have stings; others are too hard to + be eaten by small birds; while snakes with <a name="Page_135" id= + "Page_135"></a>poisonous fangs often have some characteristic + either of rattle, hood, or unusual colour, which indicates that + they had better be left alone.</p> + + <p>But there is yet another form of coloration, which consists in + special markings—bands, spots, or patches of white, or of + bright colour, which vary in every species, and are often + concealed when the creature is at rest but displayed when in + motion,—as in the case of the bands and spots so frequent + on the wings and tails of birds. Now these specific markings are + believed, with good reason, to serve the purpose of enabling each + species to be quickly recognised, even at a distance, by its + fellows, especially the parents by their young and the two sexes + by each other; and this recognition must often be an important + factor in securing the safety of individuals, and therefore the + wellbeing and continuance of the species. These interesting + peculiarities will be more fully described in a future chapter, + but they are briefly referred to here in order to show that the + most common of all the characters by which species are + distinguished from each other—their colours and + markings—can be shown to be adaptive or utilitarian in + their nature.</p> + + <p>But besides colour there are almost always some structural + characters which distinguish species from species, and, as + regards many of these also, an adaptive character can be often + discerned. In birds, for instance, we have differences in the + size or shape of the bill or the feet, in the length of the wing + or the tail, and in the proportions of the several feathers of + which these organs are composed. All these differences in the + organs on which the very existence of birds depends, which + determine the character of flight, facility for running or + climbing, for inhabiting chiefly the ground or trees, and the + kind of food that can be most easily obtained for themselves and + their offspring, must surely be in the highest degree + utilitarian; although in each individual case we, in our + ignorance of the minutiae of their life-history, may be quite + unable to see the use. In mammalia specific differences other + than colour usually consist in the length or shape of the ears + and tail, in the proportions of the limbs, or in the length and + quality of the hair on different parts of the body. As regards + the ears and tail, one of the objections by Professor <a name= + "Page_136" id="Page_136"></a>Bronn relates to this very point. He + states that the length of these organs differ in the various + species of hares and of mice, and he considers that this + difference can be of no service whatever to their possessors. But + to this objection Darwin replies, that it has been shown by Dr. + Schöbl that the ears of mice "are supplied in an + extraordinary manner with nerves, so that they no doubt serve as + tactile organs." Hence, when we consider the life of mice, either + nocturnal or seeking their food in dark and confined places, the + length of the ears may be in each case adapted to the particular + habits and surroundings of the species. Again, the tail, in the + larger mammals, often serves the purpose of driving off flies and + other insects from the body; and when we consider in how many + parts of the world flies are injurious or even fatal to large + mammals, we see that the peculiar characteristics of this organ + may in each case have been adapted to its requirements in the + particular area where the species was developed. The tail is also + believed to have some use as a balancing organ, which assists an + animal to turn easily and rapidly, much as our arms are used when + running; while in whole groups it is a prehensile organ, and has + become modified in accordance with the habits and needs of each + species. In the case of mice it is thus used by the young. Darwin + informs us that the late Professor Henslow kept some harvest-mice + in confinement, and observed that they frequently curled their + tails round the branches of a bush placed in the cage, and thus + aided themselves in climbing; while Dr. Günther has actually + seen a mouse suspend itself by the tail (<i>Origin</i>, p. + 189).</p> + + <p>Again, Mr. Lawson Tait has called attention to the use of the + tail in the cat, squirrel, yak, and many other animals as a means + of preserving the heat of the body during the nocturnal and the + winter sleep. He says, that in cold weather animals with long or + bushy tails will be found lying curled up, with their tails + carefully laid over their feet like a rug, and with their noses + buried in the fur of the tail, which is thus used exactly in the + same way and for the same purpose as we use respirators.<a name= + "FNanchor_43_43" id="FNanchor_43_43"></a><a href= + "#Footnote_43_43" class="fnanchor">[43]</a></p> + + <p>Another illustration is furnished by the horns of deer which, + especially when very large, have been supposed to be <a name= + "Page_137" id="Page_137"></a>a danger to the animal in passing + rapidly through dense thickets. But Sir James Hector states, that + the wapiti, in North America, throws back its head, thus placing + the horns along the sides of the back, and is then enabled to + rush through the thickest forest with great rapidity. The + brow-antlers protect the face and eyes, while the widely + spreading horns prevent injury to the neck or flanks. Thus an + organ which was certainly developed as a sexual weapon, has been + so guided and modified during its increase in size as to be of + use in other ways. A similar use of the antlers of deer has been + observed in India.<a name="FNanchor_44_44" id= + "FNanchor_44_44"></a><a href="#Footnote_44_44" class= + "fnanchor">[44]</a></p> + + <p>The various classes of facts now referred to serve to show us + that, in the case of the two higher groups—mammalia and + birds—almost all the characters by which species are + distinguished from each other are, or may be, adaptive. It is + these two classes of animals which have been most studied and + whose life-histories are supposed to be most fully known, yet + even here the assertion of inutility, by an eminent naturalist, + in the case of two important organs, has been sufficiently met by + minute details either in the anatomy or in the habits of the + groups referred to. Such a fact as this, together with the + extensive series of characters already enumerated which have been + of late years transferred from the "useless" to the "useful" + class, should convince us, that the assertion of "inutility" in + the case of any organ or peculiarity which is not a rudiment or a + correlation, is not, and can never be, the statement of a fact, + but merely an expression of our ignorance of its purpose or + origin.<a name="FNanchor_45_45" id="FNanchor_45_45"></a><a href= + "#Footnote_45_45" class="fnanchor">[45]</a><a name="Page_138" id= + "Page_138"></a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Instability of Non-adaptive Characters.</i></p> + + <p>One very weighty objection to the theory that <i>specific</i> + characters can ever be wholly useless (or wholly unconnected with + useful organs by correlation of growth) appears to have been + overlooked by those who have maintained the frequency of such + characters, and that is, their almost necessary instability. + Darwin has remarked on the extreme variability of secondary + sexual characters—such as the horns, crests, plumes, etc., + which are found in males only,—the reason being, that, + although of some use, they are not of such direct and vital + importance as those adaptive characters on which the wellbeing + and very existence of the animals depend. But in the case of + wholly useless structures, <a name="Page_139" id= + "Page_139"></a>which are not rudiments of once useful organs, we + cannot see what there is to ensure any amount of constancy or + stability. One of the cases on which Mr. Romanes lays great + stress in his paper on "Physiological Selection" (<i>Journ. Linn. + Soc.</i>, vol. xix. p. 384) is that of the fleshy appendages on + the corners of the jaw of Normandy pigs and of some other breeds. + But it is expressly stated that they are not constant; they + appear "frequently," or "occasionally," they are "not strictly + inherited, for they occur or fail in animals of the same litter;" + and they are not always symmetrical, sometimes appearing on one + side of the face alone. Now whatever may be the cause or + explanation of these anomalous appendages they cannot be classed + with "specific characters," the most essential features of which + are, that they <i>are</i> symmetrical, <a name="Page_140" id= + "Page_140"></a>that they <i>are</i> inherited, and that they + <i>are</i> constant. Admitting that this peculiar appendage is + (as Mr. Romanes says rather confidently, "we happen to know it to + be") wholly useless and meaningless, the fact would be rather an + argument against specific characters being also meaningless, + because the latter never have the characteristics which this + particular variation possesses.</p> + + <p>These useless or non-adaptive characters are, apparently, of + the same nature as the "sports" that arise in our domestic + productions, but which, as Mr. Darwin says, without the aid of + selection would soon disappear; while some of them may be + correlations with other characters which are or have been useful. + Some of these correlations are very curious. Mr. Tegetmeier + informed Mr. Darwin that the young of white, yellow, or + dun-coloured pigeons are born almost naked, whereas other + coloured pigeons are born well clothed with down. Now, if this + difference occurred between wild species of different colours, it + might be said that the nakedness of the young could not be of any + use. But the colour with which it is correlated might, as has + been shown, be useful in many ways. The skin and its various + appendages, as horns, hoofs, hair, feathers, and teeth, are + homologous parts, and are subject to very strange correlations of + growth. In Paraguay, horses with curled hair occur, and these + always have hoofs exactly like those of a mule, while the hair of + the mane and tail is much shorter than usual. Now, if any one of + these characters were useful, the others correlated with it might + be themselves useless, but would still be tolerably constant + because dependent on a useful organ. So the tusks and the + bristles of the boar are correlated and vary in development + together, and the former only may be useful, or both may be + useful in unequal degrees.</p> + + <p>The difficulty as to how individual differences or sports can + become fixed and perpetuated, if altogether useless, is evaded by + those who hold that such characters are exceedingly common. Mr. + Romanes says that, upon his theory of physiological selection, + "it is quite intelligible that when a varietal form is + differentiated from its parent form by the bar of sterility, any + little meaningless peculiarities of structure or of instinct + <i>should at first be allowed to arise</i>, and that they should + then <i>be allowed to perpetuate themselves</i> by heredity," + until they are finally <a name="Page_141" id= + "Page_141"></a>eliminated by disuse. But this is entirely begging + the question. Do meaningless peculiarities, which we admit often + arise as spontaneous variations, ever perpetuate themselves in + all the individuals constituting a variety or race, without + selection either human or natural? Such characters present + themselves as unstable variations, and as such they remain, + unless preserved and accumulated by selection; and they can + therefore never become "specific" characters unless they are + strictly correlated with some useful and important + peculiarities.</p> + + <p>As bearing upon this question we may refer to what is termed + Delboeuf's law, which has been thus briefly stated by Mr. Murphy + in his work on <i>Habit and Intelligence</i>, p. 241.</p> + + <div class="blockquot"> + <p>"If, in any species, a number of individuals, bearing a + ratio not infinitely small to the entire number of births, are + in every generation born with a particular variation which is + neither beneficial nor injurious, and if it is not counteracted + by reversion, then the proportion of the new variety to the + original form will increase till it approaches indefinitely + near to equality."</p> + </div> + + <p>It is not impossible that some definite varieties, such as the + melanic form of the jaguar and the bridled variety of the + guillemot are due to this cause; but from their very nature such + varieties are unstable, and are continually reproduced in varying + proportions from the parent forms. They can, therefore, never + constitute species unless the variation in question becomes + beneficial, when it will be fixed by natural selection. Darwin, + it is true, says—"There can be little doubt that the + tendency to vary in the same manner has often been so strong that + all the individuals of the same species have been similarly + modified without the aid of any form of selection."<a name= + "FNanchor_46_46" id="FNanchor_46_46"></a><a href= + "#Footnote_46_46" class="fnanchor">[46]</a> But no proof whatever + is offered of this statement, and it is so entirely opposed to + all we know of the facts of variation as given by Darwin himself, + that the important word "all" is probably an oversight.</p> + + <p>On the whole, then, I submit, not only has it not been proved + that an "enormous number of specific peculiarities" are useless, + and that, as a logical result, natural selection is "not a theory + of the origin of species," but only of the origin <a name= + "Page_142" id="Page_142"></a>of adaptations which are usually + common to many species, or, more commonly, to genera and + families; but, I urge further, it has not even been proved that + any truly "specific" characters—those which either singly + or in combination distinguish each species from its nearest + allies—are entirely unadaptive, useless, and meaningless; + while a great body of facts on the one hand, and some weighty + arguments on the other, alike prove that specific characters have + been, and could only have been, developed and fixed by natural + selection because of their utility. We may admit, that among the + great number of variations and sports which continually arise + many are altogether useless without being hurtful; but no cause + or influence has been adduced adequate to render such characters + fixed and constant throughout the vast number of individuals + which constitute any of the more dominant species.<a name= + "FNanchor_47_47" id="FNanchor_47_47"></a><a href= + "#Footnote_47_47" class="fnanchor">[47]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Swamping Effects of Intercrossing.</i></p> + + <p>This supposed insuperable difficulty was first advanced in an + article in the <i>North British Review</i> in 1867, and much + attention has been attracted to it by the acknowledgment of Mr. + Darwin that it proved to him that "single variations," or what + are usually termed "sports," could very rarely, if ever, be + perpetuated in a state of nature, as he had at first thought + might occasionally be the case. But he had always considered that + the chief part, and latterly the whole, of the materials with + which natural selection works, was afforded by individual + variations, or that amount of ever fluctuating variability which + exists in all organisms and in all their parts. Other writers + have urged the same objection, even as against individual + variability, apparently in total ignorance of its amount and + range; and quite recently Professor G.J. Romanes has adduced + <a name="Page_143" id="Page_143"></a>it as one of the + difficulties which can alone be overcome by his theory of + physiological selection. He urges, that the same variation does + not occur simultaneously in a number of individuals inhabiting + the same area, and that it is mere assumption to say it does; + while he admits that "if the assumption were granted there would + be an end of the present difficulty; for if a sufficient number + of individuals were thus simultaneously and similarly modified, + there need be no longer any danger of the variety becoming + swamped by intercrossing." I must again refer my readers to my + third chapter for the proof that such simultaneous variability is + not an assumption but a fact; but, even admitting this to be + proved, the problem is not altogether solved, and there is so + much misconception regarding variation, and the actual process of + the origin of new species is so obscure, that some further + discussion and elucidation of the subject are desirable.</p> + + <p>In one of the preliminary chapters of Mr. Seebohm's recent + work on the <i>Charadriidae</i>, he discusses the differentiation + of species; and he expresses a rather widespread view among + naturalists when, speaking of the swamping effects of + intercrossing, he adds: "This is unquestionably a very grave + difficulty, to my mind an absolutely fatal one, to the theory of + accidental variation." And in another passage he says: "The + simultaneous appearance, and its repetition in successive + generations, of a beneficial variation, in a large number of + individuals in the same locality, cannot possibly be ascribed to + chance." These remarks appear to me to exhibit an entire + misconception of the facts of variation as they actually occur, + and as they have been utilised by natural selection in the + modification of species. I have already shown that every part of + the organism, in common species, does vary to a very considerable + amount, in a large number of individuals, and in the same + locality; the only point that remains to be discussed is, whether + any or most of these variations are "beneficial." But every one + of these variations consists either in increase or diminution of + size or power of the organ or faculty that varies; they can all + be divided into a more effective and a less effective + group—that is, into one that is more beneficial or less + beneficial. If less size of body would be beneficial, then, as + half the variations in size are above and half below the mean or + existing standard of the species, there <a name="Page_144" id= + "Page_144"></a>would be ample beneficial variations; if a darker + colour or a longer beak or wing were required, there are always a + considerable number of individuals darker and lighter in colour + than the average, with longer or with shorter beaks and wings, + and thus the beneficial variation must always be present. And so + with every other part, organ, function, or habit; because, as + variation, so far as we know, is and always must be in the two + directions of excess and defect in relation to the mean amount, + whichever kind of variation is wanted is always present in some + degree, and thus the difficulty as to "beneficial" variations + occurring, as if they were a special and rare class, falls to the + ground. No doubt some organs may vary in three or perhaps more + directions, as in the length, breadth, thickness, or curvature of + the bill. But these may be taken as separate variations, each of + which again occurs as "more" or "less"; and thus the "right" or + "beneficial" or "useful" variation must always be present so long + as any variation at all occurs; and it has not yet been proved + that in any large or dominant species, or in any part, organ, or + faculty of such species, there is no variation. And even were + such a case found it would prove nothing, so long as in numerous + other species variation was shown to exist; because we know that + great numbers of species and groups throughout all geological + time have died out, leaving no descendants; and the obvious and + sufficient explanation of this fact is, that they did <i>not</i> + vary enough at the time when variation was required to bring them + into harmony with changed conditions. The objection as to the + "right" or "beneficial" variation occurring when required, seems + therefore to have no weight in view of the actual facts of + variation.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Isolation to prevent Intercrossing.</i></p> + + <p>Most writers on the subject consider the isolation of a + portion of a species a very important factor in the formation of + new species, while others maintain it to be absolutely essential. + This latter view has arisen from an exaggerated opinion as to the + power of intercrossing to keep down any variety or incipient + species, and merge it in the parent stock. But it is evident that + this can only occur with varieties which are not useful, or + which, if useful, occur in very small numbers; and from this kind + of variations it is clear that <a name="Page_145" id= + "Page_145"></a>new species do not arise. Complete isolation, as + in an oceanic island, will no doubt enable natural selection to + act more rapidly, for several reasons. In the first place, the + absence of competition will for some time allow the new + immigrants to increase rapidly till they reach the limits of + subsistence. They will then struggle among themselves, and by + survival of the fittest will quickly become adapted to the new + conditions of their environment. Organs which they formerly + needed, to defend themselves against, or to escape from, enemies, + being no longer required, would be encumbrances to be got rid of, + while the power of appropriating and digesting new and varied + food would rise in importance. Thus we may explain the origin of + so many flightless and rather bulky birds in oceanic islands, as + the dodo, the cassowary, and the extinct moas. Again, while this + process was going on, the complete isolation would prevent its + being checked by the immigration of new competitors or enemies, + which would be very likely to occur in a continuous area; while, + of course, any intercrossing with the original unmodified stock + would be absolutely prevented. If, now, before this change has + gone very far, the variety spreads into adjacent but rather + distant islands, the somewhat different conditions in each may + lead to the development of distinct forms constituting what are + termed representative species; and these we find in the separate + islands of the Galapagos, the West Indies, and other ancient + groups of islands.</p> + + <p>But such cases as these will only lead to the production of a + few peculiar species, descended from the original settlers which + happened to reach the islands; whereas, in wide areas, and in + continents, we have variation and adaptation on a much larger + scale; and, whenever important physical changes demand them, with + even greater rapidity. The far greater complexity of the + environment, together with the occurrence of variations in + constitution and habits, will often allow of effective isolation, + even here, producing all the results of actual physical + isolation. As we have already explained, one of the most frequent + modes in which natural selection acts is, by adapting some + individuals of a species to a somewhat different mode of life, + whereby they are able to seize upon unappropriated places in + nature, and in so doing they become practically <a name= + "Page_146" id="Page_146"></a>isolated from their parent form. Let + us suppose, for example, that one portion of a species usually + living in forests ranges into the open plains, and finding + abundance of food remains there permanently. So long as the + struggle for existence is not exceptionally severe, these two + portions of the species may remain almost unchanged; but suppose + some fresh enemies are attracted to the plains by the presence of + these new immigrants, then variation and natural selection would + lead to the preservation of those individuals best able to cope + with the difficulty, and thus the open country form would become + modified into a marked variety or into a distinct species; and + there would evidently be little chance of this modification being + checked by intercrossing with the parent form which remained in + the forest.</p> + + <p>Another mode of isolation is brought about by the + variety—either owing to habits, climate, or constitutional + change—breeding at a slightly different time from the + parent species. This is known to produce complete isolation in + the case of many varieties of plants. Yet another mode of + isolation is brought about by changes of colour, and by the fact + that in a wild state animals of similar colours prefer to keep + together and refuse to pair with individuals of another colour. + The probable reason and utility of this habit will be explained + in another chapter, but the fact is well illustrated by the + cattle which have run wild in the Falkland Islands. These are of + several different colours, but each colour keeps in a separate + herd, often restricted to one part of the island; and one of + these varieties—the mouse-coloured—is said to breed a + month earlier than the others; so that if this variety inhabited + a larger area it might very soon be established as a distinct + race or species.<a name="FNanchor_48_48" id= + "FNanchor_48_48"></a><a href="#Footnote_48_48" class= + "fnanchor">[48]</a> Of course where the change of habits or of + station is still greater, as when a terrestrial animal becomes + sub-aquatic, or when aquatic animals come to live in tree-tops, + as with the frogs and Crustacea described at p. 118, the danger + of intercrossing is reduced to a minimum.</p> + + <p>Several writers, however, not content with the indirect + effects of isolation here indicated, maintain that it is in + itself a cause of modification, and ultimately of the origination + of <a name="Page_147" id="Page_147"></a>new species. This was the + keynote of Mr. Vernon Wollaston's essay on "Variation of + Species," published in 1856, and it is adopted by the Rev. J.G. + Gulick in his paper on "Diversity of Evolution under one Set of + External Conditions" (<i>Journ. Linn. Soc. Zool.</i>, vol. xi. p. + 496). The idea seems to be that there is an inherent tendency to + variation in certain divergent lines, and that when one portion + of a species is isolated, even though under identical conditions, + that tendency sets up a divergence which carries that portion + farther and farther away from the original species. This view is + held to be supported by the case of the land shells of the + Sandwich Islands, which certainly present some very remarkable + phenomena. In this comparatively small area there are about 300 + species of land shells, almost all of which belong to one family + (or sub-family), the Achatinellidae, found nowhere else in the + world. The interesting point is the extreme restriction of the + species and varieties. The average range of each species is only + five or six miles, while some are restricted to but one or two + square miles, and only a very few range over a whole island. The + forest region that extends over one of the mountain-ranges of the + island of Oahu, is about forty miles in length and five or six + miles in breadth; and this small territory furnishes about 175 + species, represented by 700 or 800 varieties. Mr. Gulick states, + that the vegetation of the different valleys on the same side of + this range is much the same, yet each has a molluscan fauna + differing in some degree from that of any other. "We frequently + find a genus represented in several successive valleys by allied + species, sometimes feeding on the same, sometimes on different + plants. In every such case the valleys that are nearest to each + other furnish the most nearly allied forms; and a full set of the + varieties of each species presents a minute gradation of forms + between the more divergent types found in the more widely + separated localities." He urges, that these constant differences + cannot be attributed to natural selection, because they occur in + different valleys on the same side of the mountain, where food, + climate, and enemies are the same; and also, because there is no + greater difference in passing from the rainy to the dry side of + the mountains than in passing from one valley to <a name= + "Page_148" id="Page_148"></a>another on the same side an equal + distance apart. In a very lengthy paper, presented to the Linnean + Society last year, on "Divergent Evolution through Cumulative + Segregation," Mr. Gulick endeavours to work out his views into a + complete theory, the main point of which may perhaps be indicated + by the following passage: "No two portions of a species possess + exactly the same average character, and the initial differences + are for ever reacting on the environment and on each other in + such a way as to ensure increasing divergence in each successive + generation as long as the individuals of the two groups are kept + from intercrossing."<a name="FNanchor_49_49" id= + "FNanchor_49_49"></a><a href="#Footnote_49_49" class= + "fnanchor">[49]</a></p> + + <p>It need hardly be said that the views of Mr. Darwin and myself + are inconsistent with the notion that, if the environment were + absolutely similar for the two isolated portions of the species, + any such necessary and constant divergence would take place. It + is an error to assume that what seem to us identical conditions + are really identical to such small and delicate organisms as + these land molluscs, of whose needs and difficulties at each + successive stage of their existence, from the freshly-laid egg up + to the adult animal, we are so profoundly ignorant. The exact + proportions of the various species of plants, the numbers of each + kind of insect or of bird, the peculiarities of more or less + exposure to sunshine or to wind at certain critical epochs, and + other slight differences which to us are absolutely immaterial + and unrecognisable, may be of the highest significance to these + humble creatures, and be quite sufficient to require some slight + adjustments of size, form, or colour, which natural selection + will bring about. All we know of the facts of variation leads us + to believe that, without this action of natural selection, there + would be produced over the whole area a series of inconstant + varieties mingled together, not a distinct segregation of forms + each confined to its own limited area.</p> + + <p>Mr. Darwin has shown that, in the distribution and + modification of species, the biological is of more importance + than the physical environment, the struggle with other organisms + being often more severe than that with the forces of nature. This + is particularly evident in the case of plants, many of which, + when protected from competition, thrive in a <a name="Page_149" + id="Page_149"></a>soil, climate, and atmosphere widely different + from those of their native habitat. Thus, many alpine plants only + found near perpetual snow thrive well in our gardens at the level + of the sea; as do the tritomas from the sultry plains of South + Africa, the yuccas from the arid hills of Texas and Mexico, and + the fuchsias from the damp and dreary shores of the Straits of + Magellan. It has been well said that plants do not live where + they like, but where they can; and the same remark will apply to + the animal world. Horses and cattle run wild and thrive both in + North and South America; rabbits, once confined to the south of + Europe, have established themselves in our own country and in + Australia; while the domestic fowl, a native of tropical India, + thrives well in every part of the temperate zone.</p> + + <p>If, then, we admit that when one portion of a species is + separated from the rest, there will necessarily be a slight + difference in the average characters of the two portions, it does + not follow that this difference has much if any effect upon the + characteristics that are developed by a long period of isolation. + In the first place, the difference itself will necessarily be + very slight unless there is an exceptional amount of variability + in the species; and in the next place, if the average characters + of the species are the expression of its exact adaptation to its + whole environment, then, given a precisely similar environment, + and the isolated portion will inevitably be brought back to the + same average of characters. But, as a matter of fact, it is + impossible that the environment of the isolated portion can be + exactly like that of the bulk of the species. It cannot be so + physically, since no two separated areas can be absolutely alike + in climate and soil; and even if these are the same, the + geographical features, size, contour, and relation to winds, + seas, and rivers, would certainly differ. Biologically, the + differences are sure to be considerable. The isolated portion of + a species will almost always be in a much smaller area than that + occupied by the species as a whole, hence it is at once in a + different position as regards its own kind. The proportions of + all the other species of animals and plants are also sure to + differ in the two areas, and some species will almost always be + absent in the smaller which are present in the larger country. + These differences will act and react on <a name="Page_150" id= + "Page_150"></a>the isolated portion of the species. The struggle + for existence will differ in its severity and in its incidence + from that which affects the bulk of the species. The absence of + some one insect or other creature inimical to the young animal or + plant may cause a vast difference in its conditions of existence, + and may necessitate a modification of its external or internal + characters in quite a different direction from that which + happened to be present in the average of the individuals which + were first isolated.</p> + + <p>On the whole, then, we conclude that, while isolation is an + important factor in effecting some modification of species, it is + so, not on account of any effect produced, or influence exerted + by isolation <i>per se</i>, but because it is always and + necessarily accompanied by a change of environment, both physical + and biological. Natural selection will then begin to act in + adapting the isolated portion to its new conditions, and will do + this the more quickly and the more effectually because of the + isolation. We have, however, seen reason to believe that + geographical or local isolation is by no means essential to the + differentiation of species, because the same result is brought + about by the incipient species acquiring different habits or + frequenting a different station; and also by the fact that + different varieties of the same species are known to prefer to + pair with their like, and thus to bring about a physiological + isolation of the most effective kind. This part of the subject + will be again referred to when the very difficult problems + presented by hybridity are discussed.<a name="FNanchor_50_50" id= + "FNanchor_50_50"></a><a href="#Footnote_50_50" class= + "fnanchor">[50]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cases in which Isolation is Ineffective.</i></p> + + <p>One objection to the views of those who, like Mr. Gulick, + believe isolation itself to be a cause of modification of species + deserves attention, namely, the entire absence of change where, + <a name="Page_151" id="Page_151"></a>if this were a <i>vera + causa</i>, we should expect to find it. In Ireland we have an + excellent test case, for we know that it has been separated from + Britain since the end of the glacial epoch, certainly many + thousand years. Yet hardly one of its mammals, reptiles, or land + molluscs has undergone the slightest change, even although there + is certainly a distinct difference in the environment both + inorganic and organic. That changes have not occurred through + natural selection, is perhaps due to the less severe struggle for + existence owing to the smaller number of competing species; but, + if isolation itself were an efficient cause, acting continuously + and cumulatively, it is incredible that a decided change should + not have been produced in thousands of years. That no such change + has occurred in this, and many other cases of isolation, seems to + prove that it is not in itself a cause of modification.</p> + + <p>There yet remain a number of difficulties and objections + relating to the question of hybridity, which are so important as + to require a separate chapter for their adequate discussion.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_41_41" id="Footnote_41_41"></a><a href= + "#FNanchor_41_41"><span class="label">[41]</span></a> See + <i>Origin of Species</i>, pp. 176-198.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_42_42" id="Footnote_42_42"></a><a href= + "#FNanchor_42_42"><span class="label">[42]</span></a> See + Kerner's <i>Flowers and their Unbidden Guests</i> for + numerous other structures and peculiarities of plants which + are shown to be adaptive and useful.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_43_43" id="Footnote_43_43"></a><a href= + "#FNanchor_43_43"><span class="label">[43]</span></a> + <i>Nature</i>, vol. xx. p. 603.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_44_44" id="Footnote_44_44"></a><a href= + "#FNanchor_44_44"><span class="label">[44]</span></a> + <i>Nature</i>, vol. xxxviii. p. 328.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_45_45" id="Footnote_45_45"></a><a href= + "#FNanchor_45_45"><span class="label">[45]</span></a> A very + remarkable illustration of function in an apparently useless + ornament is given by Semper. He says, "It is known that the + skin of reptiles encloses the body with scales. These scales + are distinguished by very various sculpturings, highly + characteristic of the different species. Irrespective of + their systematic significance they appear to be of no value + in the life of the animal; indeed, they are viewed as + ornamental without regard to the fact that they are + microscopic and much too delicate to be visible to other + animals of their own species. It might, therefore, seem + hopeless to show the necessity for their existence on + Darwinian principles, and to prove that they are + physiologically active organs. Nevertheless, recent + investigations on this point have furnished evidence that + this is possible.</p> + + <p>"It is known that many reptiles, and above all the snakes, + cast off the whole skin at once, whereas human beings do so + by degrees. If by any accident they are prevented doing so, + they infallibly die, because the old skin has grown so tough + and hard that it hinders the increase in volume which is + inseparable from the growth of the animal. The casting of the + skin is induced by the formation on the surface of the inner + epidermis, of a layer of very fine and equally distributed + hairs, which evidently serve the purpose of mechanically + raising the old skin by their rigidity and position. These + hairs then may be designated as <i>casting hairs</i>. That + they are destined and calculated for this end is evident to + me from the fact established by Dr. Braun, that the casting + of the shells of the river crayfish is induced in exactly the + same manner by the formation of a coating of hairs which + mechanically loosens the old skin or shell from the new. Now + the researches of Braun and Cartier have shown that these + casting hairs—which serve the same purpose in two + groups of animals so far apart in the systematic + scale—after the casting, are partly transformed into + the concentric stripes, sharp spikes, ridges, or warts which + ornament the outer edges of the skin-scales of reptiles or + the carapace of crabs." [<i>The Natural Conditions of + Existance as they affect Animal Life</i>, p. 19.] Professor + Semper adds that this example, with many others that might be + quoted, shows that we need not abandon the hope of explaining + morphological characters on Darwinian principles, although + their nature is often difficult to understand.</p> + + <p>During a recent discussion of this question in the pages + of <i>Nature</i>, Mr. St. George Mivart adduces several + examples of what he deems useless specific characters. Among + them are the aborted index finger of the lemurine Potto, and + the thumbless hands of Colobus and Ateles, the "life-saving + action" of either of which he thinks incredible. These cases + suggest two remarks. In the first place, they involve + <i>generic</i>, not <i>specific</i>, characters; and the + three genera adduced are somewhat isolated, implying + considerable antiquity and the extinction of many allied + forms. This is important, because it affords ample time for + great changes of conditions since the structures in question + originated; and without a knowledge of these changes we can + never safely assert that any detail of structure could not + have been useful. In the second place, all three are cases of + aborted or rudimentary organs; and these are admitted to be + explained by non-use, leading to diminution of size, a + further reduction being brought about by the action of the + principle of economy of growth. But, when so reduced, the + rudiment might be inconvenient or even hurtful, and then + natural selection would aid in its complete abortion; in + other words, the abortion of the part would be <i>useful</i>, + and would therefore be subject to the law of survival of the + fittest. The genera Ateles and Colobus are two of the most + purely arboreal types of monkeys, and it is not difficult to + conceive that the constant use of the elongated fingers for + climbing from tree to tree, and catching on to branches while + making great leaps, might require all the nervous energy and + muscular growth to be directed to the fingers, the small + thumb remaining useless. The case of the Potto is more + difficult, both because it is, presumably, a more ancient + type, and its actual life-history and habits are completely + unknown. These cases are, therefore, not at all to the point + as proving that positive specific characters—not mere + rudiments characterising whole genera—are in any case + useless.</p> + + <p>Mr. Mivart further objects to the alleged rigidity of the + action of natural selection, because wounded or malformed + animals have been found which had evidently lived a + considerable time in their imperfect condition. But this + simply proves that they were living under a temporarily + favourable environment, and that the real struggle for + existence, in their case, had not yet taken place. We must + surely admit that, when the pinch came, and when perfectly + formed stoats were dying for want of food, the one-footed + animal, referred to by Mr. Mivart, would be among the first + to succumb; and the same remark will apply to his abnormally + toothed hares and rheumatic monkeys, which might, + nevertheless, get on very well under favourable conditions. + The struggle for existence, under which all animals and + plants have been developed, is intermittent, and exceedingly + irregular in its incidence and severity. It is most severe + and fatal to the young; but when an animal has once reached + maturity, and especially when it has gained experience by + several years of an eventful existence, it may be able to + maintain itself under conditions which would be fatal to a + young and inexperienced creature of the same species. The + examples adduced by Mr. Mivart do not, therefore, in any way + impugn the hardness of nature as a taskmaster, or the extreme + severity of the recurring struggle for existence. [See + <i>Nature</i>, vol. xxxix. p. 127.]</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_46_46" id="Footnote_46_46"></a><a href= + "#FNanchor_46_46"><span class="label">[46]</span></a> + <i>Origin of Species,</i> p. 72.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_47_47" id="Footnote_47_47"></a><a href= + "#FNanchor_47_47"><span class="label">[47]</span></a> + Darwin's latest expression of opinion on this question is + interesting, since it shows that he was inclined to return to + his earlier view of the general, or universal, utility of + specific characters. In a letter to Semper (30th Nov. 1878) + he writes: "As our knowledge advances, very slight + differences, considered by systematists as of no importance + in structure, are continually found to be functionally + important; and I have been especially struck with this fact + in the case of plants, to which my observations have, of late + years, been confined. Therefore it seems to me rather rash to + consider slight differences between representative species, + for instance, those inhabiting the different islands of the + same archipelago, as of no functional importance, and as not + in any way due to natural selection" <i>(Life of Darwin</i>, + vol. iii. p. 161).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_48_48" id="Footnote_48_48"></a><a href= + "#FNanchor_48_48"><span class="label">[48]</span></a> See + <i>Variation of Animals and Plants</i>, vol. i. p. 86.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_49_49" id="Footnote_49_49"></a><a href= + "#FNanchor_49_49"><span class="label">[49]</span></a> + <i>Journal of the Linnean Society, Zoology,</i> vol. xx. p. + 215.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_50_50" id="Footnote_50_50"></a><a href= + "#FNanchor_50_50"><span class="label">[50]</span></a> In Mr. + Gulick's last paper (<i>Journal of Linn. Soc. Zool.</i>, vol. + xx. pp. 189-274) he discusses the various forms of isolation + above referred to, under no less than thirty-eight different + divisions and subdivisions, with an elaborate terminology, + and he argues that these will frequently bring about + divergent evolution without any change in the environment or + any action of natural selection. The discussion of the + problem here given will, I believe, sufficiently expose the + fallacy of his contention; but his illustration of the varied + and often recondite modes by which practical isolation may be + brought about, may help to remove one of the popular + difficulties in the way of the action of natural selection in + the origination of species.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a><a name="Page_152" + id="Page_152"></a>CHAPTER VII</h2> + + <p style='font-weight:bold;'>ON THE INFERTILITY OF CROSSES + BETWEEN DISTINCT SPECIES AND THE USUAL STERILITY OF THEIR HYBRID + OFFSPRING</p> + + <div class="blockquot"> + <p>Statement of the problem—Extreme susceptibility of the + reproductive functions—Reciprocal + crosses—Individual differences in respect to + cross-fertilisation—Dimorphism and trimorphism among + plants—Cases of the fertility of hybrids and of the + infertility of mongrels—The effects of close + interbreeding—Mr. Huth's objections—Fertile hybrids + among animals—Fertility of hybrids among + plants—Cases of sterility of mongrels—Parallelism + between crossing and change of conditions—Remarks on the + facts of hybridity—Sterility due to changed conditions + and usually correlated with other characters—Correlation + of colour with constitutional peculiarities—The isolation + of varieties by selective association—The influence of + natural selection upon sterility and + fertility—Physiological selection—Summary and + concluding remarks.</p> + </div> + + <p>One of the greatest, or perhaps we may say the greatest, of + all the difficulties in the way of accepting the theory of + natural selection as a complete explanation of the origin of + species, has been the remarkable difference between varieties and + species in respect of fertility when crossed. Generally speaking, + it may be said that the varieties of any one species, however + different they may be in external appearance, are perfectly + fertile when crossed, and their mongrel offspring are equally + fertile when bred among themselves; while distinct species, on + the other hand, however closely they may resemble each other + externally, are usually infertile when crossed, and their hybrid + offspring absolutely sterile. This used to be considered a fixed + law of nature, constituting the absolute test and criterion of a + <i>species</i> as distinct from a <i>variety</i>; and so long as + it was believed that species were separate creations, or <a name= + "Page_153" id="Page_153"></a>at all events had an origin quite + distinct from that of varieties, this law could have no + exceptions, because, if any two species had been found to be + fertile when crossed and their hybrid offspring to be also + fertile, this fact would have been held to prove them to be not + <i>species</i> but <i>varieties</i>. On the other hand, if two + varieties had been found to be infertile, or their mongrel + offspring to be sterile, then it would have been said: These are + not varieties but true species. Thus the old theory led to + inevitable reasoning in a circle; and what might be only a rather + common fact was elevated into a law which had no exceptions.</p> + + <p>The elaborate and careful examination of the whole subject by + Mr. Darwin, who has brought together a vast mass of evidence from + the experience of agriculturists and horticulturists, as well as + from scientific experimenters, has demonstrated that there is no + such fixed law in nature as was formerly supposed. He shows us + that crosses between some varieties are infertile or even + sterile, while crosses between some species are quite fertile; + and that there are besides a number of curious phenomena + connected with the subject which render it impossible to believe + that sterility is anything more than an incidental property of + species, due to the extreme delicacy and susceptibility of the + reproductive powers, and dependent on physiological causes we + have not yet been able to trace. Nevertheless, the fact remains + that most species which have hitherto been crossed produce + sterile hybrids, as in the well-known case of the mule; while + almost all domestic varieties, when crossed, produce offspring + which are perfectly fertile among themselves. I will now + endeavour to give such a sketch of the subject as may enable the + reader to see something of the complexity of the problem, + referring him to Mr. Darwin's works for fuller details.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Extreme Susceptibility of the Reproductive Functions.</i></p> + + <p>One of the most interesting facts, as showing how susceptible + to changed conditions or to slight constitutional changes are the + reproductive powers of animals, is the very general difficulty of + getting those which are kept in confinement to breed; and this is + frequently the only bar to domesticating wild species. Thus, + elephants, bears, foxes, <a name="Page_154" id="Page_154"></a>and + numbers of species of rodents, very rarely breed in confinement; + while other species do so more or less freely. Hawks, vultures, + and owls hardly ever breed in confinement; neither did the + falcons kept for hawking ever breed. Of the numerous small + seed-eating birds kept in aviaries, hardly any breed, neither do + parrots. Gallinaceous birds usually breed freely in confinement, + but some do not; and even the guans and curassows, kept tame by + the South American Indians, never breed. This shows that change + of climate has nothing to do with the phenomenon; and, in fact, + the same species that refuse to breed in Europe do so, in almost + every case, when tamed or confined in their native countries. + This inability to reproduce is not due to ill-health, since many + of these creatures are perfectly vigorous and live very long.</p> + + <p>With our true domestic animals, on the other hand, fertility + is perfect, and is very little affected by changed conditions. + Thus, we see the common fowl, a native of tropical India, living + and multiplying in almost every part of the world; and the same + is the case with our cattle, sheep, and goats, our dogs and + horses, and especially with domestic pigeons. It therefore seems + probable, that this facility for breeding under changed + conditions was an original property of the species which man has + domesticated—a property which, more than any other, enabled + him to domesticate them. Yet, even with these, there is evidence + that great changes of conditions affect the fertility. In the hot + valleys of the Andes sheep are less fertile; while geese taken to + the high plateau of Bogota were at first almost sterile, but + after some generations recovered their fertility. These and many + other facts seem to show that, with the majority of animals, even + a slight change of conditions may produce infertility or + sterility; and also that after a time, when the animal has become + thoroughly acclimatised, as it were, to the new conditions, the + infertility is in some cases diminished or altogether ceases. It + is stated by Bechstein that the canary was long infertile, and it + is only of late years that good breeding birds have become + common; but in this case no doubt selection has aided the + change.</p> + + <p>As showing that these phenomena depend on deep-seated causes + and are of a very general nature, it is interesting <a name= + "Page_155" id="Page_155"></a>to note that they occur also in the + vegetable kingdom. Allowing for all the circumstances which are + known to prevent the production of seed, such as too great + luxuriance of foliage, too little or too much heat, or the + absence of insects to cross-fertilise the flowers, Mr. Darwin + shows that many species which grow and flower with us, apparently + in perfect health, yet never produce seed. Other plants are + affected by very slight changes of conditions, producing seed + freely in one soil and not in another, though apparently growing + equally well in both; while, in some cases, a difference of + position even in the same garden produces a similar + result.<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a href= + "#Footnote_51_51" class="fnanchor">[51]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Reciprocal Crosses.</i></p> + + <p>Another indication of the extreme delicacy of the adjustment + between the sexes, which is necessary to produce fertility, is + afforded by the behaviour of many species and varieties when + reciprocally crossed. This will be best illustrated by a few of + the examples furnished us by Mr. Darwin. The two distinct species + of plants, Mirabilis jalapa and M. longiflora, can be easily + crossed, and will produce healthy and fertile hybrids when the + pollen of the latter is applied to the stigma of the former + plant. But the same experimenter, Kölreuter, tried in vain, + more than two hundred times during eight years, to cross them by + applying the pollen of M. jalapa to the stigma of M. longiflora. + In other cases two plants are so closely allied that some + botanists class them as varieties (as with Matthiola annua and M. + glabra), and yet there is the same great difference in the result + when they are reciprocally crossed.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Individual Differences in respect to + Cross-Fertilisation.</i></p> + + <p>A still more remarkable illustration of the delicate balance + of organisation needful for reproduction, is afforded by the + individual differences of animals and plants, as regards both + their power of intercrossing with other individuals or other + species, and the fertility of the offspring thus produced. Among + domestic animals, Darwin states that it is by no means rare to + find certain males and females which will not breed <a name= + "Page_156" id="Page_156"></a>together, though both are known to + be perfectly fertile with other males and females. Cases of this + kind have occurred among horses, cattle, pigs, dogs, and pigeons; + and the experiment has been tried so frequently that there can be + no doubt of the fact. Professor G.J. Romanes states that he has a + number of additional cases of this individual incompatibility, or + of absolute sterility, between two individuals, each of which is + perfectly fertile with other individuals.</p> + + <p>During the numerous experiments that have been made on the + hybridisation of plants similar peculiarities have been noticed, + some individuals being capable, others incapable, of being + crossed with a distinct species. The same individual + peculiarities are found in varieties, species, and genera. + Kölreuter crossed five varieties of the common tobacco + (Nicotiana tabacum) with a distinct species, Nicotiana glutinosa, + and they all yielded very sterile hybrids; but those raised from + one variety were less sterile, in all the experiments, than the + hybrids from the four other varieties. Again, most of the species + of the genus Nicotiana have been crossed, and freely produce + hybrids; but one species, N. acuminata, not particularly distinct + from the others, could neither fertilise, nor be fertilised by, + any of the eight other species experimented on. Among genera we + find some—such as Hippeastrum, Crinum, Calceolaria, + Dianthus—almost all the species of which will fertilise + other species and produce hybrid offspring; while other allied + genera, as Zephyranthes and Silene, notwithstanding the most + persevering efforts, have not produced a single hybrid even + between the most closely allied species.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Dimorphism and Trimorphism.</i></p> + + <p>Peculiarities in the reproductive system affecting individuals + of the same species reach their maximum in what are called + heterostyled, or dimorphic and trimorphic flowers, the phenomena + presented by which form one of the most remarkable of Mr. + Darwin's many discoveries. Our common cowslip and primrose, as + well as many other species of the genus Primula, have two kinds + of flowers in about equal proportions. In one kind the stamens + are short, being situated about the middle of the tube of the + corolla, while the <a name="Page_157" id="Page_157"></a>style is + long, the globular stigma appearing just in the centre of the + open flower. In the other kind the stamens are long, appearing in + the centre or throat of the flower, while the style is short, the + stigma being situated halfway down the tube at the same level as + the stamens in the other form. These two forms have long been + known to florists as the "pin-eyed" and the "thrum-eyed," but + they are called by Darwin the long-styled and short-styled forms + (see woodcut).</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig17" id="fig17"></a> <img src="images/fig17.jpg" + width="400" height="338" alt= + "FIG. 17.—Primula veris (Cowslip)." title= + "FIG. 17.—Primula veris (Cowslip)." /> <b>FIG. + 17.—Primula veris (Cowslip).</b> + </div> + + <p>The meaning and use of these different forms was quite unknown + till Darwin discovered, first, that cowslips and primroses are + absolutely barren if insects are prevented from visiting them, + and then, what is still more extraordinary, that each form is + almost sterile when fertilised by its own pollen, and + comparatively infertile when crossed with any other plant of its + own form, but is perfectly fertile when the pollen of a + long-styled is carried to the stigma of a short-styled plant, or + <i>vice versâ</i>. It will be seen, by the figures, that + the arrangement is such that a bee visiting the flowers will + carry the pollen from the long anthers of the short-styled form + to the stigma of the long-styled form, while it would never reach + the stigma of another plant of the short-styled form. <a name= + "Page_158" id="Page_158"></a>But an insect visiting, first, a + long-styled plant, would deposit the pollen on the stigma of + another plant of the same kind if it were next visited; and this + is probably the reason why the wild short-styled plants were + found to be almost always most productive of seed, since they + must be all fertilised by the other form, whereas the long-styled + plants might often be fertilised by their own form. The whole + arrangement, however, ensures cross-fertilisation; and this, as + Mr. Darwin has shown by copious experiments, adds both to the + vigour and fertility of almost all plants as well as animals.</p> + + <p>Besides the primrose family, many other plants of several + distinct natural orders present similar phenomena, one or two of + the most curious of which must be referred to. The beautiful + crimson flax (Linum grandiflorum) has also two forms, the styles + only differing in length; and in this case Mr. Darwin found by + numerous experiments, which have since been repeated and + confirmed by other observers, that each form is absolutely + sterile with pollen from another plant of its own form, but + abundantly fertile when crossed with any plant of the other form. + In this case the pollen of the two forms cannot be distinguished + under the microscope (whereas that of the two forms of Primula + differs in size and shape), yet it has the remarkable property of + being absolutely powerless on the stigmas of half the plants of + its own species. The crosses between the opposite forms, which + are fertile, are termed by Mr. Darwin "legitimate," and those + between similar forms, which are sterile, "illegitimate"; and he + remarks that we have here, within the limits of the same species, + a degree of sterility which rarely occurs except between plants + or animals not only of different <i>species</i> but of different + <i>genera</i>.</p> + + <p>But there is another set of plants, the trimorphic, in which + the styles and stamens have each three forms—long, medium, + and short, and in these it is possible to have eighteen different + crosses. By an elaborate series of experiments it was shown that + the six legitimate unions—that is, when a plant was + fertilised by pollen from stamens of length corresponding to that + of its style in the two other forms—were all abundantly + fertile; while the twelve illegitimate unions, when a plant was + fertilised by pollen from stamens of a different length from its + <a name="Page_159" id="Page_159"></a>own style, in any of the + three forms, were either comparatively or wholly sterile.<a name= + "FNanchor_52_52" id="FNanchor_52_52"></a><a href= + "#Footnote_52_52" class="fnanchor">[52]</a></p> + + <p>We have here a wonderful amount of constitutional difference + of the reproductive organs within a single species, greater than + usually occurs within the numerous distinct species of a genus or + group of genera; and all this diversity appears to have arisen + for a purpose which has been obtained by many other, and + apparently simpler, changes of structure or of function, in other + plants. This seems to show us, in the first place, that + variations in the mutual relations of the reproductive organs of + different individuals must be as frequent as structural + variations have been shown to be; and, also, that sterility in + itself can be no test of specific distinctness. But this point + will be better considered when we have further illustrated and + discussed the complex phenomena of hybridity.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cases of the Fertility of Hybrids, and of the Infertility of + Mongrels.</i></p> + + <p>I now propose to adduce a few cases in which it has been + proved, by experiment, that hybrids between two distinct species + are fertile <i>inter se</i>; and then to consider why it is that + such cases are so few in number.</p> + + <p>The common domestic goose (Anser ferns) and the Chinese goose + (A. cygnoides) are very distinct species, so distinct that some + naturalists have placed them in different genera; yet they have + bred together, and Mr. Eyton raised from a pair of these hybrids + a brood of eight. This fact was confirmed by Mr. Darwin himself, + who raised several fine birds from a pair of hybrids which were + sent him.<a name="FNanchor_53_53" id= + "FNanchor_53_53"></a><a href="#Footnote_53_53" class= + "fnanchor">[53]</a> In India, according to Mr. Blyth and Captain + Hutton, whole flocks of these hybrid geese are kept in various + parts of the country where neither of the pure parent species + exists, and as they are kept for profit they must certainly be + fully fertile.</p> + + <p>Another equally striking case is that of the Indian humped and + the common cattle, species which differ osteologically, and also + in habits, form, voice, and constitution, so that they are by no + means closely allied; yet Mr. Darwin assures us that he <a name= + "Page_160" id="Page_160"></a>has received decisive evidence that + the hybrids between these are perfectly fertile <i>inter + se</i>.</p> + + <p>Dogs have been frequently crossed with wolves and with + jackals, and their hybrid offspring have been found to be fertile + <i>inter se</i> to the third or fourth generation, and then + usually to show some signs of sterility or of deterioration. The + wolf and dog may be originally the same species, but the jackal + is certainly distinct; and the appearance of infertility or of + weakness is probably due to the fact that, in almost all these + experiments, the offspring of a single pair—themselves + usually from the same litter—- were bred in-and-in, and + this alone sometimes produces the most deleterious effects. Thus, + Mr. Low in his great work on the <i>Domesticated Animals of Great + Britain</i>, says: "If we shall breed a pair of dogs from the + same litter, and unite again the offspring of this pair, we shall + produce at once a feeble race of creatures; and the process being + repeated for one or two generations more, the family will die + out, or be incapable of propagating their race. A gentleman of + Scotland made the experiment on a large scale with certain + foxhounds, and he found that the race actually became monstrous + and perished utterly." The same writer tells us that hogs have + been made the subject of similar experiments: "After a few + generations the victims manifest the change induced in the + system. They become of diminished size; the bristles are changed + into hairs; the limbs become feeble and short; the litters + diminish in frequency, and in the number of the young produced; + the mother becomes unable to nourish them, and, if the experiment + be carried as far as the case will allow, the feeble, and + frequently monstrous offspring, will be incapable of being reared + up, and the miserable race will utterly perish."<a name= + "FNanchor_54_54" id="FNanchor_54_54"></a><a href= + "#Footnote_54_54" class="fnanchor">[54]</a></p> + + <p>These precise statements, by one of the greatest authorities + on our domesticated animals, are sufficient to show that the fact + of infertility or degeneracy appearing in the offspring of + hybrids after a few generations need not be imputed to the fact + of the first parents being distinct species, since exactly the + same phenomena appear when individuals of the same species are + bred under similar adverse conditions. But in almost all the + experiments that have hitherto been made in crossing distinct + species, no care has been taken to avoid close inter<a name= + "Page_161" id="Page_161"></a>breeding by securing several hybrids + from quite distinct stocks to start with, and by having two or + more sets of experiments carried on at once, so that crosses + between the hybrids produced may be occasionally made. Till this + is done no experiments, such as those hitherto tried, can be held + to prove that hybrids are in all cases infertile <i>inter + se</i>.</p> + + <p>It has, however, been denied by Mr. A.H. Huth, in his + interesting work on <i>The Marriage of Near Kin</i>, that any + amount of breeding in-and-in is in itself hurtful; and he quotes + the evidence of numerous breeders whose choicest stocks have + always been so bred, as well as cases like the Porto Santo + rabbits, the goats of Juan Fernandez, and other cases in which + animals allowed to run wild have increased prodigiously and + continued in perfect health and vigour, although all derived from + a single pair. But in all these cases there has been rigid + selection by which the weak or the infertile have been + eliminated, and with such selection there is no doubt that the + ill effects of close interbreeding can be prevented for a long + time; but this by no means proves that no ill effects are + produced. Mr. Huth himself quotes M. Allié, M. + Aubé, Stephens, Giblett, Sir John Sebright, Youatt, Druce, + Lord Weston, and other eminent breeders, as finding from + experience that close interbreeding <i>does</i> produce bad + effects; and it cannot be supposed that there would be such a + consensus of opinion on this point if the evil were altogether + imaginary. Mr. Huth argues, that the evil results which do occur + do not depend on the close interbreeding itself, but on the + tendency it has to perpetuate any constitutional weakness or + other hereditary taints; and he attempts to prove this by the + argument that "if crosses act by virtue of being a cross, and not + by virtue of removing an hereditary taint, then the greater the + difference between the two animals crossed the more beneficial + will that act be." He then shows that, the wider the difference + the less is the benefit, and concludes that a cross, as such, has + no beneficial effect. A parallel argument would be, that change + of air, as from inland to the sea-coast, or from a low to an + elevated site, is not beneficial in itself, because, if so, a + change to the tropics or to the polar regions should be more + beneficial. In both these cases it may well be that no benefit + would accrue to a person in perfect health; but then there is no + <a name="Page_162" id="Page_162"></a>such thing as "perfect + health" in man, and probably no such thing as absolute freedom + from constitutional taint in animals. The experiments of Mr. + Darwin, showing the great and immediate good effects of a cross + between distinct strains in plants, cannot be explained away; + neither can the innumerable arrangements to secure + cross-fertilisation by insects, the real use and purport of which + will be discussed in our eleventh chapter. On the whole, then, + the evidence at our command proves that, whatever may be its + ultimate cause, close interbreeding <i>does</i> usually produce + bad results; and it is only by the most rigid selection, whether + natural or artificial, that the danger can be altogether + obviated.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Fertile Hybrids among Animals.</i></p> + + <p>One or two more cases of fertile hybrids may be given before + we pass on to the corresponding experiments in plants. Professor + Alfred Newton received from a friend a pair of hybrid ducks, bred + from a common duck (Anas boschas), and a pintail (Dafila acuta). + From these he obtained four ducklings, but these latter, when + grown up, proved infertile, and did not breed again. In this case + we have the results of close interbreeding, with too great a + difference between the original species, combining to produce + infertility, yet the fact of a hybrid from such a pair producing + healthy offspring is itself noteworthy.</p> + + <p>Still more extraordinary is the following statement of Mr. + Low: "It has been long known to shepherds, though questioned by + naturalists, that the progeny of the cross between the sheep and + goat is fertile. Breeds of this mixed race are numerous in the + north of Europe."<a name="FNanchor_55_55" id= + "FNanchor_55_55"></a><a href="#Footnote_55_55" class= + "fnanchor">[55]</a> Nothing appears to be known of such hybrids + either in Scandinavia or in Italy; but Professor Giglioli of + Florence has kindly given me some useful references to works in + which they are described. The following extract from his letter + is very interesting: "I need not tell you that there being such + hybrids is now generally accepted as a fact. Buffon + (<i>Supplements</i>, tom. iii. p. 7, 1756) obtained one such + hybrid in 1751 and eight in 1752. Sanson (<i>La Culture</i>, vol. + vi. p. 372, 1865) mentions a case observed in the Vosges, France. + Geoff. St. Hilaire (<i>Hist. Nat. Gén. des reg. org.</i>, + vol. iii. p. <a name="Page_163" id="Page_163"></a>163) was the + first to mention, I believe, that in different parts of South + America the ram is more usually crossed with the she-goat than + the sheep with the he-goat. The well-known 'pellones' of Chile + are produced by the second and third generation of such hybrids + (Gay, 'Hist, de Chile,' vol. i. p. 466, <i>Agriculture</i>, + 1862). Hybrids bred from goat and sheep are called 'chabin' in + French, and 'cabruno' in Spanish. In Chile such hybrids are + called 'carneros lanudos'; their breeding <i>inter se</i> appears + to be not always successful, and often the original cross has to + be recommenced to obtain the proportion of three-eighths of + he-goat and five-eighths of sheep, or of three-eighths of ram and + five-eighths of she-goat; such being the reputed best + hybrids."</p> + + <p>With these numerous facts recorded by competent observers we + can hardly doubt that races of hybrids between these very + distinct species have been produced, and that such hybrids are + fairly fertile <i>inter se</i>; and the analogous facts already + given lead us to believe that whatever amount of infertility may + at first exist could be eliminated by careful selection, if the + crossed races were bred in large numbers and over a considerable + area of country. This case is especially valuable, as showing how + careful we should be in assuming the infertility of hybrids when + experiments have been made with the progeny of a single pair, and + have been continued only for one or two generations.</p> + + <p>Among insects one case only appears to have been recorded. The + hybrids of two moths (Bombyx cynthia and B. arrindia) were proved + in Paris, according to M. Quatrefages, to be fertile <i>inter + se</i> for eight generations.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Fertility of Hybrids among Plants.</i></p> + + <p>Among plants the cases of fertile hybrids are more numerous, + owing, in part, to the large scale on which they are grown by + gardeners and nurserymen, and to the greater facility with which + experiments can be made. Darwin tells us that Kölreuter + found ten cases in which two plants considered by botanists to be + distinct species were quite fertile together, and he therefore + ranked them all as varieties of each other. In some cases these + were grown for six to ten successive generations, but after a + time the fertility decreased, as we saw to be the case in + <a name="Page_164" id="Page_164"></a>animals, and presumably from + the same cause, too close interbreeding.</p> + + <p>Dean Herbert, who carried on experiments with great care and + skill for many years, found numerous cases of hybrids which were + perfectly fertile <i>inter se</i>. Crinum capense, fertilised by + three other species—C. pedunculatum, C. canaliculatum, or + C. defixum—all very distinct from it, produced perfectly + fertile hybrids; while other species less different in appearance + were quite sterile with the same C. capense.</p> + + <p>All the species of the genus Hippeastrum produce hybrid + offspring which are invariably fertile. Lobelia syphylitica and + L. fulgens, two very distinct species, have produced a hybrid + which has been named Lobelia speciosa, and which reproduces + itself abundantly. Many of the beautiful pelargoniums of our + greenhouses are hybrids, such as P. ignescens from a cross + between P. citrinodorum and P. fulgidum, which is quite fertile, + and has become the parent of innumerable varieties of beautiful + plants. All the varied species of Calceolaria, however different + in appearance, intermix with the greatest readiness, and the + hybrids are all more or less fertile. But the most remarkable + case is that of two species of Petunia, of which Dean Herbert + says: "It is very remarkable that, although there is a great + difference in the form of the flower, especially of the tube, of + P. nyctanigenaeflora and P. phoenicea the mules between them are + not only fertile, but I have found them seed much more freely + with me than either parent.... From a pod of the above-mentioned + mule, to which no pollen but its own had access, I had a large + batch of seedlings in which there was no variability or + difference from itself; and it is evident that the mule planted + by itself, in a congenial climate, would reproduce itself as a + species; at least as much deserving to be so considered as the + various Calceolarias of different districts of South + America."<a name="FNanchor_56_56" id= + "FNanchor_56_56"></a><a href="#Footnote_56_56" class= + "fnanchor">[56]</a></p> + + <p>Darwin was informed by Mr. C. Noble that he raises stocks for + grafting from a hybrid between Rhododendron ponticum and R. + catawbiense, and that this hybrid seeds as freely as it is + possible to imagine. He adds that horticulturists raise large + beds of the same hybrid, and such alone are fairly treated; for, + by insect agency, the several individuals are freely <a name= + "Page_165" id="Page_165"></a>crossed with each other, and the + injurious influence of close interbreeding is thus prevented. Had + hybrids, when fairly treated, always gone on decreasing in + fertility in each successive generation, as Gartner believed to + be the case, the fact would have been notorious to + nurserymen.<a name="FNanchor_57_57" id= + "FNanchor_57_57"></a><a href="#Footnote_57_57" class= + "fnanchor">[57]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cases of Sterility of Mongrels.</i></p> + + <p>The reverse phenomenon to the fertility of hybrids, the + sterility of mongrels or of the crosses between <i>varieties</i> + of the same species, is a comparatively rare one, yet some + undoubted cases have occurred. Gartner, who believed in the + absolute distinctness of species and varieties, had two varieties + of maize—one dwarf with yellow seeds, the other taller with + red seeds; yet they never naturally crossed, and, when fertilised + artificially, only a single head produced any seeds, and this one + only five grains. Yet these few seeds were fertile; so that in + this case the first cross was almost sterile, though the hybrid + when at length produced was fertile. In like manner, dissimilarly + coloured varieties of Verbascum or mullein have been found by two + distinct observers to be comparatively infertile. The two + pimpernels (Anagallis arvensis and A. coerulea), classed by most + botanists as varieties of one species, have been found, after + repeated trials, to be perfectly sterile when crossed.</p> + + <p>No cases of this kind are recorded among animals; but this is + not to be wondered at, when we consider how very few experiments + have been made with natural varieties; while there is good reason + for believing that domestic varieties are exceptionally fertile, + partly because one of the conditions of domestication was + fertility under changed conditions, and also because long + continued domestication is believed to have the effect of + increasing fertility and eliminating whatever sterility may + exist. This is shown by the fact that, in many cases, domestic + animals are descended from two or more distinct species. This is + almost certainly the case with the dog, and probably with the + hog, the ox, and the sheep; yet the various breeds are now all + perfectly fertile, although we have every reason to suppose that + there would be some degree of infertility if the several + aboriginal species were crossed together for the first time.</p> + + <p><a name="Page_166" id="Page_166"></a><i>Parallelism between + Crossing and Change of Conditions.</i></p> + + <p>In the whole series of these phenomena, from the beneficial + effects of the crossing of different stocks and the evil effects + of close interbreeding, up to the partial or complete sterility + induced by crosses between species belonging to different genera, + we have, as Mr. Darwin points out, a curious parallelism with the + effects produced by change of physical conditions. It is well + known that slight changes in the conditions of life are + beneficial to all living things. Plants, if constantly grown in + one soil and locality from their own seeds, are greatly benefited + by the importation of seed from some other locality. The same + thing happens with animals; and the benefit we ourselves + experience from "change of air" is an illustration of the same + phenomenon. But the amount of the change which is beneficial has + its limits, and then a greater amount is injurious. A change to a + climate a few degrees warmer or colder may be good, while a + change to the tropics or to the arctic regions might be + injurious.</p> + + <p>Thus we see that, both slight changes of conditions and a + slight amount of crossing, are beneficial; while extreme changes, + and crosses between individuals too far removed in structure or + constitution, are injurious. And there is not only a parallelism + but an actual connection between the two classes of facts, for, + as we have already shown, many species of animals and plants are + rendered infertile, or altogether sterile, by the change from + their natural conditions which occurs in confinement or in + cultivation; while, on the other hand, the increased vigour or + fertility which is invariably produced by a judicious cross may + be also effected by a judicious change of climate and + surroundings. We shall see in a subsequent chapter, that this + interchangeability of the beneficial effects of crossing and of + new conditions, serves to explain some very puzzling phenomena in + the forms and economy of flowers.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Remarks on the Facts of Hybridity.</i></p> + + <p>The facts that have now been adduced, though not very + numerous, are sufficiently conclusive to prove that the old + belief, of the universal sterility of hybrids and fertility of + mongrels, is incorrect. The doctrine that such a universal + <a name="Page_167" id="Page_167"></a>law existed was never more + than a plausible generalisation, founded on a few inconclusive + facts derived from domesticated animals and cultivated plants. + The facts were, and still are, inconclusive for several reasons. + They are founded, primarily, on what occurs among animals in + domestication; and it has been shown that domestication both + tends to increase fertility, and was itself rendered possible by + the fertility of those particular species being little affected + by changed conditions. The exceptional fertility of all the + varieties of domesticated animals does not prove that a similar + fertility exists among natural varieties. In the next place, the + generalisation is founded on too remote crosses, as in the case + of the horse and the ass, the two most distinct and widely + separated species of the genus Equus, so distinct indeed that + they have been held by some naturalists to form distinct genera. + Crosses between the two species of zebra, or even between the + zebra and the quagga, or the quagga and the ass, might have led + to a very different result. Again, in pre-Darwinian times it was + so universally the practice to argue in a circle, and declare + that the fertility of the offspring of a cross proved the + identity of species of the parents, that experiments in hybridity + were usually made between very remote species and even between + species of different genera, to avoid the possibility of the + reply: "They are both really the same species;" and the sterility + of the hybrid offspring of such remote crosses of course served + to strengthen the popular belief.</p> + + <p>Now that we have arrived at a different standpoint, and look + upon a species, not as a distinct entity due to special creation, + but as an assemblage of individuals which have become somewhat + modified in structure, form, and constitution so as to adapt them + to slightly different conditions of life; which can be + differentiated from other allied assemblages; which reproduce + their like, and which usually breed together—we require a + fresh set of experiments calculated to determine the matter of + fact,—whether such species crossed with their near allies + do always produce offspring which are more or less sterile + <i>inter se</i>. Ample materials for such experiments exist, in + the numerous "representative species" inhabiting distinct areas + on a continent or different islands of a group; or even <a name= + "Page_168" id="Page_168"></a>in those found in the same area but + frequenting somewhat different stations.</p> + + <p>To carry out these experiments with any satisfactory result, + it will be necessary to avoid the evil effects of confinement and + of too close interbreeding. If birds are experimented with, they + should be allowed as much liberty as possible, a plot of ground + with trees and bushes being enclosed with wire netting overhead + so as to form a large open aviary. The species experimented with + should be obtained in considerable numbers, and by two separate + persons, each making the opposite reciprocal cross, as explained + at p. 155. In the second generation these two stocks might be + themselves crossed to prevent the evil effects of too close + interbreeding. By such experiments, carefully carried out with + different groups of animals and plants, we should obtain a body + of facts of a character now sadly wanting, and without which it + is hopeless to expect to arrive at a complete solution of this + difficult problem. There are, however, some other aspects of the + question that need to be considered, and some theoretical views + which require to be carefully examined, having done which we + shall be in a condition to state the general conclusions to which + the facts and reasonings at our command seem to point.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sterility due to changed Conditions and usually correlated + with other Characters, especially with Colour.</i></p> + + <p>The evidence already adduced as to the extreme susceptibility + of the reproductive system, and the curious irregularity with + which infertility or sterility appears in the crosses between + some varieties or species while quite absent in those between + others, seem to indicate that sterility is a characteristic which + has a constant tendency to appear, either by itself or in + correlation with other characters. It is known to be especially + liable to occur under changed conditions of life; and, as such + change is usually the starting-point and cause of the development + of new species, we have already found a reason why it should so + often appear when species become fully differentiated.</p> + + <p>In almost all the cases of infertility or sterility between + varieties or species, we have some external differences with + <a name="Page_169" id="Page_169"></a>which it is correlated; and + though these differences are sometimes slight, and the amount of + the infertility is not always, or even usually, proportionate to + the external difference between the two forms crossed, we must + believe that there is some connection between the two classes of + facts. This is especially the case as regards colour; and Mr. + Darwin has collected a body of facts which go far to prove that + colour, instead of being an altogether trifling and unimportant + character, as was supposed by the older naturalists, is really + one of great significance, since it is undoubtedly often + correlated with important constitutional differences. Now colour + is one of the characters that most usually distinguishes closely + allied species; and when we hear that the most closely allied + species of plants are infertile together, while those more remote + are fertile, the meaning usually is that the former differ + chiefly in the <i>colour</i> of their flowers, while the latter + differ in the form of the flowers or foliage, in habit, or in + other structural characters.</p> + + <p>It is therefore a most curious and suggestive fact, that in + all the recorded cases, in which a decided infertility occurs + between varieties of the same species, those varieties are + distinguished by a difference of colour. The infertile varieties + of Verbascum were white and yellow flowered respectively; the + infertile varieties of maize were red and yellow seeded; while + the infertile pimpernels were the red and the blue flowered + varieties. So, the differently coloured varieties of hollyhocks, + though grown close together, each reproduce their own colour from + seed, showing that they are not capable of freely intercrossing. + Yet Mr. Darwin assures us that the agency of bees is necessary to + carry the pollen from one plant to another, because in each + flower the pollen is shed before the stigma is ready to receive + it. We have here, therefore, either almost complete sterility + between varieties of different colours, or a prepotent effect of + pollen from a flower of the same colour, bringing about the same + result.</p> + + <p>Similar phenomena have not been recorded among animals; but + this is not to be wondered at when we consider that most of our + pure and valued domestic breeds are characterised by definite + colours which constitute one of their <a name="Page_170" id= + "Page_170"></a>distinctive marks, and they are, therefore, seldom + crossed with these of another colour; and even when they are so + crossed, no notice would be taken of any slight diminution of + fertility, since this is liable to occur from many causes. We + have also reason to believe that fertility has been increased by + long domestication, in addition to the fact of the original + stocks being exceptionally fertile; and no experiments have been + made on the differently coloured varieties of wild animals. There + are, however, a number of very curious facts showing that colour + in animals, as in plants, is often correlated with constitutional + differences of a remarkable kind, and as these have a close + relation to the subject we are discussing, a brief summary of + them will be here given.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Correlation of Colour with Constitutional + Peculiarities.</i></p> + + <p>The correlation of a white colour and blue eyes in male cats + with deafness, and of the tortoise-shell marking with the female + sex of the same animal, are two well-known but most extraordinary + cases. Equally remarkable is the fact, communicated to Darwin by + Mr. Tegetmeier, that white, yellow, pale blue, or dun pigeons, of + all breeds, have the young birds born naked, while in all other + colours they are well covered with down. Here we have a case in + which colour seems of more physiological importance than all the + varied structural differences between the varieties and breeds of + pigeons. In Virginia there is a plant called the paint-root + (Lachnanthes tinctoria), which, when eaten by pigs, colours their + bones pink, and causes the hoofs of all but the black varieties + to drop off; so that black pigs only can be kept in the + district.<a name="FNanchor_58_58" id= + "FNanchor_58_58"></a><a href="#Footnote_58_58" class= + "fnanchor">[58]</a> Buckwheat in flower is also said to be + injurious to white pigs but not to black. In the Tarentino, black + sheep are not injured by eating the Hypericum crispum—a + species of St. John's-wort—which kills white sheep. White + terriers suffer most from distemper; white chickens from the + gapes. White-haired horses or cattle are subject to cutaneous + diseases from which the dark coloured are free; while, both in + Thuringia and the West Indies, it has been noticed that white or + pale coloured cattle are much more troubled by flies than are + those which are brown or black. The same law even extends + <a name="Page_171" id="Page_171"></a>to insects, for it is found + that silkworms which produce white cocoons resist the fungus + disease much better than do those which produce yellow + cocoons.<a name="FNanchor_59_59" id="FNanchor_59_59"></a><a href= + "#Footnote_59_59" class="fnanchor">[59]</a> Among plants, we have + in North America green and yellow-fruited plums not affected by a + disease that attacked the purple-fruited varieties. + Yellow-fleshed peaches suffer more from disease than + white-fleshed kinds. In Mauritius, white sugar-canes were + attacked by a disease from which the red canes were free. White + onions and verbenas are most liable to mildew; and red-flowered + hyacinths were more injured by the cold during a severe winter in + Holland than any other kinds.<a name="FNanchor_60_60" id= + "FNanchor_60_60"></a><a href="#Footnote_60_60" class= + "fnanchor">[60]</a></p> + + <p>These curious and inexplicable correlations of colour with + constitutional peculiarities, both in animals and plants, render + it probable that the correlation of colour with infertility, + which has been detected in several cases in plants, may also + extend to animals in a state of nature; and if so, the fact is of + the highest importance as throwing light on the origin of the + infertility of many allied species. This will be better + understood after considering the facts which will be now + described.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Isolation of Varieties by Selective Association.</i></p> + + <p>In the last chapter I have shown that the importance of + geographical isolation for the formation of new species by + natural selection has been greatly exaggerated, because the + <a name="Page_172" id="Page_172"></a>very change of conditions, + which is the initial power in starting such new forms, leads also + to a local or stational segregation of the forms acted upon. But + there is also a very powerful cause of isolation in the mental + nature—the likes and dislikes—of animals; and to this + is probably due the fact of the comparative rarity of hybrids in + a state of nature. The differently coloured herds of cattle in + the Falkland Islands, each of which keeps separate, have been + already mentioned; and it may be added, that the mouse-coloured + variety seem to have already developed a physiological + peculiarity in breeding a month earlier than the others. Similar + facts occur, however, among our domestic animals and are well + known to breeders. Professor Low, one of the greatest authorities + on our domesticated animals, says: "The female of the dog, when + not under restraint, makes selection of her mate, the mastiff + selecting the mastiff, the terrier the terrier, and so on." And + again: "The Merino sheep and Heath sheep of Scotland, if two + flocks are mixed together, each will breed with its own variety." + Mr. Darwin has collected many facts illustrating this point. One + of the chief pigeon-fanciers in England informed him that, if + free to choose, each breed would prefer pairing with its own + kind. Among the wild horses in Paraguay those of the same colour + and size associate together; while in Circassia there are three + races of horses which have received special names, and which, + when living a free life, almost always refuse to mingle and + cross, and will even attack one another. On one of the Faroe + Islands, not more than half a mile in diameter, the half-wild + native black sheep do not readily mix with imported white sheep. + In the Forest of Dean, and in the New Forest, the dark and pale + coloured herds of fallow deer have never been known to mingle; + and even the curious Ancon sheep of quite modern origin have been + observed to keep together, separating themselves from the rest of + the flock when put into enclosures with other sheep. The same + rule applies to birds, for Darwin was informed by the Rev. W.D. + Fox that his flocks of white and Chinese geese kept + distinct.<a name="FNanchor_61_61" id= + "FNanchor_61_61"></a><a href="#Footnote_61_61" class= + "fnanchor">[61]</a></p> + + <p>This constant preference of animals for their like, even in + the case of slightly different varieties of the same species, is + evidently <a name="Page_173" id="Page_173"></a>a fact of great + importance in considering the origin of species by natural + selection, since it shows us that, so soon as a slight + differentiation of form or colour has been effected, isolation + will at once arise by the selective association of the animals + themselves; and thus the great stumbling-block of "the swamping + effects of intercrossing," which has been so prominently brought + forward by many naturalists, will be completely obviated.</p> + + <p>If now we combine with this fact the correlation of colour + with important constitutional peculiarities, and, in some cases, + with infertility; and consider, further, the curious parallelism + that has been shown to exist between the effects of changed + conditions and the intercrossing of varieties in producing either + an increase or a decrease of fertility, we shall have obtained, + at all events, a starting-point for the production of that + infertility which is so characteristic a feature of distinct + species when intercrossed. All we need, now, is some means of + increasing or accumulating this initial tendency; and to a + discussion of this problem we will therefore address + ourselves.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Influence of Natural Selection upon Sterility and + Fertility.</i></p> + + <p>It will occur to many persons that, as the infertility or + sterility of incipient species would be useful to them when + occupying the same or adjacent areas, by neutralising the effects + of intercrossing, this infertility might have been increased by + the action of natural selection; and this will be thought the + more probable if we admit, as we have seen reason to do, that + variations in fertility occur, perhaps as frequently as other + variations. Mr. Darwin tells us that, at one time, this appeared + to him probable, but he found the problem to be one of extreme + complexity; and he was also influenced against the view by many + considerations which seemed to render such an origin of the + sterility or infertility of species when intercrossed very + improbable. The fact that species which occupy distinct areas, + and which nowhere come in contact with each other, are often + sterile when crossed, is one of the difficulties; but this may + perhaps be overcome by the consideration that, though now + isolated, they may, and often must, have been in contact at their + origination. More important is the objection that natural + selection could not <a name="Page_174" id="Page_174"></a>possibly + have produced the difference that often occurs between reciprocal + crosses, one of these being sometimes fertile, while the other is + sterile. The extremely different amounts of infertility or + sterility between different species of the same genus, the + infertility often bearing no proportion to the difference between + the species crossed, is also an important objection. But none of + these objections would have much weight if it could be clearly + shown that natural selection <i>is</i> able to increase the + infertility variations of incipient species, as it is certainly + able to increase and develop all useful variations of form, + structure, instincts, or habits. Ample causes of infertility have + been shown to exist, in the nature of the organism and the laws + of correlation; the agency of natural selection is only needed to + accumulate the effects produced by these causes, and to render + their final results more uniform and more in accordance with the + facts that exist.</p> + + <p>About twenty years ago I had much correspondence and + discussion with Mr. Darwin on this question. I then believed that + I was able to demonstrate the action of natural selection in + accumulating infertility; but I could not convince him, owing to + the extreme complexity of the process under the conditions which + he thought most probable. I have recently returned to the + question; and, with the fuller knowledge of the facts of + variation we now possess, I think it may be shown that natural + selection <i>is</i>, in some probable cases at all events, able + to accumulate variations in infertility between incipient + species.</p> + + <p>The simplest case to consider, will be that in which two forms + or varieties of a species, occupying an extensive area, are in + process of adaptation to somewhat different modes of life within + the same area. If these two forms freely intercross with each + other, and produce mongrel offspring which are quite fertile + <i>inter se</i>, then the further differentiation of the forms + into two distinct species will be retarded, or perhaps entirely + prevented; for the offspring of the crossed unions will be, + perhaps, more vigorous on account of the cross, although less + perfectly adapted to the conditions of existence than either of + the pure breeds; and this would certainly establish a powerful + antagonistic influence to the further differentiation of the two + forms.</p> + + <p><a name="Page_175" id="Page_175"></a>Now, let us suppose that + a partial sterility of the hybrids between the two forms arises, + in correlation with the different modes of life and the slight + external or internal peculiarities that exist between them, both + of which we have seen to be real causes of infertility. The + result will be that, even if the hybrids between the two forms + are still freely produced, these hybrids will not themselves + increase so rapidly as the two pure forms; and as these latter + are, by the terms of the problem, better suited to their + conditions of life than are the hybrids between them, they will + not only increase more rapidly, but will also tend to supplant + the hybrids altogether whenever the struggle for existence + becomes exceptionally severe. Thus, the more complete the + sterility of the hybrids the more rapidly will they die out and + leave the two parent forms pure. Hence it will follow that, if + there is greater infertility between the two forms in one part of + the area than the other, these forms will be kept more pure + wherever this greater infertility prevails, will therefore have + an advantage at each recurring period of severe struggle for + existence, and will thus ultimately supplant the less infertile + or completely fertile forms that may exist in other portions of + the area. It thus appears that, in such a case as here supposed, + natural selection would preserve those portions of the two breeds + which were most infertile with each other, or whose hybrid + offspring were most infertile; and would, therefore, if + variations in fertility continued to arise, tend to increase that + infertility. It must particularly be noted that this effect would + result, not by the preservation of the infertile variations on + account of their infertility, but by the inferiority of the + hybrid offspring, both as being fewer in numbers, less able to + continue their race, and less adapted to the conditions of + existence than either of the pure forms. It is this inferiority + of the hybrid offspring that is the essential point; and as the + number of these hybrids will be permanently less where the + infertility is greatest, therefore those portions of the two + forms in which infertility is greatest will have the advantage, + and will ultimately survive in the struggle for existence.</p> + + <p>The differentiation of the two forms into distinct species, + with the increase of infertility between them, would be <a name= + "Page_176" id="Page_176"></a>greatly assisted by two other + important factors in the problem. It has already been shown that, + with each modification of form and habits, and especially with + modifications of colour, there arises a disinclination of the two + forms to pair together; and this would produce an amount of + isolation which would greatly assist the specialisation of the + forms in adaptation to their different conditions of life. Again, + evidence has been adduced that change of conditions or of mode of + life is a potent cause of disturbance of the reproductive system, + and, consequently, of infertility. We may therefore assume that, + as the two forms adopted more and more different modes of life, + and perhaps acquired also decided peculiarities of form and + coloration, the infertility between them would increase or become + more general; and as we have seen that every such increase of + infertility would give that portion of the species in which it + arose an advantage over the remaining portions in which the two + varieties were more fertile together, all this induced + infertility would maintain itself, and still further increase the + general infertility between the two forms of the species.</p> + + <p>It follows, then, that specialisation to separate conditions + of life, differentiation of external characters, disinclination + to cross-unions, and the infertility of the hybrid produce of + these unions, would all proceed <i>pari passu</i>, and would + ultimately lead to the production of two distinct forms having + all the characteristics, physiological as well as structural, of + true species.</p> + + <p>In the case now discussed it has been supposed, that some + amount of general infertility might arise in correlation with the + different modes of life of two varieties or incipient species. A + considerable body of facts already adduced renders it probable + that this <i>is</i> the mode in which any widespread infertility + would arise; and, if so, it has been shown that, by the influence + of natural selection and the known laws which affect varieties, + the infertility would be gradually increased. But, if we suppose + the infertility to arise sporadically within the two forms, and + to affect only a small proportion of the individuals in any area, + it will be difficult, if not impossible, to show that such + infertility would have any tendency to increase, or would produce + any but a <a name="Page_177" id="Page_177"></a>prejudicial + effect. If, for example, five per cent of each form thus varied + so as to be infertile with the other form, the result would be + hardly perceptible, because the individuals which formed + cross-unions and produced hybrids would constitute a very small + portion of the whole species; and the hybrid offspring, being at + a disadvantage in the struggle for existence and being themselves + infertile, would soon die out, while the much more numerous + fertile portion of the two forms would increase rapidly, and + furnish a sufficient number of pure-bred offspring of each form + to take the place of the somewhat inferior hybrids between them + whenever the struggle for existence became severe. We must + suppose that the normal fertile forms would transmit their + fertility to their progeny, and the few infertile forms their + infertility; but the latter would necessarily lose half their + proper increase by the sterility of their hybrid offspring + whenever they crossed with the other form, and when they bred + with their own form the tendency to sterility would die out + except in the very minute proportion of the five per cent + (one-twentieth) that chance would lead to pair together. Under + these circumstances the incipient sterility between the two forms + would rapidly be eliminated, and could never rise much above the + numbers which were produced by sporadic variation each year.</p> + + <p>It was, probably, by a consideration of some such case as this + that Mr. Darwin came to the conclusion that infertility arising + between incipient species could not be increased by natural + selection; and this is the more likely, as he was always disposed + to minimise both the frequency and the amount even of structural + variations.</p> + + <p>We have yet to notice another mode of action of natural + selection in favouring and perpetuating any infertility that may + arise between two incipient species. If several distinct species + are undergoing modification at the same time and in the same + area, to adapt them to some new conditions that have arisen + there, then any species in which the structural or colour + differences that have arisen between it and its varieties or + close allies were correlated with infertility of the crosses + between them, would have an advantage over the corresponding + varieties of other species in which there was no such <a name= + "Page_178" id="Page_178"></a>physiological peculiarity. Thus, + incipient species which were infertile together would have an + advantage over other incipient species which were fertile, and, + whenever the struggle for existence became severe, would prevail + over them and take their place. Such infertility, being + correlated with constitutional or structural differences, would + probably, as already suggested, go on increasing as these + differences increased; and thus, by the time the new species + became fully differentiated from its parent form (or brother + variety) the infertility might have become as well marked as we + usually find it to be between distinct species.</p> + + <p>This discussion has led us to some conclusions of the greatest + importance as bearing on the difficult problem of the cause of + the sterility of the hybrids between distinct species. Accepting, + as highly probable, the fact of variations in fertility occurring + in correlation with variations in habits, colour, or structure, + we see, that so long as such variations occurred only + sporadically, and affected but a small proportion of the + individuals in any area, the infertility could not be increased + by natural selection, but would tend to die out almost as fast as + it was produced. If, however, it was so closely correlated with + physical variations or diverse modes of life as to affect, even + in a small degree, a considerable proportion of the individuals + of the two forms in definite areas, it would be preserved by + natural selection, and the portion of the varying species thus + affected would increase at the expense of those portions which + were more fertile when crossed. Each further variation towards + infertility between the two forms would be again preserved, and + thus the incipient infertility of the hybrid offspring might be + increased till it became so great as almost to amount to + sterility. Yet further, we have seen that if several competing + species in the same area were being simultaneously modified, + those between whose varieties infertility arose would have an + advantage over those whose varieties remained fertile <i>inter + se</i>, and would ultimately supplant them.</p> + + <p>The preceding argument, it will be seen, depends entirely upon + the assumption that some amount of infertility characterises the + distinct varieties which are in process of differentiation into + species; and it may be objected that of <a name="Page_179" id= + "Page_179"></a>such infertility there is no proof. This is + admitted; but it is urged that facts have been adduced which + render such infertility probable, at least in some cases, and + this is all that is required. It is by no means necessary that + <i>all</i> varieties should exhibit incipient infertility, but + only, some varieties; for we know that, of the innumerable + varieties that occur but few become developed into distinct + species, and it may be that the absence of infertility, to + obviate the effects of intercrossing, is one of the usual causes + of their failure. All I have attempted to show is, that + <i>when</i> incipient infertility does occur in correlation with + other varietal differences, that infertility can be, and in fact + must be, increased by natural selection; and this, it appears to + me, is a decided step in advance in the solution of the + problem.<a name="FNanchor_62_62" id="FNanchor_62_62"></a><a href= + "#Footnote_62_62" class="fnanchor">[62]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_180" id="Page_180"></a><i>Physiological + Selection.</i></p> + + <p>Another form of infertility has been suggested by Professor + G.J. Romanes as having aided in bringing about the characteristic + infertility or sterility of hybrids. It is founded on the fact, + already noticed, that certain individuals of some species possess + what may be termed selective sterility—that is, while + fertile with some individuals of the species they are sterile + with others, and this altogether independently of any differences + of form, colour, or structure. The phenomenon, in the only form + in which it has been observed, is that of "infertility or + absolute sterility between two individuals, each of which is + perfectly fertile with all other individuals;" but Mr. Romanes + thinks that "it would not be nearly so remarkable, or + physiologically improbable, that such incompatibility should run + through a whole race or strain."<a name="FNanchor_63_63" id= + "FNanchor_63_63"></a><a href="#Footnote_63_63" class= + "fnanchor">[63]</a> Admitting that this may be <a name="Page_181" + id="Page_181"></a>so, though we have at present no evidence + whatever in support of it, it remains to be considered whether + such physiological varieties could maintain themselves, or + whether, as in the cases of sporadic infertility already + discussed, they would necessarily die out unless correlated with + useful characters. Mr. Romanes thinks that they would persist, + and urges that "whenever this one kind of variation occurs <i>it + cannot escape the preserving agency</i> of physiological + selection. Hence, even if it be granted that the variation which + affects the reproductive system in this particular way is a + variation of comparatively rare occurrence, still, as <i>it must + always be preserved</i> whenever it does occur, its influence in + the manufacture of specific types <i>must be cumulative</i>." The + very positive statements which I have italicised would lead most + readers to believe that the alleged fact had been demonstrated by + a careful working out of the process in some definite supposed + cases. This, however, has nowhere been done in Mr. Romanes' + paper; and as it is <i>the</i> vital theoretical point on which + any possible value of the new theory rests, and as it appears so + opposed to the self-destructive effects of simple infertility, + which we have already demonstrated when it occurs between the + intermingled portion of two varieties, it must be carefully + examined. In doing so, I will suppose that the required variation + is not of "rare occurrence," but of considerable amount, and that + it appears afresh each year to about the same extent, thus giving + the theory every possible advantage.</p> + + <p>Let us then suppose that a given species consists of 100,000 + individuals of each sex, with only the usual amount of + fluctuating external variability. Let a physiological variation + arise, so that 10 per cent of the whole number—10,000 + individuals of each sex—while remaining fertile <i>inter + se</i> become quite sterile with the remaining 90,000. This + peculiarity is not correlated with any external differences of + <a name="Page_182" id="Page_182"></a>form or colour, or with + inherent peculiarities of likes or dislikes leading to any choice + as to the pairing of the two sets of individuals. We have now to + inquire, What would be the result?</p> + + <p>Taking, first, the 10,000 pairs of the physiological or + abnormal variety, we find that each male of these might pair with + any one of the whole 100,000 of the opposite sex. If, therefore, + there was nothing to limit their choice to particular individuals + of either variety, the probabilities are that 9000 of them would + pair with the opposite variety, and only 1000 with their own + variety—that is, that 9000 would form sterile unions, and + only <i>one</i> thousand would form fertile unions.</p> + + <p>Taking, next, the 90,000 normal individuals of either sex, we + find, that each male of these has also a choice of 100,000 to + pair with. The probabilities are, therefore, that nine-tenths of + them—that is, 81,000—would pair with their normal + fellows, while 9000 would pair with the opposite abnormal variety + forming the above-mentioned sterile unions.</p> + + <p>Now, as the number of individuals forming a species remains + constant, generally speaking, from year to year, we shall have + next year also 100,000 pairs, of which the two physiological + varieties will be in the proportion of eighty-one to one, or + 98,780 pairs of the normal variety to 1220<a name= + "FNanchor_64_64" id="FNanchor_64_64"></a><a href= + "#Footnote_64_64" class="fnanchor">[64]</a> of the abnormal, that + being the proportion of the fertile unions of each. In this year + we shall find, by the same rule of probabilities, that only 15 + males of the abnormal variety will pair with their like and be + fertile, the remaining 1205 forming sterile unions with some of + the normal variety. The following year the total 100,000 pairs + will consist of 99,984 of the normal, and only 16 of the abnormal + variety; and the probabilities, of course, are, that the whole of + these latter will pair with some of the enormous preponderance of + normal individuals, and, their unions being sterile, the + physiological variety will become extinct in the third year.</p> + + <p>If now in the second and each succeeding year a similar + proportion as at first (10 per cent) of the physiological variety + is produced afresh from the ranks of the normal variety, the same + rate of diminution will go on, and it will be found that, + <a name="Page_183" id="Page_183"></a>on the most favourable + estimate, the physiological variety can never exceed 12,000 to + the 88,000 of the normal form of the species, as shown by the + following table:—</p> + + <pre> + 1st Year. 10,000 of physiological variety to 90,000 of normal variety. + 2d " 1,220 + 10,000 again produced. + 3d " 16 + 1,220 + 10,000 do. = 11,236 + 4th " O + 16 + 1,220 + 10,000 do. = 11,236 + 5th " O + 16 + 1,220 + 10,000 = 11,236 + and so on for any number of generations. + </pre> + + <p>In the preceding discussion we have given the theory the + advantage of the large proportion of 10 per cent of this very + exceptional variety arising in its midst year by year, and we + have seen that, even under these favourable conditions, it is + unable to increase its numbers much above its starting-point, and + that it remains wholly dependent on the continued renewal of the + variety for its existence beyond a few years. It appears, then, + that this form of inter-specific sterility cannot be increased by + natural or any other known form of selection, but that it + contains within itself its own principle of destruction. If it is + proposed to get over the difficulty by postulating a larger + percentage of the variety annually arising within the species, we + shall not affect the law of decrease until we approach equality + in the numbers of the two varieties. But with any such increase + of the physiological variety the species itself would inevitably + suffer by the large proportion of sterile unions in its midst, + and would thus be at a great disadvantage in competition with + other species which were fertile throughout. Thus, natural + selection will always tend to weed out any species with too great + a tendency to sterility among its own members, and will therefore + prevent such sterility from becoming the general characteristic + of varying species, which this theory demands should be the + case.</p> + + <p>On the whole, then, it appears clear that no form of + infertility or sterility between the individuals of a species, + can be increased by natural selection unless correlated with some + useful variation, while all infertility not so correlated has a + constant tendency to effect its own elimination. But the opposite + property, fertility, is of vital importance to every species, and + gives the offspring of the individuals which possess it, in + consequence of their superior numbers, a greater <a name= + "Page_184" id="Page_184"></a>chance of survival in the battle of + life. It is, therefore, directly under the control of natural + selection, which acts both by the self-preservation of fertile + and the self-destruction of infertile stocks—except always + where correlated as above, when they become useful, and therefore + subject to be increased by natural selection.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Summary and Concluding Remarks on Hybridity.</i></p> + + <p>The facts which are of the greatest importance to a + comprehension of this very difficult subject are those which show + the extreme susceptibility of the reproductive system both in + plants and animals. We have seen how both these classes of + organisms may be rendered infertile, by a change of conditions + which does not affect their general health, by captivity, or by + too close interbreeding. We have seen, also, that infertility is + frequently correlated with a difference of colour, or with other + characters; that it is not proportionate to divergence of + structure; that it varies in reciprocal crosses between pairs of + the same species; while in the cases of dimorphic and trimorphic + plants the different crosses between the same pair of individuals + may be fertile or sterile at the same time. It appears as if + fertility depended on such a delicate adjustment of the male and + female elements to each other, that, unless constantly kept up by + the preservation of the most fertile individuals, sterility is + always liable to arise. This preservation always occurs within + the limits of each species, both because fertility is of the + highest importance to the continuance of the race, and also + because sterility (and to a less extent infertility) is + self-destructive as well as injurious to the species.</p> + + <p>So long therefore as a species remains undivided, and in + occupation of a continuous area, its fertility is kept up by + natural selection; but the moment it becomes separated, either by + geographical or selective isolation, or by diversity of station + or of habits, then, while each portion must be kept fertile + <i>inter se</i>, there is nothing to prevent infertility arising + between the two separated portions. As the two portions will + necessarily exist under somewhat different conditions of life, + and will usually have acquired some diversity of form and + colour—both which circumstances we know to be either the + cause of infertility or to be correlated with it,—the fact + of <a name="Page_185" id="Page_185"></a>some degree of + infertility usually appearing between closely allied but locally + or physiologically segregated species is exactly what we should + expect.</p> + + <p>The reason why varieties do not usually exhibit a similar + amount of infertility is not difficult to explain. The popular + conclusions on this matter have been drawn chiefly from what + occurs among domestic animals, and we have seen that the very + first essential to their becoming domesticated was that they + should continue fertile under changed conditions of life. During + the slow process of the formation of new varieties by conscious + or unconscious selection, fertility has always been an essential + character, and has thus been invariably preserved or increased; + while there is some evidence to show that domestication itself + tends to increase fertility.</p> + + <p>Among plants, wild species and varieties have been more + frequently experimented on than among animals, and we accordingly + find numerous cases in which distinct species of plants are + perfectly fertile when crossed, their hybrid offspring being also + fertile <i>inter se</i>. We also find some few examples of the + converse fact—varieties of the same species which when + crossed are infertile or even sterile.</p> + + <p>The idea that either infertility or geographical isolation is + absolutely essential to the formation of new species, in order to + prevent the swamping effects of intercrossing, has been shown to + be unsound, because the varieties or incipient species will, in + most cases, be sufficiently isolated by having adopted different + habits or by frequenting different stations; while selective + association, which is known to be general among distinct + varieties or breeds of the same species, will produce an + effective isolation even when the two forms occupy the same + area.</p> + + <p>From the various considerations now adverted to, Mr. Darwin + arrived at the conclusion that the sterility or infertility of + species with each other, whether manifested in the difficulty of + obtaining first crosses between them or in the sterility of the + hybrids thus obtained, is not a constant or necessary result of + specific difference, but is incidental on unknown peculiarities + of the reproductive system. These peculiarities constantly tend + to arise under changed conditions owing to the extreme + susceptibility of that system, and they <a name="Page_186" id= + "Page_186"></a>are usually correlated with variations of form or + of colour. Hence, as fixed differences of form and colour, slowly + gained by natural selection in adaptation to changed conditions, + are what essentially characterise distinct species, some amount + of infertility between species is the usual result.</p> + + <p>Here the problem was left by Mr. Darwin; but we have shown + that its solution may be carried a step further. If we accept the + association of some degree of infertility, however slight, as a + not unfrequent accompaniment of the external differences which + always arise in a state of nature between varieties and incipient + species, it has been shown that natural selection <i>has</i> + power to increase that infertility just as it has power to + increase other favourable variations. Such an increase of + infertility will be beneficial, whenever new species arise in the + same area with the parent form; and we thus see how, out of the + fluctuating and very unequal amounts of infertility correlated + with physical variations, there may have arisen that larger and + more constant amount which appears usually to characterise + well-marked species.</p> + + <p>The great body of facts of which a condensed account has been + given in the present chapter, although from an experimental point + of view very insufficient, all point to the general conclusion we + have now reached, and afford us a not unsatisfactory solution of + the great problem of hybridism in relation to the origin of + species by means of natural selection. Further experimental + research is needed in order to complete the elucidation of the + subject; but until these additional facts are forthcoming no new + theory seems required for the explanation of the phenomena.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_51_51" id="Footnote_51_51"></a><a href= + "#FNanchor_51_51"><span class="label">[51]</span></a> + Darwin's <i>Animals and Plants under Domestication</i>, vol. + ii. pp. 163-170.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_52_52" id="Footnote_52_52"></a><a href= + "#FNanchor_52_52"><span class="label">[52]</span></a> For a + full account of these interesting facts and of the various + problems to which they give rise, the reader must consult + Darwin's volume on <i>The Different Forms of Flowers in + Plants of the same Species</i>, chaps, i.-iv.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_53_53" id="Footnote_53_53"></a><a href= + "#FNanchor_53_53"><span class="label">[53]</span></a> See + <i>Nature</i>, vol. xxi. p. 207.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_54_54" id="Footnote_54_54"></a><a href= + "#FNanchor_54_54"><span class="label">[54]</span></a> Low's + <i>Domesticated Animals of Great Britain</i>, Introduction, + p. lxiv.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_55_55" id="Footnote_55_55"></a><a href= + "#FNanchor_55_55"><span class="label">[55]</span></a> Low's + <i>Domesticated Animals</i>, p. 28.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_56_56" id="Footnote_56_56"></a><a href= + "#FNanchor_56_56"><span class="label">[56]</span></a> + <i>Amaryllidaceae</i>, by the Hon. and Rev. William Herbert, + p. 379.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_57_57" id="Footnote_57_57"></a><a href= + "#FNanchor_57_57"><span class="label">[57]</span></a> + <i>Origin of Species</i>, p. 239.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_58_58" id="Footnote_58_58"></a><a href= + "#FNanchor_58_58"><span class="label">[58]</span></a> + <i>Origin of Species</i>, sixth edition, p. 9.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_59_59" id="Footnote_59_59"></a><a href= + "#FNanchor_59_59"><span class="label">[59]</span></a> In the + <i>Medico-Chirurgical Transactions</i>, vol. liii. (1870), + Dr. Ogle has adduced some curious physiological facts bearing + on the presence or absence of white colours in the higher + animals. He states that a dark pigment in the olfactory + region of the nostrils is essential to perfect smell, and + that this pigment is rarely deficient except when the whole + animal is pure white, and the creature is then almost without + smell or taste. He observes that there is no proof that, in + any of the cases given above, the black animals actually eat + the poisonous root or plant; and that the facts are readily + understood if the senses of smell and taste are dependent on + a pigment which is absent in the white animals, who therefore + eat what those gifted with normal senses avoid. This + explanation however hardly seems to cover the facts. We + cannot suppose that almost all the sheep in the world (which + are mostly white) are without smell or taste. The cutaneous + disease on the white patches of hair on horses, the special + liability of white terriers to distemper, of white chickens + to the gapes, and of silkworms which produce yellow silk to + the fungus, are not explained by it. The analogous facts in + plants also indicate a real constitutional relation with + colour, not an affection of the sense of smell and taste + only.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_60_60" id="Footnote_60_60"></a><a href= + "#FNanchor_60_60"><span class="label">[60]</span></a> For all + these facts, see <i>Animals and Plants under + Domestication</i>, vol. ii. pp. 335-338.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_61_61" id="Footnote_61_61"></a><a href= + "#FNanchor_61_61"><span class="label">[61]</span></a> + <i>Animals and Plants under Domestication</i>, vol. ii. pp. + 102, 103.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_62_62" id="Footnote_62_62"></a><a href= + "#FNanchor_62_62"><span class="label">[62]</span></a> As this + argument is a rather difficult one to follow, while its + theoretical importance is very great, I add here the + following briefer exposition of it, in a series of + propositions; being, with a few verbal alterations, a copy of + what I wrote on the subject about twenty years back. Some + readers may find this easier to follow than the fuller + discussion in the text:—</p> + + <div class="blockquot" style='font-size: 100%;'> + <p style= + 'text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Can Sterility of Hybrids have been Produced by Natural + Selection?</i></p> + + <p>1. Let there be a species which has varied into <i>two + forms</i> each adapted to certain existing conditions + better than the parent form, which they soon supplant.</p> + + <p>2. If these <i>two forms</i>, which are supposed to + coexist in the same district, do not intercross, natural + selection will accumulate all favourable variations till + they become well suited to their conditions of life, and + form two slightly differing species.</p> + + <p>3. But if these <i>two forms</i> freely intercross with + each other, and produce hybrids, which are also quite + fertile <i>inter se</i>, then the formation of the two + distinct races or species will be retarded, or perhaps + entirely prevented; for the offspring of the crossed unions + will be <i>more vigorous</i> owing to the cross, although + <i>less adapted</i> to their conditions of life than either + of the pure breeds.</p> + + <p>4. Now, let a partial sterility of the hybrids of some + considerable proportion of these two forms arise; and, as + this would probably be due to some special conditions of + life, we may fairly suppose it to arise in some definite + portion of the area occupied by the two forms.</p> + + <p>5. The result will be that, in that area, the hybrids + (although continually produced by first crosses almost as + freely as before) will not themselves increase so rapidly + as the two pure forms; and as the two pure forms are, by + the terms of the problem, better suited to their several + conditions of life than the hybrids, they will inevitably + increase more rapidly, and will continually tend to + supplant the hybrids altogether at every recurrent severe + struggle for existence.</p> + + <p>6. We may fairly suppose, also, that as soon as any + sterility appears some disinclination to <i>cross + unions</i> will appear, and this will further tend to the + diminution of the production of hybrids.</p> + + <p>7. In the other part of the area, however, where + hybridism occurs with perfect freedom, hybrids of various + degrees may increase till they equal or even exceed in + number the pure species—that is, the incipient + species will be liable to be swamped by intercrossing.</p> + + <p>8. The first result, then, of a partial sterility of + crosses appearing in one part of the area occupied by the + two forms, will be—that the great majority of the + individuals will there consist of the two pure forms only, + while in the remaining part these will be in a + minority,—which is the same as saying that the new + <i>physiological variety</i> of the two forms will be + better suited to the conditions of existence than the + remaining portion which has not varied physiologically.</p> + + <p>9. But when the struggle for existence becomes severe, + that variety which is best adapted to the conditions of + existence always supplants that which is imperfectly + adapted; therefore, <i>by natural selection</i> the + <i>varieties</i> which are <i>sterile</i> when crossed will + become established as the only ones.</p> + + <p>10. Now let variations in the <i>amount of + sterility</i>and in the <i>disinclination to crossed + unions</i> continue to occur—also in certain parts of + the area: exactly the same result must recur, and the + progeny of this new physiological variety will in time + occupy the whole area.</p> + + <p>11. There is yet another consideration that would + facilitate the process. It seems probable that the + <i>sterility variations</i> would, to some extent, concur + with, and perhaps depend upon, the <i>specific + variations</i>; so that, just in proportion as the <i>two + forms</i> diverged and became better adapted to the + conditions of existence, they would become more sterile + when intercrossed. If this were the case, then natural + selection would act with double strength; and those which + were better adapted to survive both structurally and + physiologically would certainly do so.</p> + </div> + </div> + + <div class="footnote"> + <p><a name="Footnote_63_63" id="Footnote_63_63"></a><a href= + "#FNanchor_63_63"><span class="label">[63]</span></a> Cases + of this kind are referred to at p. 155. It must, however, be + noted, that such sterility in first crosses appears to be + equally rare between different species of the same genus as + between individuals of the same species. Mules and other + hybrids are freely produced between very distinct species, + but are themselves infertile or quite sterile; and it is this + infertility or sterility of the hybrids that is the + characteristic—and was once thought to be the + criterion—of species, not the sterility of their first + crosses. Hence we should not expect to find any constant + infertility in the first crosses between the distinct strains + or varieties that formed the starting-point of new species, + but only a slight amount of infertility in their mongrel + offspring. It follows, that Mr. Romanes' theory of + <i>Physiological Selection</i>—which assumes sterility + or infertility between first crosses as the fundamental fact + in the origin of species—does not accord with the + general phenomena of hybridism in nature.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_64_64" id="Footnote_64_64"></a><a href= + "#FNanchor_64_64"><span class="label">[64]</span></a> The + exact number is 1219.51, but the fractions are omitted for + clearness.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a><a name= + "Page_187" id="Page_187"></a>CHAPTER VIII</h2> + + <p style='font-weight:bold;'>THE ORIGIN AND USES OF COLOUR IN + ANIMALS</p> + + <div class="blockquot"> + <p>The Darwinian theory threw new light on organic + colour—The problem to be solved—The constancy of + animal colour indicates utility—Colour and + environment—Arctic animals white—Exceptions prove + the rule—Desert, forest, nocturnal, and oceanic + animals—General theories of animal colour—Variable + protective colouring—Mr. Poulton's + experiments—Special or local colour + adaptations—Imitation of particular objects—How + they have been produced—Special protective colouring of + butterflies—Protective resemblance among marine + animals—Protection by terrifying enemies—Alluring + coloration—The coloration of birds' eggs—Colour as + a means of recognition—Summary of the preceding + exposition—Influence of locality or of climate on + colour—Concluding remarks.</p> + </div> + + <p>Among the numerous applications of the Darwinian theory in the + interpretation of the complex phenomena presented by the organic + world, none have been more successful, or are more interesting, + than those which deal with the colours of animals and plants. To + the older school of naturalists colour was a trivial character, + eminently unstable and untrustworthy in the determination of + species; and it appeared to have, in most cases, no use or + meaning to the objects which displayed it. The bright and often + gorgeous coloration of insect, bird, or flower, was either looked + upon as having been created for the enjoyment of mankind, or as + due to unknown and perhaps undiscoverable laws of nature.</p> + + <p>But the researches of Mr. Darwin totally changed our point of + view in this matter. He showed, clearly, that some of the colours + of animals are useful, some hurtful to them; and he believed that + many of the most brilliant colours were developed by sexual + choice; while his great general principle, that all <a name= + "Page_188" id="Page_188"></a>the fixed characters of organic + beings have been developed under the action of the law of + utility, led to the inevitable conclusion that so remarkable and + conspicuous a character as colour, which so often constitutes the + most obvious distinction of species from species, or group from + group, must also have arisen from survival of the fittest, and + must, therefore, in most cases have some relation to the + wellbeing of its possessors. Continuous observation and research, + carried on by multitudes of observers during the last thirty + years, have shown this to be the case; but the problem is found + to be far more complex than was at first supposed. The modes in + which colour is of use to different classes of organisms is very + varied, and have probably not yet been all discovered; while the + infinite variety and marvellous beauty of some of its + developments are such as to render it hopeless to arrive at a + complete and satisfactory explanation of every individual case. + So much, however, has been achieved, so many curious facts have + been explained, and so much light has been thrown on some of the + most obscure phenomena of nature, that the subject deserves a + prominent place in any account of the Darwinian theory.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Problem to be Solved.</i></p> + + <p>Before dealing with the various modifications of colour in the + animal world it is necessary to say a few words on colour in + general, on its prevalence in nature, and how it is that the + colours of animals and plants require any special explanation. + What we term colour is a subjective phenomenon, due to the + constitution of our mind and nervous system; while, objectively, + it consists of light-vibrations of different wave-lengths emitted + by, or reflected from, various objects. Every visible object must + be coloured, because to be visible it must send rays of light to + our eye. The kind of light it sends is modified by the molecular + constitution or the surface texture of the object. Pigments + absorb certain rays and reflect the remainder, and this reflected + portion has to our eyes a definite colour, according to the + portion of the rays constituting white light which are absorbed. + Interference colours are produced either by thin films or by very + fine striae on the surfaces of bodies, which cause rays of + certain wave-lengths to neutralise each other, leaving the + remainder to produce the effects of colour. Such <a name= + "Page_189" id="Page_189"></a>are the colours of soap-bubbles, or + of steel or glass on which extremely fine lines have been ruled; + and these colours often produce the effect of metallic lustre, + and are the cause of most of the metallic hues of birds and + insects.</p> + + <p>As colour thus depends on molecular or chemical constitution + or on the minute surface texture of bodies, and, as the matter of + which organic beings are composed consists of chemical compounds + of great complexity and extreme instability, and is also subject + to innumerable changes during growth and development, we might + naturally expect the phenomena of colour to be more varied here + than in less complex and more stable compounds. Yet even in the + inorganic world we find abundant and varied colours; in the earth + and in the water; in metals, gems, and minerals; in the sky and + in the ocean; in sunset clouds and in the many-tinted rainbow. + Here we can have no question of <i>use</i> to the coloured + object, and almost as little perhaps in the vivid red of blood, + in the brilliant colours of red snow and other low algae and + fungi, or even in the universal mantle of green which clothes so + large a portion of the earth's surface. The presence of some + colour, or even of many brilliant colours, in animals and plants + would require no other explanation than does that of the sky or + the ocean, of the ruby or the emerald—that is, it would + require a purely physical explanation only. It is the wonderful + individuality of the colours of animals and plants that attracts + our attention—the fact that the colours are localised in + definite patterns, sometimes in accordance with structural + characters, sometimes altogether independent of them; while often + differing in the most striking and fantastic manner in allied + species. We are thus compelled to look upon colour not merely as + a physical but also as a biological characteristic, which has + been differentiated and specialised by natural selection, and + must, therefore, find its explanation in the principle of + adaptation or utility.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Constancy of Animal Colour indicates Utility.</i></p> + + <p>That the colours and markings of animals have been acquired + under the fundamental law of utility is indicated by a general + fact which has received very little attention. As a rule, colour + and marking are constant in each species of wild animal, while, + in almost every domesticated animal, there arises <a name= + "Page_190" id="Page_190"></a>great variability. We see this in + our horses and cattle, our dogs and cats, our pigeons and + poultry. Now, the essential difference between the conditions of + life of domesticated and wild animals is, that the former are + protected by man, while the latter have to protect themselves. + The extreme variations in colour that immediately arise under + domestication indicate a tendency to vary in this way, and the + occasional occurrence of white or piebald or other exceptionally + coloured individuals of many species in a state of nature, shows + that this tendency exists there also; and, as these exceptionally + coloured individuals rarely or never increase, there must be some + constant power at work to keep it in check. This power can only + be natural selection or the survival of the fittest, which again + implies that some colours are useful, some injurious, in each + particular case. With this principle as our guide, let us see how + far we can account both for the general and special colours of + the animal world.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Colour and Environment.</i></p> + + <p>The fact that first strikes us in our examination of the + colours of animals as a whole, is the close relation that exists + between these colours and the general environment. Thus, white + prevails among arctic animals; yellow or brown in desert species; + while green is only a common colour in tropical evergreen + forests. If we consider these cases somewhat carefully we shall + find, that they afford us excellent materials for forming a + judgment on the various theories that have been suggested to + account for the colours of the animal world.</p> + + <p>In the arctic regions there are a number of animals which are + wholly white all the year round, or which only turn white in + winter. Among the former are the polar bear and the American + polar hare, the snowy owl and the Greenland falcon; among the + latter the arctic fox, the arctic hare, the ermine, and the + ptarmigan. Those which are permanently white remain among the + snow nearly all the year round, while those which change their + colour inhabit regions which are free from snow in summer. The + obvious explanation of this style of coloration is, that it is + protective, serving to conceal the herbivorous species from their + enemies, and enabling carnivorous animals to approach their prey + unperceived. Two other explanations have, how<a name="Page_191" + id="Page_191"></a>ever, been suggested. One is, that the + prevalent white of the arctic regions has a direct effect in + producing the white colour in animals, either by some + photographic or chemical action on the skin or by a reflex action + through vision. The other is, that the white colour is chiefly + beneficial as a means of checking radiation and so preserving + animal heat during the severity of an arctic winter. The first is + part of the general theory that colour is the effect of coloured + light on the objects—a pure hypothesis which has, I + believe, no facts whatever to support it. The second suggestion + is also an hypothesis merely, since it has not been proved by + experiment that a white colour, <i>per se</i>, independently of + the fur or feathers which is so coloured, has any effect whatever + in checking the radiation of low-grade heat like that of the + animal body. But both alike are sufficiently disproved by the + interesting exceptions to the rule of white coloration in the + arctic regions, which exceptions are, nevertheless, quite in + harmony with the theory of protection.</p> + + <p>Whenever we find arctic animals which, from whatever cause, do + not require protection by the white colour, then neither the cold + nor the snow-glare has any effect upon their coloration. The + sable retains its rich brown fur throughout the Siberian winter; + but it frequents trees at that season and not only feeds + partially on fruits or seeds, but is able to catch birds among + the branches of the fir-trees, with the bark of which its colour + assimilates. Then we have that thoroughly arctic animal, the + musk-sheep, which is brown and conspicuous; but this animal is + gregarious, and its safety depends on its association in small + herds. It is, therefore, of more importance for it to be able to + recognise its kind at a distance than to be concealed from its + enemies, against which it can well protect itself so long as it + keeps together in a compact body. But the most striking example + is that of the common raven, which is a true arctic bird, and is + found even in mid-winter as far north as any known bird or + mammal. Yet it always retains its black coat, and the reason, + from our point of view, is obvious. The raven is a powerful bird + and fears no enemy, while, being a carrion-feeder, it has no need + for concealment in order to approach its prey. The colour of the + raven and of the musk-sheep are, therefore, <a name="Page_192" + id="Page_192"></a>both inconsistent with any other theory than + that the white colour of arctic animals has been acquired for + concealment, and to that theory both afford a strong support. + Here we have a striking example of the exception proving the + rule.</p> + + <p>In the desert regions of the earth we find an even more + general accordance of colour with surroundings. The lion, the + camel, and all the desert antelopes have more or less the colour + of the sand or rock among which they live. The Egyptian cat and + the Pampas cat are sandy or earth coloured. The Australian + kangaroos are of similar tints, and the original colour of the + wild horse is supposed to have been sandy or clay coloured. Birds + are equally well protected by assimilative hues; the larks, + quails, goatsuckers, and grouse which abound in the North African + and Asiatic deserts are all tinted or mottled so as closely to + resemble the average colour of the soil in the districts they + inhabit. Canon Tristram, who knows these regions and their + natural history so well, says, in an often quoted passage: "In + the desert, where neither trees, brushwood, nor even undulations + of the surface afford the slightest protection to its foes, a + modification of colour which shall be assimilated to that of the + surrounding country is absolutely necessary. Hence, without + exception, the upper plumage of every bird, whether lark, chat, + sylvain, or sand-grouse, and also the fur of all the smaller + mammals, and the skin of all the snakes and lizards, is of one + uniform isabelline or sand colour."</p> + + <p>Passing on to the tropical regions, it is among their + evergreen forests alone that we find whole groups of birds whose + ground colour is green. Parrots are very generally green, and in + the East we have an extensive group of green fruit-eating + pigeons; while the barbets, bee-eaters, turacos, leaf-thrushes + (Phyllornis), white-eyes (Zosterops), and many other groups, have + so much green in their plumage as to tend greatly to their + concealment among the dense foliage. There can be no doubt that + these colours have been acquired as a protection, when we see + that in all the temperate regions, where the leaves are + deciduous, the ground colour of the great majority of birds, + especially on the upper surface, is a rusty brown of various + shades, well corresponding with the bark, withered leaves, ferns, + and bare thickets among which <a name="Page_193" id= + "Page_193"></a>they live in autumn and winter, and especially in + early spring when so many of them build their nests.</p> + + <p>Nocturnal animals supply another illustration of the same + rule, in the dusky colours of mice, rats, bats, and moles, and in + the soft mottled plumage of owls and goatsuckers which, while + almost equally inconspicuous in the twilight, are such as to + favour their concealment in the daytime.</p> + + <p>An additional illustration of general assimilation of colour + to the surroundings of animals, is furnished by the inhabitants + of the deep oceans. Professor Moseley of the Challenger + Expedition, in his British Association lecture on this subject, + says: "Most characteristic of pelagic animals is the almost + crystalline transparency of their bodies. So perfect is this + transparency that very many of them are rendered almost entirely + invisible when floating in the water, while some, even when + caught and held up in a glass globe, are hardly to be seen. The + skin, nerves, muscles, and other organs are absolutely hyaline + and transparent, but the liver and digestive tract often remain + opaque and of a yellow or brown colour, and exactly resemble when + seen in the water small pieces of floating seaweed." Such marine + organisms, however, as are of larger size, and either + occasionally or habitually float on the surface, are beautifully + tinged with blue above, thus harmonising with the colour of the + sea as seen by hovering birds; while they are white below, and + are thus invisible against the wave-foam and clouds as seen by + enemies beneath the surface. Such are the tints of the beautiful + nudibranchiate mollusc, Glaucus atlanticus, and many others.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>General Theories of Animal Colour.</i></p> + + <p>We are now in a position to test the general theories, or, to + speak more correctly, the popular notions, as to the origin of + animal coloration, before proceeding to apply the principle of + utility to the explanation of some among the many extraordinary + manifestations of colour in the animal world. The most generally + received theory undoubtedly is, that brilliancy and variety of + colour are due to the direct action of light and heat; a theory + no doubt derived from the abundance of bright-coloured birds, + insects, and flowers which are brought from tropical regions. + There are, however, <a name="Page_194" id="Page_194"></a>two + strong arguments against this theory. We have already seen how + generally bright coloration is wanting in desert animals, yet + here heat and light are both at a maximum, and if these alone + were the agents in the production of colour, desert animals + should be the most brilliant. Again, all naturalists who have + lived in tropical regions know that the proportion of bright to + dull coloured species is little if any greater there than in the + temperate zone, while there are many tropical groups in which + bright colours are almost entirely unknown. No part of the world + presents so many brilliant birds as South America, yet there are + extensive families, containing many hundreds of species, which + are as plainly coloured as our average temperate birds. Such are + the families of the bush-shrikes and ant-thrushes + (Formicariidae), the tyrant-shrikes (Tyrannidae), the American + creepers (Dendrocolaptidae), together with a large proportion of + the wood-warblers (Mniotiltidae), the finches, the wrens, and + some other groups. In the eastern hemisphere, also, we have the + babbling-thrushes (Timaliidae), the cuckoo-shrikes + (Campephagidae), the honey-suckers (Meliphagidae), and several + other smaller groups which are certainly not coloured above the + average standard of temperate birds.</p> + + <p>Again, there are many families of birds which spread over the + whole world, temperate and tropical, and among these the tropical + species rarely present any exceptional brilliancy of colour. Such + are the thrushes, goatsuckers, hawks, plovers, and ducks; and in + the last-named group it is the temperate and arctic zones that + afford the most brilliant coloration.</p> + + <p>The same general facts are found to prevail among insects. + Although tropical insects present some of the most gorgeous + coloration in the whole realm of nature, yet there are thousands + and tens of thousands of species which are as dull coloured as + any in our cloudy land. The extensive family of the carnivorous + ground-beetles (Carabidae) attains its greatest brilliancy in the + temperate zone; while by far the larger proportion of the great + families of the longicorns and the weevils, are of obscure + colours even in the tropics. In butterflies, there is undoubtedly + a larger proportion of brilliant colour in the tropics; but if we + compare families which are almost equally developed over the + globe—as the Pieridae or <a name="Page_195" id= + "Page_195"></a>whites and yellows, and the Satyridae or + ringlets—we shall find no great disproportion in colour + between those of temperate and tropical regions.</p> + + <p>The various facts which have now briefly been noticed are + sufficient to indicate that the light and heat of the sun are not + the direct causes of the colours of animals, although they may + favour the production of colour when, as in tropical regions, the + persistent high temperature favours the development of the + maximum of life. We will now consider the next suggestion, that + light reflected from surrounding coloured objects tends to + produce corresponding colours in the animal world.</p> + + <p>This theory is founded on a number of very curious facts which + prove, that such a change does sometimes occur and is directly + dependent on the colours of surrounding objects; but these facts + are comparatively rare and exceptional in their nature, and the + same theory will certainly not apply to the infinitely varied + colours of the higher animals, many of which are exposed to a + constantly varying amount of light and colour during their active + existence. A brief sketch of these dependent changes of colour + may, however, be advantageously given here.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variable Protective Colouring.</i></p> + + <p>There are two distinct kinds of change of colour in animals + due to the colouring of the environment. In one case the change + is caused by reflex action set up by the animal <i>seeing</i> the + colour to be imitated, and the change produced can be altered or + repeated as the animal changes its position. In the other case + the change occurs but once, and is probably not due to any + conscious or sense action, but to some direct influence on the + surface tissues while the creature is undergoing a moult or + change to the pupa form.</p> + + <p>The most striking example of the first class is that of the + chameleon, which changes to white, brown, yellowish, or green, + according to the colour of the object on which it rests. This + change is brought about by means of two layers of pigment cells, + deeply seated in the skin, and of bluish and yellowish colours. + By suitable muscles these cells can be forced upwards so as to + modify the colour of the skin, which, <a name="Page_196" id= + "Page_196"></a>when they are not brought into action, is a dirty + white. These animals are excessively sluggish and defenceless, + and the power of changing their colour to that of their immediate + surroundings is no doubt of great service to them. Many of the + flatfish are also capable of changing their colour according to + the colour of the bottom they rest on; and frogs have a similar + power to a limited extent. Some crustacea also change colour, and + the power is much developed in the Chameleon shrimp (Mysis + Chamaeleon) which is gray when on sand, but brown or green when + among brown or green seaweed. It has been proved by experiment + that when this animal is blinded the change does not occur. In + all these cases, therefore, we have some form of reflex or sense + action by which the change is produced, probably by means of + pigment cells beneath the skin as in the chameleon.</p> + + <p>The second class consists of certain larvae, and pupae, which + undergo changes of colour when exposed to differently coloured + surroundings. This subject has been carefully investigated by Mr. + E.B. Poulton, who has communicated the results of his experiments + to the Royal Society.<a name="FNanchor_65_65" id= + "FNanchor_65_65"></a><a href="#Footnote_65_65" class= + "fnanchor">[65]</a> It had been noticed that some species of + larvae which fed on several different plants had colours more or + less corresponding to the particular plant the individual fed on. + Numerous cases are given in Professor Meldola's article on + "Variable Protective Colouring" (<i>Proc. Zool. Soc.</i>, 1873, + p. 153), and while the general green coloration was attributed to + the presence of chlorophyll beneath the skin, the particular + change in correspondence to each food-plant was attributed to a + special function which had been developed by natural selection. + Later on, in a note to his translation of Weissmann's <i>Theory + of Descent</i>, Professor Meldola seemed disposed to think that + the variations of colour of some of the species might be + phytophagic—that is, due to the direct action of the + differently coloured leaves on which the insect fed. Mr. + Poulton's experiments have thrown much light on this question, + since he has conclusively proved that, in the case of the sphinx + caterpillar of Smerinthus ocellatus, the change of colour is not + due to the food but to the coloured light reflected from the + leaves.</p> + + <p><a name="Page_197" id="Page_197"></a>This was shown by feeding + two sets of larvae on the same plant but exposed to differently + coloured surroundings, obtained by sewing the leaves together, so + that in one case only the dark upper surface, in the other the + whitish under surface was exposed to view. The result in each + case was a corresponding change of colour in the larvae, + confirming the experiments on different individuals of the same + batch of larvae which had been supplied with different + food-plants or exposed to a different coloured light.</p> + + <p>An even more interesting series of experiments was made on the + colours of pupae, which in many cases were known to be affected + by the material on which they underwent their transformations. + The late Mr. T.W. Wood proved, in 1867, that the pupae of the + common cabbage butterflies (Pieris brassicae and P. rapae) were + either light, or dark, or green, according to the coloured boxes + they were kept in, or the colours of the fences, walls, etc., + against which they were suspended. Mrs. Barber in South Africa + found that the pupae of Papilio Nireus underwent a similar + change, being deep green when attached to orange leaves of the + same tint, pale yellowish-green when on a branch of the + bottle-brush tree whose half-dried leaves were of this colour, + and yellowish when attached to the wooden frame of a box. A few + other observers noted similar phenomena, but nothing more was + done till Mr. Poulton's elaborate series of experiments with the + larvae of several of our common butterflies were the means of + clearing up several important points. He showed that the action + of the coloured light did not affect the pupa itself but the + larva, and that only for a limited period of time. After a + caterpillar has done feeding it wanders about seeking a suitable + place to undergo its transformation. When this is found it rests + quietly for a day or two, spinning the web from which it is to + suspend itself; and it is during this period of quiescence, and + perhaps also the first hour or two after its suspension, that the + action of the surrounding coloured surfaces determines, to a + considerable extent, the colour of the pupa. By the application + of various surrounding colours during this period, Mr. Poulton + was able to modify the colour of the pupa of the common + tortoise-shell butterfly from nearly black to pale, or to a + brilliant golden; and that of Pieris rapae <a name="Page_198" id= + "Page_198"></a>from dusky through pinkish to pale green. It is + interesting to note, that the colours produced were in all cases + such only as assimilated with the surroundings usually occupied + by the species, and also, that colours which did not occur in + such surroundings, as dark red or blue, only produced the same + effects as dusky or black.</p> + + <p>Careful experiments were made to ascertain whether the effect + was produced through the sight of the caterpillar. The ocelli + were covered with black varnish, but neither this, nor cutting + off the spines of the tortoise-shell larva to ascertain whether + they might be sense-organs, produced any effect on the resulting + colour. Mr. Poulton concludes, therefore, that the colour-action + probably occurs over the whole surface of the body, setting up + physiological processes which result in the corresponding + colour-change of the pupa. Such changes are, however, by no means + universal, or even common, in protectively coloured pupae, since + in Papilio machaon and some others which have been experimented + on, both in this country and abroad, no change can be produced on + the pupa by any amount of exposure to differently coloured + surroundings. It is a curious point that, with the small + tortoise-shell larva, exposure to light from gilded surfaces + produced pupae with a brilliant golden lustre; and the + explanation is supposed to be that mica abounded in the original + habitat of the species, and that the pupae thus obtained + protection when suspended against micaceous rock. Looking, + however, at the wide range of the species and the comparatively + limited area in which micaceous rocks occur, this seems a rather + improbable explanation, and the occurrence of this metallic + appearance is still a difficulty. It does not, however, commonly + occur in this country in a natural state.</p> + + <p>The two classes of variable colouring here discussed are + evidently exceptional, and can have little if any relation to the + colours of those more active creatures which are continually + changing their position with regard to surrounding objects, and + whose colours and markings are nearly constant throughout the + life of the individual, and (with the exception of sexual + differences) in all the individuals of the species. We will now + briefly pass in review the various characteristics and uses of + the colours which more generally prevail in nature; <a name= + "Page_199" id="Page_199"></a>and having already discussed those + protective colours which serve to harmonise animals with their + general environment, we have to consider only those cases in + which the colour resemblance is more local or special in its + character.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Special or Local Colour Adaptations.</i></p> + + <p>This form of colour adaptation is generally manifested by + markings rather than by colour alone, and is extremely prevalent + both among insects and vertebrates, so that we shall be able to + notice only a few illustrative cases. Among our native birds we + have the snipe and woodcock, whose markings and tints strikingly + accord with the dead marsh vegetation among which they live; the + ptarmigan in its summer dress is mottled and tinted exactly like + the lichens which cover the stones of the higher mountains; while + young unfledged plovers are spotted so as exactly to resemble the + beach pebbles among which they crouch for protection, as + beautifully exhibited in one of the cases of British birds in the + Natural History Museum at South Kensington.</p> + + <p>In mammalia, we notice the frequency of rounded spots on + forest or tree haunting animals of large size, as the forest deer + and the forest cats; while those that frequent reedy or grassy + places are striped vertically, as the marsh antelopes and the + tiger. I had long been of opinion that the brilliant yellow and + black stripes of the tiger were adaptive, but have only recently + obtained proof that it is so. An experienced tiger-hunter, Major + Walford, states in a letter, that the haunts of the tiger are + invariably full of the long grass, dry and pale yellow for at + least nine months of the year, which covers the ground wherever + there is water in the rainy season, and he adds: "I once, while + following up a wounded tiger, failed for at least a minute to see + him under a tree in grass at a distance of about twenty + yards—jungle open—but the natives saw him, and I + eventually made him out well enough to shoot him, but even then I + could not see at what part of him I was aiming. There can be no + doubt whatever that the colour of both the tiger and the panther + renders them almost invisible, especially in a strong blaze of + light, when among grass, and one does not seem to notice stripes + or spots till they are dead." It is the black shadows of the + vegetation that <a name="Page_200" id="Page_200"></a>assimilate + with the black stripes of the tiger; and, in like manner, the + spotty shadows of leaves in the forest so harmonise with the + spots of ocelots, jaguars, tiger-cats, and spotted deer as to + afford them a very perfect concealment.</p> + + <p>In some cases the concealment is effected by colours and + markings which are so striking and peculiar that no one who had + not seen the creature in its native haunts would imagine them to + be protective. An example of this is afforded by the banded fruit + pigeon of Timor, whose pure white head and neck, black wings and + back, yellow belly, and deeply-curved black band across the + breast, render it a very handsome and conspicuous bird. Yet this + is what Mr. H.O. Forbes says of it: "On the trees the + white-headed fruit pigeon (Ptilopus cinctus) sate motionless + during the heat of the day in numbers, on well-exposed branches; + but it was with the utmost difficulty that I or my sharp-eyed + native servant could ever detect them, even in trees where we + knew they were sitting."<a name="FNanchor_66_66" id= + "FNanchor_66_66"></a><a href="#Footnote_66_66" class= + "fnanchor">[66]</a> The trees referred to are species of + Eucalyptus which abound in Timor. They have whitish or yellowish + bark and very open foliage, and it is the intense sunlight + casting black curved shadows of one branch upon another, with the + white and yellow bark and deep blue sky seen through openings of + the foliage, that produces the peculiar combination of colours + and shadows to which the colours and markings of this bird have + become so closely assimilated.</p> + + <p>Even such brilliant and gorgeously coloured birds as the + sun-birds of Africa are, according to an excellent observer, + often protectively coloured. Mrs. M.E. Barber remarks that "A + casual observer would scarcely imagine that the highly varnished + and magnificently coloured plumage of the various species of + Noctarinea could be of service to them, yet this is undoubtedly + the case. The most unguarded moments of the lives of these birds + are those that are spent amongst the flowers, and it is then that + they are less wary than at any other time. The different species + of aloes, which blossom in succession, form the principal sources + of their winter supplies of food; and a legion of other gay + flowering plants in spring and summer, the aloe blossoms + especially, are all brilliantly coloured, and they harmonise + admirably with the gay plumage <a name="Page_201" id= + "Page_201"></a>of the different species of sun-birds. Even the + keen eye of a hawk will fail to detect them, so closely do they + resemble the flowers they frequent. The sun-birds are fully aware + of this fact, for no sooner have they relinquished the flowers + than they become exceedingly wary and rapid in flight, darting + arrow-like through the air and seldom remaining in exposed + situations. The black sun-bird (Nectarinea amethystina) is never + absent from that magnificent forest-tree, the 'Kaffir Boom' + (Erythrina caffra); all day long the cheerful notes of these + birds may be heard amongst its spreading branches, yet the + general aspect of the tree, which consists of a huge mass of + scarlet and purple-black blossoms without a single green leaf, + blends and harmonises with the colours of the black sun-bird to + such an extent that a dozen of them may be feeding amongst its + blossoms without being conspicuous, or even visible."<a name= + "FNanchor_67_67" id="FNanchor_67_67"></a><a href= + "#Footnote_67_67" class="fnanchor">[67]</a></p> + + <p>Some other cases will still further illustrate how the colours + of even very conspicuous animals may be adapted to their peculiar + haunts.</p> + + <p>The late Mr. Swinhoe says of the Kerivoula picta, which he + observed in Formosa: "The body of this bat was of an orange + colour, but the wings were painted with orange-yellow and black. + It was caught suspended, head downwards, on a cluster of the + fruit of the longan tree (Nephelium longanum). Now this tree is + an evergreen, and all the year round some portion of its foliage + is undergoing decay, the particular leaves being, in such a + stage, partially orange and black. This bat can, therefore, at + all seasons suspend from its branches and elude its enemies by + its resemblance to the leaves of the tree."<a name= + "FNanchor_68_68" id="FNanchor_68_68"></a><a href= + "#Footnote_68_68" class="fnanchor">[68]</a></p> + + <p>Even more curious is the case of the sloths—defenceless + animals which feed upon leaves, and hang from the branches of + trees with their back downwards. Most of the species have a + curious buff-coloured spot on the back, rounded or oval in shape + and often with a darker border, which seems placed there on + purpose to make them conspicuous; and this was a great puzzle to + naturalists, because the long coarse gray or greenish hair was + evidently like tree-moss and therefore protective. But an old + writer, Baron von Slack, in his <i>Voyage</i> <a name="Page_202" + id="Page_202"></a><i>to Surinam</i> (1810), had already explained + the matter. He says: "The colour and even the shape of the hair + are much like withered moss, and serve to hide the animal in the + trees, but particularly when it has that orange-coloured spot + between the shoulders and lies close to the tree; it looks then + exactly like a piece of branch where the rest has been broken + off, by which the hunters are often deceived." Even such a huge + animal as the giraffe is said to be perfectly concealed by its + colour and form when standing among the dead and broken trees + that so often occur on the outskirts of the thickets where it + feeds. The large blotch-like spots on the skin and the strange + shape of the head and horns, like broken branches, so tend to its + concealment that even the keen-eyed natives have been known to + mistake trees for giraffes or giraffes for trees.</p> + + <p>Innumerable examples of this kind of protective colouring + occur among insects; beetles mottled like the bark of trees or + resembling the sand or rock or moss on which they live, with + green caterpillars of the exact general tints of the foliage they + feed on; but there are also many cases of detailed imitation of + particular objects by insects that must be briefly + described.<a name="FNanchor_69_69" id= + "FNanchor_69_69"></a><a href="#Footnote_69_69" class= + "fnanchor">[69]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Protective Imitation of Particular Objects.</i></p> + + <p>The insects which present this kind of imitation most + perfectly are the Phasmidae, or stick and leaf insects. The + well-<a name="Page_203" id="Page_203"></a>known leaf-insects of + Ceylon and of Java, species of Phyllium, are so wonderfully + coloured and veined, with leafy expansions on the legs and + thorax, that not one person in ten can see them when resting on + the food-plant close beneath their eyes. Others resemble pieces + of stick with all the minutiae of knots and branches, formed by + the insects' legs, which are stuck out rigidly and + unsymmetrically. I have often been unable to distinguish between + one of these insects and a real piece of stick, till I satisfied + myself by touching it and found it to be alive. One species, + which was brought me in Borneo, was covered with delicate + semitransparent green foliations, exactly resembling the + hepaticae which cover pieces of rotten stick in the damp forests. + Others resemble dead leaves in all their varieties of colour and + form; and to show how perfect is the protection obtained and how + important it is to the possessors of it, the following incident, + observed by Mr. Belt in Nicaragua, is most instructive. + Describing the armies of foraging ants in the forest which devour + every insect they can catch, he says: "I was much surprised with + the behaviour of a green leaf-like locust. This insect stood + immovably among a host of ants, many of which ran over its legs + without ever discovering there was food within their reach. So + fixed was its instinctive knowledge that its safety depended on + its immovability, that it allowed me to pick it up and replace it + among the ants without making a single effort to escape. This + species closely resembles a green leaf."<a name="FNanchor_70_70" + id="FNanchor_70_70"></a><a href="#Footnote_70_70" class= + "fnanchor">[70]</a></p> + + <p>Caterpillars also exhibit a considerable amount of detailed + resemblance to the plants on which they live. Grass-feeders are + striped longitudinally, while those on ordinary leaves are always + striped obliquely. Some very beautiful protective resemblances + are shown among the caterpillars figured in Smith and Abbott's + <i>Lepidopterous Insects of Georgia</i>, a work published in the + early part of the century, before any theories of protection were + started. The plates in this work are most beautifully executed + from drawings made by Mr. Abbott, representing the insects, in + every case, on the plants which they frequented, and no reference + is made in the descriptions to the remarkable protective details + which appear upon the plates. We have, first, the larva of Sphinx + fuciformis feeding <a name="Page_204" id="Page_204"></a>on a + plant with linear grass-like leaves and small blue flowers; and + we find the insect of the same green as the leaves, striped + longitudinally in accordance with the linear leaves, and with the + head blue corresponding both in size and colour with the flowers. + Another species (Sphinx tersa) is represented feeding on a plant + with small red flowers situated in the axils of the leaves; and + the larva has a row of seven red spots, unequal in size, and + corresponding very closely with the colour and size of the + flowers. Two other figures of sphinx larvae are very curious. + That of Sphinx pampinatrix feeds on a wild vine (Vitis indivisa), + having green tendrils, and in this species the curved horn on the + tail is green, and closely imitates in its curve the tip of the + tendril. But in another species (Sphinx cranta), which feeds on + the fox-grape (Vitis vulpina), the horn is very long and red, + corresponding with the long red-tipped tendrils of the plant. + Both these larvae are green with oblique stripes, to harmonise + with the veined leaves of the vines; but a figure is also given + of the last-named species after it has done feeding, when it is + of a decided brown colour and has entirely lost its horn. This is + because it then descends to the ground to bury itself, and the + green colour and red horn would be conspicuous and dangerous; it + therefore loses both at the last moult. Such a change of colour + occurs in many species of caterpillars. Sometimes the change is + seasonal; and, in those which hibernate with us, the colour of + some species, which is brownish in autumn in adaptation to the + fading foliage, becomes green in spring to harmonise with the + newly-opened leaves at that season.<a name="FNanchor_71_71" id= + "FNanchor_71_71"></a><a href="#Footnote_71_71" class= + "fnanchor">[71]</a></p> + + <p>Some of the most curious examples of minute imitation are + afforded by the caterpillars of the geometer moths, which are + always brown or reddish, and resemble in form little twigs of the + plant on which they feed. They have the habit, when at rest, of + standing out obliquely from the branch, to which they hold on by + their hind pair of prolegs or claspers, and remain motionless for + hours. Speaking of these protective resemblances Mr. Jenner Weir + says: "After being thirty years an entomologist I was deceived + myself, and took out my pruning scissors to cut from a plum tree + a spur which I thought I had overlooked. This turned out to be + the larva <a name="Page_205" id="Page_205"></a>of a geometer two + inches long. I showed it to several members of my family, and + defined a space of four inches in which it was to be seen, but + none of them could perceive that it was a caterpillar."<a name= + "FNanchor_72_72" id="FNanchor_72_72"></a><a href= + "#Footnote_72_72" class="fnanchor">[72]</a></p> + + <p>One more example of a protected caterpillar must be given. Mr. + A. Everett, writing from Sarawak, Borneo, says: "I had a + caterpillar brought me, which, being mixed by my boy with some + other things, I took to be a bit of moss with two exquisite + pinky-white seed-capsules; but I soon saw that it moved, and + examining it more closely found out its real character: it is + covered with hair, with two little pink spots on the upper + surface, the general hue being more green. Its motions are very + slow, and when eating the head is withdrawn beneath a fleshy + mobile hood, so that the action of feeding does not produce any + movement externally. It was found in the limestone hills at + Busan, the situation of all others where mosses are most + plentiful and delicate, and where they partially clothe most of + the protruding masses of rock."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>How these Imitations have been Produced.</i></p> + + <p>To many persons it will seem impossible that such beautiful + and detailed resemblances as those now described—and these + are only samples of thousands that occur in all parts of the + world—can have been brought about by the preservation of + accidental useful variations. But this will not seem so + surprising if we keep in mind the facts set forth in our earlier + chapters—the rapid multiplication, the severe struggle for + existence, and the constant variability of these and all other + organisms. And, further, we must remember that these delicate + adjustments are the result of a process which has been going on + for millions of years, and that we now see the small percentage + of successes among the myriads of failures. From the very first + appearance of insects and their various kinds of enemies the need + of protection arose, and was usually most easily met by + modifications of colour. Hence, we may be sure that the earliest + leaf-eating insects acquired a green colour as one of the + necessities of their existence; and, as the species became + modified and specialised, <a name="Page_206" id= + "Page_206"></a>those feeding on particular species of plants + would rapidly acquire the peculiar tints and markings best + adapted to conceal them upon those plants. Then, every little + variation that, once in a hundred years perhaps, led to the + preservation of some larva which was thereby rather better + concealed than its fellows, would form the starting-point of a + further development, leading ultimately to that perfection of + imitation in details which now astonishes us. The researches of + Dr. Weismann illustrate this progressive adaptation. The very + young larvae of several species are green or yellowish without + any markings; they then, in subsequent moults, obtain certain + markings, some of which are often lost again before the larva is + fully grown. The early stages of those species which, like + elephant hawk-moths (Chaerocampa), have the anterior segments + elongated and retractile, with large eye-like spots to imitate + the head of a vertebrate, are at first like those of + non-retractile species, the anterior segments being as large as + the rest. After the first moult they become smaller, + comparatively; but it is only after the second moult that the + ocelli begin to appear, and these are not fully defined till + after the third moult. This progressive development of the + individual—the ontogeny—gives us a clue to the + ancestral development of the whole race—the phylogeny; and + we are enabled to picture to ourselves the very slow and gradual + steps by which the existing perfect adaptation has been brought + about. In many larvae great variability still exists, and in some + there are two or more distinctly-coloured forms—usually a + dark and a light or a brown and a green form. The larva of the + humming-bird hawk-moth (Macroglossa stellatarum) varies in this + manner, and Dr. Weismann raised five varieties from a batch of + eggs from one moth. It feeds on species of bedstraw (Galium verum + and G. mollugo), and as the green forms are less abundant than + the brown, it has probably undergone some recent change of + food-plant or of habits which renders brown the more protective + colour.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Special Protective Colouring of Butterflies.</i></p> + + <p>We will now consider a few cases of special protective + colouring in the perfect butterfly or moth. Mr. Mansel Weale + states that in South Africa there is a great prevalence <a name= + "Page_207" id="Page_207"></a>of white and silvery foliage or + bark, sometimes of dazzling brilliancy, and that many insects and + their larvae have brilliant silvery tints which are protective, + among them being three species of butterflies whose undersides + are silvery, and which are thus effectually protected when at + rest.<a name="FNanchor_73_73" id="FNanchor_73_73"></a><a href= + "#Footnote_73_73" class="fnanchor">[73]</a> A common African + butterfly (Aterica meleagris) always settles on the ground with + closed wings, which so closely resemble the soil of the district + that it can with difficulty be seen, and the colour varies with + the soil in different localities. Thus specimens from Senegambia + were dull brown, the soil being reddish sand and iron-clay; those + from Calabar and Cameroons were light brown with numerous small + white spots, the soil of those countries being light brown clay + with small quartz pebbles; while in other localities where the + colours of the soil were more varied the colours of the butterfly + varied also. Here we have variation in a single species which has + become specialised in certain areas to harmonise with the colour + of the soil.<a name="FNanchor_74_74" id= + "FNanchor_74_74"></a><a href="#Footnote_74_74" class= + "fnanchor">[74]</a></p> + + <p>Many butterflies, in all parts of the world, resemble dead + leaves on their under side, but those in which this form of + protection is carried to the greatest perfection are the species + of the Eastern genus Kallima. In India K. inachis, and in the + larger Malay islands K. paralekta, are very common. They are + rather large and showy butterflies, orange and bluish on the + upper side, with a very rapid flight, and frequenting dry + forests. Their habit is to settle always where there is some dead + or decaying foliage, and the shape and colour of the wings (on + the under surface), together with the attitude of the insect, is + such as to produce an absolutely perfect imitation of a dead + leaf. This is effected by the butterfly always settling on a + twig, with the short tail of the hind wings just touching it and + forming the leaf-stalk. From this a dark curved line runs across + to the elongated tip of the upper wings, imitating the midrib, on + both sides of which are oblique lines, formed partly by the + nervures and partly by markings, which give the effect of the + usual veining of a leaf. The head and antennae fit exactly + between the closed upper wings so as not to interfere with the + outline, <a name="Page_208" id="Page_208"></a>which has just that + amount of irregular curvature that is seen in dry and withered + leaves. The colour is very remarkable for its extreme amount of + variability, from deep reddish-brown to olive or pale yellow, + hardly two specimens being exactly alike, but all coming within + the range of colour of leaves in various stages of decay. Still + more curious is the fact that the paler wings, which imitate + leaves most decayed, are usually covered with small black dots, + often gathered into circular groups, and so exactly resembling + the minute fungi on decaying leaves that it is hard at first to + believe that the insects themselves are not attacked by some such + fungus. The concealment produced by this wonderful imitation is + most complete, and in Sumatra I have often seen one enter a bush + and then disappear like magic. Once I was so fortunate as to see + the exact spot on which the insect settled; but even then I lost + sight of it for some time, and only after a persistent search + discovered that it was close before my eyes.<a name= + "FNanchor_75_75" id="FNanchor_75_75"></a><a href= + "#Footnote_75_75" class="fnanchor">[75]</a> Here we have a kind + of imitation, which is very common in a less developed form, + carried to extreme perfection, with the result that the species + is very abundant over a considerable area of country.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Protective Resemblance among Marine Animals.</i></p> + + <p>Among marine animals this form of protection is very common. + Professor Moseley tells us that all the inhabitants of the + Gulf-weed are most remarkably coloured, for purposes of + protection and concealment, exactly like the weed itself. "The + shrimps and crabs which swarm in the weed are of exactly the same + shade of yellow as the weed, and have white markings upon their + bodies to represent the patches of Membranipora. The small fish, + Antennarius, is in the same way weed-colour with white spots. + Even a Planarian worm, which lives in the weed, is similarly + yellow-coloured, and also a mollusc, Scyllaea pelagica." The same + writer tells us that "a number of little crabs found clinging to + the floats of the blue-shelled mollusc, Ianthina, were all + coloured of a corresponding blue for concealment."<a name= + "FNanchor_76_76" id="FNanchor_76_76"></a><a href= + "#Footnote_76_76" class="fnanchor">[76]</a></p> + + <p><a name="Page_209" id="Page_209"></a>Professor E.S. Morse of + Salem, Mass., found that most of the New England marine mollusca + were protectively coloured; instancing among others a little red + chiton on rocks clothed with red calcareous algae, and Crepidula + plana, living within the apertures of the shells of larger + species of Gasteropods and of a pure white colour corresponding + to its habitat, while allied species living on seaweed or on the + outside of dark shells were dark brown.<a name="FNanchor_77_77" + id="FNanchor_77_77"></a><a href="#Footnote_77_77" class= + "fnanchor">[77]</a> A still more interesting case has been + recorded by Mr. George Brady. He says: "Amongst the Nullipore + which matted together the laminaria roots in the Firth of Clyde + were living numerous small starfishes (Ophiocoma bellis) which, + except when their writhing movements betrayed them, were quite + undistinguishable from the calcareous branches of the alga; their + rigid angularly twisted rays had all the appearance of the + coralline, and exactly assimilated to its dark purple colour, so + that though I held in my hand a root in which were half a dozen + of the starfishes, I was really unable to detect them until + revealed by their movements."<a name="FNanchor_78_78" id= + "FNanchor_78_78"></a><a href="#Footnote_78_78" class= + "fnanchor">[78]</a></p> + + <p>These few examples are sufficient to show that the principle + of protective coloration extends to the ocean as well as over the + earth; and if we consider how completely ignorant we are of the + habits and surroundings of most marine animals, it may well + happen that many of the colours of tropical fishes, which seem to + us so strange and so conspicuous, are really protective, owing to + the number of equally strange and brilliant forms of corals, + sea-anemones, sponges, and seaweeds among which they live.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Protection by Terrifying Enemies.</i></p> + + <p>A considerable number of quite defenceless insects obtain + protection from some of their enemies by having acquired a + resemblance to dangerous animals, or by some threatening or + unusual appearance. This is obtained either by a modification of + shape, of habits, of colour, or of all combined. The simplest + form of this protection is the aggressive attitude of the + caterpillars of the Sphingidae, the forepart of the body <a name= + "Page_210" id="Page_210"></a>being erected so as to produce a + rude resemblance to the figure of a sphinx, hence the name of the + family. The protection is carried further by those species which + retract the first three segments and have large ocelli on each + side of the fourth segment, thus giving to the caterpillar, when + the forepart of its body is elevated, the appearance of a snake + in a threatening attitude.</p> + + <p>The blood-red forked tentacle, thrown out of the neck of the + larvae of the genus Papilio when alarmed, is, no doubt, a + protection against the attacks of ichneumons, and may, perhaps, + also frighten small birds; and the habit of turning up the tail + possessed by the harmless rove-beetles (Staphylinidae), giving + the idea that they can sting, has, probably, a similar use. Even + an unusual angular form, like a crooked twig or inorganic + substance, may be protective; as Mr. Poulton thinks is the case + with the curious caterpillar of Notodonta ziczac, which, by means + of a few slight protuberances on its body, is able to assume an + angular and very unorganic-looking appearance. But perhaps the + most perfect example of this kind of protection is exhibited by + the large caterpillar of the Royal Persimmon moth (Bombyx regia), + a native of the southern states of North America, and known there + as the "Hickory-horned devil." It is a large green caterpillar, + often six inches long, ornamented with an immense crown of + orange-red tubercles, which, if disturbed, it erects and shakes + from side to side in a very alarming manner. In its native + country the negroes believe it to be as deadly as a rattlesnake, + whereas it is perfectly innocuous. The green colour of the body + suggests that its ancestors were once protectively coloured; but, + growing too large to be effectually concealed, it acquired the + habit of shaking its head about in order to frighten away its + enemies, and ultimately developed the crown of tentacles as an + addition to its terrifying powers. This species is beautifully + figured in Abbott and Smith's <i>Lepidopterous Insects of + Georgia</i>.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Alluring Coloration.</i></p> + + <p>Besides those numerous insects which obtain protection through + their resemblance to the natural objects among which they live, + there are some whose disguise is not used for <a name="Page_211" + id="Page_211"></a>concealment, but as a direct means of securing + their prey by attracting them within the enemy's reach. Only a + few cases of this kind of coloration have yet been observed, + chiefly among spiders and mantidae; but, no doubt, if attention + were given to the subject in tropical countries, many more would + be discovered. Mr. H.O. Forbes has described a most interesting + example of this kind of simulation in Java. While pursuing a + large butterfly through the jungle, he was stopped by a dense + bush, on a leaf of which he observed one of the skipper + butterflies sitting on a bird's dropping. "I had often," he says, + "observed small Blues at rest on similar spots on the ground, and + have wondered what such a refined and beautiful family as the + Lycaenidae could find to enjoy, in food apparently so incongruous + for a butterfly. I approached with gentle steps, but ready net, + to see if possible how the present species was engaged. It + permitted me to get quite close, and even to seize it between my + fingers; to my surprise, however, part of the body remained + behind, adhering as I thought to the excreta. I looked closely, + and finally touched with my finger the excreta to find if it were + glutinous. To my delighted astonishment I found that my eyes had + been most perfectly deceived, and that what seemed to be the + excreta was a most artfully coloured spider, lying on its back + with its feet crossed over and closely adpressed to the body." + Mr. Forbes then goes on to describe the exact appearance of such + excreta, and how the various parts of the spider are coloured to + produce the imitation, even to the liquid portion which usually + runs a little down the leaf. This is exactly imitated by a + portion of the thin web which the spider first spins to secure + himself firmly to the leaf; thus producing, as Mr. Forbes + remarks, a living bait for butterflies and other insects so + artfully contrived as to deceive a pair of human eyes, even when + intently examining it.<a name="FNanchor_79_79" id= + "FNanchor_79_79"></a><a href="#Footnote_79_79" class= + "fnanchor">[79]</a></p> + + <p>A native species of spider (Thomisus citreus) exhibits a + somewhat similar alluring protection by its close resemblance to + buds of the wayfaring tree, Viburnum lantana. It is pure + creamy-white, the abdomen exactly resembling in shape and colour + the unopened buds of the flowers among which it takes <a name= + "Page_212" id="Page_212"></a>its station; and it has been seen to + capture flies which came to the flowers.</p> + + <p>But the most curious and beautiful case of alluring protection + is that of a wingless Mantis in India, which is so formed and + coloured as to resemble a pink orchis or some other fantastic + flower. The whole insect is of a bright pink colour, the large + and oval abdomen looking like the labellum of an orchid. On each + side, the two posterior legs have immensely dilated and flattened + thighs which represent the petals of a flower, while the neck and + forelegs imitate the upper sepal and column of an orchid. The + insect rests motionless, in this symmetrical attitude, among + bright green foliage, being of course very conspicuous, but so + exactly resembling a flower that butterflies and other insects + settle upon it and are instantly captured. It is a living trap, + baited in the most alluring manner to catch the unwary + flower-haunting insects.<a name="FNanchor_80_80" id= + "FNanchor_80_80"></a><a href="#Footnote_80_80" class= + "fnanchor">[80]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Coloration of Birds' Eggs.</i></p> + + <p>The colours of birds' eggs have long been a difficulty on the + theory of adaptive coloration, because, in so many cases it has + not been easy to see what can be the use of the particular + colours, which are often so bright and conspicuous that they seem + intended to attract attention rather than to be concealed. A more + careful consideration of the subject in all its bearings shows, + however, that here too, in a great number of cases, we have + examples of protective coloration. When, therefore, we cannot see + the meaning of the colour, we may suppose that it has been + protective in some ancestral form, and, not being hurtful, has + persisted under changed conditions which rendered the protection + needless.</p> + + <p>We may divide all eggs, for our present purpose, into two + <a name="Page_213" id="Page_213"></a>great divisions; those which + are white or nearly so, and those which are distinctly coloured + or spotted. Egg-shells being composed mainly of carbonate of + lime, we may assume that the primitive colour of birds' eggs was + white, a colour that prevails now among the other egg-bearing + vertebrates—lizards, crocodiles, turtles, and snakes; and + we might, therefore, expect that this colour would continue where + its presence had no disadvantages. Now, as a matter of fact, we + find that in all the groups of birds which lay their eggs in + concealed places, whether in holes of trees or in the ground, or + in domed or covered nests, the eggs are either pure white or of + very pale uniform coloration. Such is the case with kingfishers, + bee-eaters, penguins, and puffins, which nest in holes in the + ground; with the great parrot family, the woodpeckers, the + rollers, hoopoes, trogons, owls, and some others, which build in + holes in trees or other concealed places; while martins, wrens, + willow-warblers, and Australian finches, build domed or covered + nests, and usually have white eggs.</p> + + <p>There are, however, many other birds which lay their white + eggs in open nests; and these afford some very interesting + examples of the varied modes by which concealment may be + obtained. All the duck tribe, the grebes, and the pheasants + belong to this class; but these birds all have the habit of + covering their eggs with dead leaves or other material whenever + they leave the nest, so as effectually to conceal them. Other + birds, as the short-eared owl, the goatsucker, the partridge, and + some of the Australian ground pigeons, lay their white or pale + eggs on the bare soil; but in these cases the birds themselves + are protectively coloured, so that, when sitting, they are almost + invisible; and they have the habit of sitting close and almost + continuously, thus effectually concealing their eggs.</p> + + <p>Pigeons and doves offer a very curious case of the protection + of exposed eggs. They usually build very slight and loose nests + of sticks and twigs, so open that light can be seen through them + from below, while they are generally well concealed by foliage + above. Their eggs are white and shining; yet it is a difficult + matter to discover, from beneath, whether there are eggs in the + nest or not, while they are well hidden by the thick foliage + above. The Australian podargi<a name="Page_214" id= + "Page_214"></a>huge goatsuckers—build very similar nests, + and their white eggs are protected in the same manner. Some large + and powerful birds, as the swans, herons, pelicans, cormorants, + and storks, lay white eggs in open nests; but they keep careful + watch over them, and are able to drive away intruders. On the + whole, then, we see that, while white eggs are conspicuous, and + therefore especially liable to attack by egg-eating animals, they + are concealed from observation in many and various ways. We may, + therefore, assume that, in cases where there seems to be no such + concealment, we are too ignorant of the whole of the conditions + to form a correct judgment.</p> + + <p>We now come to the large class of coloured or richly spotted + eggs, and here we have a more difficult task, though many of them + decidedly exhibit protective tints or markings. There are two + birds which nest on sandy shores—the lesser tern and the + ringed plover,—and both lay sand-coloured eggs, the former + spotted so as to harmonise with coarse shingle, the latter + minutely speckled like fine sand, which are the kinds of ground + the two birds choose respectively for their nests. "The common + sandpipers' eggs assimilate so closely with the tints around them + as to make their discovery a matter of no small difficulty, as + every oologist can testify who has searched for them. The pewits' + eggs, dark in ground colour and boldly marked, are in strict + harmony with the sober tints of moor and fallow, and on this + circumstance alone their concealment and safety depend. The + divers' eggs furnish another example of protective colour; they + are generally laid close to the water's edge, amongst drift and + shingle, where their dark tints and black spots conceal them by + harmonising closely with surrounding objects. The snipes and the + great army of sandpipers furnish innumerable instances of + protectively coloured eggs. In all the instances given the + sitting-bird invariably leaves the eggs uncovered when it quits + them, and consequently their safety depends solely on the colours + which adorn them."<a name="FNanchor_81_81" id= + "FNanchor_81_81"></a><a href="#Footnote_81_81" class= + "fnanchor">[81]</a> The wonderful range of colour and marking in + the eggs of the guillemot may be imputed to the inaccessible + rocks on which <a name="Page_215" id="Page_215"></a>it breeds, + giving it complete protection from enemies. Thus the pale or + bluish ground colour of the eggs of its allies, the auks and + puffins, has become intensified and blotched and spotted in the + most marvellous variety of patterns, owing to there being no + selective agency to prevent individual variation having full + sway.</p> + + <p>The common black coot (Fulica atra) has eggs which are + coloured in a specially protective manner. Dr. William Marshall + writes, that it only breeds in certain localities where a large + water reed (Phragmites arundinacea) abounds. The eggs of the coot + are stained and spotted with black on a yellowish-gray ground, + and the dead leaves of the reed are of the same colour, and are + stained black by small parasitic fungi of the Uredo family; and + these leaves form the bed on which the eggs are laid. The eggs + and the leaves agree so closely in colour and markings that it is + a difficult thing to distinguish the eggs at any distance. It is + to be noted that the coot never covers up its eggs, as its ally + the moor-hen usually does.</p> + + <p>The beautiful blue or greenish eggs of the hedge-sparrow, the + song-thrush, and sometimes those of the blackbird, seem at first + sight especially calculated to attract attention, but it is very + doubtful whether they are really so conspicuous when seen at a + little distance among their usual surroundings. For the nests of + these birds are either in evergreens, as holly or ivy, or + surrounded by the delicate green tints of our early spring + vegetation, and may thus harmonise very well with the colours + around them. The great majority of the eggs of our smaller birds + are so spotted or streaked with brown or black on variously + tinted grounds that, when lying in the shadow of the nest and + surrounded by the many colours and tints of bark and moss, of + purple buds and tender green or yellow foliage, with all the + complex glittering lights and mottled shades produced among these + by the spring sunshine and by sparkling raindrops, they must have + a quite different aspect from that which they possess when we + observe them torn from their natural surroundings. We have here, + probably, a similar case of general protective harmony to that of + the green caterpillars with beautiful white or purple bands and + spots, which, though gaudily conspicuous when seen alone, + <a name="Page_216" id="Page_216"></a>become practically invisible + among the complex lights and shadows of the foliage they feed + upon.</p> + + <p>In the case of the cuckoo, which lays its eggs in the nests of + a variety of other birds, the eggs themselves are subject to + considerable variations of colour, the most common type, however, + resembling those of the pipits, wagtails, or warblers, in whose + nests they are most frequently laid. It also often lays in the + nest of the hedge-sparrow, whose bright blue eggs are usually not + at all nearly matched, although they are sometimes said to be so + on the Continent. It is the opinion of many ornithologists that + each female cuckoo lays the same coloured eggs, and that it + usually chooses a nest the owners of which lay somewhat similar + eggs, though this is by no means universally the case. Although + birds which have cuckoos' eggs imposed upon them do not seem to + neglect them on account of any difference of colour, yet they + probably do so occasionally; and if, as seems probable, each + bird's eggs are to some extent protected by their harmony of + colour with their surroundings, the presence of a larger and very + differently coloured egg in the nest might be dangerous, and lead + to the destruction of the whole set. Those cuckoos, therefore, + which most frequently placed their eggs among the kinds which + they resembled, would in the long run leave most progeny, and + thus the very frequent accord in colour might have been brought + about.</p> + + <p>Some writers have suggested that the varied colours of birds' + eggs are primarily due to the effect of surrounding coloured + objects on the female bird during the period preceding + incubation; and have expended much ingenuity in suggesting the + objects that may have caused the eggs of one bird to be blue, + another brown, and another pink.<a name="FNanchor_82_82" id= + "FNanchor_82_82"></a><a href="#Footnote_82_82" class= + "fnanchor">[82]</a> But no evidence has been presented to prove + that any effects whatever are produced by this cause, while there + seems no difficulty in accounting for the facts by individual + variability and the action of natural selection. The changes that + occur in the conditions of existence of birds must sometimes + render the concealment less perfect than it may once have been; + and when any danger arises from this cause, it may be met either + <a name="Page_217" id="Page_217"></a>by some change in the colour + of the eggs, or in the structure or position of the nest, or by + the increased care which the parents bestow upon the eggs. In + this way the various divergences which now so often puzzle us may + have arisen.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Colour as a Means of Recognition.</i></p> + + <p>If we consider the habits and life-histories of those animals + which are more or less gregarious, comprising a large proportion + of the herbivora, some carnivora, and a considerable number of + all orders of birds, we shall see that a means of ready + recognition of its own kind, at a distance or during rapid + motion, in the dusk of twilight or in partial cover, must be of + the greatest advantage and often lead to the preservation of + life. Animals of this kind will not usually receive a stranger + into their midst. While they keep together they are generally + safe from attack, but a solitary straggler becomes an easy prey + to the enemy; it is, therefore, of the highest importance that, + in such a case, the wanderer should have every facility for + discovering its companions with certainty at any distance within + the range of vision.</p> + + <p>Some means of easy recognition must be of vital importance to + the young and inexperienced of each flock, and it also enables + the sexes to recognise their kind and thus avoid the evils of + infertile crosses; and I am inclined to believe that its + necessity has had a more widespread influence in determining the + diversities of animal coloration than any other cause whatever. + To it may probably be imputed the singular fact that, whereas + bilateral symmetry of coloration is very frequently lost among + domesticated animals, it almost universally prevails in a state + of nature; for if the two sides of an animal were unlike, and the + diversity of coloration among domestic animals occurred in a wild + state, easy recognition would be impossible among numerous + closely allied forms.<a name="FNanchor_83_83" id= + "FNanchor_83_83"></a><a href="#Footnote_83_83" class= + "fnanchor">[83]</a> <a name="Page_218" id="Page_218"></a>The + wonderful diversity of colour and of marking that prevails, + especially in birds and insects, may be due to the fact that one + of the first needs of a new species would be, to keep separate + from its nearest allies, and this could be most readily done by + some easily seen external mark of difference. A few illustrations + will serve to show how this principle acts in nature.</p> + + <p>My attention was first called to the subject by a remark of + Mr. Darwin's that, though, "the hare on her form is a familiar + instance of concealment through colour, yet the principle partly + fails in a closely allied species, the rabbit; for when running + to its burrow it is made conspicuous to the sportsman, and no + doubt to all beasts of prey, by its upturned white tail."<a name= + "FNanchor_84_84" id="FNanchor_84_84"></a><a href= + "#Footnote_84_84" class="fnanchor">[84]</a> But a little + consideration of the habits of the animal will show that the + white upturned tail is of the greatest value, and is really, as + it has been termed by a writer in <i>The Field</i>, a "signal + flag of danger." For the rabbit is usually a crepuscular animal, + feeding soon after sunset or on moonlight nights. When disturbed + or alarmed it makes for its burrow, and the white upturned tails + of those in front serve as guides and signals to those more + remote from home, to the young and the feeble; and thus each + following the one or two before it, all are able with the least + possible delay to regain a place of comparative safety. The + apparent danger, therefore, becomes a most important means of + security.</p> + + <p>The same general principle enables us to understand the + singular, and often conspicuous, markings on so many gregarious + herbivora which are yet, on the whole, protectively coloured. + Thus, the American prong-buck has a white patch behind and a + black muzzle. The Tartarian antelope, the Ovis poli of High Asia, + the Java wild ox, several species of deer, and a large number of + antelopes have a similar conspicuous white patch behind, which, + in contrast to the dusky body, must enable them to be seen and + followed from a distance by their fellows. Where there are many + species of nearly the same general size and form inhabiting the + same region—as with the antelopes <a name="Page_219" id= + "Page_219"></a>of Africa—we find many distinctive markings + of a similar kind. The gazelles have variously striped and banded + faces, besides white patches behind and on the flanks, as shown + in the woodcut. The spring-bok has a white patch on the face and + one on the sides, with a curiously distinctive white stripe above + the tail, which is nearly concealed when the animal is at rest by + a fold of skin but comes into full view when it is in motion, + being thus quite analogous to the upturned white tail of the + rabbit. In the pallah the white rump-mark is bordered with black, + and the peculiar shape of the horns distinguishes it when seen + from the front. The sable-antelope, the gems-bok, the oryx, the + hart-beest, the bonte-bok, and the addax have each peculiar white + markings; and they are besides characterised by horns so + remarkably different in each species and so conspicuous, that it + seems probable that the peculiarities in length, twist, and + curvature have been differentiated for the purpose of + recognition, rather than for any speciality of defence in species + whose general habits are so similar.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig18" id="fig18"></a> <img src="images/fig18.jpg" + width="400" height="468" alt= + "FIG. 18.—Gazella soemmerringi." title= + "FIG. 18.—Gazella soemmerringi." /> <b>FIG. + 18.—Gazella soemmerringi.</b> + </div> + + <p><a name="Page_220" id="Page_220"></a>It is interesting to note + that these markings for recognition are very slightly developed + in the antelopes of the woods and marshes. Thus, the grys-bok is + nearly uniform in colour, except the long black-tipped ears; and + it frequents the wooded mountains. The duyker-bok and the + rhoode-bok are wary bush-haunters, and have no marks but the + small white patch behind. The wood-haunting bosch-bok goes in + pairs, and has hardly any distinctive marks on its dusky chestnut + coat, but the male alone is horned. The large and handsome koodoo + frequents brushwood, and its vertical white stripes are no doubt + protective, while its magnificent spiral horns afford easy + recognition. The eland, which is an inhabitant of the open + country, is uniformly coloured, being sufficiently recognisable + by its large size and distinctive form; but the Derbyan eland is + a forest animal, and has a protectively striped coat. In like + manner, the fine Speke's antelope, which lives entirely in the + swamps and among reeds, has pale vertical stripes on the sides + (protective), with white markings on face and breast for + recognition. An inspection of the figures of antelopes and other + animals in Wood's <i>Natural History</i>, or in other illustrated + works, will give a better idea of the peculiarities of + recognition markings than any amount of description.</p> + + <p>Other examples of such coloration are to be seen in the dusky + tints of the musk-sheep and the reindeer, to whom recognition at + a distance on the snowy plains is of more importance than + concealment from their few enemies. The conspicuous stripes and + bands of the zebra and the quagga are probably due to the same + cause, as may be the singular crests and face-marks of several of + the monkeys and lemurs.<a name="FNanchor_85_85" id= + "FNanchor_85_85"></a><a href="#Footnote_85_85" class= + "fnanchor">[85]</a></p> + + <div class="figcenter" style="width: 500px;"> + <a name="fig19" id="fig19"></a> <a name="Page_221" id= + "Page_221"></a><img src="images/fig19.jpg" width="500" height= + "300" alt= + "FIG. 19—Recognition marks of three African plovers." + title= + "FIG. 19—Recognition marks of three African plovers." /> + <b>FIG. 19—Recognition marks of three African + plovers.</b> + </div> + + <p><a name="Page_222" id="Page_222"></a>Among birds, these + recognition marks are especially numerous and suggestive. Species + which inhabit open districts are usually protectively coloured; + but they generally possess some distinctive markings for the + purpose of being easily recognised by their kind, both when at + rest and during flight. Such are, the white bands or patches on + the breast or belly of many birds, but more especially the head + and neck markings in the form of white or black caps, collars, + eye-marks or frontal patches, examples of which are seen in the + three species of African plovers figured on page 221.</p> + + <p>Recognition marks during flight are very important for all + birds which congregate in flocks or which migrate together; and + it is essential that, while being as conspicuous as possible, the + marks shall not interfere with the general protective tints of + the species when at rest. Hence they usually consist of + well-contrasted markings on the wings and tail, which are + concealed during repose but become fully visible when the bird + takes flight. Such markings are well seen in our four British + species of shrikes, each having quite different white marks on + the expanded wings and on the tail feathers; and the same is the + case with our three species of Saxicola—the stone-chat, + whin-chat, and wheat-ear—which are thus easily recognisable + on the wing, especially when seen from above, as they would be by + stragglers looking out for their companions. The figures + opposite, of the wings of two African species of stone-curlew + which are sometimes found in the same districts, well illustrates + these specific recognition marks. Though not very greatly + different to our eyes, they are no doubt amply so to the sharp + vision of the birds themselves.</p> + + <p>Besides the white patches on the primaries here shown, the + secondary feathers are, in some cases, so coloured as to afford + very distinctive markings during flight, as seen in the central + secondary quills of two African coursers (Fig. 21).</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig20" id="fig20"></a> <img src="images/fig20.jpg" + width="400" height="560" alt= + "FIG. 20.—Oedicnemus vermiculatus (above). Oe. senegalensis (below)." + title= + "FIG. 20.—Oedicnemus vermiculatus (above). Oe. senegalensis (below)." /> + <b>FIG. 20.—Oedicnemus vermiculatus (above). Oe. + senegalensis (below).</b> + </div> + + <p>Most characteristic of all, however, are the varied markings + of the outer tail-feathers, whose purpose is so well shown by + their being almost always covered during repose by the two middle + feathers, which are themselves quite unmarked and protectively + tinted like the rest of the upper surface of the body. The + figures of the expanded tails of two species of East Asiatic + snipe, whose geographical ranges overlap each other, <a name= + "Page_223" id="Page_223"></a><a name="Page_224" id= + "Page_224"></a>will serve to illustrate this difference; which is + frequently much greater and modified in an endless variety of + ways (Fig. 22).</p> + + <p>Numbers of species of pigeons, hawks, finches, warblers, + ducks, and innumerable other birds possess this class of + markings; and they correspond so exactly in general character + with those of the mammalia, already described, that we cannot + doubt they serve a similar purpose.<a name="FNanchor_86_86" id= + "FNanchor_86_86"></a><a href="#Footnote_86_86" class= + "fnanchor">[86]</a></p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig21" id="fig21"></a> <img src="images/fig21.jpg" + width="400" height="532" alt="FIG. 21.—Secondary quills." + title="FIG. 21.—Secondary quills." /> <b>FIG. + 21.—Secondary quills.</b> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig22" id="fig22"></a> <img src="images/fig22.jpg" + width="400" height="558" alt= + "FIG. 22.—Scolopax megala (upper). S. stenura (lower)." + title= + "FIG. 22.—Scolopax megala (upper). S. stenura (lower)." /> + <b>FIG. 22.—Scolopax megala (upper). S. stenura + (lower).</b> + </div> + + <p>Those birds which are inhabitants of tropical forests, and + which need recognition marks that shall be at all times visible + among the dense foliage, and not solely or chiefly during flight, + have usually small but brilliant patches of colour <a name= + "Page_225" id="Page_225"></a><a name="Page_226" id= + "Page_226"></a>on the head or neck, often not interfering with + the generally protective character of their plumage. Such are the + bright patches of blue, red, or yellow, by which the usually + green Eastern barbets are distinguished; and similar bright + patches of colour characterise the separate species of small + green fruit-doves. To this necessity for specialisation in + colour, by which each bird may easily recognise its kind, is + probably due that marvellous variety in the peculiar beauties of + some groups of birds. The Duke of Argyll, speaking of the humming + birds, made the objection that "A crest of topaz is no better in + the struggle for existence than a crest of sapphire. A frill + ending in spangles of the emerald is no better in the battle of + life than a frill ending in spangles of the ruby. A tail is not + affected for the purposes of flight, whether its marginal or its + central feathers are decorated with white;" and he goes on to + urge that mere beauty and variety for their own sake are the only + causes of these differences. But, on the principles here + suggested, the divergence itself is useful, and must have been + produced <i>pari passu</i> with the structural differences on + which the differentiation of species depends; and thus we have + explained the curious fact that prominent differences of colour + often distinguish species otherwise very closely allied to each + other.</p> + + <p>Among insects, the principle of distinctive coloration for + recognition has probably been at work in the production of the + wonderful diversity of colour and marking we find everywhere, + more especially among the butterflies and moths; and here its + chief function may have been to secure the pairing together of + individuals of the same species. In some of the moths this has + been secured by a peculiar odour, which attracts the males to the + females from a distance; but there is no evidence that this is + universal or even general, and among butterflies, especially, the + characteristic colour and marking, aided by size and form, afford + the most probable means of recognition. That this is so is shown + by the fact that "the common white butterfly often flies down to + a bit of paper on the ground, no doubt mistaking it for one of + its own species;" while, according to Mr. Collingwood, in the + Malay Archipelago, "a dead butterfly pinned upon a conspicuous + twig will often arrest an insect of the same species in its + headlong flight, and <a name="Page_227" id="Page_227"></a>bring + it down within easy reach of the net, especially if it be of the + opposite sex."<a name="FNanchor_87_87" id= + "FNanchor_87_87"></a><a href="#Footnote_87_87" class= + "fnanchor">[87]</a> In a great number of insects, no doubt, form, + motions, stridulating sounds, or peculiar odours, serve to + distinguish allied species from each other, and this must be + especially the case with nocturnal insects, or with those whose + colours are nearly uniform and are determined by the need of + protection; but by far the larger number of day-flying and active + insects exhibit varieties of colour and marking, forming the most + obvious distinction between allied species, and which have, + therefore, in all probability been acquired in the process of + differentiation for the purpose of checking the intercrossing of + closely allied forms.<a name="FNanchor_88_88" id= + "FNanchor_88_88"></a><a href="#Footnote_88_88" class= + "fnanchor">[88]</a></p> + + <p>Whether this principle extends to any of the less highly + organised animals is doubtful, though it may perhaps have + affected the higher mollusca. But in marine animals it seems + probable that the colours, however beautiful, varied, and + brilliant they may often be, are in most cases protective, + assimilating them to the various bright-coloured seaweeds, or to + some other animals which it is advantageous for them to + imitate.<a name="FNanchor_89_89" id="FNanchor_89_89"></a><a href= + "#Footnote_89_89" class="fnanchor">[89]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Summary of the Preceding Exposition.</i></p> + + <p>Before proceeding to discuss some of the more recondite + phenomena of animal coloration, it will be well to consider for a + moment the extent of the ground we have already covered. + Protective coloration, in some of its varied forms, has not + improbably modified the appearance of one-half of the animals + living on the globe. The white of arctic animals, the yellowish + tints of the desert forms, the dusky hues of crepuscular and + nocturnal species, the transparent or bluish tints of oceanic + creatures, represent a vast host in themselves; but we have an + equally numerous body whose tints are adapted to tropical + foliage, to the bark of trees, or to the soil <a name="Page_228" + id="Page_228"></a>or dead leaves on or among which they + habitually live. Then we have the innumerable special adaptations + to the tints and forms of leaves, or twigs, or flowers; to bark + or moss; to rock or pebble; by which such vast numbers of the + insect tribes obtain protection; and we have seen that these + various forms of coloration are equally prevalent in the waters + of the seas and oceans, and are thus coextensive with the domain + of life upon the earth. The comparatively small numbers which + possess "terrifying" or "alluring" coloration may be classed + under the general head of the protectively coloured.</p> + + <p>But under the next head—colour for recognition—we + have a totally distinct category, to some extent antagonistic or + complementary to the last, since its essential principle is + visibility rather than concealment. Yet it has been shown, I + think, that this mode of coloration is almost equally important, + since it not only aids in the preservation of existing species + and in the perpetuation of pure races, but was, perhaps, in its + earlier stages, a not unimportant factor in their development. To + it we owe most of the variety and much of the beauty in the + colours of animals; it has caused at once bilateral symmetry and + general permanence of type; and its range of action has been + perhaps equally extensive with that of coloration for + concealment.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Influence of Locality or of Climate on Colour.</i></p> + + <p>Certain relations between locality and coloration have long + been noticed. Mr. Gould observed that birds from inland or + continental localities were more brightly coloured than those + living near the sea-coast or on islands, and he supposed that the + more brilliant atmosphere of the inland stations was the + explanation of the phenomenon.<a name="FNanchor_90_90" id= + "FNanchor_90_90"></a><a href="#Footnote_90_90" class= + "fnanchor">[90]</a> Many American naturalists have observed + similar facts, and they assert that the intensity of the colours + of birds and mammals increases from north to south, and also with + the increase of humidity. This change is imputed by Mr. J.A. + Allen to the direct action of the environment. He says: "In + respect to the correlation of intensity of colour in animals with + the degree of humidity, it would perhaps be more in accordance + with cause and effect to express the law of correlation as a + <i>decrease</i> of intensity of colour with <a name="Page_229" + id="Page_229"></a>a <i>decrease</i> of humidity, the paleness + evidently resulting from exposure and the blanching effect of + intense sunlight, and a dry, often intensely heated atmosphere. + With the decrease of the aqueous precipitation the forest growth + and the protection afforded by arborescent vegetation gradually + also decreases, as of course does also the protection afforded by + clouds, the excessively humid regions being also regions of + extreme cloudiness, while the dry regions are comparatively + cloudless districts."<a name="FNanchor_91_91" id= + "FNanchor_91_91"></a><a href="#Footnote_91_91" class= + "fnanchor">[91]</a> Almost identical changes occur in birds, and + are imputed by Mr. Allen to similar causes.</p> + + <p>It will be seen that Mr. Gould and Mr. Allen impute opposite + effects to the same cause, brilliancy or intensity of colour + being due to a brilliant atmosphere according to the former, + while paleness of colour is imputed by the latter to a too + brilliant sun. According to the principles which have been + established by the consideration of arctic, desert, and forest + animals respectively, we shall be led to conclude that there has + been no direct action in this case, but that the effects observed + are due to the greater or less need of protection. The pale + colour that is prevalent in arid districts is in harmony with the + general tints of the surface; while the brighter tints or more + intense coloration, both southward and in humid districts, are + sufficiently explained by the greater shelter due to a more + luxuriant vegetation and a shorter winter. The advocates of the + theory that intensity of light directly affects the colours of + organisms, are led into perpetual inconsistencies. At one time + the brilliant colours of tropical birds and insects are imputed + to the intensity of a tropical sun, while the same intensity of + sunlight is now said to have a "bleaching" effect. The + comparatively dull and sober hues of our northern fauna were once + supposed to be the result of our cloudy skies; but now we are + told that cloudy skies and a humid atmosphere intensify + colour.</p> + + <p>In my <i>Tropical Nature</i> (pp. 257-264) I have called + attention to what is perhaps the most curious and decided + relation of colour to locality which has yet been + observed—the prevalence of white markings in the + butterflies and birds of islands.</p> + + <p><a name="Page_230" id="Page_230"></a>So many cases are adduced + from so many different islands, both in the eastern and western + hemisphere, that it is impossible to doubt the existence of some + common cause; and it seems probable to me now, after a fuller + consideration of the whole subject of colour, that here too we + have one of the almost innumerable results of the principle of + protective coloration. White is, as a rule, an uncommon colour in + animals, but probably only because it is so conspicuous. Whenever + it becomes protective, as in the case of arctic animals and + aquatic birds, it appears freely enough; while we know that white + varieties of many species occur occasionally in the wild state, + and that, under domestication, white or parti-coloured breeds are + freely produced. Now in all the islands in which exceptionally + white-marked birds and butterflies have been observed, we find + two features which would tend to render the conspicuous white + markings less injurious—a luxuriant tropical vegetation, + and a decided scarcity of rapacious mammals and birds. White + colours, therefore, would not be eliminated by natural selection; + but variations in this direction would bear their part in + producing the recognition marks which are everywhere essential, + and which, in these islands, need not be so small or so + inconspicuous as elsewhere.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>On a review of the whole subject, then, we must conclude that + there is no evidence of the individual or prevalent colours of + organisms being directly determined by the amount of light, or + heat, or moisture, to which they are exposed; while, on the other + hand, the two great principles of the need of concealment from + enemies or from their prey, and of recognition by their own kind, + are so wide-reaching in their application that they appear at + first sight to cover almost the whole ground of animal + coloration. But, although they are indeed wonderfully general and + have as yet been very imperfectly studied, we are acquainted with + other modes of coloration which have a different origin. These + chiefly appertain to the very singular class of warning colours, + from which arise the yet more extraordinary phenomena of mimicry; + and they open up so curious a field of inquiry and present so + many interesting problems, that a chapter must be devoted to + them. Yet another chapter will <a name="Page_231" id= + "Page_231"></a>be required by the subject of sexual + differentiation of colour and ornament, as to the origin and + meaning of which I have arrived at different conclusions from Mr. + Darwin. These various forms of coloration having been discussed + and illustrated, we shall be in a position to attempt a brief + sketch of the fundamental laws which have determined the general + coloration of the animal world.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_65_65" id="Footnote_65_65"></a><a href= + "#FNanchor_65_65"><span class="label">[65]</span></a> + <i>Proceedings of the Royal Society</i>, No. 243, 1886; + <i>Transactions of the Royal Society</i>, vol. clxxviii. B. + pp. 311-441.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_66_66" id="Footnote_66_66"></a><a href= + "#FNanchor_66_66"><span class="label">[66]</span></a> <i>A + Naturalist's Wanderings in the Eastern Archipelago</i>, p. + 460.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_67_67" id="Footnote_67_67"></a><a href= + "#FNanchor_67_67"><span class="label">[67]</span></a> + <i>Trans. Phil. Soc.</i> (? <i>of S. Africa</i>), 1878, part + iv, p. 27.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_68_68" id="Footnote_68_68"></a><a href= + "#FNanchor_68_68"><span class="label">[68]</span></a> + <i>Proc. Zool. Soc.</i>, 1862 p. 357.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_69_69" id="Footnote_69_69"></a><a href= + "#FNanchor_69_69"><span class="label">[69]</span></a> With + reference to this general resemblance of insects to their + environment the following remarks by Mr. Poulton are very + instructive. He says: "Holding the larva of Sphinx ligustri + in one hand and a twig of its food-plant in the other, the + wonder we feel is, not at the resemblance but at the + difference; we are surprised at the difficulty experienced in + detecting so conspicuous an object. And yet the protection is + very real, for the larvae will be passed over by those who + are not accustomed to their appearance, although the searcher + may be told of the presence of a large caterpillar. An + experienced entomologist may also fail to find the larvae + till after a considerable search. This is general protective + resemblance, and it depends upon a general harmony between + the appearance of the organism and its whole environment. It + is impossible to understand the force of this protection for + any larva, without seeing it on its food-plant and in an + entirely normal condition. The artistic effect of green + foliage is more complex than we often imagine; numberless + modifications are wrought by varied lights and shadows upon + colours which are in themselves far from uniform. In the + larva of Papilio machaon the protection is very real when the + larva is on the food-plant, and can hardly be appreciated at + all when the two are apart." Numerous other examples are + given in the chapter on "Mimicry and other Protective + Resemblances among Animals," in my <i>Contributions to the + Theory of Natural Selection</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_70_70" id="Footnote_70_70"></a><a href= + "#FNanchor_70_70"><span class="label">[70]</span></a> <i>The + Naturalist in Nicaragua</i>, p. 19.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_71_71" id="Footnote_71_71"></a><a href= + "#FNanchor_71_71"><span class="label">[71]</span></a> R. + Meldola, in <i>Proc. Zool. Soc.</i>, 1873, p. 155.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_72_72" id="Footnote_72_72"></a><a href= + "#FNanchor_72_72"><span class="label">[72]</span></a> + <i>Nature</i>, vol. iii. p. 166.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_73_73" id="Footnote_73_73"></a><a href= + "#FNanchor_73_73"><span class="label">[73]</span></a> + <i>Trans. Ent. Soc. Lond.</i>, 1878, p. 185.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_74_74" id="Footnote_74_74"></a><a href= + "#FNanchor_74_74"><span class="label">[74]</span></a> + <i>Ibid.</i> (<i>Proceedings</i>, p. xlii.)</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_75_75" id="Footnote_75_75"></a><a href= + "#FNanchor_75_75"><span class="label">[75]</span></a> + Wallace's <i>Malay Archipelago</i>, vol. i. p. 204 (fifth + edition, p. 130), with figure.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_76_76" id="Footnote_76_76"></a><a href= + "#FNanchor_76_76"><span class="label">[76]</span></a> + Moseley's <i>Notes by a Naturalist on the Challenger</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_77_77" id="Footnote_77_77"></a><a href= + "#FNanchor_77_77"><span class="label">[77]</span></a> + <i>Proceedings of the Boston Soc. of Nat. Hist.</i>, vol. + xiv. 1871.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_78_78" id="Footnote_78_78"></a><a href= + "#FNanchor_78_78"><span class="label">[78]</span></a> + <i>Nature</i>, 1870, p. 376.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_79_79" id="Footnote_79_79"></a><a href= + "#FNanchor_79_79"><span class="label">[79]</span></a> <i>A + Naturalist's Wanderings in the Eastern Archipelago</i>, p. + 63.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_80_80" id="Footnote_80_80"></a><a href= + "#FNanchor_80_80"><span class="label">[80]</span></a> A + beautiful drawing of this rare insect, Hymenopus bicornis (in + the nymph or active pupa state), was kindly sent me by Mr. + Wood-Mason, Curator of the Indian Museum at Calcutta. A + species, very similar to it, inhabits Java, where it is said + to resemble a pink orchid. Other Mantidae, of the genus + Gongylus, have the anterior part of the thorax dilated and + coloured either white, pink, or purple; and they so closely + resemble flowers that, according to Mr. Wood-Mason, one of + them, having a bright violet-blue prothoracic shield, was + found in Pegu by a botanist, and was for a moment mistaken by + him for a flower. See <i>Proc. Ent. Soc. Lond.</i>, 1878, p. + liii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_81_81" id="Footnote_81_81"></a><a href= + "#FNanchor_81_81"><span class="label">[81]</span></a> C. + Dixon, in Seebohm's <i>History of British Birds</i>, vol. ii. + Introduction, p. xxvi. Many of the other examples here cited + are taken from the same valuable work.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_82_82" id="Footnote_82_82"></a><a href= + "#FNanchor_82_82"><span class="label">[82]</span></a> See + A.H.S. Lucas, in <i>Proceedings of Royal Society of + Victoria</i>, 1887, p. 56.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_83_83" id="Footnote_83_83"></a><a href= + "#FNanchor_83_83"><span class="label">[83]</span></a> + Professor Wm.H. Brewer of Yale College has shown that the + white marks or the spots of domesticated animals are rarely + symmetrical, but have a tendency to appear more frequently on + the left side. This is the case with horses, cattle, dogs, + and swine. Among wild animals the skunk varies considerably + in the amount of white on the body, and this too was found to + be usually greatest on the left side. A close examination of + numerous striped or spotted species, as tigers, leopards, + jaguars, zebras, etc., showed that the bilateral symmetry was + not exact, although the general effect of the two sides was + the same. This is precisely what we should expect if the + symmetry is not the result of a general law of the + organisation, but has been, in part at least, produced and + preserved for the useful purpose of recognition by the + animal's fellows of the same species, and especially by the + sexes and the young. See <i>Proc. of the Am. Ass. for + Advancement of Science</i>, vol. xxx. p. 246.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_84_84" id="Footnote_84_84"></a><a href= + "#FNanchor_84_84"><span class="label">[84]</span></a> + <i>Descent of Man</i>, p. 542.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_85_85" id="Footnote_85_85"></a><a href= + "#FNanchor_85_85"><span class="label">[85]</span></a> It may + be thought that such extremely conspicuous markings as those + of the zebra would be a great danger in a country abounding + with lions, leopards, and other beasts of prey; but it is not + so. Zebras usually go in bands, and are so swift and wary + that they are in little danger during the day. It is in the + evening, or on moonlight nights, when they go to drink, that + they are chiefly exposed to attack; and Mr. Francis Galton, + who has studied these animals in their native haunts, assures + me, that in twilight they are not at all conspicuous, the + stripes of white and black so merging together into a gray + tint that it is very difficult to see them at a little + distance. We have here an admirable illustration of how a + glaringly conspicuous style of marking for recognition may be + so arranged as to become also protective at the time when + protection is most needed; and we may also learn how + impossible it is for us to decide on the inutility of any + kind of coloration without a careful study of the habits of + the species in its native country.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_86_86" id="Footnote_86_86"></a><a href= + "#FNanchor_86_86"><span class="label">[86]</span></a> The + principle of colouring for recognition was, I believe, first + stated in my article on "The Colours of Animals and Plants" + in Macmillan's <i>Magazine</i>, and more fully in my volume + on <i>Tropical Nature</i>. Subsequently Mrs. Barber gave a + few examples under the head of "Indicative or Banner + Colours," but she applied it to the distinctive colours of + the males of birds, which I explain on another principle, + though this may assist.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_87_87" id="Footnote_87_87"></a><a href= + "#FNanchor_87_87"><span class="label">[87]</span></a> Quoted + by Darwin in <i>Descent of Man</i>, p. 317.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_88_88" id="Footnote_88_88"></a><a href= + "#FNanchor_88_88"><span class="label">[88]</span></a> In the + <i>American Naturalist</i> of March 1888, Mr. J.E. Todd has + an article on "Directive Coloration in Animals," in which he + recognises many of the cases here referred to, and suggests a + few others, though I think he includes many forms of + coloration—as "paleness of belly and inner side of + legs"—which do not belong to this class.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_89_89" id="Footnote_89_89"></a><a href= + "#FNanchor_89_89"><span class="label">[89]</span></a> For + numerous examples of this protective colouring of marine + animals see Moseley's <i>Voyage of the Challenger</i>, and + Dr. E.S. Morse in <i>Proc. of Bost. Soc. of Nat. Hist.</i>, + vol. xiv. 1871.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_90_90" id="Footnote_90_90"></a><a href= + "#FNanchor_90_90"><span class="label">[90]</span></a> See + <i>Origin of Species</i>, p. 107.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_91_91" id="Footnote_91_91"></a><a href= + "#FNanchor_91_91"><span class="label">[91]</span></a> The + "Geographical Variation of North American Squirrels," + <i>Proc. Bost. Soc. of Nat. Hist.</i>, 1874, p. 284; and + <i>Mammals and Winter Birds of Florida</i>, pp. 233-241.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a><a name="Page_232" + id="Page_232"></a>CHAPTER IX</h2> + + <p style='font-weight:bold;'>WARNING COLORATION AND MIMICRY</p> + + <div class="blockquot"> + <p>The skunk as an example of warning coloration—Warning + colours among + insects—Butterflies—Caterpillars—Mimicry—How + mimicry has been produced—Heliconidae—Perfection of + the imitation—Other cases of mimicry among + Lepidoptera—Mimicry among protected groups—Its + explanation—Extension of the principle—Mimicry in + other orders of insects—Mimicry among the + vertebrata—Snakes—The rattlesnake and the + cobra—Mimicry among birds—Objections to the theory + of mimicry—Concluding remarks on warning colours and + mimicry.</p> + </div> + + <p>We have now to deal with a class of colours which are the very + opposite of those we have hitherto considered, since, instead of + serving to conceal the animals that possess them or as + recognition marks to their associates, they are developed for the + express purpose of rendering the species conspicuous. The reason + of this is that the animals in question are either the possessors + of some deadly weapons, as stings or poison fangs, or they are + uneatable, and are thus so disagreeable to the usual enemies of + their kind that they are never attacked when their peculiar + powers or properties are known. It is, therefore, important that + they should not be mistaken for defenceless or eatable species of + the same class or order, since in that case they might suffer + injury, or even death, before their enemies discovered the danger + or the uselessness of the attack. They require some signal or + danger-flag which shall serve as a warning to would-be enemies + not to attack them, and they have usually obtained this in the + form of conspicuous or brilliant coloration, very distinct from + the protective tints of the defenceless animals allied to + them.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_233" id="Page_233"></a><i>The Skunk as illustrating + Warning Coloration.</i></p> + + <p>While staying a few days, in July 1887, at the Summit Hotel on + the Central Pacific Railway, I strolled out one evening after + dinner, and on the road, not fifty yards from the house, I saw a + pretty little white and black animal with a bushy tail coming + towards me. As it came on at a slow pace and without any fear, + although it evidently saw me, I thought at first that it must be + some tame creature, when it suddenly occurred to me that it was a + skunk. It came on till within five or six yards of me, then + quietly climbed over a dwarf wall and disappeared under a small + outhouse, in search of chickens, as the landlord afterwards told + me. This animal possesses, as is well known, a most offensive + secretion, which it has the power of ejecting over its enemies, + and which effectually protects it from attack. The odour of this + substance is so penetrating that it taints, and renders useless, + everything it touches, or in its vicinity. Provisions near it + become uneatable, and clothes saturated with it will retain the + smell for several weeks, even though they are repeatedly washed + and dried. A drop of the liquid in the eyes will cause blindness, + and Indians are said not unfrequently to lose their sight from + this cause. Owing to this remarkable power of offence the skunk + is rarely attacked by other animals, and its black and white fur, + and the bushy white tail carried erect when disturbed, form the + danger-signals by which it is easily distinguished in the + twilight or moonlight from unprotected animals. Its consciousness + that it needs only to be seen to be avoided gives it that + slowness of motion and fearlessness of aspect which are, as we + shall see, characteristic of most creatures so protected.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Warning Colours among Insects.</i></p> + + <p>It is among insects that warning colours are best developed, + and most abundant. We all know how well marked and conspicuous + are the colours and forms of the stinging wasps and bees, no one + of which in any part of the world is known to be protectively + coloured like the majority of defenceless insects. Most of the + great tribe of Malacoderms among beetles are distasteful to + insect-eating animals. Our red and <a name="Page_234" id= + "Page_234"></a>black Telephoridae, commonly called "soldiers and + sailors," were found, by Mr. Jenner Weir, to be refused by small + birds. These and the allied Lampyridae (the fireflies and + glow-worms) in Nicaragua, were rejected by Mr. Belt's tame monkey + and by his fowls, though most other insects were greedily eaten + by them. The Coccinellidae or lady-birds are another uneatable + group, and their conspicuous and singularly spotted bodies serve + to distinguish them at a glance from all other beetles.</p> + + <p>These uneatable insects are probably more numerous than is + supposed, although we already know immense numbers that are so + protected. The most remarkable are the three families of + butterflies—Heliconidae, Danaidae, and + Acraeidae—comprising more than a thousand species, and + characteristic respectively of the three great tropical + regions—South America, Southern Asia, and Africa. All these + butterflies have peculiarities which serve to distinguish them + from every other group in their respective regions. They all have + ample but rather weak wings, and fly slowly; they are always very + abundant; and they all have conspicuous colours or markings, so + distinct from those of other families that, in conjunction with + their peculiar outline and mode of flight, they can usually be + recognised at a glance. Other distinctive features are, that + their colours are always nearly the same on the under surface of + their wings as on the upper; they never try to conceal + themselves, but rest on the upper surfaces of leaves or flowers; + and, lastly, they all have juices which exhale a powerful scent, + so that when one kills them by pinching the body, the liquid that + exudes stains the fingers yellow, and leaves an odour that can + only be removed by repeated washings.</p> + + <p>Now, there is much direct evidence to show that this odour, + though not very offensive to us, is so to most insect-eating + creatures. Mr. Bates observed that, when set out to dry, + specimens of Heliconidae were less subject to the attacks of + vermin; while both he and I noticed that they were not attacked + by insect-eating birds or dragonflies, and that their wings were + not found in the forest paths among the numerous wings of other + butterflies whose bodies had been devoured. Mr. Belt once + observed a pair of birds capturing insects for <a name="Page_235" + id="Page_235"></a>their young; and although the Heliconidae + swarmed in the vicinity, and from their slow flight could have + been easily caught, not one was ever pursued, although other + butterflies did not escape. His tame monkey also, which would + greedily munch up other butterflies, would never eat the + Heliconidae. It would sometimes smell them, but always rolled + them up in its hand and then dropped them.</p> + + <p>We have also some corresponding evidence as to the + distastefulness of the Eastern Danaidae. The Hon. Mr. Justice + Newton, who assiduously collected and took notes upon the + Lepidoptera of Bombay, informed Mr. Butler of the British Museum + that the large and swift-flying butterfly Charaxes psaphon, was + continually persecuted by the bulbul, so that he rarely caught a + specimen of this species which had not a piece snipped out of the + hind wings. He offered one to a bulbul which he had in a cage, + and it was greedily devoured, whilst it was only by repeated + persecution that he succeeded in inducing the bird to touch a + Danais.<a name="FNanchor_92_92" id="FNanchor_92_92"></a><a href= + "#Footnote_92_92" class="fnanchor">[92]</a></p> + + <p>Besides these three families of butterflies, there are certain + groups of the great genus Papilio—the true swallow-tailed + butterflies—which have all the characteristics of uneatable + insects. They have a special coloration, usually red and black + (at least in the females), they fly slowly, they are very + abundant, and they possess a peculiar odour somewhat like that of + the Heliconidae. One of these groups is common in tropical + America, another in tropical Asia, and it is curious that, + although not very closely allied, they have each the same red and + black colours, and are very distinct from all the other + butterflies of their respective countries. There is reason to + believe also that many of the brilliantly coloured and + weak-flying diurnal moths, like the fine tropical Agaristidae and + burnet-moths, are similarly protected, and that their conspicuous + colours serve as a warning of inedibility. The common burnet-moth + (Anthrocera filipendula) and the equally conspicuous ragwort-moth + (Euchelia jacobeae) have been proved to be distasteful to + insect-eating creatures.</p> + + <p><a name="Page_236" id="Page_236"></a>The most interesting and + most conclusive example of warning coloration is, however, + furnished by caterpillars, because in this case the facts have + been carefully ascertained experimentally by competent observers. + In the year 1866, when Mr. Darwin was collecting evidence as to + the supposed effect of sexual selection in bringing about the + brilliant coloration of the higher animals, he was struck by the + fact that many caterpillars have brilliant and conspicuous + colours, in the production of which sexual selection could have + no place. We have numbers of such caterpillars in this country, + and they are characterised not only by their gay colours but by + not concealing themselves. Such are the mullein and the + gooseberry caterpillars, the larvae of the spurge hawk-moth, of + the buff-tip, and many others. Some of these caterpillars are + wonderfully conspicuous, as in the case of that noticed by Mr. + Bates in South America, which was four inches long, banded across + with black and yellow, and with bright red head, legs, and tail. + Hence it caught the eye of any one who passed by, even at the + distance of many yards.</p> + + <p>Mr. Darwin asked me to try and suggest some explanation of + this coloration; and, having been recently interested in the + question of the warning coloration of butterflies, I suggested + that this was probably a similar case,—that these + conspicuous caterpillars were distasteful to birds and other + insect-eating creatures, and that their bright non-protective + colours and habit of exposing themselves to view, enabled their + enemies to distinguish them at a glance from the edible kinds and + thus learn not to touch them; for it must be remembered that the + bodies of caterpillars while growing are so delicate, that a + wound from a bird's beak would be perhaps as fatal as if they + were devoured.<a name="FNanchor_93_93" id= + "FNanchor_93_93"></a><a href="#Footnote_93_93" class= + "fnanchor">[93]</a> At this time not a single experiment or + observation had been made on the subject, but after I had brought + the matter before the Entomological Society, two gentlemen, who + kept birds and other tame animals, undertook to make experiments + with a variety of caterpillars.</p> + + <p>Mr. Jenner Weir was the first to experiment with ten species + of small birds in his aviary, and he found that none of them + would eat the following smooth-skinned conspicuous cater<a name= + "Page_237" id="Page_237"></a>pillars—Abraxas grossulariata, + Diloba caeruleocephala, Anthrocera filipendula, and Cucullia + verbasci. He also found that they would not touch any hairy or + spiny larvae, and he was satisfied that it was not the hairs or + the spines, but the unpleasant taste that caused them to be + rejected, because in one case a young smooth larva of a hairy + species, and in another case the pupa of a spiny larva, were + equally rejected. On the other hand, all green or brown + caterpillars as well as those that resemble twigs were greedily + devoured.<a name="FNanchor_94_94" id= + "FNanchor_94_94"></a><a href="#Footnote_94_94" class= + "fnanchor">[94]</a></p> + + <p>Mr. A.G. Butler also made experiments with some green lizards + (Lacerta viridis), which greedily ate all kinds of food, + including flies of many kinds, spiders, bees, butterflies, and + green caterpillars; but they would not touch the caterpillar of + the gooseberry-moth (Abraxas grossulariata), or the imago of the + burnet-moth (Anthrocera filipendula). The same thing happened + with frogs. When the gooseberry caterpillars were first given to + them, "they sprang forward and licked them eagerly into their + mouths; no sooner, however, had they done so, than they seemed to + become aware of the mistake that they had made, and sat with + gaping mouths, rolling their tongues about, until they had got + quit of the nauseous morsels, which seemed perfectly uninjured, + and walked off as briskly as ever." Spiders seemed equally to + dislike them. This and another conspicuous caterpillar (Halia + wavaria) were rejected by two species—the geometrical + garden spider (Epeira diadema) and a hunting spider.<a name= + "FNanchor_95_95" id="FNanchor_95_95"></a><a href= + "#Footnote_95_95" class="fnanchor">[95]</a></p> + + <p>Some further experiments with lizards were made by Professor + Weismann, quite confirming the previous observations; and in 1886 + Mr. E.B. Poulton of Oxford undertook a considerable series of + experiments, with many other species of larvae and fresh kinds of + lizards and frogs. Mr. Poulton then reviewed the whole subject, + incorporating all recorded facts, as well as some additional + observations made by Mr. Jenner Weir in 1886. More than a hundred + species of larvae or of perfect insects of various orders have + now been made the subject of experiment, and the results + completely confirm my original suggestion. In almost every case + the protectively coloured larvae have been greedily eaten by all + kinds of insectivorous <a name="Page_238" id= + "Page_238"></a>animals, while, in the immense majority of cases, + the conspicuous, hairy, or brightly coloured larvae have been + rejected by some or all of them. In some instances the + inedibility of the larvae extends to the perfect insect, but not + in others. In the former cases the perfect insect is usually + adorned with conspicuous colours, as the burnet and ragwort + moths; but in the case of the buff-tip, the moth resembles a + broken piece of rotten stick, yet it is partly inedible, being + refused by lizards. It is, however, very doubtful whether these + are its chief enemies, and its protective form and colour may be + needed against insectivorous birds or mammals.</p> + + <p>Mr. Samuel H. Scudder, who has largely bred North American + butterflies, has found so many of the eggs and larvae destroyed + by hymenopterous and dipterous parasites that he thinks at least + nine-tenths, perhaps a greater proportion, never reach maturity. + Yet he has never found any evidence that such parasites attack + either the egg or the larva of the inedible Danais archippus, so + that in this case the insect is distasteful to its most dangerous + foes in all the stages of its existence, a fact which serves to + explain its great abundance and its extension over almost the + whole world.<a name="FNanchor_96_96" id= + "FNanchor_96_96"></a><a href="#Footnote_96_96" class= + "fnanchor">[96]</a></p> + + <p>One case has been found of a protectively coloured + larva,—one, moreover, which in all its habits shows that it + trusts to concealment to escape its enemies—which was yet + always rejected by lizards after they had seized it, evidently + under the impression that from its colour it would be eatable. + This is the caterpillar of the very common moth Mania typica; and + Mr. Poulton thinks that, in this case, the unpleasant taste is an + incidental result of some physiological processes in the + organism, and is itself a merely useless character. It is evident + that the insect would not conceal itself so carefully as it does + if it had not some enemies, and these are probably birds or small + mammals, as its food-plants are said to be dock and willow-herb, + not suggestive of places frequented by lizards; and it has been + found by experiment that lizards and birds have not always the + same likes and dislikes. The case is interesting, because it + shows that nauseous fluids sometimes occur sporadically, and may + thus be intensified by natural selection when required for the + purpose <a name="Page_239" id="Page_239"></a>of protection. + Another exceptional case is that of the very conspicuous + caterpillar of the spurge hawk-moth (Deilephila euphorbiae), + which was at once eaten by a lizard, although, as it exposes + itself on its food-plant in the daytime and is very abundant in + some localities, it must almost certainly be disliked by birds or + by some animals who would otherwise devour it. If disturbed while + feeding it is said to turn round with fury and eject a quantity + of green liquid, of an acid and disagreeable smell similar to + that of the spurge milk, only worse.<a name="FNanchor_97_97" id= + "FNanchor_97_97"></a><a href="#Footnote_97_97" class= + "fnanchor">[97]</a></p> + + <p>These facts, and Mr. Poulton's evidence that some larvae + rejected by lizards at first will be eaten if the lizards are + very hungry, show that there are differences in the amount of the + distastefulness, and render it probable that if other food were + wanting many of these conspicuous insects would be eaten. It is + the abundance of the eatable kinds that gives value to the + inedibility of the smaller number; and this is probably the + reason why so many insects rely on protective colouring rather + than on the acquisition of any kind of defensive weapons. In the + long run the powers of attack and defence must balance each + other. Hence we see that even the powerful stings of bees and + wasps only protect them against some enemies, since a tribe of + birds, the bee-eaters, have been developed which feed upon them, + and some frogs and lizards do so occasionally.</p> + + <p>The preceding outline will sufficiently explain the + characteristics of "warning coloration" and the end it serves in + nature. There are many other curious modifications of it, but + these will be best appreciated after we have discussed the + remarkable phenomenon of "mimicry," which is bound up with and + altogether depends upon "warning colour," and is in some cases + the chief indication we have of the possession of some offensive + weapon to secure the safety of the species imitated.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mimicry.</i></p> + + <p>This term has been given to a form of protective resemblance, + in which one species so closely resembles another in external + form and colouring as to be mistaken for it, although the two may + not be really allied and often belong to distinct <a name= + "Page_240" id="Page_240"></a>families or orders. One creature + seems disguised in order to be made like another; hence the terms + "mimic" and mimicry, which imply no voluntary action on the part + of the imitator. It has long been known that such resemblances do + occur, as, for example, the clear-winged moths of the families + Sesiidae and Aegeriidae, many of which resemble bees, wasps, + ichneumons, or saw-flies, and have received names expressive of + the resemblance; and the parasitic flies (Volucella) which + closely resemble bees, on whose larvae the larvae of the flies + feed.</p> + + <p>The great bulk of such cases remained, however, unnoticed, and + the subject was looked upon as one of the inexplicable + curiosities of nature, till Mr. Bates studied the phenomenon + among the butterflies of the Amazon, and, on his return home, + gave the first rational explanation of it.<a name= + "FNanchor_98_98" id="FNanchor_98_98"></a><a href= + "#Footnote_98_98" class="fnanchor">[98]</a> The facts are, + briefly, these. Everywhere in that fertile region for the + entomologist the brilliantly coloured Heliconidae abound, with + all the characteristics which I have already referred to when + describing them as illustrative of "warning coloration." But + along with them other butterflies were occasionally captured, + which, though often mistaken for them, on account of their close + resemblance in form, colour, and mode of flight, were found on + examination to belong to a very distinct family, the Pieridae. + Mr. Bates notices fifteen distinct species of Pieridae, belonging + to the genera Leptalis and Euterpe, each of which closely + imitates some one species of Heliconidae, inhabiting the same + region and frequenting the same localities. It must be remembered + that the two families are altogether distinct in structure. The + larvae of the Heliconidae are tubercled or spined, the pupae + suspended head downwards, and the imago has imperfect forelegs in + the male; while the larvae of the Pieridae are smooth, the pupae + are suspended with a brace to keep the head erect, and the + forefeet are fully developed in both sexes. These differences are + as large and as important as those between pigs and sheep, or + between swallows and sparrows; while English entomologists will + best understand the case by supposing that a species of Pieris in + this country was coloured and shaped like a small tortoise-shell, + while another species on the Continent was equally like a + Camberwell beauty—so like in both <a name="Page_241" id= + "Page_241"></a>cases as to be mistaken when on the wing, and the + difference only to be detected by close examination. As an + example of the resemblance, woodcuts are given of one pair in + which the colours are simple, being olive, yellow, and black, + while the very distinct neuration of the wings and form of the + head and body can be easily seen.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig23" id="fig23"></a> <img src="images/fig23.jpg" + width="400" height="429" alt= + "FIG. 23.—Methona psidii (Heliconidae). Leptalis orise (Pieridae)." + title= + "FIG. 23.—Methona psidii (Heliconidae). Leptalis orise (Pieridae)." /> + <b>FIG. 23.—Methona psidii (Heliconidae).<br /> + Leptalis orise (Pieridae).</b> + </div> + + <p>Besides these Pieridae, Mr. Bates found four true Papilios, + seven Erycinidae, three Castnias (a genus of day-flying moths), + and fourteen species of diurnal Bombycidae, all imitating some + species of Heliconidae which inhabited the same district; and it + is to be especially noted that none of these insects were so + abundant as the Heliconidae they resembled, generally they + <a name="Page_242" id="Page_242"></a>were far less common, so + that Mr. Bates estimated the proportion in some cases as not one + to a thousand. Before giving an account of the numerous + remarkable cases of mimicry in other parts of the world, and + between various groups of insects and of higher animals, it will + be well to explain briefly the use and purport of the phenomenon, + and also the mode by which it has been brought about.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>How Mimicry has been Produced.</i></p> + + <p>The fact has been now established that the Heliconidae possess + an offensive odour and taste, which lead to their being almost + entirely free from attack by insectivorous creatures; they + possess a peculiar form and mode of flight, and do not seek + concealment; while their colours—although very varied, + ranging from deep blue-black, with white, yellow, or vivid red + bands and spots, to the most delicate semitransparent wings + adorned with pale brown or yellow markings—are yet always + very distinctive, and unlike those of all the other families of + butterflies in the same country. It is, therefore, clear that if + any other butterflies in the same region, which are eatable and + suffer great persecution from insectivorous animals, should come + to resemble any of these uneatable species so closely as to be + mistaken for them by their enemies, they will obtain thereby + immunity from persecution. This is the obvious and sufficient + reason why the imitation is useful, and therefore why it occurs + in nature. We have now to explain how it has probably been + brought about, and also why a still larger number of persecuted + groups have not availed themselves of this simple means of + protection.</p> + + <p>From the great abundance of the Heliconidae<a name= + "FNanchor_99_99" id="FNanchor_99_99"></a><a href= + "#Footnote_99_99" class="fnanchor">[99]</a> all over tropical + America, the vast number of their genera and species, and their + marked distinctions from all other butterflies, it follows that + they constitute a group of high antiquity, which in the course of + ages has become more and more specialised, and owing to its + peculiar advantages has now become a dominant and aggressive + race. But when they first arose from some ancestral species or + group which, owing to the food <a name="Page_243" id= + "Page_243"></a>of the larvae or some other cause, possessed + disagreeable juices that caused them to be disliked by the usual + enemies of their kind, they were in all probability not very + different either in form or coloration from many other + butterflies. They would at that time be subject to repeated + attacks by insect-eaters, and, even if finally rejected, would + often receive a fatal injury. Hence arose the necessity for some + distinguishing mark, by which the devourers of butterflies in + general might learn that these particular butterflies were + uneatable; and every variation leading to such distinction, + whether by form, colour, or mode of flight, was preserved and + accumulated by natural selection, till the ancestral Heliconoids + became well distinguished from eatable butterflies, and + thenceforth comparatively free from persecution. Then they had a + good time of it. They acquired lazy habits, and flew about + slowly. They increased abundantly and spread all over the + country, their larvae feeding on many plants and acquiring + different habits; while the butterflies themselves varied + greatly, and colour being useful rather than injurious to them, + gradually diverged into the many coloured and beautifully varied + forms we now behold.</p> + + <p>But, during the early stages of this process, some of the + Pieridae, inhabiting the same district, happened to be + sufficiently like some of the Heliconidae to be occasionally + mistaken for them. These, of course, survived while their + companions were devoured. Those among their descendants that were + still more like Heliconidae again survived, and at length the + imitation would become tolerably perfect. Thereafter, as the + protected group diverged into distinct species of many different + colours, the imitative group would occasionally be able to follow + it with similar variations,—a process that is going on now, + for Mr. Bates informs us that in each fresh district he visited + he found closely allied representative species or varieties of + Heliconidae, and along with them species of Leptalis (Pieridae), + which had varied in the same way so as still to be exact + imitations. But this process of imitation would be subject to + check by the increasing acuteness of birds and other animals + which, whenever the eatable Leptalis became numerous, would + surely find them out, and would then probably attack both these + and their friends the Heliconidae in order to devour <a name= + "Page_244" id="Page_244"></a>the former and reject the latter. + The Pieridae would, however, usually be less numerous, because + their larvae are often protectively coloured and therefore + edible, while the larvae of the Heliconidae are adorned with + warning colours, spines, or tubercles, and are uneatable. It + seems probable that the larvae and pupae of the Heliconidae were + the first to acquire the protective distastefulness, both because + in this stage they are more defenceless and more liable to fatal + injury, and also because we now find many instances in which the + larvae are distasteful while the perfect insects are eatable, but + I believe none in which the reverse is the case. The larvae of + the Pieridae are now beginning to acquire offensive juices, but + have not yet obtained the corresponding conspicuous colours; + while the perfect insects remain eatable, except perhaps in some + Eastern groups, the under sides of whose wings are brilliantly + coloured although this is the part which is exposed when at + rest.</p> + + <p>It is clear that if a large majority of the larvae of + Lepidoptera, as well as the perfect insects, acquired these + distasteful properties, so as seriously to diminish the food + supply of insectivorous and nestling birds, these latter would be + forced by necessity to acquire corresponding tastes, and to eat + with pleasure what some of them now eat only under pressure of + hunger; and variation and natural selection would soon bring + about this change.</p> + + <p>Many writers have denied the possibility of such wonderful + resemblances being produced by the accumulation of fortuitous + variations, but if the reader will call to mind the large amount + of variability that has been shown to exist in all organisms, the + exceptional power of rapid increase possessed by insects, and the + tremendous struggle for existence always going on, the difficulty + will vanish, especially when we remember that nature has the same + fundamental groundwork to act upon in the two groups, general + similarity of forms, wings of similar texture and outline, and + probably some original similarity of colour and marking. Yet + there is evidently considerable difficulty in the process, or + with these great resources at her command nature would have + produced more of these mimicking forms than she has done. One + reason of this deficiency probably is, that the imitators, being + always fewer in number, have <a name="Page_245" id= + "Page_245"></a>not been able to keep pace with the variations of + the much more numerous imitated form; another reason may be the + ever-increasing acuteness of the enemies, which have again and + again detected the imposture and exterminated the feeble race + before it has had time to become further modified. The result of + this growing acuteness of enemies has been, that those mimics + that now survive exhibit, as Mr. Bates well remarks, "a palpably + intentional likeness that is perfectly staggering," and also + "that those features of the portrait are most attended to by + nature which produce the most effective deception when the + insects are seen in nature." No one, in fact, can understand the + perfection of the imitation who has not seen these species in + their native wilds. So complete is it in general effect that in + almost every box of butterflies, brought from tropical America by + amateurs, are to be found some species of the mimicking Pieridae, + Erycinidae, or moths, and the mimicked Heliconidae, placed + together under the impression that they are the same species. Yet + more extraordinary, it sometimes deceives the very insects + themselves. Mr. Trimen states that the male Danais chrysippus is + sometimes deceived by the female Diadema bolina which mimics that + species. Dr. Fritz Müller, writing from Brazil to Professor + Meldola, says, "One of the most interesting of our mimicking + butterflies is Leptalis melite. The female alone of this species + imitates one of our common white Pieridae, which she copies so + well that even her own male is often deceived; for I have + repeatedly seen the male pursuing the mimicked species, till, + after closely approaching and becoming aware of his error, he + suddenly returned."<a name="FNanchor_100_100" id= + "FNanchor_100_100"></a><a href="#Footnote_100_100" class= + "fnanchor">[100]</a> This is evidently not a case of true + mimicry, since the species imitated is not protected; but it may + be that the less abundant Leptalis is able to mingle with the + female Pieridae and thus obtain partial immunity from attack. Mr. + Kirby of the insect department of the British Museum informs me + that there are several species of South American Pieridae which + the female Leptalis melite very nearly resembles. The case, + however, is interesting as showing that the butterflies are + themselves deceived by a resemblance which is not so great as + that of some mimicking species.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_246" id="Page_246"></a><i>Other Examples of Mimicry + among Lepidoptera.</i></p> + + <p>In tropical Asia, and eastward to the Pacific Islands, the + Danaidae take the place of the Heliconidae of America, in their + abundance, their conspicuousness, their slow flight, and their + being the subjects of mimicry. They exist under three principal + forms or genera. The genus Euploea is the most abundant both in + species and individuals, and consists of fine broad-winged + butterflies of a glossy or metallic blue-black colour, adorned + with pure white, or rich blue, or dusky markings situated round + the margins of the wings. Danais has generally more lengthened + wings, of a semitransparent greenish or a rich brown colour, with + radial or marginal pale spots; while the fine Hestias are of + enormous size, of a papery or semitransparent white colour, with + dusky or black spots and markings. Each of these groups is + mimicked by various species of the genus Papilio, usually with + such accuracy that it is impossible to distinguish them on the + wing.<a name="FNanchor_101_101" id= + "FNanchor_101_101"></a><a href="#Footnote_101_101" class= + "fnanchor">[101]</a> Several species of Diadema, a genus of + butterflies allied to our Vanessas, also mimic species of Danais, + but in this case the females only are affected, a subject which + will be discussed in another chapter.</p> + + <p>Another protected group in the Eastern tropics is that of the + beautiful day-flying moths forming the family Agaristidae. These + are usually adorned with the most brilliant colours or + conspicuous markings, they fly slowly in forests among the + butterflies and other diurnal insects, and their great abundance + sufficiently indicates their possession of some distastefulness + which saves them from attack. Under these conditions we may + expect to find other moths which are not so protected imitating + them, and this is the case. One of the common and wide-ranging + species (Opthalmis lincea), found in the islands from Amboyna to + New Ireland, is mimicked in a wonderful manner by one of the + Liparidae (the family to which our common "tussock" and + "vapourer" moths belong). This is a new species collected at + Amboyna during the voyage of the <i>Challenger</i>, and has been + named Artaxa simulans. Both <a name="Page_247" id= + "Page_247"></a>insects are black, with the apex of the fore wings + ochre coloured, and the outer half of the hind wings bright + orange. The accompanying woodcuts (for the use of which I am + indebted to Mr. John Murray of the <i>Challenger</i> Office) well + exhibit their striking resemblance to each other.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig24" id="fig24"></a> <img src="images/fig24.jpg" + width="400" height="333" alt= + "FIG. 24.—Opthalmis lincea (Agaristidae). Artaxa simulans (Liparidae)." + title= + "FIG. 24.—Opthalmis lincea (Agaristidae). Artaxa simulans (Liparidae)." /> + <b>FIG. 24.—Opthalmis lincea (Agaristidae).<br /> + Artaxa simulans (Liparidae).</b> + </div> + + <p>In Africa exactly similar phenomena recur, species of Papilio + and of Diadema mimicking Danaidae or Acraeidae with the most + curious accuracy. Mr. Trimen, who studied this subject in South + Africa, has recorded eight species or varieties of Diadema, and + eight of Papilio, which each mimic some species of Danais; while + eight species or varieties of Panopaea (another genus of + Nymphalidae), three of Melanitis (Eurytelidae), and two of + Papilio, resemble with equal accuracy some species of + Acraea.<a name="FNanchor_102_102" id= + "FNanchor_102_102"></a><a href="#Footnote_102_102" class= + "fnanchor">[102]</a> He has also independently observed the main + facts on which the explanation of the phenomenon rests,—the + unpleasant odour of the Danais and Acraea, extending to their + larvae and pupae; their great abundance, slow flight, and + disregard of concealment; and he states that while lizards, + mantidae, and dragonflies all hunt butterflies, and the rejected + wings are to be found abundantly at some of their <a name= + "Page_248" id="Page_248"></a>feeding-places, those of the two + genera Danais and Acraea were never among them.</p> + + <p>The two groups of the great genus Papilio (the true + swallow-tailed butterflies) which have been already referred to + as having the special characteristics of uneatable insects, have + also their imitators in other groups; and thus, the belief in + their inedibility—derived mainly from their style of + warning coloration and their peculiar habits—is confirmed. + In South America, several species of the "Aeneas" group of these + butterflies are mimicked by Pieridae and by day-flying moths of + the genera Castnia and Pericopis. In the East, Papilio hector, P. + diphilus, and P. liris, all belonging to the inedible group, are + mimicked by the females of other species of Papilio belonging to + very distinct groups; while in Northern India and China, many + fine day-flying moths (Epicopeia) have acquired the strange forms + and peculiar colours of some of the large inedible Papilios of + the same regions.</p> + + <p>In North America, the large and handsome Danais archippus, + with rich reddish-brown wings, is very common; and it is closely + imitated by Limenitis misippus, a butterfly allied to our "white + admiral," but which has acquired a colour quite distinct from + that of the great bulk of its allies. In the same country there + is a still more interesting case. The beautiful dark bronzy green + butterfly, Papilio philenor, is inedible both in larva and + perfect insect, and it is mimicked by the equally dark Limenitis + ursula. There is also in the Southern and Western States a dark + female form of the yellow Papilio turnus, which in all + probability obtains protection from its general resemblance to P. + philenor. Mr. W.H. Edwards has found, by extensive experiment, + that both the dark and yellow females produce their own kinds, + with very few exceptions; and he thinks that the dark form has + the advantage in the more open regions and in the prairies, where + insectivorous birds abound. But in open country the dark form + would be quite as conspicuous as the yellow form, if not more so, + so that the resemblance to an inedible species would be there + more needed.<a name="FNanchor_103_103" id= + "FNanchor_103_103"></a><a href="#Footnote_103_103" class= + "fnanchor">[103]</a></p> + + <p>The only probable case of mimicry in this country is that of + the moth, Diaphora mendica, whose female only is white, <a name= + "Page_249" id="Page_249"></a>while the larva is of protective + colours, and therefore almost certainly edible. A much more + abundant moth, of about the same size and appearing about the + same time, is Spilosoma menthrasti, also white, but in this case + both it and its larva have been proved to be inedible. The white + colour of the female Diaphora, although it must be very + conspicuous at night, may, therefore, have been acquired in order + to resemble the uneatable Spilosoma, and thus gain some + protection.<a name="FNanchor_104_104" id= + "FNanchor_104_104"></a><a href="#Footnote_104_104" class= + "fnanchor">[104]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mimicry among Protected (Uneatable) Genera.</i></p> + + <p>Before giving some account of the numerous other cases of + warning colours and of mimicry that occur in the animal kingdom, + it will be well to notice a curious phenomenon which long puzzled + entomologists, but which has at length received a satisfactory + explanation.</p> + + <p>We have hitherto considered, that mimicry could only occur + when a comparatively scarce and much persecuted species obtained + protection by its close external resemblance to a much more + abundant uneatable species inhabiting its own district; and this + rule undoubtedly prevails among the great majority of mimicking + species all over the world. But Mr. Bates also found a number of + pairs of species of different genera of Heliconidae, which + resembled each other quite as closely as did the other mimicking + species he has described; and since all these insects appear to + be equally protected by their inedibility, and to be equally free + from persecution, it was not easy to see why this curious + resemblance existed, or how it had been brought about. That it is + not due to close affinity is shown by the fact that the + resemblance occurs most frequently between the two distinct + sub-families into which (as Mr. Bates first pointed out) the + Heliconidae are naturally divided on account of very important + structural differences. One of these sub-families (the true + Heliconinae) consists of two genera only, Heliconius and Eueides, + the other (the Danaoid Heliconinae) of no less than sixteen + genera; and, in the instances of mimicry we are now discussing, + one of the pairs or <a name="Page_250" id="Page_250"></a>triplets + that resemble each other is usually a species of the large and + handsome genus Heliconius, the others being species of the genera + Mechanitis, Melinaea, or Tithorea, though several species of + other Danaoid genera also imitate each other. The following lists + will give some idea of the number of these curious imitative + forms, and of their presence in every part of the Neotropical + area. The bracketed species are those that resemble each other so + closely that the difference is not perceptible when they are on + the wing.</p> + + <p>In the Lower Amazon region are found—</p> + + <p><span style="margin-left: 2em;">{ Heliconius + sylvana.</span><br /> + <span style="margin-left: 2em;">{ Melinaea egina.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Heliconius numata.</span><br /> + <span style="margin-left: 2em;">{ Melinaea mneme.</span><br /> + <span style="margin-left: 2em;">{ Tithorea harmonia.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Methona psidii.</span><br /> + <span style="margin-left: 2em;">{ Thyridia ino.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Ceratina ninonia.</span><br /> + <span style="margin-left: 2em;">{ Melinaea + mnasias.</span><br /></p> + + <p>In Central America are found—</p> + + <p><span style="margin-left: 7em;">{ Heliconius + zuleika.</span><br /> + <span style="margin-left: 2em;">Nicaragua { Melinaea + hezia.</span><br /> + <span style="margin-left: 7em;">{ Mechanitis sp.</span><br /> + <br /> + <span style="margin-left: 7em;">{ Heliconius + formosus.</span><br /> + <span style="margin-left: 7em;">{ Tithorea penthias.</span><br /> + <br /> + <span style="margin-left: 2em;">Guatemala { Heliconius + telchina.</span><br /> + <span style="margin-left: 7em;">{ Melinaea imitata.</span><br /> + <br /></p> + + <p>In the Upper Amazon region—</p> + + <p><span style="margin-left: 2em;">{ Heliconius + pardalinus.</span><br /> + <span style="margin-left: 2em;">{ Melinaea pardalis.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Heliconius aurora.</span><br /> + <span style="margin-left: 2em;">{ Melinaea + lucifer.</span><br /></p> + + <p>In New Grenada—</p> + + <p><span style="margin-left: 2em;">{ Heliconius + ismenius.</span><br /> + <span style="margin-left: 2em;">{ Melinaea messatis.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Heliconius + messene.</span><br /> + <span style="margin-left: 2em;">{ Melinaea mesenina.</span><br /> + <span style="margin-left: 2em;">{ (?) Mechanitis sp.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Heliconius + hecalesia.</span><br /> + <span style="margin-left: 2em;">{ Tithorea + hecalesina.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Heliconius hecuba.</span><br /> + <span style="margin-left: 2em;">{ Tithorea + bonplandi.</span><br /></p> + + <p><a name="Page_251" id="Page_251"></a>In Eastern Peru and + Bolivia—</p> + + <p><span style="margin-left: 2em;">{ Heliconius + aristona.</span><br /> + <span style="margin-left: 2em;">{ Melinaea cydippe.</span><br /> + <span style="margin-left: 2em;">{ (?) Mechanitis + mothone.</span><br /></p> + + <p>In Pernambuco—</p> + + <p><span style="margin-left: 2em;">{ Heliconius + ethra.</span><br /> + <span style="margin-left: 2em;">{ Mechanitis + nesaea.</span><br /></p> + + <p>In Rio Janeiro—</p> + + <p><span style="margin-left: 2em;">{ Helieonius + eucrate.</span><br /> + <span style="margin-left: 2em;">{ Mechanitis + lysimnia.</span><br /></p> + + <p>In South Brazil—</p> + + <p><span style="margin-left: 2em;">{ Thyridia + megisto.</span><br /> + <span style="margin-left: 2em;">{ Ituna ilione.</span><br /> + <br /> + <span style="margin-left: 2em;">{ Acraea thalia.</span><br /> + <span style="margin-left: 2em;">{ Eueides + pavana.</span><br /></p> + + <p>Besides these, a number of species of Ithomia and Napeogenes, + and of Napeogenes and Mechanitis, resemble each other with equal + accuracy, so that they are liable to be mistaken for each other + when on the wing; and no doubt many other equally remarkable + cases are yet unnoticed.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig25" id="fig25"></a> <img src="images/fig25.jpg" + width="400" height="251" alt= + "FIG. 25.—Wings of Ituna Ilione, female. Wings of Thyridia megisto, female." + title= + "FIG. 25.—Wings of Ituna Ilione, female. Wings of Thyridia megisto, female." /> + <b>FIG. 25.—Wings of Ituna Ilione, female.<br /> + Wings of Thyridia megisto, female.</b> + </div> + + <p>The figures above of the fore and hind wings of two of these + mimicking species, from Dr. Fritz Müller's original paper in + <i>Kosmos</i>, will serve to show the considerable amount of + <a name="Page_252" id="Page_252"></a>difference, in the important + character of the neuration of the wings, between these + butterflies, which really belong to very distinct and not at all + closely allied genera. Other important characters are—(1) + The existence of a small basal cell in the hind wings of Ituna + which is wanting in Thyridia; (2) the division of the cell + between the veins 1<i>b</i> and 2 of the hind wings in the former + genus, while it is undivided in the latter; and (3) the existence + in Thyridia of scent-producing tufts of hair on the upper edge of + the hind wing, while in Ituna these are wanting; but in place of + them are extensible processes at the end of the abdomen, also + emitting a powerful scent. These differences characterise two + marked subdivisions of the Danaoid Heliconinae, each containing + several distinct genera; and these subdivisions are further + distinguished by very different forms of larvae, that to which + Ituna belongs having from two to four long threadlike tentacles + on the back, while in that containing Thyridia these are always + absent. The former usually feed on Asclepiadeae, the latter on + Solanaceae or Scrophulariaceae.</p> + + <p>The two species figured, though belonging to such distinct and + even remote genera, have acquired almost identical tints and + markings so as to be deceptively alike. The surface of the wings + is, in both, transparent yellowish, with black transverse bands + and white marginal spots, while both have similar black-and + white-marked bodies and long yellow antennae. Dr. Müller + states that they both show a preference for the same flowers + growing on the edges of the forest paths.<a name= + "FNanchor_105_105" id="FNanchor_105_105"></a><a href= + "#Footnote_105_105" class="fnanchor">[105]</a></p> + + <p>We will now proceed to give the explanation of these curious + similarities, which have remained a complete puzzle for twenty + years. Mr. Bates, when first describing them, suggested that they + might be due to some form of parallel variation dependent on + climatic influences; and I myself adduced other cases of + coincident local modifications of colour, which did not appear to + be explicable by any form of mimicry.<a name="FNanchor_106_106" + id="FNanchor_106_106"></a><a href="#Footnote_106_106" class= + "fnanchor">[106]</a> But we neither of us hit upon the simple + explanation given by Dr. Fritz Müller in 1879.</p> + + <p>His theory is founded on the assumed, but probable, <a name= + "Page_253" id="Page_253"></a>fact, that insect-eating birds only + learn by experience to distinguish the edible from the inedible + butterflies, and in doing so necessarily sacrifice a certain + number of the latter. The quantity of insectivorous birds in + tropical America is enormous; and the number of young birds which + every year have to learn wisdom by experience, as regards the + species of butterflies to be caught or to be avoided, is so great + that the sacrifice of life of the inedible species must be + considerable, and, to a comparatively weak or scarce species, of + vital importance. The number thus sacrificed will be fixed by the + quantity of young birds, and by the number of experiences + requisite to cause them to avoid the inedible species for the + future, and not at all by the numbers of individuals of which + each species consists. Hence, if two species are so much alike as + to be mistaken for one another, the fixed number annually + sacrificed by inexperienced birds will be divided between them, + and both will benefit. But if the two species are very unequal in + numbers, the benefit will be comparatively slight for the more + abundant species, but very great for the rare one. To the latter + it may make all the difference between safety and + destruction.</p> + + <p>To give a rough numerical example. Let us suppose that in a + given limited district there are two species of Heliconidae, one + consisting of only 1000, the other of 100,000 individuals, and + that the quota required annually in the same district for the + instruction of young insectivorous birds is 500. By the larger + species this loss will be hardly felt; to the smaller it will + mean the most dreadful persecution resulting in a loss of half + the total population. But, let the two species become + superficially alike, so that the birds see no difference between + them. The quota of 500 will now be taken from a combined + population of 101,000 butterflies, and if proportionate numbers + of each suffer, then the weak species will only lose five + individuals instead of 500 as it did before. Now we know that the + different species of Heliconidae are not equally abundant, some + being quite rare; so that the benefit to be derived in these + latter cases would be very important. A slight inferiority in + rapidity of flight or in powers of eluding attack might also be a + cause of danger to an inedible species of scanty numbers, and in + this case too the being <a name="Page_254" id= + "Page_254"></a>merged in another much more abundant species, by + similarity of external appearance, would be an advantage.</p> + + <p>The question of fact remains. Do young birds pursue and + capture these distasteful butterflies till they have learned by + bitter experience what species to avoid? On this point Dr. + Müller has fortunately been able to obtain some direct + evidence, by capturing several Acraeas and Heliconidae which had + evidently been seized by birds but had afterwards escaped, as + they had pieces torn out of the wing, sometimes symmetrically out + of both wings, showing that the insect had been seized when at + rest and with the two pairs of wings in contact. There is, + however, a general impression that this knowledge is hereditary, + and does not need to be acquired by young birds; in support of + which view Mr. Jenner Weir states that his birds always + disregarded inedible caterpillars. When, day by day, he threw + into his aviary various larvae, those which were edible were + eaten immediately, those which were inedible were no more noticed + than if a pebble had been thrown before the birds.</p> + + <p>The cases, however, are not strictly comparable. The birds + were not young birds of the first year; and, what is more + important, edible larvae have a comparatively simple coloration, + being always brown or green and smooth. Uneatable larvae, on the + other hand, comprise all that are of conspicuous colours and are + hairy or spiny. But with butterflies there is no such simplicity + of contrast. The eatable butterflies comprise not only brown or + white species, but hundreds of Nymphalidae, Papilionidae, + Lycaenidae, etc., which are gaily coloured and of an immense + variety of patterns. The colours and patterns of the inedible + kinds are also greatly varied, while they are often equally gay; + and it is quite impossible to suppose that any amount of instinct + or inherited habit (if such a thing exists) could enable young + insectivorous birds to distinguish all the species of one kind + from all those of the other. There is also some evidence to show + that animals do learn by experience what to eat and what to + avoid. Mr. Poulton was assured by Rev. G.J. Bursch that very + young chickens peck at insects which they afterwards avoid. + Lizards, too, often seized larvae which they were unable to eat + and ultimately rejected.</p> + + <p><a name="Page_255" id="Page_255"></a>Although the Heliconidae + present, on the whole, many varieties of coloration and pattern, + yet, in proportion to the number of distinct species in each + district, the types of coloration are few and very well marked, + and thus it becomes easier for a bird or other animal to learn + that all belonging to such types are uneatable. This must be a + decided advantage to the family in question, because, not only do + fewer individuals of each species need to be sacrificed in order + that their enemies may learn the lesson of their inedibility, but + they are more easily recognised at a distance, and thus escape + even pursuit. There is thus a kind of mimicry between closely + allied species as well as between species of distinct genera, all + tending to the same beneficial end. This may be seen in the four + or five distinct species of the genus Heliconius which all have + the same peculiar type of coloration—a yellow band across + the upper wings and radiating red stripes on the lower,—and + are all found in the same forests of the Lower Amazon; in the + numerous very similar species of Ithomia with transparent wings, + found in every locality of the same region; and in the very + numerous species of Papilio of the "Aeneas" group, all having a + similar style of marking, the resemblance being especially close + in the females. The very uniform type of colouring of the + blue-black Euplaeas and of the fulvous Acraeas is of the same + character.<a name="FNanchor_107_107" id= + "FNanchor_107_107"></a><a href="#Footnote_107_107" class= + "fnanchor">[107]</a> In all these cases the similarity of the + allied species is so great, that, when they are on the wing at + some distance off, it is difficult to distinguish one species + from another. But this close external resemblance is not always a + sign of very near affinity; for minute examination detects + differences in the form and scalloping of the wings, in the + markings on the body, and in those on the under surface of the + wings, which do not usually characterise the closest allies. It + is to be further noted, that the presence of groups of very + similar species of the same genus, in one locality, is not at all + a common phenomenon among unprotected groups. Usually the species + of a genus found in one locality are each well marked and belong + to somewhat distinct types, while the <a name="Page_256" id= + "Page_256"></a>closely allied forms—those that require + minute examination to discriminate them as distinct + species—are most generally found in separate areas, and are + what are termed representative forms.</p> + + <p>The extension we have now given to the theory of mimicry is + important, since it enables us to explain a much wider range of + colour phenomena than those which were first imputed to mimicry. + It is in the richest butterfly region in the world—the + Amazon valley—that we find the most abundant evidence of + the three distinct sets of facts, all depending on the same + general principle. The form of mimicry first elucidated by Mr. + Bates is characterised by the presence in each locality of + certain butterflies, or other insects, themselves edible and + belonging to edible groups, which derived protection from having + acquired a deceptive resemblance to some of the inedible + butterflies in the same localities, which latter were believed to + be wholly free from the attacks of insectivorous birds. Then came + the extension of the principle, by Dr. F. Müller, to the + case of species of distinct genera of the inedible butterflies + resembling each other quite as closely as in the former cases, + and like them always found in the same localities. They derive + mutual benefit from becoming, in appearance, one species, from + which a certain toll is taken annually to teach the young + insectivorous birds that they are uneatable. Even when the two or + more species are approximately equal in numbers, they each derive + a considerable benefit from thus combining their forces; but when + one of the species is scarce or verging on extinction, the + benefit becomes exceedingly great, being, in fact, exactly + apportioned to the need of the species.</p> + + <p>The third extension of the same principle explains the + grouping of allied species of the same genera of inedible + butterflies into sets, each having a distinct type of coloration, + and each consisting of a number of species which can hardly be + distinguished on the wing. This must be useful exactly in the + same way as in the last case, since it divides the inevitable + toll to insectivorous birds and other animals among a number of + species. It also explains the fact of the great similarity of + many species of inedible insects in the same locality—a + similarity which does not obtain to anything <a name="Page_257" + id="Page_257"></a>like the same extent among the edible species. + The explanation of the various phenomena of resemblance and + mimicry, presented by the distasteful butterflies, may now be + considered tolerably complete.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mimicry in other Orders of Insects.</i></p> + + <p>A very brief sketch of these phenomena will be given, chiefly + to show that the same principle prevails throughout nature, and + that, wherever a rather extensive group is protected, either by + distastefulness or offensive weapons, there are usually some + species of edible and inoffensive groups that gain protection by + imitating them. It has been already stated that the Telephoridae, + Lampyridae, and other families of soft-winged beetles, are + distasteful; and as they abound in all parts of the world, and + especially in the tropics, it is not surprising that insects of + many other groups should imitate them. This is especially the + case with the longicorn beetles, which are much persecuted by + insectivorous birds; and everywhere in tropical regions some of + these are to be found so completely disguised as to be mistaken + for species of the protected groups. Numbers of these imitations + have been already recorded by Mr. Bates and myself, but I will + here refer to a few others.</p> + + <p>In the recently published volumes on the Longicorn and + Malacoderm beetles of Central America<a name="FNanchor_108_108" + id="FNanchor_108_108"></a><a href="#Footnote_108_108" class= + "fnanchor">[108]</a> there are numbers of beautifully coloured + figures of the new species; and on looking over them we are + struck by the curious resemblance of some of the Longicorns to + species of the Malacoderm group. In some cases we discover + perfect mimics, and on turning to the descriptions we always find + these pairs to come from the same locality. Thus the Otheostethus + melanurus, one of the Prionidae, imitates the malacoderm, + Lucidota discolor, in form, peculiar coloration, and size, and + both are found at Chontales in Nicaragua, the species mimicked + having, however, as is usual, a wider range. The curious and very + rare little longicorn, Tethlimmena aliena, quite unlike its + nearest allies in the same country, is an exact copy on a + somewhat smaller scale of a malacoderm, Lygistopterus amabilis, + both <a name="Page_258" id="Page_258"></a>found at Chontales. The + pretty longicorn, Callia albicornis, closely resembles two + species of malacoderms (Silis chalybeipennis and Colyphus + signaticollis), all being small beetles with red head and thorax + and bright blue elytra, and all three have been found at Panama. + Many other species of Callia also resemble other malacoderms; and + the longicorn genus Lycidola has been named from its resemblance + to various species of the Lycidae, one of the species here + figured (Lycidola belti) being a good mimic of Calopteron + corrugatum and of several other allied species, all being of + about the same size and found at Chontales. In these cases, and + in most others, the longicorn beetles have lost the general form + and aspect of their allies to take on the appearance of a + distinct tribe. Some other groups of beetles, as the Elateridae + and Eucnemidae, also deceptively mimic malacoderms.</p> + + <p>Wasps and bees are often closely imitated by insects of other + orders. Many longicorn beetles in the tropics exactly mimic + wasps, bees, or ants. In Borneo a large black wasp, whose wings + have a broad white patch near the apex (Mygnimia aviculus), is + closely imitated by a heteromerous beetle (Coloborhombus + fasciatipennis), which, contrary to the general habit of beetles, + keeps its wings expanded in order to show the white patch on + their apex, the wing-coverts being reduced to small oval scales, + as shown in the figure. This is a most remarkable instance of + mimicry, because the beetle has had to acquire so many characters + which are unknown among its allies (except in another species + from Java)—the expanded wings, the white band on them, and + the oval scale-like elytra.<a name="FNanchor_109_109" id= + "FNanchor_109_109"></a><a href="#Footnote_109_109" class= + "fnanchor">[109]</a> Another remarkable case has been noted by + Mr. Neville Goodman, in Egypt, where a common hornet (Vespa + orientalis) is exactly imitated in colour, size, shape, attitude + when at rest, and mode of flight, by a beetle of the genus + Laphria.<a name="FNanchor_110_110" id= + "FNanchor_110_110"></a><a href="#Footnote_110_110" class= + "fnanchor">[110]</a></p> + + <p>The tiger-beetles (Cicindelidae) are also the subjects of + mimicry by more harmless insects. In the Malay Islands I found a + heteromerous beetle which exactly resembled a Therates, both + being found running on the trunks of trees. A longicorn + (Collyrodes Lacordairei) mimics Collyris, another genus of the + same family; while in the Philippine Islands <a name="Page_259" + id="Page_259"></a>there is a cricket (Condylodeira + tricondyloides), which so closely resembles a tiger-beetle of the + genus Tricondyla that the experienced entomologist, Professor + Westwood, at first placed it in his cabinet among those + beetles.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig26" id="fig26"></a> <img src="images/fig26.jpg" + width="400" height="485" alt= + "FIG. 26.—Mygnimia aviculus (Wasp). Coloborhombus fasciatipennis (Beetle)." + title= + "FIG. 26.—Mygnimia aviculus (Wasp). Coloborhombus fasciatipennis (Beetle)." /> + <b>FIG. 26.—Mygnimia aviculus (Wasp).<br /> + Coloborhombus fasciatipennis (Beetle).</b> + </div> + + <p><a name="Page_260" id="Page_260"></a></p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig27" id="fig27"></a> <img src="images/fig27.jpg" + width="400" height="502" alt= + "FIG. 27.—a. Doliops sp. (Longicorn) mimics Pachyrhynchus orbifae." + title= + "FIG. 27. a. Doliops sp. (Longicorn) mimics Pachyrhynchus orbifae." /> + + <p>FIG. 27.</p> + + <p style= + 'font-size:smaller; font-weight:bolder; text-align:left;'>a. + Doliops sp. (Longicorn) mimics Pachyrhynchus orbifae, (b) (a + hard curculio).<br /> + c. Doliops curculionoides mimics (d) Pachyrhynchus sp.<br /> + e. Scepastus pachyrhynchoides (a grasshopper), mimics (f) + Apocyrtus sp. (a hard curculio).<br /> + g. Doliops sp. mimics (h) Pachyrhynchus sp.<br /> + i. Phoraspis (grasshopper) mimics (k) a Coccinella.<br /> + <br /> + All the above are from the Philippines. The exact + correspondence of the colours of the insects themselves renders + the mimicry much more complete in nature than it appears in the + above figures.</p> + </div> + + <p>One of the characters by which some beetles are protected is + excessive hardness of the elytra and integuments. Several genera + of weevils (Curculionidae) are thus saved from attack, and these + are often mimicked by species of softer and more eatable groups. + In South America, the genus Heilipus is one of these hard groups, + and both Mr. Bates and M. Roelofs, a Belgian entomologist, have + noticed that species of other genera exactly mimic them. So, in + the Philippines, there <a name="Page_261" id="Page_261"></a>is a + group of Curculionidae, forming the genus Pachyrhynchus, in which + all the species are adorned with the most brilliant metallic + colours, banded and spotted in a curious manner, and are very + smooth and hard. Other genera of Curculionidae (Desmidophorus, + Alcides), which are usually very differently coloured, have + species in the Philippines which mimic the Pachyrhynchi; and + there are also several longicorn beetles (Aprophata, Doliops, + Acronia, and Agnia), which also mimic them. Besides these, there + are some longicorns and cetonias which reproduce the same colours + and markings; and there is even a cricket (Scepastus + pachyrhynchoides), which has taken on the form and peculiar + coloration of these beetles in order to escape from enemies, + which then avoid them as uneatable.<a name="FNanchor_111_111" id= + "FNanchor_111_111"></a><a href="#Footnote_111_111" class= + "fnanchor">[111]</a> The figures on the opposite page exhibit + several other examples of these mimicking insects.</p> + + <p>Innumerable other cases of mimicry occur among tropical + insects; but we must now pass on to consider a few of the very + remarkable, but much rarer instances, that are found among the + higher animals.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mimicry among the Vertebrata.</i></p> + + <p>Perhaps the most remarkable cases yet known are those of + certain harmless snakes which mimic poisonous species. The genus + Elaps, in tropical America, consists of poisonous snakes which do + not belong to the viper family (in which are included the + rattlesnakes and most of those which are poisonous), and which do + not possess the broad triangular head which characterises the + latter. They have a peculiar style of coloration, consisting of + alternate rings of red and black, or red, black, and yellow, of + different widths and grouped in various ways in the different + species; and it is a style of coloration which does not occur in + any other group of snakes in the world. But in the same regions + are found three genera of harmless snakes, belonging to other + families, some few species of which mimic the poisonous Elaps, + often so exactly that it is with difficulty one can be + distinguished from the other. Thus Elaps fulvius in Guatemala is + imitated by the harmless Pliocerus equalis; Elaps corallinus in + Mexico is mimicked by the <a name="Page_262" id= + "Page_262"></a>harmless Homalocranium semicinctum; and Elaps + lemniscatus in Brazil is copied by Oxyrhopus trigeminus; while in + other parts of South America similar cases of mimicry occur, + sometimes two harmless species imitating the same poisonous + snake.</p> + + <p>A few other instances of mimicry in this group have been + recorded. There is in South Africa an egg-eating snake + (Dasypeltis scaber), which has neither fangs nor teeth, yet it is + very like the Berg adder (Clothos atropos), and when alarmed + renders itself still more like by flattening out its head and + darting forward with a hiss as if to strike a foe.<a name= + "FNanchor_112_112" id="FNanchor_112_112"></a><a href= + "#Footnote_112_112" class="fnanchor">[112]</a> Dr. A.B. Meyer has + also discovered that, while some species of the genus Callophis + (belonging to the same family as the American Elaps) have large + poison fangs, other species of the same genus have none; and that + one of the latter (C. gracilis) resembles a poisonous species (C. + intestinalis) so closely, that only an exact comparison will + discover the difference of colour and marking. A similar kind of + resemblance is said to exist between another harmless snake, + Megaerophis flaviceps, and the poisonous Callophis bivirgatus; + and in both these cases the harmless snake is less abundant than + the poisonous one, as occurs in all examples of true + mimicry.<a name="FNanchor_113_113" id= + "FNanchor_113_113"></a><a href="#Footnote_113_113" class= + "fnanchor">[113]</a></p> + + <p>In the genus Elaps, above referred to, the very peculiar style + of colour and marking is evidently a "warning colour" for the + purpose of indicating to snake-eating birds and mammals that + these species are poisonous; and this throws light on the + long-disputed question of the use of the rattle of the + rattlesnake. This reptile is really both sluggish and timid, and + is very easily captured by those who know its habits. If gently + tapped on the head with a stick, it will coil itself up and lie + still, only raising its tail and rattling. It may then be easily + caught. This shows that the rattle is a warning to its enemies + that it is dangerous to proceed to extremities; and the creature + has probably acquired this structure and habit because it + frequents open or rocky districts where protective colour is + needful to save it from being pounced upon by buzzards or other + snake-eaters. Quite parallel in function is the expanded hood of + the Indian cobra, a <a name="Page_263" id= + "Page_263"></a>poisonous snake which belongs also to the + Elapidae. This is, no doubt, a warning to its foes, not an + attempt to terrify its prey; and the hood has been acquired, as + in the case of the rattlesnake, because, protective coloration + being on the whole useful, some mark was required to distinguish + it from other protectively coloured, but harmless, snakes. Both + these species feed on active creatures capable of escaping if + their enemy were visible at a moderate distance.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mimicry among Birds.</i></p> + + <p>The varied forms and habits of birds do not favour the + production among them of the phenomena of warning colours or of + mimicry; and the extreme development of their instincts and + reasoning powers, as well as their activity and their power of + flight, usually afford them other means of evading their enemies. + Yet there are a few imperfect, and one or two very perfect cases + of true mimicry to be found among them. The less perfect examples + are those presented by several species of cuckoos, an exceedingly + weak and defenceless group of birds. Our own cuckoo is, in colour + and markings, very like a sparrow-hawk. In the East, several of + the small black cuckoos closely resemble the aggressive + drongo-shrikes of the same country, and the small metallic + cuckoos are like glossy starlings; while a large ground-cuckoo of + Borneo (Carpococcyx radiatus) resembles one of the fine pheasants + (Euplocamus) of the same country, both in form and in its rich + metallic colours.</p> + + <p>More perfect cases of mimicry occur between some of the + dull-coloured orioles in the Malay Archipelago and a genus of + large honey-suckers—the Tropidorhynchi or "Friar-birds." + These latter are powerful and noisy birds which go in small + flocks. They have long, curved, and sharp beaks, and powerful + grasping claws; and they are quite able to defend themselves, + often driving away crows and hawks which venture to approach them + too nearly. The orioles, on the other hand, are weak and timid + birds, and trust chiefly to concealment and to their retiring + habits to escape persecution. In each of the great islands of the + Austro-Malayan region there is a distinct species of + Tropidorhynchus, and there is always along with it an oriole that + exactly mimics it. All the Tropidorhynchi <a name="Page_264" id= + "Page_264"></a>have a patch of bare black skin round the eyes, + and a ruff of curious pale recurved feathers on the nape, whence + their name of Friar-birds, the ruff being supposed to resemble + the cowl of a friar. These peculiarities are imitated in the + orioles by patches of feathers of corresponding colours; while + the different tints of the two species in each island are exactly + the same. Thus in Bouru both are earthy brown; in Ceram they are + both washed with yellow ochre; in Timor the under surface is pale + and the throat nearly white, and Mr. H.O. Forbes has recently + discovered another pair in the island of Timor Laut. The close + resemblance of these several pairs of birds, of widely different + families, is quite comparable with that of many of the insects + already described. It is so close that the preserved specimens + have even deceived naturalists; for, in the great French work, + <i>Voyage de l'Astrolabe</i>, the oriole of Bouru is actually + described and figured as a honey-sucker; and Mr. Forbes tells us + that, when his birds were submitted to Dr. Sclater for + description, the oriole and the honey-sucker were, previous to + close examination, considered to be the same species.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Objections to the Theory of Mimicry.</i></p> + + <p>To set forth adequately the varied and surprising facts of + mimicry would need a large and copiously illustrated volume; and + no more interesting subject could be taken up by a naturalist who + has access to our great collections and can devote the necessary + time to search out the many examples of mimicry that lie hidden + in our museums. The brief sketch of the subject that has been + here given will, however, serve to indicate its nature, and to + show the weakness of the objections that were at first made to + it. It was urged that the action of "like conditions," with + "accidental resemblances" and "reversion to ancestral types," + would account for the facts. If, however, we consider the actual + phenomena as here set forth, and the very constant conditions + under which they occur, we shall see how utterly inadequate are + these causes, either singly or combined. These constant + conditions are—</p> + + <div class="blockquot"> + <p>1. That the imitative species occur in the same area and + occupy the very same station as the imitated.</p> + + <p>2. That the imitators are always the more defenceless.</p> + + <p><a name="Page_265" id="Page_265"></a>3. That the imitators + are always less numerous in individuals.</p> + + <p>4. That the imitators differ from the bulk of their + allies.</p> + + <p>5. That the imitation, however minute, is <i>external</i> + and <i>visible</i> only, never extending to internal characters + or to such as do not affect the external appearance.</p> + </div> + + <p>These five characteristic features of mimicry show us that it + is really an exceptional form of protective resemblance. + Different species in the same group of organisms may obtain + protection in different ways: some by a general resemblance to + their environment; some by more exactly imitating the objects + that surround them—bark, or leaf, or flower; while others + again gain an equal protection by resembling some species which, + from whatever cause, is almost as free from attack as if it were + a leaf or a flower. This immunity may depend on its being + uneatable, or dangerous, or merely strong; and it is the + resemblance to such creatures for the purpose of sharing in their + safety that constitutes mimicry.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks on Warning Colours and Mimicry.</i></p> + + <p>Colours which have been acquired for the purpose of serving as + a warning of inedibility, or of the possession of dangerous + offensive weapons, are probably more numerous than have been + hitherto supposed; and, if so, we shall be able to explain a + considerable amount of colour in nature for which no use has + hitherto been conjectured. The brilliant and varied colours of + sea-anemones and of many coral animals will probably come under + this head, since we know that many of them possess the power of + ejecting stinging threads from various parts of their bodies + which render them quite uneatable to most animals. Mr. Gosse + describes how, on putting an Anthea into a tank containing a + half-grown bullhead (Cottus bubalis) which had not been fed for + some time, the fish opened his mouth and sucked in the morsel, + but instantly shot it out again. He then seized it a second time, + and after rolling it about in his mouth for a moment shot it out + again, and then darted away to hide himself in a hole. Some + tropical fishes, however, of the genera Tetrodon, Pseudoscarus, + Astracion, and a few others, seem <a name="Page_266" id= + "Page_266"></a>to have acquired the power of feeding on corals + and medusae; and the beautiful bands and spots and bright colours + with which they are frequently adorned, may be either protective + when feeding in the submarine coral groves, or may, in some + cases, be warning colours to show that they themselves are + poisonous and uneatable.</p> + + <p>A remarkable illustration of the wide extension of warning + colours, and their very definite purpose in nature, is afforded + by what may now be termed "Mr. Belt's frog." Frogs in all parts + of the world are, usually, protectively coloured with greens or + browns; and the little tree-frogs are either green like the + leaves they rest upon, or curiously mottled to imitate bark or + dead leaves. But there are a certain number of very gaily + coloured frogs, and these do not conceal themselves as frogs + usually do. Such was the small toad found by Darwin at Bahia + Blanca, which was intense black and bright vermilion, and crawled + about in the sunshine over dry sand-hills and arid plains. And in + Nicaragua, Mr. Belt found a little frog gorgeously dressed in a + livery of red and blue, which did not attempt concealment and was + very abundant, a combination of characters which convinced him + that it was uneatable. He, therefore, took a few specimens home + with him and gave them to his fowls and ducks, but none would + touch them. At last, by throwing down pieces of meat, for which + there was a great competition among the poultry, he managed to + entice a young duck into snatching up one of the little frogs. + Instead of swallowing it, however, the duck instantly threw it + out of its mouth, and went about jerking its head as if trying to + get rid of some unpleasant taste.<a name="FNanchor_114_114" id= + "FNanchor_114_114"></a><a href="#Footnote_114_114" class= + "fnanchor">[114]</a></p> + + <p>The power of predicting what will happen in a given case is + always considered to be a crucial test of a true theory, and if + so, the theory of warning colours, and with it that of mimicry, + must be held to be well established. Among the creatures which + probably have warning colours as a sign of inedibility are, the + brilliantly coloured nudibranchiate molluscs, those curious + annelids the Nereis and the Aphrodite or sea-mouse, and many + other marine animals. The brilliant colours of the scallops + (Pecten)and some other bivalve shells are perhaps <a name= + "Page_267" id="Page_267"></a>an indication of their hardness and + consequent inedibility, as in the case of the hard beetles; and + it is not improbable that some of the phosphorescent fishes and + other marine organisms may, like the glow-worm, hold out their + lamp as a warning to enemies.<a name="FNanchor_115_115" id= + "FNanchor_115_115"></a><a href="#Footnote_115_115" class= + "fnanchor">[115]</a> In Queensland there is an exceedingly + poisonous spider, whose bite will kill a dog, and cause severe + illness with excruciating pain in man. It is black, with a bright + vermilion patch on the middle of the body; and it is so well + recognised by this conspicuous coloration that even the + spider-hunting wasps avoid it.<a name="FNanchor_116_116" id= + "FNanchor_116_116"></a><a href="#Footnote_116_116" class= + "fnanchor">[116]</a></p> + + <p>Locusts and grasshoppers are generally of green protective + tints, but there are many tropical species most gaudily decorated + with red, blue, and black colours. On the same general grounds as + those by which Mr. Belt predicted the inedibility of his + conspicuous frog, we might safely predict the same for these + insects; but we have fortunately a proof that they are so + protected, since Mr. Charles Home states that one of the bright + coloured Indian locusts was invariably rejected when offered to + birds and lizards.<a name="FNanchor_117_117" id= + "FNanchor_117_117"></a><a href="#Footnote_117_117" class= + "fnanchor">[117]</a></p> + <hr style='width: 45%;' /> + + <p>The examples now given lead us to the conclusion that colours + acquired for the purpose of serving as a danger-signal to enemies + are very widespread in nature, and, with the corresponding + colours of the species which mimic them, furnish us with a + rational explanation of a considerable portion of the coloration + of animals which is outside the limits of those colours that have + been acquired for either protection or recognition. There + remains, however, another set of colours, chiefly among the + higher animals, which, being connected with some of the most + interesting and most disputed questions in natural history, must + be discussed in a separate chapter.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_92_92" id="Footnote_92_92"></a><a href= + "#FNanchor_92_92"><span class="label">[92]</span></a> + <i>Nature</i>, vol. iii. p. 165. Professor Meldola observed + that specimens of Danais and Euplaea in collections were less + subject to the attacks of mites <i>(Proc. Ent. Soc.</i>, + 1877, p. xii.); and this was corroborated by Mr. Jenner Weir. + <i>Entomologist</i>, 1882, vol. xv. p. 160.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_93_93" id="Footnote_93_93"></a><a href= + "#FNanchor_93_93"><span class="label">[93]</span></a> See + Darwin's <i>Descent of Man</i>, p. 325.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_94_94" id="Footnote_94_94"></a><a href= + "#FNanchor_94_94"><span class="label">[94]</span></a> + <i>Transactions of the Entomological Society of London</i>, + 1869, p. 21.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_95_95" id="Footnote_95_95"></a><a href= + "#FNanchor_95_95"><span class="label">[95]</span></a> + <i>Ibid.</i>, p. 27.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_96_96" id="Footnote_96_96"></a><a href= + "#FNanchor_96_96"><span class="label">[96]</span></a> + <i>Nature</i>, vol. iii. p. 147.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_97_97" id="Footnote_97_97"></a><a href= + "#FNanchor_97_97"><span class="label">[97]</span></a> + Stainton's <i>Manual of Butterflies and Moths</i>, vol. i. p. + 93; E.B. Poulton, <i>Proceedings of the Zool. Soc. of + London</i>, 1887, pp. 191-274.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_98_98" id="Footnote_98_98"></a><a href= + "#FNanchor_98_98"><span class="label">[98]</span></a> See + <i>Transactions of the Linnean Society</i>, vol. xxiii. pp. + 495-566, coloured plates.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_99_99" id="Footnote_99_99"></a><a href= + "#FNanchor_99_99"><span class="label">[99]</span></a> These + butterflies are now divided into two sub-families, one of + which is placed with the Danaidae; but to avoid confusion I + shall always speak of the American genera under the old term + Heliconidae.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_100_100" id= + "Footnote_100_100"></a><a href= + "#FNanchor_100_100"><span class="label">[100]</span></a> R. + Meldola in <i>Ann. and Mag. of Nat. Hist.</i>, Feb. 1878, p. + 158.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_101_101" id= + "Footnote_101_101"></a><a href= + "#FNanchor_101_101"><span class="label">[101]</span></a> See + <i>Trans. Linn. Soc.</i>, vol. xxv. Wallace, on Variation of + Malayan Papilionidae; and, Wallace's <i>Contributions to + Natural Selection</i> chaps. iii. and iv., where full details + are given.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_102_102" id= + "Footnote_102_102"></a><a href= + "#FNanchor_102_102"><span class="label">[102]</span></a> See + <i>Trans. Linn. Soc.</i>, vol. xxvi., with two coloured + plates illustrating cases of mimicry.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_103_103" id= + "Footnote_103_103"></a><a href= + "#FNanchor_103_103"><span class="label">[103]</span></a> + Edwards's <i>Butterflies of North America</i>, second series, + part vi.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_104_104" id= + "Footnote_104_104"></a><a href= + "#FNanchor_104_104"><span class="label">[104]</span></a> + Professor Meldola informs me that he has recorded another + case of mimicry among British moths, in which Acidalia + subsericata imitates Asthena candidata. See <i>Ent. Mo. + Mag.</i>, vol. iv. p. 163.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_105_105" id= + "Footnote_105_105"></a><a href= + "#FNanchor_105_105"><span class="label">[105]</span></a> From + Professor Meldola's translation of Dr. F. Müller's + paper, in <i>Proc. Ent. Soc. Lond.</i>, 1879, p. xx.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_106_106" id= + "Footnote_106_106"></a><a href= + "#FNanchor_106_106"><span class="label">[106]</span></a> + <i>Island Life</i>, p. 255.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_107_107" id= + "Footnote_107_107"></a><a href= + "#FNanchor_107_107"><span class="label">[107]</span></a> This + extension of the theory of mimicry was pointed out by + Professor Meldola in the paper already referred to; and he + has answered the objections to Dr. F. Müller's theory + with great force in the <i>Annals and Mag. of Nat. Hist.</i>, + 1882, p. 417.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_108_108" id= + "Footnote_108_108"></a><a href= + "#FNanchor_108_108"><span class="label">[108]</span></a> + Godman and Salvin's <i>Biologia Centrali-Americana, Insecta, + Coleoptera</i>, vol. iii. part ii., and vol. v.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_109_109" id= + "Footnote_109_109"></a><a href= + "#FNanchor_109_109"><span class="label">[109]</span></a> + <i>Trans. Ent. Soc.</i>, 1885, p. 369.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_110_110" id= + "Footnote_110_110"></a><a href= + "#FNanchor_110_110"><span class="label">[110]</span></a> + <i>Proc. Cambridge Phil. Soc.</i>, vol. iii. part ii., + 1877.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_111_111" id= + "Footnote_111_111"></a><a href= + "#FNanchor_111_111"><span class="label">[111]</span></a> + <i>Compte-Rendu de la Société Entomologique de + Belgaue</i>, series ii., No. 59, 1878.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_112_112" id= + "Footnote_112_112"></a><a href= + "#FNanchor_112_112"><span class="label">[112]</span></a> + <i>Nature</i>, vol. xxxiv. p. 547.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_113_113" id= + "Footnote_113_113"></a><a href= + "#FNanchor_113_113"><span class="label">[113]</span></a> + <i>Proceedings of the Zool. Soc. of London</i>, 1870, p. + 369.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_114_114" id= + "Footnote_114_114"></a><a href= + "#FNanchor_114_114"><span class="label">[114]</span></a> + <i>The Naturalist in Nicaragua</i>, p. 321.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_115_115" id= + "Footnote_115_115"></a><a href= + "#FNanchor_115_115"><span class="label">[115]</span></a> Mr. + Belt first suggested this use of the light of the Lampyridae + (fireflies and glow-worms)—<i>Naturalist in + Nicaragua</i>, p. 320. Mr. Verrill and Professor Meldola made + the same suggestion in the case of medusae and other + phosphorescent marine organisms (<i>Nature</i>, vol. xxx. pp. + 281, 289).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_116_116" id= + "Footnote_116_116"></a><a href= + "#FNanchor_116_116"><span class="label">[116]</span></a> W.E. + Armit, in <i>Nature</i>, vol. xviii. p. 642.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_117_117" id= + "Footnote_117_117"></a><a href= + "#FNanchor_117_117"><span class="label">[117]</span></a> + <i>Proc. Ent. Soc.</i>, 1869, p. xiii.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_X" id="CHAPTER_X"></a><a name="Page_268" id= + "Page_268"></a>CHAPTER X</h2> + + <p style='font-weight:bold;'>COLOURS AND ORNAMENTS CHARACTERISTIC + OF SEX</p> + + <div class="blockquot"> + <p>Sex colours in the mollusca and crustacea—In + insects—In butterflies and moths—Probable causes of + these colours—Sexual selection as a supposed + cause—Sexual coloration of birds—Cause of dull + colours of female birds—Relation of sex colour to nesting + habits—Sexual colours of other vertebrates—Sexual + selection by the struggles of males—Sexual characters due + to natural selection—Decorative plumage of males and its + effect on the females—Display of decorative plumage by + the males—A theory of animal coloration—The origin + of accessory plumes—Development of accessory plumes and + their display—The effect of female preference will be + neutralised by natural selection—General laws of animal + coloration—Concluding remarks.</p> + </div> + + <p>In the preceding chapters we have dealt chiefly with the + coloration of animals as distinctive of the several species; and + we have seen that, in an enormous number of cases, the colours + can be shown to have a definite purpose, and to be useful either + as a means of protection or concealment, of warning to enemies, + or of recognition by their own kind. We have now to consider a + subordinate but very widespread phenomenon—-the differences + of colour or of ornamental appendages in the two sexes. These + differences are found to have special relations with the three + classes of coloration above referred to, in many cases confirming + the explanation already given of their purport and use, and + furnishing us with important aid in formulating a general theory + of animal coloration.</p> + + <p>In comparing the colours of the two sexes we find a perfect + gradation, from absolute identity of colour up to such extreme + difference that it is difficult to believe that the two forms can + belong to the same species; and this diversity in the <a name= + "Page_269" id="Page_269"></a>colours of the sexes does not bear + any constant relation to affinity or systematic position. In both + insects and birds we find examples of complete identity and + extreme diversity of the sexes; and these differences occur + sometimes in the same tribe or family, and sometimes even in the + same genus.</p> + + <p>It is only among the higher and more active animals that + sexual differences of colour acquire any prominence. In the + mollusca the two sexes, when separated, are always alike in + colour, and only very rarely present slight differences in the + form of the shell. In the extensive group of crustacea the two + sexes as a rule are identical in colour, though there are often + differences in the form of the prehensile organs; but in a very + few cases there are differences of colour also. Thus, in a + Brazilian species of shore-crab (Gelasimus) the female is + grayish-brown, while in the male the posterior part of the + cephalo-thorax is pure white, with the anterior part of a rich + green. This colour is only acquired by the males when they become + mature, and is liable to rapid change in a few minutes to dusky + tints.<a name="FNanchor_118_118" id= + "FNanchor_118_118"></a><a href="#Footnote_118_118" class= + "fnanchor">[118]</a> In some of the freshwater fleas (Daphnoidae) + the males are ornamented with red and blue spots, while in others + similar colours occur in both sexes. In spiders also, though as a + rule the two sexes are alike in colour, there are a few + exceptions, the males being ornamented with brilliant colours on + the abdomen, while the female is dull coloured.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Coloration in Insects.</i></p> + + <p>It is only when we come to the winged insects that we find any + large amount of peculiarity in sexual coloration, and even here + it is only developed in certain orders. Flies (Diptera), + field-bugs (Hemiptera), cicadas (Homoptera), and the + grasshoppers, locusts, and crickets (Orthoptera) present very few + and unimportant sexual differences of colour; but the last two + groups have special musical organs very fully developed in the + males of some of the species, and these no doubt enable the sexes + to discover and recognise each other. In some cases, however, + when the female is protectively coloured, as in the well-known + leaf-insects already referred to (p. 207), the male <a name= + "Page_270" id="Page_270"></a>is smaller and much less + protectively formed and coloured. In the bees and wasps + (Hymenoptera) it is also the rule that the sexes are alike in + colour, though there are several cases among solitary bees where + they differ; the female being black, and the male brown in + Anthophora retusa, while in Andraena fulva the female is more + brightly coloured than the male. Of the great order of beetles + (Coleoptera) the same thing may be said. Though often so rich and + varied in their colours the sexes are usually alike, and Mr. + Darwin was only able to find about a dozen cases in which there + was any conspicuous difference between them.<a name= + "FNanchor_119_119" id="FNanchor_119_119"></a><a href= + "#Footnote_119_119" class="fnanchor">[119]</a> They exhibit, + however, numerous sexual characters, in the length of the + antennae, and in horns, legs, or jaws remarkably enlarged or + curiously modified in the male sex.</p> + + <p>It is in the family of dragonflies (order Neuroptera) that we + first meet with numerous cases of distinctive sexual coloration. + In some of the Agrionidae the males have the bodies rich blue and + the wings black, while the females have the bodies green and the + wings transparent. In the North American genus Hetaerina the + males alone have a carmine spot at the base of each wing; but in + some other genera the sexes hardly differ at all.</p> + + <p>The great order of Lepidoptera, including the butterflies and + moths, affords us the most numerous and striking examples of + diversity of sexual colouring. Among the moths the difference is + usually but slight, being manifested in a greater intensity of + the colour of the smaller winged male; but in a few cases there + is a decided difference, as in the ghost-moth (Hepialus humuli), + in which the male is pure white, while the female is yellow with + darker markings. This may be a recognition colour, enabling the + female more readily to discover her mate; and this view receives + some support from the fact that in the Shetland Islands the male + is almost as yellow as the female, since it has been suggested + that at midsummer, when this moth appears, there is in that high + latitude sufficient twilight all night to render any special + coloration unnecessary.<a name="FNanchor_120_120" id= + "FNanchor_120_120"></a><a href="#Footnote_120_120" class= + "fnanchor">[120]</a></p> + + <p>Butterflies present us with a wonderful amount of sexual + <a name="Page_271" id="Page_271"></a>difference of colour, in + many cases so remarkable that the two sexes of the same species + remained for many years under different names and were thought to + be quite distinct species. We find, however, every gradation from + perfect identity to complete diversity, and in some cases we are + able to see a reason for this difference. Beginning with the most + extraordinary cases of diversity—as in Diadema misippus, + where the male is black, ornamented with a large white spot on + each wing margined with rich changeable blue, while the female is + orange-brown with black spots and stripes—we find the + explanation in the fact that the female mimics an uneatable + Danais, and thus gains protection while laying its eggs on low + plants in company with that insect. In the allied species, + Diadema bolina, the females are also very different from the + males, but are of dusky brown tints, evidently protective and + very variable, some specimens having a general resemblance to the + uneatable Euplaeas; so that we see here some of the earlier + stages of both forms of protection. The remarkable differences in + some South American Pieridae are similarly explained. The males + of Pieris pyrrha, P. lorena, and several others, are white with a + few black bands and marginal spots like so many of their allies, + while the females are gaily coloured with yellow and brown, and + exactly resemble some species of the uneatable Heliconidae of the + same district. Similarly, in the Malay Archipelago, the female of + Diadema anomala is glossy metallic blue, while the male is brown; + the reason for this reversal of the usual rule being, that the + female exactly mimics the brilliant colouring of the common and + uneatable Euplaea midamus, and thus secures protection. In the + fine Adolias dirtea, the male is black with a few specks of + ochre-yellow and a broad marginal band of rich metallic + greenish-blue, while the female is brownish-black entirely + covered with rows of ochre-yellow spots. This latter coloration + does not appear to be protective when the insect is seen in the + cabinet, but it really is so. I have observed the female of this + butterfly in Sumatra, where it settles on the ground in the + forest, and its yellow spots so harmonise with the flickering + gleams of sunlight on the dead leaves that it can only be + detected with the greatest difficulty.</p> + + <p><a name="Page_272" id="Page_272"></a>A hundred other cases + might be quoted in which the female is either more obscurely + coloured than the male, or gains protection by imitating some + inedible species; and any one who has watched these female + insects flying slowly along in search of the plants on which to + deposit their eggs, will understand how important it must be to + them not to attract the attention of insect-eating birds by too + conspicuous colours. The number of birds which capture insects on + the wing is much greater in tropical regions than in Europe; and + this is perhaps the reason why many of our showy species are + alike, or almost alike, in both sexes, while they are + protectively coloured on the under side which is exposed to view + when they are at rest. Such are our peacock, tortoise-shell, and + red admiral butterflies; while in the tropics we more commonly + find that the females are less conspicuous on the upper surface + even when protectively coloured beneath.</p> + + <p>We may here remark, that the cases already quoted prove + clearly that either male or female may be modified in colour + apart from the opposite sex. In Pieris pyrrha and its allies the + male retains the usual type of coloration of the whole genus, + while the female has acquired a distinct and peculiar style of + colouring. In Adolias dirtea, on the other hand, the female + appears to retain something like the primitive colour and + markings of the two sexes, modified perhaps for more perfect + protection; while the male has acquired more and more intense and + brilliant colours, only showing his original markings by the few + small yellow spots that remain near the base of the wings. In the + more gaily coloured Pieridae, of which our orange-tip butterfly + may be taken as a type, we see in the female the plain ancestral + colours of the group, while the male has acquired the brilliant + orange tip to its wings, probably as a recognition mark.</p> + + <p>In those species in which the under surface is protectively + coloured, we often find the upper surface alike in both sexes, + the tint of colour being usually more intense in the male. But in + some cases this leads to the female being more conspicuous, as in + some of the Lycaenidae, where the female is bright blue and the + male of a blue so much deeper and soberer in tint as to appear + the less brilliantly coloured of the two.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_273" id="Page_273"></a><i>Probable Causes of these + Colours.</i></p> + + <p>In the production of these varied results there have probably + been several causes at work. There seems to be a constant + tendency in the male of most animals—but especially of + birds and insects—to develop more and more intensity of + colour, often culminating in brilliant metallic blues or greens + or the most splendid iridescent hues; while, at the same time, + natural selection is constantly at work, preventing the female + from acquiring these same tints, or modifying her colours in + various directions to secure protection by assimilating her to + her surroundings, or by producing mimicry of some protected form. + At the same time, the need for recognition must be satisfied; and + this seems to have led to diversities of colour in allied + species, sometimes the female, sometimes the male undergoing the + greatest change according as one or other could be modified with + the greatest ease, and so as to interfere least with the welfare + of the race. Hence it is that sometimes the males of allied + species vary most, as in the different species of Epicalia; + sometimes the females, as in the magnificent green species of + Ornithoptera and the "Aeneas" group of Papilio.</p> + + <p>The importance of the two principles—the need of + protection and recognition—in modifying the comparative + coloration of the sexes among butterflies, is beautifully + illustrated in the case of the groups which are protected by + their distastefulness, and whose females do not, therefore, need + the protection afforded by sober colours.</p> + + <p>In the great families, Heliconidae and Acraeidae, we find that + the two sexes are almost always alike; and, in the very few + exceptions, that the female, though differently, is not less + gaily or less conspicuously coloured. In the Danaidae the same + general rule prevails, but the cases in which the male exhibits + greater intensity of colour than the female are perhaps more + numerous than in the other two families. There is, however, a + curious difference in this respect between the Oriental and the + American groups of distasteful Papilios with warning colours, + both of which are the subjects of mimicry. In the Eastern + groups—of which P. hector and P. coon may be taken <a name= + "Page_274" id="Page_274"></a>as types—the two sexes are + nearly alike, the male being sometimes more intensely coloured + and with fewer pale markings; but in the American + groups—represented by P. aeneas, P. sesostris, and + allies—there is a wonderful diversity, the males having a + rich green or bluish patch on the fore wings, while the females + have a band or spots of pure white, not always corresponding in + position to the green spot of the males. There are, however, + transitional forms, by which a complete series can be traced, + from close similarity to great diversity of colouring between the + sexes; and this may perhaps be only an extreme example of the + intenser colour and more concentrated markings which are a very + prevalent characteristic of male butterflies.</p> + + <p>There are, in fact, many indications of a regular succession + of tints in which colour development has occurred in the various + groups of butterflies, from an original grayish or brownish + neutral tint. Thus in the "Aeneas" group of Papilios we have the + patch on the upper wings yellowish in P. triopas, olivaceous in + P. bolivar, bronzy-gray with a white spot in P. erlaces, more + greenish and buff in P. iphidamas, gradually changing to the fine + blue of P. brissonius, and the magnificent green of P. sesostris. + In like manner, the intense crimson spots of the lower wings can + be traced step by step from a yellow or buff tint, which is one + of the most widespread colours in the whole order. The greater + purity and intensity of colour seem to be usually associated with + more pointed wings, indicating greater vigour and more rapid + flight.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Selection as a supposed Cause of Colour + Development.</i></p> + + <p>Mr. Darwin, as is well known, imputed most of the brilliant + colours and varied patterns of butterflies' wings to sexual + selection—that is, to a constant preference, by female + butterflies, for the more brilliant males; the colours thus + produced being sometimes transmitted to the males alone, + sometimes to both sexes. This view has always seemed to me to be + unsupported by evidence, while it is also quite inadequate to + account for the facts. The only direct evidence, as set forth + with his usual fairness by Mr. Darwin himself, is opposed to his + views. Several entomologists assured him that, in moths, the + females evince not the least choice of their <a name="Page_275" + id="Page_275"></a>partners; and Dr. Wallace of Colchester, who + has largely bred the fine Bombyx cynthia, confirmed this + statement. Among butterflies, several males often pursue one + female, and Mr. Darwin says, that, unless the female exerts a + choice the pairing must be left to chance. But, surely, it may be + the most vigorous or most persevering male that is chosen, not + necessarily one more brightly or differently coloured, and this + will be true "natural selection." Butterflies have been noticed + to prefer some coloured flowers to others; but that does not + prove, or even render probable, any preference for the colour + itself, but only for flowers of certain colours, on account of + the more agreeable or more abundant nectar obtained from them. + Dr. Schulte called Mr. Darwin's attention to the fact, that in + the Diadema bolina the brilliant blue colour surrounding the + white spots is only visible when we look towards the insect's + head, and this is true of many of the iridescent colours of + butterflies, and probably depends upon the direction of the + striae on the scales. It is suggested, however, that this display + of colour will be seen by the female as the male is approaching + her, and that it has been developed by sexual selection.<a name= + "FNanchor_121_121" id="FNanchor_121_121"></a><a href= + "#Footnote_121_121" class="fnanchor">[121]</a> But in the + majority of cases the males <i>follow</i> the female, hovering + over her in a position which would render it almost impossible + for her to see the particular colours or patterns on his upper + surface; to do so the female should mount higher than the male, + and fly towards him—being the seeker instead of the sought, + and this is quite opposed to the actual facts. I cannot, + therefore, think that this suggestion adds anything whatever to + the evidence for sexual selection of colour by female + butterflies. This question will, however, be again touched upon + after we have considered the phenomena of sexual colour among the + vertebrata.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Coloration of Birds.</i></p> + + <p>The general rule among vertebrates, as regards colour, is, for + the two sexes to be alike. This prevails, with only a few + exceptions, in fishes, reptiles, and mammalia; but in birds + diversity of sexual colouring is exceedingly frequent, and is, + not improbably, present in a greater or less degree in more + <a name="Page_276" id="Page_276"></a>than half of the known + species. It is this class, therefore, that will afford us the + best materials for a discussion of the problem, and that may + perhaps lead us to a satisfactory explanation of the causes to + which sexual colour is due.</p> + + <p>The most fundamental characteristic of birds, from our present + point of view, is a greater intensity of colour in the male. This + is the case in hawks and falcons; in many thrushes, warblers, and + finches; in pigeons, partridges, rails, plovers, and many others. + When the plumage is highly protective or of dull uniform tints, + as in many of the thrushes and warblers, the sexes are almost or + quite identical in colour; but when any rich markings or bright + tints are acquired, they are almost always wanting or much + fainter in the female, as we see in the black-cap among warblers, + and the chaffinch among finches.</p> + + <p>It is in tropical regions, where from a variety of causes + colour has been, developed to its fullest extent, that we find + the most remarkable examples of sexual divergence of colour. The + most gorgeously coloured birds known are the birds of paradise, + the chatterers, the tanagers, the humming-birds, and the + pheasant-tribe, including the peacocks. In all these the females + are much less brilliant, and, in the great majority of cases, + exceptionally plain and dull coloured birds. Not only are the + remarkable plumes, crests, and gorgets of the birds of paradise + entirely wanting in the females, but these latter are usually + without any bright colour at all, and rank no higher than our + thrushes in ornamental plumage. Of the humming-birds the same may + be said, except that the females are often green, and sometimes + slightly metallic, but from their small size and uniform tints + are never conspicuous. The glorious blues and purples, the pure + whites and intense crimsons of the male chatterers are + represented in the females by olive-greens or dull browns, as are + the infinitely varied tints of the male tanagers. And in + pheasants, the splendour of plumage which characterises the males + is entirely absent in the females, which, though often + ornamental, have always comparatively sober and protective tints. + The same thing occurs with many other groups. In the Eastern + tropics are many brilliant birds belonging to the families of the + warblers, flycatchers, shrikes, etc., but the female is always + <a name="Page_277" id="Page_277"></a>much less brilliant than the + male and often quite dull coloured.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cause of Dull Colours of Female Birds.</i></p> + + <p>The reason of this phenomenon is not difficult to find, if we + consider the essential conditions of a bird's existence, and the + most important function it has to fulfil. In order that the + species may be continued, young birds must be produced, and the + female birds have to sit assiduously on their eggs. While doing + this they are exposed to observation and attack by the numerous + devourers of eggs and birds, and it is of vital importance that + they should be protectively coloured in all those parts of the + body which are exposed during incubation. To secure this end all + the bright colours and showy ornaments which decorate the male + have not been acquired by the female, who often remains clothed + in the sober hues which were probably once common to the whole + order to which she belongs. The different amounts of colour + acquired by the females have no doubt depended on peculiarities + of habits and of environment, and on the powers of defence or of + concealment possessed by the species. Mr. Darwin has taught us + that natural selection cannot produce absolute, but only relative + perfection; and as a protective colour is only one out of many + means by which the female birds are able to provide for the + safety of their young, those which are best endowed in other + respects will have been allowed to acquire more colour than those + with whom the struggle for existence is more severe.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Relation of Sex Colour to Nesting Habits.</i></p> + + <p>This principle is strikingly illustrated by the existence of + considerable numbers of birds in which both sexes are similarly + and brilliantly coloured,—in some cases as brilliantly as + the males of many of the groups above referred to. Such are the + extensive families of the kingfishers, the woodpeckers, the + toucans, the parrots, the turacos, the hangnests, the starlings, + and many other smaller groups, all the species of which are + conspicuously or brilliantly coloured, while in all of them the + females are either coloured exactly like the males, or, when + differently coloured, are equally conspicuous. When <a name= + "Page_278" id="Page_278"></a>searching for some cause for this + singular apparent exception to the rule of female protective + colouring, I came upon a fact which beautifully explains it; for + in all these cases, without exception, the species either nests + in holes in the ground or in trees, or builds a domed or covered + nest, so as completely to conceal the sitting-bird. We have here + a case exactly parallel to that of the butterflies protected by + distastefulness, whose females are either exactly like the males, + or, if different, are equally conspicuous. We can hardly believe + that so exact a parallel should exist between such remote classes + of animals, except under the influence of a general law; and, in + the need of protection by all defenceless animals, and especially + by most female insects and birds, we have such a law, which has + been proved to have influenced the colours of a considerable + proportion of the animal kingdom.<a name="FNanchor_122_122" id= + "FNanchor_122_122"></a><a href="#Footnote_122_122" class= + "fnanchor">[122]</a></p> + + <p>The general relation which exists between the mode of nesting + and the coloration of the sexes in those groups of birds which + need protection from enemies, may be thus expressed: When both + sexes are brilliant or conspicuous, the nest is such as to + conceal the sitting-bird; but when the male is brightly coloured + and the female sits exposed on the nest, she is always less + brilliant and generally of quite sober and protective hues.</p> + + <p>It must be understood that the mode of nesting has influenced + the colour, not that the colour has determined the mode of + nesting; and this, I believe, has been generally, though not + perhaps universally, the case. For we know that colour varies + more rapidly, and can be more easily modified and fixed by + selection, than any other character; whereas habits, especially + when connected with structure, and when they pervade a whole + group, are much more persistent and more difficult to change, as + shown by the habit of the dog turning round two or three times + before lying down, believed to be that of the wild ancestral form + which thus smoothed down the herbage so as to form a comfortable + bed. We see, too, that the general mode of nesting is + characteristic of whole families differing widely in size, form, + and colours. Thus, all the kingfishers and their allies in every + part of the world nest <a name="Page_279" id="Page_279"></a>in + holes, usually in banks, but sometimes in trees. The motmots and + the puff-birds (Bucconidae) build in similar places; while the + toucans, barbets, trogons, woodpeckers, and parrots all make + their nests in hollow trees. This habit, pervading all the + members of extensive families, must therefore be extremely + ancient, more especially as it evidently depends in some degree + on the structure of the birds, the bills, and especially the + feet, of all these groups being unfitted for the construction of + woven arboreal nests.<a name="FNanchor_123_123" id= + "FNanchor_123_123"></a><a href="#Footnote_123_123" class= + "fnanchor">[123]</a> But in all these families the colour varies + greatly from species to species, being constant only in the one + character of the similarity of the sexes, or, at all events, in + their being equally conspicuous even though differently + coloured.</p> + + <p>When I first put forward this view of the connection between + the mode of nesting and the coloration of female birds, I + expressed the law in somewhat different terms, which gave rise to + some misunderstanding, and led to numerous criticisms and + objections. Several cases were brought forward in which the + females were far less brilliant than the males, although the nest + was covered. This is the case with the Maluridae, or superb + warblers of Australia, in which the males are very brilliant + during the pairing season and the females quite plain, yet they + build domed nests. Here, there can be little doubt, the covered + nest is a protection from rain or from some special enemies to + the eggs; while the birds themselves are protectively coloured in + both sexes, except for a short time during the breeding season + when the male acquires brilliant colours; and this is probably + connected with the fact of their inhabiting the open plains and + thin scrub of Australia, where protective colours are as + generally advantageous as they are in our north-temperate + zones.</p> + + <p>As I have now stated the law, I do not think there are any + exceptions to it, while there are an overwhelming number of cases + which give it a strong support. It has been objected that the + domed nests of many birds are as conspicuous as the birds + themselves would be, and would, therefore, be of no use as a + protection to the birds and young. But, as a matter of fact, they + do protect from attack, for hawks or crows do not pluck such + nests to pieces, as in doing so they would be <a name="Page_280" + id="Page_280"></a>exposed to the attack of the whole colony; + whereas a hawk or falcon could carry off a sitting-bird or the + young at a swoop, and entirely avoid attack. Moreover, each kind + of covered nest is doubtless directed against the attacks of the + most dangerous enemies of the species, the purse-like nests, + often a yard long, suspended from the extremity of thin twigs, + being useful against the attacks of snakes, which, if they + attempted to enter them, would be easily made to lose their hold + and fall to the ground. Such birds as jays, crows, magpies, + hawks, and other birds of prey, have also been urged as an + exception; but these are all aggressive birds, able to protect + themselves, and thus do not need any special protection for their + females during nidification. Some birds which build in covered + nests are comparatively dull coloured, like many of the weaver + birds, but in others the colours are more showy, and in all the + sexes are alike; so that none of these are in any way opposed to + the rule. The golden orioles have, however, been adduced as a + decided exception, since the females are showy and build in an + open nest. But even here the females are less brilliant than the + males, and are sometimes greenish or olivaceous on the upper + surface; while they very carefully conceal their nests among + dense foliage, and the male is sufficiently watchful and + pugnacious to drive off most intruders.</p> + + <p>On the other hand, how remarkable it is that the only small + and brightly coloured birds of our own country in which the male + and female are alike—the tits and starlings—either + build in holes or construct covered nests; while the beautiful + hangnests (Icteridae) of South America, which always build + covered or purse-shaped nests, are equally showy in both sexes, + in striking contrast with the chatterers and tanagers of the same + country, whose females are invariably less conspicuous than the + males. On a rough estimate, there are about 1200 species of birds + in the class of showy males and females, with concealed + nidification; while there are probably, from an equally rough + estimate, about the same number in the contrasted class of showy + males and dull females, with open nests. This will leave the + great bulk of known birds in the classes of those which are more + or less protectively coloured in both sexes; or which, from their + organisation and habits, do <a name="Page_281" id= + "Page_281"></a>not require special protective coloration, such as + many of the birds of prey, the larger waders, and the oceanic + birds.</p> + + <p>There are a few very curious cases in which the female bird is + actually more brilliant than the male, and which yet have open + nests. Such are the dotterel (Eudromias morinellus), several + species of phalarope, an Australian creeper (Climacteris + erythropus), and a few others; but in every one of these cases + the relation of the sexes in regard to nidification is reversed, + the male performing the duties of incubation, while the female is + the stronger and more pugnacious. This curious case, therefore, + quite accords with the general law of coloration.<a name= + "FNanchor_124_124" id="FNanchor_124_124"></a><a href= + "#Footnote_124_124" class="fnanchor">[124]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Colours of other Vertebrates.</i></p> + + <p>We may consider a few of the cases of sexual colouring of + other classes of vertebrates, as given by Mr. Darwin. In fishes, + though the sexes are usually alike, there are several species in + which the males are more brightly coloured, and have more + elongated fins, spines, or other appendages, and in some few + cases the colours are decidedly different. The males often fight + together, and are altogether more vivacious and excitable than + the females during the breeding season; and with this we may + connect a greater intensity of coloration.</p> + + <p>In frogs and toads the colours are usually alike, or a little + more intense in the males, and the same may be said of most + snakes. It is in lizards that we first meet with considerable + sexual differences, many of the species having gular pouches, + frills, dorsal crests, or horns, either confined to the males, or + more developed in them than in the females, and these ornaments + are often brightly coloured. In most cases, however, the tints of + lizards are protective, the male being usually a little more + intense in coloration; and the difference in extreme cases may be + partly due to the need of protection for the female, which, when + laden with eggs, must be less active and less able to escape from + enemies than the male, and may, therefore, have retained more + protective colours, as so many insects and birds have certainly + done.<a name="FNanchor_125_125" id= + "FNanchor_125_125"></a><a href="#Footnote_125_125" class= + "fnanchor">[125]</a></p> + + <p>In mammalia there is often a somewhat greater intensity + <a name="Page_282" id="Page_282"></a>of colour in the male, but + rarely a decided difference. The female of the great red + kangaroo, however, is a delicate gray; while in the Lemur macaco + of Madagascar the male is jet-black and the female brown. In many + monkeys also there are some differences of colour, especially on + the face. The sexual weapons and ornaments of male mammalia, as + horns, crests, manes, and dewlaps, are well known, and are very + numerous and remarkable. Having thus briefly reviewed the facts, + we will now consider the theories to which they have given + rise.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Selection by the Struggles of Males.</i></p> + + <p>Among the higher animals it is a very general fact that the + males fight together for the possession of the females. This + leads, in polygamous animals especially, to the stronger or + better armed males becoming the parents of the next generation, + which inherits the peculiarities of the parents; and thus vigour + and offensive weapons are continually increased in the males, + resulting in the strength and horns of the bull, the tusks of the + boar, the antlers of the stag, and the spurs and fighting + instinct of the gamecock. But almost all male animals fight + together, though not specially armed; even hares, moles, + squirrels, and beavers fight to the death, and are often found to + be scarred and wounded. The same rule applies to almost all male + birds; and these battles have been observed in such different + groups as humming-birds, finches, goatsuckers, woodpeckers, + ducks, and waders. Among reptiles, battles of the males are known + to occur in the cases of crocodiles, lizards, and tortoises; + among fishes, in those of salmon and sticklebats. Even among + insects the same law prevails; and male spiders, beetles of many + groups, crickets, and butterflies often fight together.</p> + + <p>From this very general phenomenon there necessarily results a + form of natural selection which increases the vigour and fighting + power of the male animal, since, in every case, the weaker are + either killed, wounded, or driven away. This selection would be + more powerful if males were always in excess of females, but + after much research Mr. Darwin could not obtain any satisfactory + evidence that this was the case. The same effect, however, is + produced in some cases by constitution or habits; thus male + insects usually emerge first from <a name="Page_283" id= + "Page_283"></a>the pupa, and among migrating birds the males + arrive first both in this country and in North America. The + struggle is thus intensified, and the most vigorous males are the + first to have offspring. This in all probability is a great + advantage, as the early breeders have the start in securing food, + and the young are strong enough to protect themselves while the + later broods are being produced.</p> + + <p>It is to this form of male rivalry that Mr. Darwin first + applied the term "sexual selection." It is evidently a real power + in nature; and to it we must impute the development of the + exceptional strength, size, and activity of the male, together + with the possession of special offensive and defensive weapons, + and of all other characters which arise from the development of + these or are correlated with them. But he has extended the + principle into a totally different field of action, which has + none of that character of constancy and of inevitable result that + attaches to natural selection, including male rivalry; for by far + the larger portion of the phenomena, which he endeavours to + explain by the direct action of sexual selection, can only be so + explained on the hypothesis that the immediate agency is female + choice or preference. It is to this that he imputes the origin of + all secondary sexual characters other than weapons of offence and + defence, of all the ornamental crests and accessory plumes of + birds, the stridulating sounds of insects, the crests and beards + of monkeys and other mammals, and the brilliant colours and + patterns of male birds and butterflies. He even goes further, and + imputes to it a large portion of the brilliant colour that occurs + in both sexes, on the principle that variations occurring in one + sex are sometimes transmitted to the same sex only, sometimes to + both, owing to peculiarities in the laws of inheritance. In this + extension of sexual selection to include the action of female + choice or preference, and in the attempt to give to that choice + such wide-reaching effects, I am unable to follow him more than a + very little way; and I will now state some of the reasons why I + think his views are unsound.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Sexual Characters due to Natural Selection.</i></p> + + <p>Besides the acquisition of weapons by the male for the purpose + of fighting with other males, there are some other <a name= + "Page_284" id="Page_284"></a>sexual characters which may have + been produced by natural selection. Such are the various sounds + and odours which are peculiar to the male, and which serve as a + call to the female or as an indication of his presence. These are + evidently a valuable addition to the means of recognition of the + two sexes, and are a further indication that the pairing season + has arrived; and the production, intensification, and + differentiation of these sounds and odours are clearly within the + power of natural selection. The same remark will apply to the + peculiar calls of birds, and even to the singing of the males. + These may well have originated merely as a means of recognition + between the two sexes of a species, and as an invitation from the + male to the female bird. When the individuals of a species are + widely scattered, such a call must be of great importance in + enabling pairing to take place as early as possible, and thus the + clearness, loudness, and individuality of the song becomes a + useful character, and therefore the subject of natural selection. + Such is especially the case with the cuckoo, and with all + solitary birds, and it may have been equally important at some + period of the development of all birds. The act of singing is + evidently a pleasurable one; and it probably serves as an outlet + for superabundant nervous energy and excitement, just as dancing, + singing, and field sports do with us. It is suggestive of this + view that the exercise of the vocal power seems to be + complementary to the development of accessory plumes and + ornaments, all our finest singing birds being plainly coloured, + and with no crests, neck or tail plumes to display; while the + gorgeously ornamented birds of the tropics have no song, and + those which expend much energy in display of plumage, as the + turkey, peacocks, birds of paradise, and humming-birds, have + comparatively an insignificant development of voice. Some birds + have, in the wings or tail, peculiarly developed feathers which + produce special sounds. In some of the little manakins of Brazil, + two or three of the wing-feathers are curiously shaped and + stiffened in the male, so that the bird is able to produce with + them a peculiar snapping or cracking sound; and the tail-feathers + of several species of snipe are so narrowed as to produce + distinct drumming, whistling, or switching sounds when the birds + <a name="Page_285" id="Page_285"></a>descend rapidly from a great + height. All these are probably recognition and call notes, useful + to each species in relation to the most important function of + their lives, and thus capable of being developed by the agency of + natural selection.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Decorative Plumage of Birds and its Display.</i></p> + + <p>Mr. Darwin has devoted four chapters of his <i>Descent of + Man</i> to the colours of birds, their decorative plumage, and + its display at the pairing season; and it is on this latter + circumstance that he founds his theory, that both the plumage and + the colours have been developed by the preference of the females, + the more ornamented males becoming the parents of each successive + generation. Any one who reads these most interesting chapters + will admit, that the fact of the display is demonstrated; and it + may also be admitted, as highly probable, that the female is + pleased or excited by the display. But it by no means follows + that slight differences in the shape, pattern, or colours of the + ornamental plumes are what lead a female to give the preference + to one male over another; still less that all the females of a + species, or the great majority of them, over a wide area of + country, and for many successive generations, prefer exactly the + same modification of the colour or ornament.</p> + + <p>The evidence on this matter is very scanty, and in most cases + not at all to the point. Some peahens preferred an old pied + peacock; albino birds in a state of nature have never been seen + paired with other birds; a Canada goose paired with a Bernicle + gander; a male widgeon preferred a pintail duck to its own + species; a hen canary preferred a male greenfinch to either + linnet, goldfinch, siskin, or chaffinch. These cases are + evidently exceptional, and are not such as generally occur in + nature; and they only prove that the female does exert some + choice between very different males, and some observations on + birds in a state of nature prove the same thing; but there is no + evidence that slight variations in the colour or plumes, in the + way of increased intensity or complexity, are what determines the + choice. On the other hand, Mr. Darwin gives much evidence that it + is <i>not</i> so determined. He tells us that Messrs. Hewitt, + Tegetmeier, and Brent, three of the highest authorities and best + observers, "do not believe that <a name="Page_286" id= + "Page_286"></a>the females prefer certain males on account of the + beauty of their plumage." Mr. Hewitt was convinced "that the + female almost invariably prefers the most vigorous, defiant, and + mettlesome male;" and Mr. Tegetmeier, "that a gamecock, though + disfigured by being dubbed, and with his hackles trimmed, would + be accepted as readily as a male retaining all his natural + ornaments."<a name="FNanchor_126_126" id= + "FNanchor_126_126"></a><a href="#Footnote_126_126" class= + "fnanchor">[126]</a> Evidence is adduced that a female pigeon + will sometimes tn antipathy to a particular male without any + assignable cause; or, in other cases, will take a strong fancy to + some one bird, and will desert her own mate for him; but it is + not stated that superiority or inferiority of plumage has + anything to do with these fancies. Two instances are indeed + given, of male birds being rejected, which had lost their + ornamental plumage; but in both cases (a widow-finch and a silver + pheasant) the long tail-plumes are the indication of sexual + maturity. Such cases do not support the idea that males with the + tail-feathers a trifle longer, or the colours a trifle brighter, + are generally preferred, and that those which are only a little + inferior are as generally rejected,—and this is what is + absolutely needed to establish the theory of the development of + these plumes by means of the choice of the female.</p> + + <p>It will be seen, that female birds have unaccountable likes + and dislikes in the matter of their partners, just as we have + ourselves, and this may afford us an illustration. A young man, + when courting, brushes or curls his hair, and has his moustache, + beard, or whiskers in perfect order, and no doubt his sweetheart + admires them; but this does not prove that she marries him on + account of these ornaments, still less that hair, beard, + whiskers, and moustache were developed by the continued + preferences of the female sex. So, a girl likes to see her lover + well and fashionably dressed, and he always dresses as well as he + can when he visits her; but we cannot conclude from this that the + whole series of male costumes, from the brilliantly coloured, + puffed, and slashed doublet and hose of the Elizabethan period, + through the gorgeous coats, long waistcoats, and pigtails of the + early Georgian era, down to the funereal dress-suit of the + present day, are the direct result of female preference. In like + manner, female birds may be <a name="Page_287" id= + "Page_287"></a>charmed or excited by the fine display of plumage + by the males; but there is no proof whatever that slight + differences in that display have any effect in determining their + choice of a partner.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Display of Decorative Plumage.</i></p> + + <p>The extraordinary manner in which most birds display their + plumage at the time of courtship, apparently with the full + knowledge that it is beautiful, constitutes one of Mr. Darwin's + strongest arguments. It is, no doubt, a very curious and + interesting phenomenon, and indicates a connection between the + exertion of particular muscles and the development of colour and + ornament; but, for the reasons just given, it does not prove that + the ornament has been developed by female choice. During + excitement, and when the organism develops superabundant energy, + many animals find it pleasurable to exercise their various + muscles, often in fantastic ways, as seen in the gambols of + kittens, lambs, and other young animals. But at the time of + pairing, male birds are in a state of the most perfect + development, and possess an enormous store of vitality; and under + the excitement of the sexual passion they perform strange antics + or rapid flights, as much probably from an internal impulse to + motion and exertion as with any desire to please their mates. + Such are the rapid descent of the snipe, the soaring and singing + of the lark, and the dances of the cock-of-the-rock and of many + other birds.</p> + + <p>It is very suggestive that similar strange movements are + performed by many birds which have no ornamental plumage to + display. Goatsuckers, geese, carrion vultures, and many other + birds of plain plumage have been observed to dance, spread their + wings or tails, and perform strange love-antics. The courtship of + the great albatross, a most unwieldy and dull coloured bird, has + been thus described by Professor Moseley: "The male, standing by + the female on the nest, raises his wings, spreads his tail and + elevates it, throws up his head with the bill in the air, or + stretches it straight out, or forwards, as far as he can, and + then utters a curious cry."<a name="FNanchor_127_127" id= + "FNanchor_127_127"></a><a href="#Footnote_127_127" class= + "fnanchor">[127]</a> Mr. Jenner Weir informs me that "the male + blackbird is full of action, spreads out his glossy wing and + tail, turns his rich golden <a name="Page_288" id= + "Page_288"></a>beak towards the female, and chuckles with + delight," while he has never seen the more plain coloured thrush + demonstrative to the female. The linnet distends his rosy breast, + and slightly expands his brown wings and tail; while the various + gay coloured Australian finches adopt such attitudes and postures + as, in every case, to show off their variously coloured plumage + to the best advantage.<a name="FNanchor_128_128" id= + "FNanchor_128_128"></a><a href="#Footnote_128_128" class= + "fnanchor">[128]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>A Theory of Animal Coloration.</i></p> + + <p>Having rejected Mr. Darwin's theory of female choice as + incompetent to account for the brilliant colours and markings of + the higher animals, the preponderance of these colours and + markings in the male sex, and their display during periods of + activity or excitement, I may be asked what explanation I have to + offer as a preferable substitute. In my <i>Tropical Nature</i> I + have already indicated such a theory, which I will now briefly + explain, supporting it by some additional facts and arguments, + which appear to me to have great weight, and for which I am + mainly indebted to a most interesting and suggestive posthumous + work by Mr. Alfred Tylor.<a name="FNanchor_129_129" id= + "FNanchor_129_129"></a><a href="#Footnote_129_129" class= + "fnanchor">[129]</a></p> + + <p>The fundamental or ground colours of animals ar has been shown + in preceding chapters, very largely protective, and it is not + improbable that the primitive colours of all animals were so. + During the long course of animal development other modes of + protection than concealment by harmony of colour arose, and + thenceforth the normal development of colour due to the complex + chemical and structural changes ever going on in the organism, + had full play; and the colours thus produced were again and again + modified by natural selection for purposes of warning, + recognition, mimicry, or special protection, as has been already + fully explained in the preceding chapters.</p> + + <p>Mr. Taylor has, however, called attention to an important + principle which underlies the various patterns or ornamental + markings of animals—namely, that diversified coloration + follows the chief lines of structure, and changes at points, such + as the joints, where function changes. He says, "If we take + highly decorated species—that is, animals marked by + <a name="Page_289" id="Page_289"></a>alternate dark or light + bands or spots, such as the zebra, some deer, or the carnivora, + we find, first, that the region of the spinal column is marked by + a dark stripe; secondly, that the regions of the appendages, or + limbs, are differently marked; thirdly, that the flanks are + striped or spotted, along or between the regions of the lines of + the ribs; fourthly, that the shoulder and hip regions are marked + by curved lines; fifthly, that the pattern changes, and the + direction of the lines, or spots, at the head, neck, and every + joint of the limbs; and lastly, that the tips of the ears, nose, + tail, and feet, and the eye are emphasised in colour. In spotted + animals the greatest length of the spot is generally in the + direction of the largest development of the skeleton."</p> + + <p>This structural decoration is well seen in many insects. In + caterpillars, similar spots and markings are repeated in each + segment, except where modified for some form of protection. In + butterflies, the spots and bands usually have reference to the + form of the wing and the arrangement of the nervures; and there + is much evidence to show that the primitive markings are always + spots in the cells, or between the nervures, or at the junctions + of nervures, the extension and coalescence of these spots forming + borders, bands, or blotches, which have become modified in + infinitely varied ways for protection, warning, or recognition. + Even in birds, the distribution of colours and markings follows + generally the same law. The crown of the head, the throat, the + ear-coverts, and the eyes have usually distinct tints in all + highly coloured birds; the region of the furcula has often a + distinct patch of colour, as have the pectoral muscles, the + uropygium or root of the tail, and the under + tail-coverts.<a name="FNanchor_130_130" id= + "FNanchor_130_130"></a><a href="#Footnote_130_130" class= + "fnanchor">[130]</a></p> + + <p>Mr. Tylor was of opinion the primitive form of ornamentation + consisted of spots, the confluence of these in certain directions + forming lines or bands; and, these again, sometimes coalescing + into blotches, or into more or less uniform tints covering a + large portion of the surface of the body. The young lion and + tiger are both spotted; and in the Java hog (Sus vittatus) very + young animals are banded, but have spots over the shoulders and + thighs. These spots run into stripes <a name="Page_290" id= + "Page_290"></a>as the animal grows older; then the stripes + expand, and at last, meeting together, the adult animal becomes + of a uniform dark brown colour. So many of the species of deer + are spotted when young, that Darwin concludes the ancestral form, + from which all deer are derived, must have been spotted. Pigs and + tapirs are banded or spotted when young; an imported young + specimen of Tapirus Bairdi was covered with white spots in + longitudinal rows, here and there forming short stripes.<a name= + "FNanchor_131_131" id="FNanchor_131_131"></a><a href= + "#Footnote_131_131" class="fnanchor">[131]</a> Even the horse, + which Darwin supposes to be descended from a striped animal, is + often spotted, as in dappled horses; and great numbers show a + tendency to spottiness, especially on the haunches.</p> + + <p>Ocelli may also be developed from spots, or from bars, as + pointed out by Mr. Darwin. Spots are an ordinary form of marking + in disease, and these spots sometimes run together, forming + blotches. There is evidence that colour markings are in some way + dependent on nerve distribution. In the disease known as frontal + herpes, an eruption occurs which corresponds exactly to the + distribution of the ophthalmic division of the fifth cranial + nerve, mapping out all its little branches even to the one which + goes to the tip of the nose. In a Hindoo suffering from herpes + the pigment was destroyed in the arm along the course of the + ulnar nerve, with its branches along both sides of one finger and + the half of another. In the leg the sciatic and scaphenous nerves + were partly mapped out, giving to the patient the appearance of + an anatomical diagram.<a name="FNanchor_132_132" id= + "FNanchor_132_132"></a><a href="#Footnote_132_132" class= + "fnanchor">[132]</a></p> + + <p>These facts are very interesting, because they help to explain + the general dependence of marking on structure which has been + already pointed out. For, as the nerves everywhere follow the + muscles, and these are attached to the various bones, we see how + it happens, that the tracts in which distinct developments of + colour appear, should so often be marked out by the chief + divisions of the bony structure in vertebrates, and by the + segments in the annulosa. There is, however, another + correspondence of even greater interest and importance. Brilliant + colours usually appear just in proportion to the <a name= + "Page_291" id="Page_291"></a>development of tegumentary + appendages. Among birds the most brilliant colours are possessed + by those which have developed frills, crests, and elongated tails + like the humming-birds; immense tail-coverts like the peacock; + enormously expanded wing-feathers, as in the argus-pheasant; or + magnificent plumes from the region of the coracoids in many of + the birds of paradise. It is to be noted, also, that all these + accessory plumes spring from parts of the body which, in other + species, are distinguished by patches of colour; so that we may + probably impute the development of colour and of accessory + plumage to the same fundamental cause.</p> + + <p>Among insects, the most brilliant and varied coloration occurs + in the butterflies and moths, groups in which the wing-membranes + have received their greatest expansion, and whose specialisation + has been carried furthest in the marvellous scaly covering which + is the seat of the colour. It is suggestive, that the only other + group in which functional wings are much coloured is that of the + dragonflies, where the membrane is exceedingly expanded. In like + manner, the colours of beetles, though greatly inferior to those + of the lepidoptera, occur in a group in which the anterior pair + of wings has been thickened and modified in order to protect the + vital parts, and in which these wing-covers (elytra), in the + course of development in the different groups, must have + undergone great changes, and have been the seat of very active + growth.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Origin of Accessory Plumes.</i></p> + + <p>Mr. Darwin supposes, that these have in almost every case been + developed by the preference of female birds for such males as + possessed them in a higher degree than others; but this theory + does not account for the fact that these plumes usually appear in + a few definite parts of the body. We require some cause to + initiate the development in one part rather than in another. Now, + the view that colour has arisen over surfaces where muscular and + nervous development is considerable, and the fact that it appears + especially upon the accessory or highly developed plumes, leads + us to inquire whether the same cause has not primarily determined + the development of these plumes. The immense tuft of golden + plumage in the best known birds of paradise (Paradisea apoda and + P. minor) <a name="Page_292" id="Page_292"></a>springs from a + very small area on the side of the breast. Mr. Frank E. Beddard, + who has kindly examined a specimen for me, says that "this area + lies upon the pectoral muscles, and near to the point where the + fibres of the muscle converge towards their attachment to the + humerus. The plumes arise, therefore, close to the most powerful + muscle of the body, and near to where the activities of that + muscle would be at a maximum. Furthermore, the area of attachment + of the plumes is just above the point where the arteries and + nerves for the supply of the pectoral muscles, and neighbouring + regions, leave the interior of the body. The area of attachment + of the plume is, also, as you say in your letter, just above the + junction of the coracoid and sternum." Ornamental plumes of + considerable size rise from the same part in many other species + of paradise birds, sometimes extending laterally in front, so as + to form breast shields. They also occur in many humming-birds, + and in some sun-birds and honey-suckers; and in all these cases + there is a wonderful amount of activity and rapid movement, + indicating a surplus of vitality, which is able to manifest + itself in the development of these accessory plumes.<a name= + "FNanchor_133_133" id="FNanchor_133_133"></a><a href= + "#Footnote_133_133" class="fnanchor">[133]</a></p> + + <p>In a quite distinct set of birds, the gallinaceae, we find the + ornamental plumage usually arising from very different parts, in + the form of elongated tail-feathers or tail-coverts, and of ruffs + or hackles from the neck. Here the wings are comparatively little + used, the most constant activities depending on the legs, since + the gallinaceae are pre-eminently walking, running, and + scratching birds. Now the magnificent train of the + peacock—the grandest development of accessory plumes in + this order—springs from an oval or circular area, about + three inches in diameter, just above the base of the tail, and, + therefore, situated over the lower part of the spinal column near + the insertion of the powerful muscles which move the hind limbs + and elevate the tail. The very frequent presence of neck-ruffs or + breast-shields in the males of birds with accessory plumes may be + partly due to selection, because they must serve as a protection + in their mutual combats, just as does the lion's or the horse's + mane. The enormously lengthened plumes of the bird of paradise + and of the peacock can, however, have no such use, <a name= + "Page_293" id="Page_293"></a>but must be rather injurious than + beneficial in the bird's ordinary life. The fact that they have + been developed to so great an extent in a few species is an + indication of such perfect adaptation to the conditions of + existence, such complete success in the battle for life, that + there is, in the adult male at all events, a surplus of strength, + vitality, and growth-power which is able to expend itself in this + way without injury. That such is the case is shown by the great + abundance of most of the species which possess these wonderful + superfluities of plumage. Birds of paradise are among the + commonest birds in New Guinea, and their loud voices can be often + heard when the birds themselves are invisible in the depths of + the forest; while Indian sportsmen have described the peafowl as + being so abundant, that from twelve to fifteen hundred have been + seen within an hour at one spot; and they range over the whole + country from the Himalayas to Ceylon. Why, in allied species, the + development of accessory plumes has taken different forms, we are + unable to say, except that it may be due to that individual + variability which has served as the starting-point for so much of + what seems to us strange in form, or fantastic in colour, both in + the animal and vegetable world.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Development of Accessory Plumes and their Display.</i></p> + + <p>If we have found a <i>vera causa</i>for the origin of + ornamental appendages of birds and other animals in a surplus of + vital energy, leading to abnormal growths in those parts of the + integument where muscular and nervous action are greatest, the + continuous development of these appendages will result from the + ordinary action of natural selection in preserving the most + healthy and vigorous individuals, and the still further selective + agency of sexual struggle in giving to the very strongest and + most energetic the parentage of the next generation. And, as all + the evidence goes to show that, so far as female birds exercise + any choice, it is of "the most vigorous, defiant, and mettlesome + male," this form of sexual selection will act in the same + direction, and help to carry on the process of plume development + to its culmination. That culmination will be reached when the + excessive length or abundance of the plumes begins to be + injurious to the bearer of them; and it may be this check to the + further lengthening of the peacock's <a name="Page_294" id= + "Page_294"></a>train that has led to the broadening of the + feathers at the ends, and the consequent production of the + magnificent eye-spots which now form its crowning ornament.</p> + + <p>The display of these plumes will result from the same causes + which led to their production. Just in proportion as the feathers + themselves increased in length and abundance, the skin-muscles + which serve to elevate them would increase also; and the nervous + development as well as the supply of blood to these parts being + at a maximum, the erection of the plumes would become a habit at + all periods of nervous or sexual excitement. The display of the + plumes, like the existence of the plumes themselves, would be the + chief external indication of the maturity and vigour of the male, + and would, therefore, be necessarily attractive to the female. We + have, thus, no reason for imputing to her any of those aesthetic + emotions which are excited in us, by the beauty of form, colour, + and pattern of these plumes; or the still more improbable + aesthetic tastes, which would cause her to choose her mate on + account of minute differences in their forms, colours, or + patterns.</p> + + <p>As co-operating causes in the production of accessory + ornamental plumes, I have elsewhere suggested<a name= + "FNanchor_134_134" id="FNanchor_134_134"></a><a href= + "#Footnote_134_134" class="fnanchor">[134]</a> that crests and + other erectile feathers may have been useful in making the bird + more formidable in appearance, and thus serving to frighten away + enemies; while long tail or wing feathers might serve to distract + the aim of a bird of prey. But though this might be of some use + in the earlier stages of their development, it is probably of + little importance compared with the vigour and pugnacity of which + the plumes are the indication, and which enable most of their + possessors to defend themselves against the enemies which are + dangerous to weaker and more timid birds. Even the tiny + humming-birds are said to attack birds of prey that approach too + near to their nests.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Effect of Female Preference will be Neutralised by Natural + Selection.</i></p> + + <p>The various facts and arguments now briefly set forth, afford + an explanation of the phenomena of male ornament, <a name= + "Page_295" id="Page_295"></a>as being due to the general laws of + growth and development, and make it unnecessary to call to our + aid so hypothetical a cause as the cumulative action of female + preference. There remains, however, a general argument, arising + from the action of natural selection itself, which renders it + almost inconceivable that female preference could have been + effective in the way suggested; while the same argument strongly + supports the view here set forth. Natural selection, as we have + seen in our earlier chapters, acts perpetually and on an enormous + scale in weeding out the "unfit" at every stage of existence, and + preserving only those which are in all respects the very best. + Each year, only a small percentage of young birds survive to take + the place of the old birds which die; and the survivors will be + those which are best able to maintain existence from the egg + onwards, an important factor being that their parents should be + well able to feed and protect them, while they themselves must in + turn be equally able to feed and protect their own offspring. Now + this extremely rigid action of natural selection must render any + attempt to select mere ornament utterly nugatory, unless the most + ornamented always coincide with "the fittest" in every other + respect; while, if they do so coincide, then any selection of + ornament is altogether superfluous. If the most brightly coloured + and fullest plumaged males are <i>not</i> the most healthy and + vigorous, have <i>not</i> the best instincts for the proper + construction and concealment of the nest, and for the care and + protection of the young, they are certainly not the fittest, and + will not survive, or be the parents of survivors. If, on the + other hand, there <i>is</i> generally this correlation—if, + as has been here argued, ornament is the natural product and + direct outcome of superabundant health and vigour, then no other + mode of selection is needed to account for the presence of such + ornament. The action of natural selection does not indeed + disprove the existence of female selection of ornament as + ornament, but it renders it entirely ineffective; and as the + direct evidence for any such female selection is almost + <i>nil</i>, while the objections to it are certainly weighty, + there can be no longer any reason for upholding a theory which + was provisionally useful in calling attention to a most curious + and suggestive body of facts, but which is now no longer tenable. + <a name="Page_296" id="Page_296"></a>The term "sexual selection" + must, therefore, be restricted to the direct results of male + struggle and combat. This is really a form of natural selection, + and is a matter of direct observation; while its results are as + clearly deducible as those of any of the other modes in which + selection acts. And if this restriction of the term is needful in + the case of the higher animals it is much more so with the lower. + In butterflies the weeding out by natural selection takes place + to an enormous extent in the egg, larva, and pupa states; and + perhaps not more than one in a hundred of the eggs laid produces + a perfect insect which lives to breed. Here, then, the impotence + of female selection, if it exist, must be complete; for, unless + the most brilliantly coloured males are those which produce the + best protected eggs, larvae, and pupae, and unless the particular + eggs, larvae, and pupae, which are able to survive, are those + which produce the most brilliantly coloured butterflies, any + choice the female might make must be completely swamped. If, on + the other hand, there <i>is</i> this correlation between colour + development and perfect adaptation to conditions in all stages, + then this development will necessarily proceed by the agency of + natural selection and the general laws which determine the + production of colour and of ornamental appendages.<a name= + "FNanchor_135_135" id="FNanchor_135_135"></a><a href= + "#Footnote_135_135" class="fnanchor">[135]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>General Laws of Animal Coloration.</i></p> + + <p>The condensed account which has now been given of the + phenomena of colour in the animal world will sufficiently show + the wonderful complexity and extreme interest of the subject; + while it affords an admirable illustration of the importance of + the great principle of utility, and of the effect of the theories + of natural selection and development in giving a new interest + <a name="Page_297" id="Page_297"></a>to the most familiar facts + of nature. Much yet remains to be done, both in the observation + of new facts as to the relations between the colours of animals + and their habits or economy, and, more especially, in the + elucidation of the laws of growth which determine changes of + colour in the various groups; but so much is already known that + we are able, with some confidence, to formulate the general + principles which have brought about all the beauty and variety of + colour which everywhere delight us in our contemplation of + animated nature. A brief statement of these principles will fitly + conclude our exposition of the subject.</p> + + <p>1. Colour may be looked upon as a necessary result of the + highly complex chemical constitution of animal tissues and + fluids. The blood, the bile, the bones, the fat, and other + tissues have characteristic, and often brilliant colours, which + we cannot suppose to have been determined for any special + purpose, as colours, since they are usually concealed. The + external organs, with their various appendages and integuments, + would, by the same general laws, naturally give rise to a greater + variety of colour.</p> + + <p>2. We find it to be the fact that colour increases in variety + and intensity as external structures and dermal appendages become + more differentiated and developed. It is on scales, hair, and + especially on the more highly specialised feathers, that colour + is most varied and beautiful; while among insects colour is most + fully developed in those whose wing membranes are most expanded, + and, as in the lepidoptera, are clothed with highly specialised + scales. Here, too, we find an additional mode of colour + production in transparent lamellae or in fine surface striae + which, by the laws of interference, produce the wonderful + metallic hues of so many birds and insects.</p> + + <p><a name="Page_298" id="Page_298"></a>3. There are indications + of a progressive change of colour, perhaps in some definite + order, accompanying the development of tissues or appendages. + Thus spots spread and fuse into bands, and when a lateral or + centrifugal expansion has occurred—as in the termination of + the peacocks' train feathers, the outer web of the secondary + quills of the Argus pheasant, or the broad and rounded wings of + many butterflies—into variously shaded or coloured ocelli. + The fact that we find gradations of colour in many of the more + extensive groups, from comparatively dull or simple to brilliant + and varied hues, is an indication of some such law of + development, due probably to progressive local segregation in the + tissues of identical chemical or organic molecules, and dependent + on laws of growth yet to be investigated.</p> + + <p>4. The colours thus produced, and subject to much individual + variation, have been modified in innumerable ways for the benefit + of each species. The most general modification has been in such + directions as to favour concealment when at rest in the usual + surroundings of the species, sometimes carried on by successive + steps till it has resulted in the most minute imitation of some + inanimate object or exact mimicry of some other animal. In other + cases bright colours or striking contrasts have been preserved, + to serve as a warning of inedibility or of dangerous powers of + attack. Most frequent of all has been the specialisation of each + distinct form by some tint or marking for purposes of easy + recognition, especially in the case of gregarious animals whose + safety largely depends upon association and mutual defence.</p> + + <p>5. As a general rule the colours of the two sexes are alike; + but in the higher animals there appears a tendency to deeper or + more intense colouring in the male, due probably to his greater + vigour and excitability. In many groups in which this + superabundant vitality is at a maximum, the development of dermal + appendages and brilliant colours has gone on increasing till it + has resulted in a great diversity between the sexes; and in most + of these cases there is evidence to show that natural selection + has caused the female to retain the primitive and more sober + colours of the group for purposes of protection.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_299" id="Page_299"></a><i>Concluding + Remarks.</i></p> + + <p>The general principles of colour development now sketched out + enable us to give some rational explanation of the wonderful + amount of brilliant colour which occurs among tropical animals. + Looking on colour as a normal product of organisation, which has + either been allowed free play, or has been checked and modified + for the benefit of the species, we can see at once that the + luxuriant and perennial vegetation of the tropics, by affording + much more constant means of concealment, has rendered brilliant + colour less hurtful there than in the temperate and colder + regions. Again, this perennial vegetation supplies abundance of + both vegetable and insect food throughout the year, and thus a + greater abundance and greater variety of the forms of life are + rendered possible, than where recurrent seasons of cold and + scarcity reduce the possibilities of life to a minimum. Geology + furnishes us with another reason, in the fact, that throughout + the tertiary period tropical conditions prevailed far into the + temperate regions, so that the possibilities of colour + development were still greater than they are at the present time. + The tropics, therefore, present to us the results of animal + development in a much larger area and under more favourable + conditions than prevail to-day. We see in them samples of the + productions of an earlier and a better world, from an animal + point of view; and this probably gives a greater variety and a + finer display of colour than would have been produced, had + conditions always been what they are now. The temperate zones, on + the other hand, have recently suffered the effects of a glacial + period of extreme severity, with the result that almost the only + gay coloured birds they now possess are summer visitors from + tropical or sub-tropical lands. It is to the unbroken and almost + unchecked course of development from remote geological times that + has prevailed in the tropics, favoured by abundant food and + perennial shelter, that we owe such superb developments as the + frills and crests and jewelled shields of the humming-birds, the + golden plumes of the birds of paradise, and the resplendent train + of the peacock. This last exhibits to us the culmination of that + marvel and mystery of animal colour which is so well expressed by + a poet-artist in the following <a name="Page_300" id= + "Page_300"></a>lines. The marvel will ever remain to the + sympathetic student of nature, but I venture to hope that in the + preceding chapters I have succeeded in lifting—if only by + one of its corners—the veil of mystery which has for long + shrouded this department of nature.</p> + + <div class="poem"> + <p style='font-weight:bold;margin-top:1.5em'><i>On a Peacock's + Feather.</i></p> + + <div class="stanza"> + <span>In Nature's workshop but a shaving,<br /></span> + <span class="i2">Of her poem but a word,<br /></span> + <span>But a tint brushed from her palette,<br /></span> + <span class="i2">This feather of a bird!<br /></span> + <span>Yet set it in the sun glance,<br /></span> <span class= + "i2">Display it in the shine,<br /></span> <span>Take + graver's lens, explore it,<br /></span> <span class="i2">Note + filament and line,<br /></span> <span>Mark amethyst to + sapphire,<br /></span> <span class="i2">And sapphire to + gold,<br /></span> <span>And gold to emerald + changing<br /></span> <span class="i2">The archetype + unfold!<br /></span> <span>Tone, tint, thread, tissue, + texture,<br /></span> <span class="i2">Through every atom + scan,<br /></span> <span>Conforming still, + developing,<br /></span> <span class="i2">Obedient to + plan.<br /></span> <span>This but to form a + pattern<br /></span> <span class="i2">On the garment of a + bird!<br /></span> <span>What then must be the + poem,<br /></span> <span class="i2">This but its lightest + word!<br /></span> <span>Sit before it; ponder o'er + it,<br /></span> <span class="i2">'Twill thy mind advantage + more,<br /></span> <span>Than a treatise, than a + sermon,<br /></span> <span class="i2">Than a library of + lore.<br /></span> + </div> + </div> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_118_118" id= + "Footnote_118_118"></a><a href= + "#FNanchor_118_118"><span class="label">[118]</span></a> + Darwin's <i>Descent of Man</i>, p. 271.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_119_119" id= + "Footnote_119_119"></a><a href= + "#FNanchor_119_119"><span class="label">[119]</span></a> + Darwin's <i>Descent of Man</i>, p. 294, and footnote.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_120_120" id= + "Footnote_120_120"></a><a href= + "#FNanchor_120_120"><span class="label">[120]</span></a> + <i>Nature</i>, 1871, p. 489.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_121_121" id= + "Footnote_121_121"></a><a href= + "#FNanchor_121_121"><span class="label">[121]</span></a> + Darwin in <i>Nature</i>, 1880, p. 237.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_122_122" id= + "Footnote_122_122"></a><a href= + "#FNanchor_122_122"><span class="label">[122]</span></a> See + the author's <i>Contributions to Natural Selection</i>, chap. + vii. in which these facts were first brought forward.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_123_123" id= + "Footnote_123_123"></a><a href= + "#FNanchor_123_123"><span class="label">[123]</span></a> On + this point see the author's <i>Contributions to Natural + Selection</i>, chap. v. i.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_124_124" id= + "Footnote_124_124"></a><a href= + "#FNanchor_124_124"><span class="label">[124]</span></a> + Seebohm's <i>History of British Birds</i>, vol. ii., + introduction, p. xiii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_125_125" id= + "Footnote_125_125"></a><a href= + "#FNanchor_125_125"><span class="label">[125]</span></a> For + details see Darwin's <i>Descent of Man</i>, chap. xii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_126_126" id= + "Footnote_126_126"></a><a href= + "#FNanchor_126_126"><span class="label">[126]</span></a> + <i>Descent of Man</i>, pp. 417, 418, 420.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_127_127" id= + "Footnote_127_127"></a><a href= + "#FNanchor_127_127"><span class="label">[127]</span></a> + <i>Notes of a Naturalist on the Challenger.</i></p> + </div> + + <div class="footnote"> + <p><a name="Footnote_128_128" id= + "Footnote_128_128"></a><a href= + "#FNanchor_128_128"><span class="label">[128]</span></a> + <i>Descent of Man</i>, pp. 401, 402.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_129_129" id= + "Footnote_129_129"></a><a href= + "#FNanchor_129_129"><span class="label">[129]</span></a> + <i>Coloration in Animals and Plants</i>, London, 1886.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_130_130" id= + "Footnote_130_130"></a><a href= + "#FNanchor_130_130"><span class="label">[130]</span></a> + <i>Coloration of Animals</i>, Pl. X, p. 90; and Pls. II, III, + and IV, pp. 30, 40, 42.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_131_131" id= + "Footnote_131_131"></a><a href= + "#FNanchor_131_131"><span class="label">[131]</span></a> See + coloured Fig. in <i>Proc. Zool. Soc.</i>, 1871, p. 626.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_132_132" id= + "Footnote_132_132"></a><a href= + "#FNanchor_132_132"><span class="label">[132]</span></a> A. + Tylor's <i>Coloration</i>, p. 40; and Photograph in + Hutchinson's <i>Illustrations of Clinical Surgery</i>, quoted + by Tylor.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_133_133" id= + "Footnote_133_133"></a><a href= + "#FNanchor_133_133"><span class="label">[133]</span></a> For + activity and pugnacity of humming-birds, see <i>Tropical + Nature</i>, pp. 130, 213.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_134_134" id= + "Footnote_134_134"></a><a href= + "#FNanchor_134_134"><span class="label">[134]</span></a> + <i>Tropical Nature</i>, p. 209. In Chapter V of this work the + views here advocated were first set forth, and the reader is + referred there for further details.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_135_135" id= + "Footnote_135_135"></a><a href= + "#FNanchor_135_135"><span class="label">[135]</span></a> The + Rev. O. Pickard-Cambridge, who has devoted himself to the + study of spiders, has kindly sent me the following extract + from a letter, written in 1869, in which he states his views + on this question:—</p> + + <div class="blockquot" style='font-size: 100%'> + <p>"I myself doubt that particular application of the + Darwinian theory which attributes male peculiarities of + form, structure, colour, and ornament to female appetency + or predilection. There is, it seems to me, undoubtedly + something in the male organisation of a special, and sexual + nature, which, of its own vital force, develops the + remarkable male peculiarities so commonly seen, and of no + imaginable use to that sex. In as far as these + peculiarities show a great vital power, they point out to + us the finest and strongest individuals of the sex, and + show us which of them would most certainly appropriate to + themselves the best and greatest number of females, and + leave behind them the strongest and greatest number of + progeny. And here would come in, as it appears to me, the + proper application of Darwin's theory of Natural Selection; + for the possessors of greatest vital power being those most + frequently produced and reproduced, the external signs of + it would go on developing in an ever-increasing + exaggeration, only to be checked where it became really + detrimental in some respect or other to the + individual."</p> + </div> + + <p>This passage, giving the independent views of a close + observer—one, moreover, who has studied the species of + an extensive group of animals both in the field and in the + laboratory—very nearly accords with my own conclusions + above given; and, so far as the matured opinions of a + competent naturalist have any weight, afford them an + important support.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a><a name="Page_301" + id="Page_301"></a>CHAPTER XI</h2> + + <p style='font-weight:bold;'>THE SPECIAL COLOURS OF PLANTS: THEIR + ORIGIN AND PURPOSE</p> + + <div class="blockquot"> + <p>The general colour relations of plants—Colours of + fruits—The meaning of nuts—Edible or attractive + fruits—The colours of flowers—Modes of securing + cross-fertilisation—The interpretation of the + facts—Summary of additional facts bearing on insect + fertilisation—Fertilisation of flowers by + birds—Self-fertilisation of flowers—Difficulties + and contradictions—Intercrossing not necessarily + advantageous—Supposed evil results of close + interbreeding—How the struggle for existence acts among + flowers—Flowers the product of insect + agency—Concluding remarks on colour in nature.</p> + </div> + + <p>The colours of plants are both less definite and less complex + than are those of animals, and their interpretation on the + principle of utility is, on the whole, more direct and more easy. + Yet here, too, we find that in our investigation of the uses of + the various colours of fruits and flowers, we are introduced to + some of the most obscure recesses of nature's workshop, and are + confronted with problems of the deepest interest and of the + utmost complexity.</p> + + <p>So much has been written on this interesting subject since Mr. + Darwin first called attention to it, and its main facts have + become so generally known by means of lectures, articles, and + popular books, that I shall give here a mere outline sketch, for + the purpose of leading up to a discussion of some of the more + fundamental problems which arise out of the facts, and which have + hitherto received less attention than they deserve.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_302" id="Page_302"></a><i>The General Colour + Relations of Plants.</i></p> + + <p>The green colour of the foliage of leafy plants is due to the + existence of a substance called chlorophyll, which is almost + universally developed in the leaves under the action of light. It + is subject to definite chemical changes during the processes of + growth and of decay, and it is owing to these changes that we + have the delicate tints of spring foliage, and the more varied, + intense, and gorgeous hues of autumn. But these all belong to the + class of intrinsic or normal colours, due to the chemical + constitution of the organism; as colours they are unadaptive, and + appear to have no more relation to the wellbeing of the plants + themselves than have the colours of gems and minerals. We may + also include in the same category those algae and fungi which + have bright colours—the "red snow" of the arctic regions, + the red, green, or purple seaweeds, the brilliant scarlet, + yellow, white, or black agarics, and other fungi. All these + colours are probably the direct results of chemical composition + or molecular structure, and, being thus normal products of the + vegetable organism, need no special explanation from our present + point of view; and the same remark will apply to the varied tints + of the bark of trunks, branches, and twigs, which are often of + various shades of brown and green, or even vivid reds or + yellows.</p> + + <p>There are, however, a few cases in which the need of + protection, which we have found to be so important an agency in + modifying the colours of animals, has also determined those of + some of the smaller members of the vegetable kingdom. Dr. + Burchell found a mesembryanthomum in South Africa like a + curiously shaped pebble, closely resembling the stones among + which it grew;<a name="FNanchor_136_136" id= + "FNanchor_136_136"></a><a href="#Footnote_136_136" class= + "fnanchor">[136]</a> and Mr. J.P. Mansel Weale states that in the + same country one of the Asclepiadeae has tubers growing above + ground among stones which they exactly resemble, and that, when + not in leaf, they are for this reason quite invisible.<a name= + "FNanchor_137_137" id="FNanchor_137_137"></a><a href= + "#Footnote_137_137" class="fnanchor">[137]</a> It is clear that + such resemblances must be highly useful to these plants, + inhabiting an arid country abounding in herbivorous mammalia, + which, <a name="Page_303" id="Page_303"></a>in times of drought + or scarcity, will devour everything in the shape of a fleshy stem + or tuber.</p> + + <p>True mimicry is very rare in plants, though adaptation to like + conditions often produces in foliage and habit a similarity that + is deceiving. Euphorbias growing in deserts often closely + resemble cacti. Seaside plants and high alpine plants of + different orders are often much alike; and innumerable + resemblances of this kind are recorded in the names of plants, as + Veronica epacridea (the veronica like an epacris), Limnanthemum + nymphaeoides (the limnanthemum like a nymphaea), the resembling + species in each case belonging to totally distinct families. But + in these cases, and in most others that have been observed, the + essential features of true mimicry are absent, inasmuch as the + one plant cannot be supposed to derive any benefit from its close + resemblance to the other, and this is still more certain from the + fact that the two species usually inhabit different localities. A + few cases exist, however, in which there does seem to be the + necessary accordance and utility. Mr. Mansel Weale mentions a + labiate plant (Ajuga ophrydis), the only species of the genus + Ajuga in South Africa, which is strikingly like an orchid of the + same country; while a balsam (Impatiens capensis), also a + solitary species of the genus in that country, is equally like an + orchid, growing in the same locality and visited by the same + insects. As both these genera of plants are specialised for + insect fertilisation, and both of the plants in question are + isolated species of their respective genera, we may suppose that, + when they first reached South Africa they were neglected by the + insects of the country; but, being both remotely like orchids in + form of flower, those varieties that approached nearest to the + familiar species of the country were visited by insects and + cross-fertilised, and thus a closer resemblance would at length + be brought about. Another case of close general resemblance, is + that of our common white dead-nettle (Lamium album) to the + stinging-nettle (Urtica dioica); and Sir John Lubbock thinks that + this is a case of true mimicry, the dead-nettle being benefited + by being mistaken by grazing animals for the + stinging-nettle.<a name="FNanchor_138_138" id= + "FNanchor_138_138"></a><a href="#Footnote_138_138" class= + "fnanchor">[138]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_304" id="Page_304"></a><i>Colours of + Fruits.</i></p> + + <p>It is when we come to the essential parts of plants on which + their perpetuation and distribution depends, that we find colour + largely utilised for a distinct purpose in flowers and fruits. In + the former we find attractive colours and guiding marks to secure + cross-fertilisation by insects; in the latter attractive or + protective coloration, the first to attract birds or other + animals when the fruits are intended to be eaten, the second to + enable them to escape being eaten when it would be injurious to + the species. The colour phenomena of fruits being much the most + simple will be considered first.</p> + + <p>The perpetuation and therefore the very existence of each + species of flowering plant depend upon its seeds being preserved + from destruction and more or less effectually dispersed over a + considerable area. The dispersal is effected either mechanically + or by the agency of animals. Mechanical dispersal is chiefly by + means of air-currents, and large numbers of seeds are specially + adapted to be so carried, either by being clothed with down or + pappus, as in the well-known thistle and dandelion seeds; by + having wings or other appendages, as in the sycamore, birch, and + many other trees; by being thrown to a considerable distance by + the splitting of the seed-vessel, and by many other curious + devices.<a name="FNanchor_139_139" id= + "FNanchor_139_139"></a><a href="#Footnote_139_139" class= + "fnanchor">[139]</a> Very large numbers of seeds, however, are so + small and light that they can be carried enormous distances by + gales of wind, more especially as most of this kind are flattened + or curved, so as to expose a large surface in proportion to their + weight. Those which are carried by animals have their surfaces, + or that of the seed-vessel, armed with minute hooks, or some + prickly covering which attaches itself to the hair of mammalia or + the feathers of birds, as in the burdock, cleavers, and many + other species. Others again are sticky, as in Plumbago europaea, + mistletoe, and many foreign plants.</p> + + <p>All the seeds or seed-vessels which are adapted to be + dispersed in any of these ways are of dull protective tints, so + that when they fall on the ground they are almost + indistinguishable; besides which, they are usually small, hard, + and <a name="Page_305" id="Page_305"></a>altogether unattractive, + never having any soft, juicy pulp; while the edible seeds often + bear such a small proportion to the hard, dry envelopes or + appendages, that few animals would care to eat them.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Meaning of Nuts.</i></p> + + <p>There is, however, another class of fruits or seeds, usually + termed nuts, in which there is a large amount of edible matter, + often very agreeable to the taste, and especially attractive and + nourishing to a large number of animals. But when eaten, the seed + is destroyed and the existence of the species endangered. It is + evident, therefore, that it is by a kind of accident that these + nuts are eatable; and that they are not intended to be eaten is + shown by the special care nature seems to have taken to conceal + or to protect them. We see that all our common nuts are green + when on the tree, so as not easily to be distinguished from the + leaves; but when ripe they turn brown, so that when they fall on + to the ground they are equally indistinguishable among the dead + leaves and twigs, or on the brown earth. Then they are almost + always protected by hard coverings, as in hazel-nuts, which are + concealed by the enlarged leafy involucre, and in the large + tropical brazil-nuts and cocoa-nuts by such a hard and tough case + as to be safe from almost every animal. Others have an external + bitter rind, as in the walnut; while in the chestnuts and + beech-nuts two or three fruits are enclosed in a prickly + involucre.</p> + + <p>Notwithstanding all these precautions, nuts are largely + devoured by mammalia and birds; but as they are chiefly the + product of trees or shrubs of considerable longevity, and are + generally produced in great profusion, the perpetuation of the + species is not endangered. In some cases the devourers of nuts + may aid in their dispersal, as they probably now and then swallow + the seed whole, or not sufficiently crushed to prevent + germination; while squirrels have been observed to bury nuts, + many of which are forgotten and afterwards grow in places they + could not have otherwise reached.<a name="FNanchor_140_140" id= + "FNanchor_140_140"></a><a href="#Footnote_140_140" class= + "fnanchor">[140]</a> Nuts, especially the larger kinds which are + so well protected by their hard, nearly globular cases, have + their dispersal facilitated by rolling down hill, and more + especially <a name="Page_306" id="Page_306"></a>by floating in + rivers and lakes, and thus reaching other localities. During the + elevation of land areas this method would be very effective, as + the new land would always be at a lower level than that already + covered with vegetation, and therefore in the best position for + being stocked with plants from it.</p> + + <p>The other modes of dispersal of seeds are so clearly adapted + to their special wants, that we feel sure they must have been + acquired by the process of variation and natural selection. The + hooked and sticky seeds are always those of such herbaceous + plants as are likely, from their size, to come in contact with + the wool of sheep or the hair of cattle; while seeds of this kind + never occur on forest trees, on aquatic plants, or even on very + dwarf creepers or trailers. The winged seed-vessels or seeds, on + the other hand, mostly belong to trees and to tall shrubs or + climbers. We have, therefore, a very exact adaptation to + conditions in these different modes of dispersal; while, when we + come to consider individual cases, we find innumerable other + adaptations, some of which the reader will find described in the + little work by Sir John Lubbock already referred to.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Edible or Attractive Fruits.</i></p> + + <p>It is, however, when we come to true fruits (in a popular + sense) that we find varied colours evidently intended to attract + animals, in order that the fruits may be eaten, while the seeds + pass through the body undigested and are then in the fittest + state for germination. This end has been gained in a great + variety of ways, and with so many corresponding adaptations as to + leave no doubt as to the value of the result. Fruits are pulpy or + juicy, and usually sweet, and form the favourite food of + innumerable birds and some mammals. They are always coloured so + as to contrast with the foliage or surroundings, red being the + most common as it is certainly the most conspicuous colour, but + yellow, purple, black, or white being not uncommon. The edible + portion of fruits is developed from different parts of the floral + envelopes, or of the ovary, in the various orders and genera. + Sometimes the calyx becomes enlarged and fleshy, as in the apple + and pear tribe; more often the integuments of the ovary itself + are enlarged, as in the plum, peach, grape, etc.; the receptacle + is enlarged and <a name="Page_307" id="Page_307"></a>forms the + fruit of the strawberry; while the mulberry, pineapple, and fig + are examples of compound fruits formed in various ways from a + dense mass of flowers.</p> + + <p>In all cases the seeds themselves are protected from injury by + various devices. They are small and hard in the strawberry, + raspberry, currant, etc., and are readily swallowed among the + copious pulp. In the grape they are hard and bitter; in the rose + (hip) disagreeably hairy; in the orange tribe very bitter; and + all these have a smooth, glutinous exterior which facilitates + their being swallowed. When the seeds are larger and are eatable, + they are enclosed in an excessively hard and thick covering, as + in the various kinds of "stone" fruit (plums, peaches, etc.), or + in a very tough core, as in the apple. In the nutmeg of the + Eastern Archipelago we have a curious adaptation to a single + group of birds. The fruit is yellow, somewhat like an oval peach, + but firm and hardly eatable. This splits open and shows the + glossy black covering of the seed or nutmeg, over which spreads + the bright scarlet arillus or "mace," an adventitious growth of + no use to the plant except to attract attention. Large fruit + pigeons pluck out this seed and swallow it entire for the sake of + the mace, while the large nutmeg passes through their bodies and + germinates; and this has led to the wide distribution of wild + nutmegs over New Guinea and the surrounding islands.</p> + + <p>In the restriction of bright colour to those edible fruits the + eating of which is beneficial to the plant, we see the undoubted + result of natural selection; and this is the more evident when we + find that the colour never appears till the fruit is + ripe—that is, till the seeds within it are fully matured + and in the best state for germination. Some brilliantly coloured + fruits are poisonous, as in our bitter-sweet (Solanum dulcamara), + cuckoo-pint (Arum) and the West Indian manchineel. Many of these + are, no doubt, eaten by animals to whom they are harmless; and it + has been suggested that even if some animals are poisoned by them + the plant is benefited, since it not only gets dispersed, but + finds, in the decaying body of its victim, a rich manure + heap.<a name="FNanchor_141_141" id= + "FNanchor_141_141"></a><a href="#Footnote_141_141" class= + "fnanchor">[141]</a> The particular colours of fruits are not, so + far as we know, of any use to them other <a name="Page_308" id= + "Page_308"></a>than as regards conspicuousness, hence a tendency + to <i>any</i> decided colour has been preserved and accumulated + as serving to render the fruit easily visible among its + surroundings of leaves or herbage. Out of 134 fruit-bearing + plants in Mongredien's <i>Trees and Shrubs</i>, and Hooker's + <i>British Flora</i>, the fruits of no less than sixty-eight, or + rather more than half, are red, forty-five are black, fourteen + yellow, and seven white. The great prevalence of red fruits is + almost certainly due to their greater conspicuousness having + favoured their dispersal, though it may also have arisen in part + from the chemical changes of chlorophyll during ripening and + decay producing red tints as in many fading leaves. Yet the + comparative scarcity of yellow in fruits, while it is the most + common tint of fading leaves, is against this supposition.</p> + + <p>There are, however, a few instances of coloured fruits which + do not seem to be intended to be eaten; such are the colocynth + plant (Cucumis colocynthus), which has a beautiful fruit the size + and colour of an orange, but nauseous beyond description to the + taste. It has a hard rind, and may perhaps be dispersed by being + blown along the ground, the colour being an adventitious product; + but it is quite possible, notwithstanding its repulsiveness to + us, that it may be eaten by some animals. With regard to the + fruit of another plant, Calotropis procera, there is less doubt, + as it is dry and full of thin, flat-winged seeds, with fine silky + filaments, eminently adapted for wind-dispersal; yet it is of a + bright yellow colour, as large as an apple, and therefore very + conspicuous. Here, therefore, we seem to have colour which is a + mere byproduct of the organism and of no use to it; but such + cases are exceedingly rare, and this rarity, when compared with + the great abundance of cases in which there is an obvious purpose + in the colour, adds weight to the evidence in favour of the + theory of the attractive coloration of edible fruits in order + that birds and other animals may assist in their dispersal. Both + the above-named plants are natives of Palestine and the adjacent + arid countries.<a name="FNanchor_142_142" id= + "FNanchor_142_142"></a><a href="#Footnote_142_142" class= + "fnanchor">[142]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Colours of Flowers.</i></p> + + <p>Flowers are much more varied in their colours than fruits, + <a name="Page_309" id="Page_309"></a>as they are more complex and + more varied in form and structure; yet there is some parallelism + between them in both respects. Flowers are frequently adapted to + attract insects as fruits are to attract birds, the object being + in the former to secure cross-fertilisation, in the latter + dispersal; while just as colour is an index of the edibility of + fruits which supply pulp or juice to birds, so are the colours of + flowers an indication of the presence of nectar or of pollen + which are devoured by insects.</p> + + <p>The main facts and many of the details, as to the relation of + insects to flowers, were discovered by Sprengel in 1793. He + noticed the curious adaptation of the structure of many flowers + to the particular insects which visit them; he proved that + insects do cross-fertilise flowers, and he believed that this was + the object of the adaptations, while the presence of nectar and + pollen ensured the continuance of their visits; yet he missed + discovering the <i>use</i> of this cross-fertilisation. Several + writers at a later period obtained evidence that + cross-fertilisation of plants was a benefit to them; but the wide + generality of this fact and its intimate connection with the + numerous and curious adaptations discovered by Sprengel, was + first shown by Mr. Darwin, and has since been demonstrated by a + vast mass of observations, foremost among which are his own + researches on orchids, primulas, and other plants.<a name= + "FNanchor_143_143" id="FNanchor_143_143"></a><a href= + "#Footnote_143_143" class="fnanchor">[143]</a></p> + + <p>By an elaborate series of experiments carried on for many + years Mr. Darwin demonstrated the great value of + cross-fertilisation in increasing the rapidity of growth, the + strength and vigour of the plant, and in adding to its fertility. + This effect is produced immediately, not as he expected would be + the case, after several generations of crosses. He planted seeds + from cross-fertilised and self-fertilised plants on two sides of + the same pot exposed to exactly similar conditions, and in most + cases the difference in size and vigour was amazing, while the + plants from cross-fertilised parents also produced more and finer + seeds. These experiments entirely confirmed the experience of + breeders of animals already referred to (p. 160), and led him to + enunciate his famous aphorism, "<a name="Page_310" id= + "Page_310"></a>Nature abhors perpetual + self-fertilisation".<a name="FNanchor_144_144" id= + "FNanchor_144_144"></a><a href="#Footnote_144_144" class= + "fnanchor">[144]</a> In this principle we appear to have a + sufficient reason for the various contrivances by which so many + flowers secure cross-fertilisation, either constantly or + occasionally. These contrivances are so numerous, so varied, and + often so highly complex and extraordinary, that they have formed + the subject of many elaborate treatises, and have also been amply + popularised in lectures and handbooks. It will be unnecessary, + therefore, to give details here, but the main facts will be + summarised in order to call attention to some difficulties of the + theory which seem to require further elucidation.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Modes of securing Cross-Fertilisation.</i></p> + + <p>When we examine the various modes in which the + cross-fertilisation of flowers is brought about, we find that + some are comparatively simple in their operation and needful + adjustments, others highly complex. The simple methods belong to + four principal classes:—(1) By dichogamy—that is, by + the anthers and the stigma becoming mature or in a fit state for + fertilisation at slightly different times on the same plant. The + result of this is that, as plants in different stations, on + different soils, or exposed to different aspects flower earlier + or later, the mature pollen of one plant can only fertilise some + plant exposed to somewhat different conditions or of different + constitution, whose stigma will be mature at the same time; and + this difference has been shown by Darwin to be that which is + adapted to secure the fullest benefit of cross-fertilisation. + This occurs in Geranium pratense, Thymus serpyllum, Arum + maculatum, and many others. (2) By the flower being self-sterile + with its own pollen, as in the crimson flax. This absolutely + prevents self-fertilisation. (3) By the stamens and anthers being + so placed that the pollen cannot fall upon the stigma, while it + does fall upon a visiting insect which carries it to the stigma + of another flower. This effect is produced in a variety of very + simple ways, and is often aided by the motion of the stamens + which bend down out of the way of the stigmas before the pollen + is ripe, as in Malva sylvestris (see Fig. 28). (4) By the male + and female flowers being on <a name="Page_311" id= + "Page_311"></a>different plants, forming the class Dioecia of + Linnaeus. In these cases the pollen may be carried to the stigmas + either by the wind or by the agency of insects.</p> + + <div class="figcenter" style="width: 300px;"> + <a name="fig28" id="fig28"></a> <img src="images/fig28.jpg" + width="300" height="340" alt= + "FIG. 28. Malva sylvestris, adapted for insect-fertilisation. Malva rotundifolia, adapted for self-fertilisation." + title= + "FIG. 28. Malva sylvestris, adapted for insect-fertilisation. Malva rotundifolia, adapted for self-fertilisation." /> + <b>FIG. 28. Malva sylvestris, adapted for + insect-fertilisation.<br /> + Malva rotundifolia, adapted for self-fertilisation.</b> + </div> + + <p>Now these four methods are all apparently very simple, and + easily produced by variation and selection. They are applicable + to flowers of any shape, requiring only such size and colour as + to attract insects, and some secretion of nectar to ensure their + repeated visits, characters common to the great majority of + flowers. All these methods are common, except perhaps the second; + but there are many flowers in which the pollen from another plant + is prepotent over the pollen from fertilisation, the same flower, + and this has nearly the same effect as self-sterility if the + flowers are frequently crossed by insects. We cannot help asking, + therefore, why have other and much more elaborate methods been + needed? And how have the more complex arrangements of so many + flowers been brought about? Before attempting to answer these + questions, and in order that the reader may appreciate the + difficulty of the problem and the nature of the facts to be + explained, it will be necessary to give a summary of the more + elaborate modes of securing cross-fertilisation.</p> + + <p>(1) We first have dimorphism and heteromorphism, the phenomena + of which have been already sketched in our seventh chapter.</p> + + <p>Here we have both a mechanical and a physiological + modification, the stamens and pistil being variously modified in + length and position, while the different stamens in the same + flower have widely different degrees of fertility when applied to + the same stigma,—a phenomenon which, if it were not so well + established, would have appeared in the highest degree + improbable. The most remarkable case is that of the three + different forms of the loosestrife (Lythrum salicaria) here + figured (Fig. 29 on next page).</p> + + <p><a name="Page_312" id="Page_312"></a>(2) Some flowers have + irritable stamens which, when their bases are touched by an + insect, spring up and dust it with pollen. This occurs in our + common berberry.</p> + + <div class="figleft" style="width: 500px;"> + <a name="fig29" id="fig29"></a> <img src="images/fig29.jpg" + width="500" height="334" alt= + "FIG. 29.—Lythrum salicaria (Purple loosestrife)." title= + "FIG. 29.—Lythrum salicaria (Purple loosestrife)." /> + <b>FIG. 29.—Lythrum salicaria (Purple loosestrife).</b> + </div> + + <p><a name="Page_313" id="Page_313"></a>(3) In others there are + levers or processes by which the anthers are mechanically brought + down on to the head or back of an insect entering the flower, in + such a position as to be carried to the stigma of the next flower + it visits. This may be well seen in many species of Salvia and + Erica.</p> + + <p>(4) In some there is a sticky secretion which, getting on to + the proboscis of an insect, carries away the pollen, and applies + it to the stigma of another flower. This occurs in our common + milkwort (Polygala vulgaris).</p> + + <p>(5) In papilionaceous plants there are many complex + adjustments, such as the squeezing out of pollen from a + receptacle on to an insect, as in Lotus corniculatus, or the + sudden springing out and exploding of the anthers so as + thoroughly to dust the insect, as in Medicago falcata, this + occurring after the stigma has touched the insect and taken off + some pollen from the last flower.</p> + + <p>(6) Some flowers or spathes form closed boxes in which insects + find themselves entrapped, and when they have fertilised the + flower, the fringe of hairs opens and allows them to escape. This + occurs in many species of Arum and Aristolochia.</p> + + <p>(7) Still more remarkable are the traps in the flower of + Asclepias which catch flies, butterflies, and wasps by the legs, + and the wonderfully complex arrangements of the orchids. One of + these, our common Orchis pyramidalis, may be briefly described to + show how varied and beautiful are the arrangements to secure + cross-fertilisation. The broad trifid lip of the flower offers a + support to the moth which is attracted by its sweet odour, and + two ridges at the base guide the proboscis with certainty to the + narrow entrance of the nectary. When the proboscis has reached + the end of the spur, its basal portion depresses the little + hinged rostellum that covers the saddle-shaped sticky glands to + which the pollen masses (pollinia) are attached. On the proboscis + being withdrawn, the two pollinia stand erect and parallel, + firmly attached to the proboscis. In this position, however, they + would be useless, as they would miss the stigmatic surface of the + next flower visited by the moth. But as soon as the proboscis is + withdrawn, the two pollen masses begin to diverge till they are + exactly as far apart as are the stigmas of the flower; and then + commences a second move<a name="Page_314" id= + "Page_314"></a><a name="Page_315" id="Page_315"></a>ment which + brings them down till they project straight forward nearly at + right angles to their first position, so as exactly to hit + against the stigmatic surfaces of the next flower visited on + which they leave a portion of their pollen. The whole of these + motions take about half a minute, and in that time the moth will + usually have flown to another plant, and thus effect the most + beneficial kind of cross-fertilisation.<a name="FNanchor_145_145" + id="FNanchor_145_145"></a><a href="#Footnote_145_145" class= + "fnanchor">[145]</a> This description will be better understood + by referring to the illustration opposite, from Darwin's + <i>Fertilisation of Orchids</i>(Fig. 30).</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig30" id="fig30"></a> <img src="images/fig30.jpg" + width="400" height="666" alt= + "FIG. 30.—Orchis pyramidalis." title= + "FIG. 30.—Orchis pyramidalis." /> <b>FIG. + 30.—Orchis pyramidalis.</b> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Interpretation of these Facts.</i></p> + + <p>Having thus briefly indicated the general character of the + more complex adaptations for cross-fertilisation, the details of + which are to be found in any of the numerous works on the + subject,<a name="FNanchor_146_146" id= + "FNanchor_146_146"></a><a href="#Footnote_146_146" class= + "fnanchor">[146]</a> we find ourselves confronted with the very + puzzling question—Why were these innumerable highly complex + adaptations produced, when the very same result may be + effected—and often is effected—by extremely simple + means? Supposing, as we must do, that all flowers were once of + simple and regular forms, like a buttercup or a rose, how did + such irregular and often complicated flowers as the + papilionaceous or pea family, the labiates or sage family, and + the infinitely varied and fantastic orchids ever come into + existence? No cause has yet been suggested but the need of + attracting insects to cross-fertilise them; yet the + attractiveness of regular flowers with bright colours and an + ample supply of nectar is equally great, and cross-fertilisation + can be quite as effectively secured in these by any of the four + simple methods already described. Before attempting to suggest a + possible solution of this difficult problem, we have yet to pass + in review a large body of curious adaptations connected with + insect fertilisation, and will first call attention to that + portion of the phenomena which throw some light upon the special + colours of flowers in their relation to the various kinds of + insects which visit them. For these facts we are largely + in<a name="Page_316" id="Page_316"></a>debted to the exact and + long-continued researches of Professor Hermann Müller.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Summary of Additional Facts bearing on Insect + Fertilisation.</i></p> + + <p>1. That the size and colour of a flower are important factors + in determining the visits of insects, is shown by the general + fact of more insects visiting conspicuous than inconspicuous + flowers. As a single instance, the handsome Geranium palustre was + observed by Professor Müller to be visited by sixteen + different species of insects, the equally showy G. pratense by + thirteen species, while the smaller and much less conspicuous G. + molle was visited by eight species, and G. pusillum by only one. + In many cases, however, a flower may be very attractive to only a + few species of insects; and Professor Müller states, as the + result of many years' assiduous observation, that "a species of + flower is the more visited by insects the more conspicuous it + is."</p> + + <p>2. Sweet odour is usually supplementary to the attraction of + colour. Thus it is rarely present in the largest and most gaudily + coloured flowers which inhabit open places, such as poppies, + paeonies, sunflowers, and many others; while it is often the + accompaniment of inconspicuous flowers, as the mignonette; of + such as grow in shady places, as the violet and primrose; and + especially of white or yellowish flowers, as the white jasmine, + clematis, stephanotis, etc.</p> + + <p>3. White flowers are often fertilised by moths, and very + frequently give out their scent only by night, as in our + butterfly-orchis (Habenaria chlorantha); and they sometimes open + only at night, as do many of the evening primroses and other + flowers. These flowers are often long tubed in accordance with + the length of the moths' probosces, as in the genus Pancratium, + our butterfly orchis, white jasmine, and a host of others.</p> + + <p>4. Bright red flowers are very attractive to butterflies, and + are sometimes specially adapted to be fertilised by them, as in + many pinks (Dianthus deltoides, D. superbus, D. atrorubens), the + corn-cockle (Lychnis Githago), and many others. Blue flowers are + especially attractive to bees and other hymenoptera (though they + frequent flowers of all colours), no less than sixty-seven + species of this order having been observed to visit the common + "sheep's-bit" (Jasione montana). Dull yellow or <a name= + "Page_317" id="Page_317"></a>brownish flowers, some of which + smell like carrion, are attractive to flies, as the Arum and + Aristolochia; while the dull purplish flowers of the Scrophularia + are specially attractive to wasps.</p> + + <p>5. Some flowers have neither scent nor nectar, and yet attract + insects by sham nectaries! In the herb-paris (Paris quadrifolia) + the ovary glistens as if moist, and flies alight on it and carry + away pollen to another flower; while in grass of parnassus + (Parnassia palustris) there are a number of small stalked yellow + balls near the base of the flower, which look like drops of honey + but are really dry. In this case there is a little nectar lower + down, but the special attraction is a sham; and as there are + fresh broods of insects every year, it takes time for them to + learn by experience, and thus enough are always deceived to + effect cross-fertilisation.<a name="FNanchor_147_147" id= + "FNanchor_147_147"></a><a href="#Footnote_147_147" class= + "fnanchor">[147]</a> This is analogous to the case of the young + birds, which have to learn by experience the insects that are + inedible, as explained at page 253.</p> + + <p>6. Many flowers change their colour as soon as fertilised; and + this is beneficial, as it enables bees to avoid wasting time in + visiting those blossoms which have been already fertilised and + their nectar exhausted. The common lungwort (Pulmonaria + officinalis), is at first red, but later turns blue; and H. + Müller observed bees visiting many red flowers in + succession, but neglecting the blue. In South Brazil there is a + species of Lantana, whose flowers are yellow the first day, + orange the second, and purple the third; and Dr. Fritz + Müller observed that many butterflies visited the yellow + flowers only, some both the yellow and the orange flowers, but + none the purple.</p> + + <p>7. Many flowers have markings which serve as guides to + insects; in some cases a bright central eye, as in the borage and + forget-me-not; or lines or spots converging to the centre, as in + geraniums, pinks, and many others. This enables insects to go + quickly and directly to the opening of the flower, and is equally + important in aiding them to obtain a better supply of food, and + to fertilise a larger number of flowers.</p> + + <p>8. Flowers have been specially adapted to the kinds of + <a name="Page_318" id="Page_318"></a>insects that most abound + where they grow. Thus the gentians of the lowlands are adapted to + bees, those of the high alps to butterflies only; and while most + species of Rhinanthus (a genus to which our common "yellow + rattle" belongs) are bee-flowers, one high alpine species (R. + alpinus) has been also adapted for fertilisation by butterflies + only. The reason of this is, that in the high alps butterflies + are immensely more plentiful than bees, and flowers adapted to be + fertilised by bees can often have their nectar extracted by + butterflies without effecting cross-fertilisation. It is, + therefore, important to have a modification of structure which + shall make butterflies the fertilisers, and this in many cases + has been done.<a name="FNanchor_148_148" id= + "FNanchor_148_148"></a><a href="#Footnote_148_148" class= + "fnanchor">[148]</a></p> + + <p>9. Economy of time is very important both to the insects and + the flowers, because the fine working days are comparatively few, + and if no time is wasted the bees will get more honey, and in + doing so will fertilise more flowers. Now, it has been + ascertained by several observers that many insects, bees + especially, keep to one kind of flower at a time, visiting + hundreds of blossoms in succession, and passing over other + species that may be mixed with them. They thus acquire quickness + in going at once to the nectar, and the change of colour in the + flower, or incipient withering when fertilised, enables them to + avoid those flowers that have already had their honey exhausted. + It is probably to assist the insects in keeping to one flower at + a time, which is of vital importance to the perpetuation of the + species, that the flowers which bloom intermingled at the same + season are usually very distinct both in form and colour. In the + sandy districts of Surrey, in the early spring, the copses are + gay with three flowers—the primrose, the wood-anemone, and + the lesser celandine, forming a beautiful contrast, while at the + same time the purple and the white dead-nettles abound on hedge + banks. A little later, in the same copses, we have the blue wild + hyacinth (Scilla nutans), the red campion (Lychnis dioica), the + pure white great starwort (Stellaria Holosteum), and the yellow + dead-nettle (Lamium Galeobdolon), all distinct and + well-contrasted flowers. In damp meadows in summer we have the + ragged robin (Lychnis Floscuculi), the spotted orchis (O. + maculata), and the yellow rattle (Rhinanthus <a name="Page_319" + id="Page_319"></a>Crista-galli); while in drier meadows we have + cowslips, ox-eye daisies, and buttercups, all very distinct both + in form and colour. So in cornfields we have the scarlet poppies, + the purple corn-cockle, the yellow corn-marygold, and the blue + cornflower; while on our moors the purple heath and the dwarf + gorse make a gorgeous contrast. Thus the difference of colour + which enables the insect to visit with rapidity and unerring aim + a number of flowers of the same kind in succession, serves to + adorn our meadows, banks, woods, and heaths with a charming + variety of floral colour and form at each season of the + year.<a name="FNanchor_149_149" id= + "FNanchor_149_149"></a><a href="#Footnote_149_149" class= + "fnanchor">[149]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Fertilisation of Flowers by Birds.</i></p> + + <p>In the temperate regions of the Northern Hemisphere, insects + are the chief agents in cross-fertilisation when this is not + effected by the wind; but in warmer regions, and in the Southern + hemisphere, birds are found to take a considerable part in the + operation, and have in many cases led to modifications in the + form and colour of flowers. Each part of the globe has special + groups of birds which are flower-haunters. America has the + humming-birds (Trochilidae), and the smaller group of the + sugar-birds (Caerebidae). In the Eastern tropics the sun-birds + (Nectarineidae) take the place of the humming-birds, and another + small group, the flower-peckers (Dicaeidae), assist them. In the + Australian region there are also two flower-feeding groups, the + Meliphagidae, or honey-suckers, and the brush-tongued lories + (Trichoglossidae). Recent researches by American naturalists have + shown that many flowers are fertilised by humming-birds, such as + passion-flowers, trumpet-flowers, fuchsias, and lobelias; while + some, as the Salvia splendens of Mexico, are specially adapted to + their visits. We may thus perhaps explain the number of very + large tubular flowers in the tropics, such as the huge + brugmansias and bignonias; while in the Andes and in <a name= + "Page_320" id="Page_320"></a>Chile, where humming-birds are + especially plentiful, we find great numbers of red tubular + flowers, often of large size and apparently adapted to these + little creatures. Such are the beautiful Lapageria and Philesia, + the grand Pitcairneas, and the genera Fuchsia, Mitraria, + Embothrium, Escallonia, Desfontainea, Eccremocarpus, and many + Gesneraceae. Among the most extraordinary modifications of flower + structure adapted to bird fertilisation are the species of + Marcgravia, in which the pedicels and bracts of the terminal + portion of a pendent bunch of flowers have been modified into + pitchers which secrete nectar and attract insects, while birds + feeding on the nectar, or insects, have the pollen of the + overhanging flowers dusted on their backs, and, carrying it to + other flowers, thus cross-fertilise them (see Illustration).</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig31" id="fig31"></a> <img src="images/fig31.jpg" + width="400" height="372" alt= + "FIG. 31.—Humming-bird fertilising Marcgravia nepenthoides." + title= + "FIG. 31.—Humming-bird fertilising Marcgravia nepenthoides." /> + <b>FIG. 31.—Humming-bird fertilising Marcgravia + nepenthoides.</b> + </div> + + <p>In Australia and New Zealand the fine "glory peas" + (Clianthus), the Sophora, Loranthus, many Epacrideae and + Myrtaceae, and the large flowers of the New Zealand flax <a name= + "Page_321" id="Page_321"></a>(Phormium tenax), are + cross-fertilised by birds; while in Natal the fine + trumpet-creeper (Tecoma capensis) is fertilised by + Nectarineas.</p> + + <p>The great extent to which insect and bird agency is necessary + to flowers is well shown by the case of New Zealand. The entire + country is comparatively poor in species of insects, especially + in bees and butterflies which are the chief flower fertilisers; + yet according to the researches of local botanists no less than + one-fourth of all the flowering plants are incapable of + self-fertilisation, and, therefore, wholly dependent on insect or + bird agency for the continuance of the species.</p> + + <p>The facts as to the cross-fertilisation of flowers which have + now been very briefly summarised, taken in connection with + Darwin's experiments proving the increased vigour and fertility + given by cross-fertilisation, seem amply to justify his aphorism + that "Nature abhors self-fertilisation," and his more precise + statement, that, "No plant is perpetually self-fertilised;" and + this view has been upheld by Hildebrand, Delpino, and other + botanists.<a name="FNanchor_150_150" id= + "FNanchor_150_150"></a><a href="#Footnote_150_150" class= + "fnanchor">[150]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Self-Fertilisation of Flowers.</i></p> + + <p>But all this time we have been only looking at one side of the + question, for there exists an abundance of facts which seem to + imply, just as surely, the utter uselessness of + cross-fertilisation. Let us, then, see what these facts are + before proceeding further.</p> + + <p>1. An immense variety of plants are habitually + self-fertilised, and their numbers probably far exceed those + which are habitually cross-fertilised by insects. Almost all the + very small or obscure flowered plants with hermaphrodite flowers + are of this kind. Most of these, however, may be insect + fertilised occasionally, and may, therefore, come under the rule + that no species are perpetually self-fertilised.</p> + + <p>2. There are many plants, however, in which special + arrangements exist to secure self-fertilisation. Sometimes the + corolla closes and brings the anthers and stigma into contact; in + others the anthers cluster round the stigmas, both maturing + together, as in many buttercups, stitchwort (Stellaria media), + <a name="Page_322" id="Page_322"></a>sandwort (Spergula), and + some willow-herbs (Epilobium); or they arch over the pistil, as + in Galium aparine and Alisma Plantago. The style is also modified + to bring it into contact with the anthers, as in the dandelion, + groundsel, and many other plants.<a name="FNanchor_151_151" id= + "FNanchor_151_151"></a><a href="#Footnote_151_151" class= + "fnanchor">[151]</a> All these, however, may be occasionally + cross-fertilised.</p> + + <p>3. In other cases precautions are taken to prevent + cross-fertilisation, as in the numerous cleistogamous or closed + flowers. These occur in no less than fifty-five different genera, + belonging to twenty-four natural orders, and in thirty-two of + these genera the normal flowers are irregular, and have therefore + been specially modified for insect fertilisation.<a name= + "FNanchor_152_152" id="FNanchor_152_152"></a><a href= + "#Footnote_152_152" class="fnanchor">[152]</a> These flowers + appear to be degradations of the normal flowers, and are closed + up by various modifications of the petals or other parts, so that + it is impossible for insects to reach the interior, yet they + produce seed in abundance, and are often the chief means by which + the species is continued. Thus, in our common dog-violet the + perfect flowers rarely produce seed, while the rudimentary + cleistogamic flowers do so in abundance. The sweet violet also + produces abundance of seed from its cleistogamic flowers, and few + from its perfect flowers; but in Liguria it produces only perfect + flowers which seed abundantly. No case appears to be known of a + plant which has cleistogamic flowers only, but a small rush + (Juncus bufonius) is in this condition in some parts of Russia, + while in other parts perfect flowers are also produced.<a name= + "FNanchor_153_153" id="FNanchor_153_153"></a><a href= + "#Footnote_153_153" class="fnanchor">[153]</a> Our common henbit + dead-nettle (Lamium amplexicaule) produces cleistogamic flowers, + as do also some orchids. The advantage gained by the plant is + great economy of specialised material, since with very small + flowers and very little expenditure of pollen an abundance of + seed is produced.</p> + + <p>4. A considerable number of plants which have evidently been + specially modified for insect fertilisation have, by further + <a name="Page_323" id="Page_323"></a>modification, become quite + self-fertile. This is the case with the garden-pea, and also with + our beautiful bee-orchis, in which the pollen-masses constantly + fall on to the stigmas, and the flower, being thus + self-fertilised, produces abundance of capsules and of seed. Yet + in many of its close allies insect agency is absolutely required; + but in one of these, the fly-orchis, comparatively very little + seed is produced, and self-fertilisation would therefore be + advantageous to it. When garden-peas were artificially + cross-fertilised by Mr. Darwin, it seemed to do them no good, as + the seeds from these crosses produced less vigorous plants than + seed from those which were self-fertilised; a fact directly + opposed to what usually occurs in cross-fertilised plants.</p> + + <p>5. As opposed to the theory that there is any absolute need + for cross-fertilisation, it has been urged by Mr. Henslow and + others that many self-fertilised plants are exceptionally + vigorous, such as groundsel, chickweed, sow-thistle, buttercups, + and other common weeds; while most plants of world-wide + distribution are self-fertilised, and these have proved + themselves to be best fitted to survive in the battle of life. + More than fifty species of common British plants are very widely + distributed, and all are habitually self-fertilised.<a name= + "FNanchor_154_154" id="FNanchor_154_154"></a><a href= + "#Footnote_154_154" class="fnanchor">[154]</a> That + self-fertilisation has some great advantage is shown by the fact + that it is usually the species which have the smallest and least + conspicuous flowers which have spread widely, while the large and + showy flowered species of the same genera or families, which + require insects to cross-fertilise them, have a much more limited + distribution.</p> + + <p>6. It is now believed by some botanists that many + inconspicuous and imperfect flowers, including those that are + wind-fertilised, such as plantains, nettles, sedges, and grasses, + do not represent primitive or undeveloped forms, but are + degradations from more perfect flowers which were once adapted to + insect fertilisation. In almost every order we find some plants + which have become thus reduced or degraded for wind or + self-fertilisation, as Poterium and Sanguisorba among the + Rosaceae; while this has certainly been the case in the + cleistogamic flowers. In most of the above-mentioned plants there + are distinct rudiments of petals or other floral organs, <a name= + "Page_324" id="Page_324"></a>and as the chief use of these is to + attract insects, they could hardly have existed in primitive + flowers.<a name="FNanchor_155_155" id= + "FNanchor_155_155"></a><a href="#Footnote_155_155" class= + "fnanchor">[155]</a> We know, moreover, that when the petals + cease to be required for the attraction of <a name="Page_325" id= + "Page_325"></a>insects, they rapidly diminish in size, lose their + bright colour or almost wholly disappear.<a name= + "FNanchor_156_156" id="FNanchor_156_156"></a><a href= + "#Footnote_156_156" class="fnanchor">[156]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Difficulties and Contradictions.</i></p> + + <p>The very bare summary that has now been given of the main + facts relating to the fertilisation of flowers, will have served + to show the vast extent and complexity of the inquiry, and the + extraordinary contradictions and difficulties which it presents. + We have direct proof of the beneficial results of intercrossing + in a great number of cases; we have an overwhelming mass of facts + as to the varied and complex structure of flowers evidently + adapted to secure this intercrossing by insect agency; yet we see + many of the most vigorous plants which spread widely over the + globe, with none of these adaptations, and evidently depending on + self-fertilisation for their continued existence and success in + the battle of life. Yet more extraordinary is it to find numerous + cases in which the special arrangements for cross-fertilisation + appear to have been a failure, since they have either been + supplemented by special means for self-fertilisation, or have + reverted back in various degrees to simpler forms in which + self-fertilisation becomes the rule. There is also a further + difficulty in the highly complex modes by which + cross-fertilisation is often brought about; for we have seen that + there are several very effective yet very simple modes of + securing intercrossing, involving a minimum of change in the form + and structure of the flower; and when we consider that the result + attained with so much cost of structural modification is by no + means an unmixed good, and is far less certain in securing the + perpetuation of the species than is self-fertilisation, it is + most puzzling to find such complex methods resorted to, sometimes + to the extent of special precautions against the possibility of + self-fertilisation ever taking place. Let us now see whether any + light can be thrown on these various anomalies and + contradictions.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Intercrossing not necessarily Advantageous.</i></p> + + <p>No one was more fully impressed than Mr. Darwin with the + beneficial effects of intercrossing on the vigour and fertility + <a name="Page_326" id="Page_326"></a>of the species or race, yet + he clearly saw that it was not always and necessarily + advantageous. He says: "The most important conclusion at which I + have arrived is, that the mere act of intercrossing by itself + does no good. The good depends on the individuals which are + crossed differing slightly in constitution, owing to their + progenitors having been subjected during several generations to + slightly different conditions. This conclusion, as we shall + hereafter see, is closely connected with various important + physiological problems, such as the benefit derived from slight + changes in the conditions of life."<a name="FNanchor_157_157" id= + "FNanchor_157_157"></a><a href="#Footnote_157_157" class= + "fnanchor">[157]</a> Mr. Darwin has also adduced much direct + evidence proving that slight changes in the conditions of life + are beneficial to both animals and plants, maintaining or + restoring their vigour and fertility in the same way as a + favourable cross seems to restore it.<a name="FNanchor_158_158" + id="FNanchor_158_158"></a><a href="#Footnote_158_158" class= + "fnanchor">[158]</a> It is, I believe, by a careful consideration + of these two classes of facts that we shall find the clue to the + labyrinth in which this subject has appeared to involve us.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Supposed Evil Results of Close Interbreeding.</i></p> + + <p>Just as we have seen that intercrossing is not necessarily + good, we shall be forced to admit that close interbreeding is not + necessarily bad. Our finest breeds of domestic animals have been + thus produced, and by a careful statistical inquiry Mr. George + Darwin has shown that the most constant and long-continued + intermarriages among the British aristocracy have produced no + prejudicial results. The rabbits on Porto Santo are all the + produce of a single female; they have lived on the same small + island for 470 years, and they still abound there and appear to + be vigorous and healthy (see p. 161*).</p> + + <p>We have, however, on the other hand, overwhelming evidence + that in many cases, among our domestic animals and cultivated + plants, close interbreeding does produce bad results, and the + apparent contradiction may perhaps be explained on the same + general principles, and under similar limitations, as were found + to be necessary in defining the value of intercrossing. It + appears probable, then, that it is not interbreeding in itself + that is hurtful, but interbreeding without <a name="Page_327" id= + "Page_327"></a>rigid selection or some change of conditions. + Under nature, as in the case of the Porto Santo rabbits, the + rapid increase of these animals would in a very few years stock + the island with a full population, and thereafter natural + selection would act powerfully in the preservation only of the + healthiest and the most fertile, and under these conditions no + deterioration would occur. Among the aristocracy there has been a + constant selection of beauty, which is generally synonymous with + health, while any constitutional infertility has led to the + extinction of the family. With domestic animals the selection + practised is usually neither severe enough nor of the right kind. + There is no natural struggle for existence, but certain points of + form and colour characteristic of the breed are considered + essential, and thus the most vigorous or the most fertile are not + always those which are selected to continue the stock. In nature, + too, the species always extends over a larger area and consists + of much greater numbers, and thus a difference of constitution + soon arises in different parts of the area, which is wanting in + the limited numbers of pure bred domestic animals. From a + consideration of these varied facts we conclude that an + occasional disturbance of the organic equilibrium is what is + essential to keep up the vigour and fertility of any organism, + and that this disturbance may be equally well produced either by + a cross between individuals of somewhat different constitutions, + or by occasional slight changes in the conditions of life. Now + plants which have great powers of dispersal enjoy a constant + change of conditions, and can, therefore, exist permanently, or + at all events, for very long periods, without intercrossing; + while those which have limited powers of dispersal, and are + restricted to a comparatively small and uniform area, need an + occasional cross to keep up their fertility and general vigour. + We should, therefore, expect that those groups of plants which + are adapted both for cross-and self-fertilisation, which have + showy flowers and possess great powers of seed-dispersal, would + be the most abundant and most widely distributed; and this we + find to be the case, the Compositae possessing all these + characteristics in the highest degree, and being the most + generally abundant group of plants with conspicuous flowers in + all parts of the world.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_328" id="Page_328"></a><i>How the Struggle for + Existence Acts among Flowers.</i></p> + + <p>Let us now consider what will be the action of the struggle + for existence under the conditions we have seen to exist.</p> + + <p>Everywhere and at all times some species of plants will be + dominant and aggressive; while others will be diminishing in + numbers, reduced to occupy a smaller area, and generally having a + hard struggle to maintain themselves. Whenever a self-fertilising + plant is thus reduced in numbers it will be in danger of + extinction, because, being limited to a small area, it will + suffer from the effects of too uniform conditions which will + produce weakness and infertility. But while this change is in + progress, any crosses between individuals of slightly different + constitution will be beneficial, and all variations favouring + either insect agency on the one hand, or wind-dispersal of pollen + on the other, will lead to the production of a somewhat stronger + and more fertile stock. Increased size or greater brilliancy of + the flower, more abundant nectar, sweeter odour, or adaptations + for more effectual cross-fertilisation would all be preserved, + and thus would be initiated some form of specialisation for + insect agency in cross-fertilisation; and in every different + species so circumstanced the result would be different, depending + as it would on many and complex combinations of variation of + parts of the flower, and of the insect species which most + abounded in the district.</p> + + <p>Species thus favourably modified might begin a new era of + development, and, while spreading over a somewhat wider area, + give rise to new varieties or species, all adapted in various + degrees and modes to secure cross-fertilisation by insect agency. + But in course of ages some change of conditions might prove + adverse. Either the insects required might diminish in numbers or + be attracted by other competing flowers, or a change of climate + might give the advantage to other more vigorous plants. Then + self-fertilisation with greater means of dispersal might be more + advantageous; the flowers might become smaller and more numerous; + the seeds smaller and lighter so as to be more easily dispersed + by the wind, while some of the special adaptations for insect + fertilisation being useless would, by the absence of selection + and by the law of economy of growth, be reduced to a rudimentary + <a name="Page_329" id="Page_329"></a>form. With these + modifications the species might extend its range into new + districts, thereby obtaining increased vigour by the change of + conditions, as appears to have been the case with so many of the + small flowered self-fertilised plants. Thus it might continue to + exist for a long series of ages, till under other + changes—geographical or biological—it might again + suffer from competition or from other adverse circumstances, and + be at length again confined to a limited area, or reduced to very + scanty numbers.</p> + + <p>But when this cycle of change had taken place, the species + would be very different from the original form. The flower would + have been at one time modified to favour the visits of insects + and to secure cross-fertilisation by their aid, and when the need + for this passed away, some portions of these structures would + remain, though in a reduced or rudimentary condition. But when + insect agency became of importance a second time, the new + modifications would start from a different or more advanced + basis, and thus a more complex result might be produced. Owing to + the unequal rates at which the reduction of the various parts + might occur, some amount of irregularity in the flower might + arise, and on a second development towards insect + cross-fertilisation this irregularity, if useful, might be + increased by variation and selection.</p> + + <p>The rapidity and comparative certainty with which such changes + as are here supposed do really take place, are well shown by the + great differences in floral structure, as regards the mode of + fertilisation, in allied genera and species, and even in some + cases in varieties of the same species. Thus in the Ranunculaceae + we find the conspicuous part of the flower to be the petals in + Ranunculus, the sepals in Helleborus, Anemone, etc., and the + stamens in most species of Thalictrum. In all these we have a + simple regular flower, but in Aquilegia it is made complex by the + spurred petals, and in Delphinium and Aconitum it becomes quite + irregular. In the more simple class self-fertilisation occurs + freely, but it is prevented in the more complex flowers by the + stamens maturing before the pistil. In the Caprifoliaceae we have + small and regular greenish flowers, as in the moschatel (Adoxa); + more conspicuous regular open flowers without honey, as in the + elder (Sambucus); and <a name="Page_330" id= + "Page_330"></a>tubular flowers increasing in length and + irregularity, till in some, like our common honeysuckle, they are + adapted for fertilisation by moths only, with abundant honey and + delicious perfume to attract them. In the Scrophulariaceae we + find open, almost regular flowers, as Veronica and Verbascum, + fertilised by flies and bees, but also self-fertilised; + Scrophularia adapted in form and colour to be fertilised by + wasps; and the more complex and irregular flowers of Linaria, + Rhinanthus, Melampyrum, Pedicularis, etc., mostly adapted to be + fertilised by bees.</p> + + <p>In the genera Geranium, Polygonum, Veronica, and several + others there is a gradation of forms from large and bright to + small and obscure coloured flowers, and in every case the former + are adapted for insect fertilisation, often exclusively, while in + the latter self-fertilisation constantly occurs. In the yellow + rattle (Rhinanthus Crista-galli) there are two forms (which have + been named <i>major</i> and <i>minor</i>), the larger and more + conspicuous adapted to insect fertilisation only, the smaller + capable of self-fertilisation; and two similar forms exist in the + eyebright (Euphrasia officinalis). In both these cases there are + special modifications in the length and curvature of the style as + well as in the size and shape of the corolla; and the two forms + are evidently becoming each adapted to special conditions, since + in some districts the one, in other districts the other is most + abundant.<a name="FNanchor_159_159" id= + "FNanchor_159_159"></a><a href="#Footnote_159_159" class= + "fnanchor">[159]</a></p> + + <p>These examples show us that the kind of change suggested above + is actually going on, and has presumably always been going on in + nature throughout the long geological epochs during which the + development of flowers has been progressing. The two great modes + of gaining increased vigour and fertility—intercrossing and + dispersal over wider areas—have been resorted to again and + again, under the pressure of a constant struggle for existence + and the need for adaptation to ever-changing conditions. During + all the modifications that ensued, useless parts were reduced or + suppressed, owing to the absence of selection and the principle + of economy of growth; and thus at each fresh adaptation some + rudiments of old structures were <a name="Page_331" id= + "Page_331"></a>re-developed, but not unfrequently in a different + form and for a distinct purpose.</p> + + <p>The chief types of flowering plants have existed during the + millions of ages of the whole tertiary period, and during this + enormous lapse of time many of them may have been modified in the + direction of insect fertilisation, and again into that of + self-fertilisation, not once or twice only, but perhaps scores or + even hundreds of times; and at each such modification a + difference in the environment may have led to a distinct line of + development. At one epoch the highest specialisation of structure + in adaptation to a single species or group of insects may have + saved a plant from extinction; while, at other times, the + simplest mode of self-fertilisation, combined with greater powers + of dispersal and a constitution capable of supporting diverse + physical conditions, may have led to a similar result. With some + groups the tendency seems to have been almost continuously to + greater and greater specialisation, while with others a tendency + to simplification and degradation has resulted in such plants as + the grasses and sedges.</p> + + <p>We are now enabled dimly to perceive how the curious anomaly + of very simple and very complex methods of securing + cross-fertilisation—both equally effective—may have + been brought about. The simple modes may be the result of a + comparatively direct modification from the more primitive types + of flowers, which were occasionally, and, as it were, + accidentally visited and fertilised by insects; while the more + complex modes, existing for the most part in the highly irregular + flowers, may result from those cases in which adaptation to + insect-fertilisation, and partial or complete degradation to + self-fertilisation or to wind-fertilisation, have again and again + recurred, each time producing some additional complexity, arising + from the working up of old rudiments for new purposes, till there + have been reached the marvellous flower structures of the + papilionaceous tribes, of the asclepiads, or of the orchids.</p> + + <p>We thus see that the existing diversity of colour and of + structure in flowers is probably the ultimate result of the + ever-recurring struggle for existence, combined with the + ever-changing relations between the vegetable and animal kingdoms + during countless ages. The constant variability of every part + <a name="Page_332" id="Page_332"></a>and organ, with the enormous + powers of increase possessed by plants, have enabled them to + become again and again readjusted to each change of condition as + it occurred, resulting in that endless variety, that marvellous + complexity, and that exquisite colouring which excite our + admiration in the realm of flowers, and constitute them the + perennial charm and crowning glory of nature.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Flowers the Product of Insect Agency.</i></p> + + <p>In his <i>Origin of Species</i>, Mr. Darwin first stated that + flowers had been rendered conspicuous and beautiful in order to + attract insects, adding: "Hence we may conclude that, if insects + had not been developed on the earth, our plants would not have + been decked with beautiful flowers, but would have produced only + such poor flowers as we see on our fir, oak, nut, and ash trees, + on grasses, docks, and nettles, which are all fertilised through + the agency of the wind." The argument in favour of this view is + now much stronger than when he wrote; for not only have we reason + to believe that most of these wind-fertilised flowers are + degraded forms of flowers which have once been insect fertilised, + but we have abundant evidence that whenever insect agency becomes + comparatively ineffective, the colours of the flowers become less + bright, their size and beauty diminish, till they are reduced to + such small, greenish, inconspicuous flowers as those of the + rupture-wort (Herniaria glabra), the knotgrass (Polygonum + aviculare), or the cleistogamic flowers of the violet. There is + good reason to believe, therefore, not only that flowers have + been developed in order to attract insects to aid in their + fertilisation, but that, having been once produced, in however + great profusion, if the insect races were all to become extinct, + flowers (in the temperate zones at all events) would soon dwindle + away, and that ultimately all floral beauty would vanish from the + earth.</p> + + <p>We cannot, therefore, deny the vast change which insects have + produced upon the earth's surface, and which has been thus + forcibly and beautifully delineated by Mr. Grant Allen: "While + man has only tilled a few level plains, a few great river + valleys, a few peninsular mountain slopes, leaving the vast mass + of earth untouched by his hand, the insect has spread himself + over every land in a thousand shapes, and has made the whole + <a name="Page_333" id="Page_333"></a>flowering creation + subservient to his daily wants. His buttercup, his dandelion, and + his meadow-sweet grow thick in every English field. His thyme + clothes the hillside; his heather purples the bleak gray + moorland. High up among the alpine heights his gentian spreads + its lakes of blue; amid the snows of the Himalayas his + rhododendrons gleam with crimson light. Even the wayside pond + yields him the white crowfoot and the arrowhead, while the broad + expanses of Brazilian streams are beautified by his gorgeous + water-lilies. The insect has thus turned the whole surface of the + earth into a boundless flower-garden, which supplies him from + year to year with pollen or honey, and itself in turn gains + perpetuation by the baits that it offers for his + allurement."<a name="FNanchor_160_160" id= + "FNanchor_160_160"></a><a href="#Footnote_160_160" class= + "fnanchor">[160]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks on Colour in Nature.</i></p> + + <p>In the last four chapters I have endeavoured to give a general + and systematic, though necessarily condensed view of the part + which is played by colour in the organic world. We have seen in + what infinitely varied ways the need of concealment has led to + the modification of animal colours, whether among polar snows or + sandy deserts, in tropical forests or in the abysses of the + ocean. We next find these general adaptations giving way to more + specialised types of coloration, by which each species has become + more and more harmonised with its immediate surroundings, till we + reach the most curiously minute resemblances to natural objects + in the leaf and stick insects, and those which are so like + flowers or moss or birds' droppings that they deceive the acutest + eye. We have learnt, further, that these varied forms of + protective colouring are far more numerous than has been usually + suspected, because, what appear to be very conspicuous colours or + markings when the species is observed in a museum or in a + menagerie, are often highly protective when the creature is seen + under the natural conditions of its existence. From these varied + classes of facts it seems not improbable that fully one-half of + the species in the animal kingdom possess colours which have been + more or less adapted to secure for them concealment or + protection.</p> + + <p>Passing onward we find the explanation of a distinct type + <a name="Page_334" id="Page_334"></a>of colour or marking, often + superimposed upon protective tints, in the importance of easy + recognition by many animals of their fellows, their parents, or + their mates. By this need we have been able to account for + markings that seem calculated to make the animal conspicuous, + when the general tints and well-known habits of the whole group + demonstrate the need of concealment. Thus also we are able to + explain the constant symmetry in the markings of wild animals, as + well as the numerous cases in which the conspicuous colours are + concealed when at rest and only become visible during rapid + motion. In striking contrast to ordinary protective coloration we + have "warning colours," usually very conspicuous and often + brilliant or gaudy, which serve to indicate that their possessors + are either dangerous or uneatable to the usual enemies of their + tribe. This kind of coloration is probably more prevalent than + has been hitherto supposed, because in the case of many tropical + animals we are quite unacquainted with their special and most + dangerous enemies, and are also unable to determine whether they + are or are not distasteful to those enemies. As a kind of + corollary to the "warning colours," we find the extraordinary + phenomena of "mimicry," in which defenceless species obtain + protection by being mistaken for those which, from any cause, + possess immunity from attack. Although a large number of + instances of warning colour and of mimicry are now recorded, it + is probably still an almost unworked field of research, more + especially in tropical regions and among the inhabitants of the + ocean.</p> + + <p>The phenomena of sexual diversities of coloration next engaged + our attention, and the reasons why Mr. Darwin's theory of "sexual + selection," as regards colour and ornament, could not be accepted + were stated at some length, together with the theory of animal + coloration and ornament we propose to substitute for it. This + theory is held to be in harmony with the general facts of animal + coloration, while it entirely dispenses with the very + hypothetical and inadequate agency of female choice in producing + the detailed colours, patterns, and ornaments, which in so many + cases distinguish the male sex.</p> + + <p>If my arguments on this point are sound, they will dispose + also of Mr. Grant Allen's view of the direct action of the + <a name="Page_335" id="Page_335"></a>colour sense on the animal + integuments.<a name="FNanchor_161_161" id= + "FNanchor_161_161"></a><a href="#Footnote_161_161" class= + "fnanchor">[161]</a> He argues that the colours of insects and + birds reproduce generally the colours of the flowers they + frequent or the fruits they eat, and he adduces numerous cases in + which flower-haunting insects and fruit-eating birds are gaily + coloured. This he supposes to be due to the colour-taste, + developed by the constant presence of bright flowers and fruits, + being applied to the selection of each variation towards + brilliancy in their mates; thus in time producing the gorgeous + and varied hues they now possess. Mr. Allen maintains that + "insects are bright where bright flowers exist in numbers, and + dull where flowers are rare or inconspicuous;" and he urges that + "we can hardly explain this wide coincidence otherwise than by + supposing that a taste for colour is produced through the + constant search for food among entomophilous blossoms, and that + this taste has reacted upon its possessors through the action of + unconscious sexual selection."</p> + + <p>The examples Mr. Allen quotes of bright insects being + associated with bright flowers seem very forcible, but are really + deceptive or erroneous; and quite as many cases could be quoted + which prove the very opposite. For example, in the dense + equatorial forests flowers are exceedingly scarce, and there is + no comparison with the amount of floral colour to be met with in + our temperate meadows, woods, and hillsides. The forests about + Para in the lower Amazon are typical in this respect, yet they + abound with the most gorgeously coloured butterflies, almost all + of which frequent the forest depths, keeping near the ground, + where there is the greatest deficiency of brilliant flowers. In + contrast with this let us take the Cape of Good Hope—the + most flowery region probably that exists upon the + globe,—where the country is a complete flower-garden of + heaths, pelargoniums, mesembryanthemus, exquisite iridaceous and + other bulbs, and numerous flowering shrubs and trees; yet the + Cape butterflies are hardly equal, either in number or variety, + to those of any country in South Europe, and are utterly + insignificant when compared with those of the comparatively + flowerless forest-depths of the Amazon or of New Guinea. Neither + is there any relation between the colours of other insects and + their haunts. Few <a name="Page_336" id="Page_336"></a>are more + gorgeous than some of the tiger-beetles and the carabi, yet these + are all carnivorous; while many of the most brilliant metallic + buprestidae and longicorns are always found on the bark of fallen + trees. So with the humming-birds; their brilliant metallic tints + can only be compared with metals or gems, and are totally unlike + the delicate pinks and purples, yellows and reds of the majority + of flowers. Again, the Australian honey-suckers (Meliphagidae) + are genuine flower-haunters, and the Australian flora is more + brilliant in colour display than that of most tropical regions, + yet these birds are, as a rule, of dull colours, not superior on + the average to our grain-eating finches. Then, again, we have the + grand pheasant family, including the gold and the silver + pheasants, the gorgeous fire-backed and ocellated pheasants, and + the resplendent peacock, all feeding on the ground on grain or + seeds or insects, yet adorned with the most gorgeous colours.</p> + + <p>There is, therefore, no adequate basis of facts for this + theory to rest upon, even if there were the slightest reason to + believe that not only birds, but butterflies and beetles, take + any delight in colour for its own sake, apart from the + food-supply of which it indicates the presence. All that has been + proved or that appears to be probable is, that they are able to + perceive differences of colour, and to associate each colour with + the particular flowers or fruits which best satisfy their wants. + Colour being in its nature diverse, it has been beneficial for + them to be able to distinguish all its chief varieties, as + manifested more particularly in the vegetable kingdom, and among + the different species of their own group; and the fact that + certain species of insects show some preference for a particular + colour may be explained by their having found flowers of that + colour to yield them a more abundant supply of nectar or of + pollen. In those cases in which butterflies frequent flowers of + their own colour, the habit may well have been acquired from the + protection it affords them.</p> + + <p>It appears to me that, in imputing to insects and birds the + same love of colour for its own sake and the same aesthetic + tastes as we ourselves possess, we may be as far from the truth + as were those writers who held that the bee was a good + mathematician, and that the honeycomb was constructed throughout + to satisfy its refined mathematical instincts; whereas it is now + <a name="Page_337" id="Page_337"></a>generally admitted to be the + result of the simple principle of economy of material applied to + a primitive cylindrical cell.<a name="FNanchor_162_162" id= + "FNanchor_162_162"></a><a href="#Footnote_162_162" class= + "fnanchor">[162]</a></p> + + <p>In studying the phenomena of colour in the organic world we + have been led to realise the wonderful complexity of the + adaptations which bring each species into harmonious relation + with all those which surround it, and which thus link together + the whole of nature in a network of relations of marvellous + intricacy. Yet all this is but, as it were, the outward show and + garment of nature, behind which lies the inner + structure—the framework, the vessels, the cells, the + circulating fluids, and the digestive and reproductive + processes,—and behind these again those mysterious + chemical, electrical, and vital forces which constitute what we + term Life. These forces appear to be fundamentally the same for + all organisms, as is the material of which all are constructed; + and we thus find behind the outer diversities an inner + relationship which binds together the myriad forms of life.</p> + + <p>Each species of animal or plant thus forms part of one + harmonious whole, carrying in all the details of its complex + structure the record of the long story of organic development; + and it was with a truly inspired insight that our great + philosophical poet apostrophised the humble weed—</p> + + <p><span style="margin-left: 2em;">Flower in the crannied + wall,</span><br /> + <span style="margin-left: 2em;">I pluck you out of the + crannies,</span><br /> + <span style="margin-left: 2em;">I hold you here, root and all, in + my hand,</span><br /> + <span style="margin-left: 2em;">Little flower—but <i>if</i> + I could understand</span><br /> + <span style="margin-left: 2em;">What you are, root and all, and + all in all,</span><br /> + <span style="margin-left: 2em;">I should know what God and man + is.</span><br /></p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_136_136" id= + "Footnote_136_136"></a><a href= + "#FNanchor_136_136"><span class="label">[136]</span></a> + Burchell's <i>Travels</i>, vol. i. p. 10.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_137_137" id= + "Footnote_137_137"></a><a href= + "#FNanchor_137_137"><span class="label">[137]</span></a> + <i>Nature</i>, vol. iii. p. 507.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_138_138" id= + "Footnote_138_138"></a><a href= + "#FNanchor_138_138"><span class="label">[138]</span></a> + <i>Flowers, Fruits, and Leaves</i>, p. 128 (Fig. 79).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_139_139" id= + "Footnote_139_139"></a><a href= + "#FNanchor_139_139"><span class="label">[139]</span></a> For + a popular sketch of these, see Sir J. Lubbock's <i>Flowers, + Fruits, and Leaves</i>, or any general botanical work.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_140_140" id= + "Footnote_140_140"></a><a href= + "#FNanchor_140_140"><span class="label">[140]</span></a> + <i>Nature</i>, vol. xv. p, 117.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_141_141" id= + "Footnote_141_141"></a><a href= + "#FNanchor_141_141"><span class="label">[141]</span></a> + Grant Allen's <i>Colour Sense</i>, p. 113.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_142_142" id= + "Footnote_142_142"></a><a href= + "#FNanchor_142_142"><span class="label">[142]</span></a> + Canon Tristram's <i>Natural History of the Bible</i>, pp. + 483, 484.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_143_143" id= + "Footnote_143_143"></a><a href= + "#FNanchor_143_143"><span class="label">[143]</span></a> For + a complete historical account of this subject with full + references to all the works upon it, see the Introduction to + Hermann Müller's <i>Fertilisation of Flowers</i>, + translated by D'Arcy W. Thompson.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_144_144" id= + "Footnote_144_144"></a><a href= + "#FNanchor_144_144"><span class="label">[144]</span></a> For + the full detail of his experiments, see <i>Cross-and + Self-Fertilisation of Plants</i>, 1876.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_145_145" id= + "Footnote_145_145"></a><a href= + "#FNanchor_145_145"><span class="label">[145]</span></a> See + Darwin's <i>Fertilisation of Orchids</i> for the many + extraordinary and complex arrangements in these plants.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_146_146" id= + "Footnote_146_146"></a><a href= + "#FNanchor_146_146"><span class="label">[146]</span></a> The + English reader may consult Sir John Lubbock's <i>British Wild + Flowers in Relation to Insects</i>, and H. Müller's + great and original work, <i>The Fertilisation of + Flowers</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_147_147" id= + "Footnote_147_147"></a><a href= + "#FNanchor_147_147"><span class="label">[147]</span></a> + Müller's <i>Fertilisation of Flowers</i>, p. 248.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_148_148" id= + "Footnote_148_148"></a><a href= + "#FNanchor_148_148"><span class="label">[148]</span></a> + "Alpenblumen," by D.H. Müller. See <i>Nature</i>, vol. + xxiii. p. 333.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_149_149" id= + "Footnote_149_149"></a><a href= + "#FNanchor_149_149"><span class="label">[149]</span></a> This + peculiarity of local distribution of colour in flowers may be + compared, as regards its purpose, with the recognition + colours of animals. Just as these latter colours enable the + sexes to recognise each other, and thus avoid sterile unions + of distinct species, so the distinctive form and colour of + each species of flower, as compared with those that usually + grow around it, enables the fertilising insects to avoid + carrying the pollen of one flower to the stigma of a distinct + species.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_150_150" id= + "Footnote_150_150"></a><a href= + "#FNanchor_150_150"><span class="label">[150]</span></a> See + H. Müller's <i>Fertilisation of Flowers</i>, p. 18.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_151_151" id= + "Footnote_151_151"></a><a href= + "#FNanchor_151_151"><span class="label">[151]</span></a> The + above examples are taken from Rev. G. Henslow's paper on + "Self-Fertilisation of Plants," in <i>Trans. Linn. Soc.</i> + Second series, <i>Botany</i>, vol. i. pp. 317-398, with + plate. Mr. H.O. Forbes has shown that the same thing occurs + among tropical orchids, in his paper "On the Contrivances for + insuring Self-Fertilisation in some Tropical Orchids," + <i>Journ. Linn. Soc.</i>, xxi. p. 538.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_152_152" id= + "Footnote_152_152"></a><a href= + "#FNanchor_152_152"><span class="label">[152]</span></a> + These are the numbers given by Darwin, but I am informed by + Mr. Hemsley that many additions have been since made to the + list, and that cleistogamic flowers probably occur in nearly + all the natural orders.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_153_153" id= + "Footnote_153_153"></a><a href= + "#FNanchor_153_153"><span class="label">[153]</span></a> For + a full account of cleistogamic flowers, see Darwin's <i>Forms + of Flowers</i>, chap. viii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_154_154" id= + "Footnote_154_154"></a><a href= + "#FNanchor_154_154"><span class="label">[154]</span></a> + Henslow's "Self-Fertilisation," <i>Trans. Linn. Soc.</i> + Second series, <i>Botany</i>, vol. i. p. 391.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_155_155" id= + "Footnote_155_155"></a><a href= + "#FNanchor_155_155"><span class="label">[155]</span></a> The + Rev. George Henslow, in his <i>Origin of Floral + Structures</i>, says: "There is little doubt but that all + wind-fertilised angiosperms are degradations from + insect-fertilised flowers.... <i>Poterium sanguisorba</i> is + anemophilous; and <i>Sanguisorba officinalis</i> presumably + was so formerly, but has reacquired an entomophilous habit; + the whole tribe Poterieae being, in fact, a degraded group + which has descended from Potentilleae. Plantains retain their + corolla but in a degraded form. Junceae are degraded Lilies; + while Cyperaceae and Gramineae among monocotyledons may be + ranked with Amentiferae among dicotyledons, as representing + orders which have retrograded very far from the entomophilous + forms from which they were possibly and probably descended" + (p. 266).</p> + + <p>"The genus Plantago, like <i>Thalictrum minus</i>, + Poterium, and others, well illustrate the change from an + entomophilous to the anemophilous state. <i>P. lanceolata</i> + has polymorphic flowers, and is visited by pollen-seeking + insects, so that it can be fertilised either by insects or + the wind. <i>P. media</i> illustrates transitions in point of + structure, as the filaments are pink, the anthers motionless, + and the pollen grains aggregated, and it is regularly visited + by <i>Bombus terrestris</i>. On the other hand, the slender + filaments, versatile anthers, powdery pollen, and elongated + protogynous style are features of other species indicating + anemophily; while the presence of a degraded corolla shows + its ancestors to have been entomophilous. <i>P. media</i>, + therefore, illustrates, not a primitive entomophilous + condition, but a return to it; just as is the case with + <i>Sanguisorba officinalis</i> and <i>Salix Caprea</i>; but + these show no capacity of restoring the corolla, the + attractive features having to be borne by the calyx, which is + purplish in Sanguisorba, by the pink filaments of Plantago, + and by the yellow anthers in the Sallow willow" (p. 271).</p> + + <p>"The interpretation, then, I would offer of + inconspicuousness and all kinds of degradations is the exact + opposite to that of conspicuousness and great + differentiations; namely, that species with minute flowers, + rarely or never visited by insects, and habitually + self-fertilised, have primarily arisen through the neglect of + insects, and have in consequence assumed their present floral + structures" (p. 282).</p> + + <p>In a letter just received from Mr. Henslow, he gives a few + additional illustrations of his views, of which the following + are the most important: "Passing to Incompletae, the orders + known collectively as 'Cyclospermeae' are related to + Caryophylleae; and to my mind are degradations from it, of + which Orache is anemophilous. Cupuliferae have an inferior + ovary and rudimentary calyx-limb on the top. These, as far as + I know, cannot be interpreted except as degradations. The + whole of Monocotyledons appear to me (from anatomical reasons + especially) to be degradations from Dicotyledons, and + primarily through the agency of growth in water. Many + subsequently became terrestrial, but retained the effects of + their primitive habitat through heredity. The 3-merous [sic] + perianth of grasses, the parts of the flower being in whorls, + point to a degradation from a sub-liliaceous condition."</p> + + <p>Mr. Henslow informs me that he has long held these views, + but, as far as he knows, alone. Mr. Grant Allen, however, set + forth a similar theory in his <i>Vignettes from Nature</i> + (p. 15) and more fully in <i>The Colours of Flowers</i> + (chap. v.), where he develops it fully and uses similar + arguments to those of Mr. Henslow.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_156_156" id= + "Footnote_156_156"></a><a href= + "#FNanchor_156_156"><span class="label">[156]</span></a> H. + Müller gives ample proof of this in his <i>Fertilisation + of Flowers</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_157_157" id= + "Footnote_157_157"></a><a href= + "#FNanchor_157_157"><span class="label">[157]</span></a> + <i>Cross-and Self-Fertilisation</i>, p. 27.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_158_158" id= + "Footnote_158_158"></a><a href= + "#FNanchor_158_158"><span class="label">[158]</span></a> + <i>Animals and Plants</i>, vol. ii. p. 145.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_159_159" id= + "Footnote_159_159"></a><a href= + "#FNanchor_159_159"><span class="label">[159]</span></a> + Müller's <i>Fertilisation of Flowers</i>, pp. 448, 455. + Other cases of recent degradation and readaptation to + insect-fertilisation are given by Professor Henslow (see + footnote, p. 324).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_160_160" id= + "Footnote_160_160"></a><a href= + "#FNanchor_160_160"><span class="label">[160]</span></a> + <i>The Colour Sense</i>, by Grant Allen, p. 95.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_161_161" id= + "Footnote_161_161"></a><a href= + "#FNanchor_161_161"><span class="label">[161]</span></a> + <i>The Colour Sense</i>, chap. ix.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_162_162" id= + "Footnote_162_162"></a><a href= + "#FNanchor_162_162"><span class="label">[162]</span></a> See + <i>Origin of Species</i>, sixth edition, p. 220.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a><a name="Page_338" + id="Page_338"></a>CHAPTER XII</h2> + + <p style='font-weight:bold;'>THE GEOGRAPHICAL DISTRIBUTION OF + ORGANISMS</p> + + <div class="blockquot"> + <p>The facts to be explained—The conditions which have + determined distribution—The permanence of + oceans—Oceanic and continental areas—Madagascar and + New Zealand—The teachings of the thousand-fathom + line—The distribution of marsupials—The + distribution of tapirs—Powers of dispersal as illustrated + by insular organisms—Birds and insects at + sea—Insects at great altitudes—The dispersal of + plants—Dispersal of seeds by the wind—Mineral + matter carried by the wind—Objections to the theory of + wind-dispersal answered—Explanation of north temperate + plants in the southern hemisphere—No proof of glaciation + in the tropics—Lower temperature not needed to explain + the facts—Concluding remarks.</p> + </div> + + <p>The theory which we may now take as established—that all + the existing forms of life have been derived from other forms by + a natural process of descent with modification, and that this + same process has been in action during past geological + time—should enable us to give a rational account not only + of the peculiarities of form and structure presented by animals + and plants, but also of their grouping together in certain areas, + and their general distribution over the earth's surface.</p> + + <p>In the absence of any exact knowledge of the facts of + distribution, a student of the theory of evolution might + naturally anticipate that all groups of allied organisms would be + found in the same region, and that, as he travelled farther and + farther from any given centre, the forms of life would differ + more and more from those which prevailed at the starting-point, + till, in the remotest regions to which he could penetrate, he + would find an entirely new assemblage of animals and plants, + altogether unlike those with which he was <a name="Page_339" id= + "Page_339"></a>familiar. He would also anticipate that + diversities of climate would always be associated with a + corresponding diversity in the forms of life.</p> + + <p>Now these anticipations are to a considerable extent + justified. Remoteness on the earth's surface is usually an + indication of diversity in the fauna and flora, while strongly + contrasted climates are always accompanied by a considerable + contrast in the forms of life. But this correspondence is by no + means exact or proportionate, and the converse propositions are + often quite untrue. Countries which are near to each other often + differ radically in their animal and vegetable productions; while + similarity of climate, together with moderate geographical + proximity, are often accompanied by marked diversities in the + prevailing forms of life. Again, while many groups of + animals—genera, families, and sometimes even + orders—are confined to limited regions, most of the + families, many genera, and even some species are found in every + part of the earth. An enumeration of a few of these anomalies + will better illustrate the nature of the problem we have to + solve.</p> + + <p>As examples of extreme diversity, notwithstanding geographical + proximity, we may adduce Madagascar and Africa, whose animal and + vegetable productions are far less alike than are those of Great + Britain and Japan at the remotest extremities of the great + northern continent; while an equal, or perhaps even a still + greater, diversity exists between Australia and New Zealand. On + the other hand, Northern Africa and South Europe, though + separated by the Mediterranean Sea, have faunas and floras which + do not differ from each other more than do the various countries + of Europe. As a proof that similarity of climate and general + adaptability have had but a small part in determining the forms + of life in each country, we have the fact of the enormous + increase of rabbits and pigs in Australia and New Zealand, of + horses and cattle in South America, and of the common sparrow in + North America, though in none of these cases are the animals + natives of the countries in which they thrive so well. And + lastly, in illustration of the fact that allied forms are not + always found in adjacent regions, we have the tapirs, which are + found only on opposite sides of the globe, in tropical America + and the Malayan Islands; the camels of <a name="Page_340" id= + "Page_340"></a>the Asiatic deserts, whose nearest allies are the + llamas and alpacas of the Andes; and the marsupials, only found + in Australia and on the opposite side of the globe, in America. + Yet, again, although mammalia may be said to be universally + distributed over the globe, being found abundantly on all the + continents and on a great many of the larger islands, yet they + are entirely wanting in New Zealand, and in a considerable number + of other islands which are, nevertheless, perfectly able to + support them when introduced.</p> + + <p>Now most of these difficulties can be solved by means of + well-known geographical and geological facts. When the + productions of remote countries resemble each other, there is + almost always continuity of land with similarity of climate + between them. When adjacent countries differ greatly in their + productions, we find them separated by a sea or strait whose + great depth is an indication of its antiquity or permanence. When + a group of animals inhabits two countries or regions separated by + wide oceans, it is found that in past geological times the same + group was much more widely distributed, and may have reached the + countries it inhabits from an intermediate region in which it is + now extinct. We know, also, that countries now united by land + were divided by arms of the sea at a not very remote epoch; while + there is good reason to believe that others now entirely isolated + by a broad expanse of sea were formerly united and formed a + single land area. There is also another important factor to be + taken account of in considering how animals and plants have + acquired their present peculiarities of + distribution,—changes of climate. We know that quite + recently a glacial epoch extended over much of what are now the + temperate regions of the northern hemisphere, and that + consequently the organisms which inhabit those parts must be, + comparatively speaking, recent immigrants from more southern + lands. But it is a yet more important fact that, down to middle + Tertiary times at all events, an equable temperate climate, with + a luxuriant vegetation, extended to far within the arctic circle, + over what are now barren wastes, covered for ten months of the + year with snow and ice. The arctic zone has, therefore, been in + past times capable of supporting almost all the forms of life of + our temperate regions; and we <a name="Page_341" id= + "Page_341"></a>must take account of this condition of things + whenever we have to speculate on the possible migrations of + organisms between the old and new continents.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Conditions which have determined Distribution.</i></p> + + <p>When we endeavour to explain in detail the facts of the + existing distribution of organic beings, we are confronted by + several preliminary questions, upon the solution of which will + depend our treatment of the phenomena presented to us. Upon the + theory of descent which we have adopted, all the different + species of a genus, as well as all the genera which compose a + family or higher group, have descended from some common ancestor, + and must therefore, at some remote epoch, have occupied the same + area, from which their descendants have spread to the regions + they now inhabit. In the numerous cases in which the same group + now occupies countries separated by oceans or seas, by lofty + mountain-chains, by wide deserts, or by inhospitable climates, we + have to consider how the migration which must certainly have + taken place has been effected. It is possible that during some + portion of the time which has elapsed since the origin of the + group the interposing barriers have not been in existence; or, on + the other hand, the particular organisms we are dealing with may + have the power of overpassing the barriers, and thus reaching + their present remote dwelling-places. As this is really the + fundamental question of distribution on which the solution of all + its more difficult problems depends, we have to inquire, in the + first place, what is the nature of, and what are the limits to, + the changes of the earth's surface, especially during the + Tertiary and latter part of the Secondary periods, as it was + during those periods that most of the existing types of the + higher animals and plants came into existence; and, in the next + place, what are the extreme limits of the powers of dispersal + possessed by the chief groups of animals and plants. We will + first consider the question of barriers, more especially those + formed by seas and oceans.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Permanence of Oceans.</i></p> + + <p>It was formerly a very general belief, even amongst + geologists, that the great features of the earth's surface, no + less than the smaller ones, were subject to continual mutations, + <a name="Page_342" id="Page_342"></a>and that during the course + of known geological time the continents and great oceans had + again and again changed places with each other. Sir Charles + Lyell, in the last edition of his <i>Principles of Geology</i> + (1872), said: "Continents, therefore, although permanent for + whole geological epochs, shift their positions entirely in the + course of ages;" and this may be said to have been the orthodox + opinion down to the very recent period when, by means of deep-sea + soundings, the nature of the ocean bottom was made known. The + first person to throw doubt on this view appears to have been the + veteran American geologist, Professor Dana. In 1849, in the + Report of Wilke's Exploring Expedition, he adduced the argument + against a former continent in the Pacific during the Tertiary + period, from the absence of all native quadrupeds. In 1856, in + articles in the <i>American Journal</i>, he discussed the + development of the American continent, and argued for its general + permanence; and in his <i>Manual of Geology</i> in 1863 and later + editions, the same views were more fully enforced and were + latterly applied to all continents. Darwin, in his <i>Journal of + Researches</i>, published in 1845, called attention to the fact + that all the small islands far from land in the Pacific, Indian, + and Atlantic Oceans are either of coralline or volcanic + formation. He excepted, however, the Seychelles and St. Paul's + rocks; but the former have since been shown to be no exception, + as they consist entirely of coral rock; and although Darwin + himself spent a few hours on St. Paul's rocks on his outward + voyage in the <i>Beagle</i>, and believed he had found some + portions of them to be of a "cherty," and others of a + "felspathic" nature, this also has been shown to be erroneous, + and the careful examination of the rocks by the Abbé + Renard clearly proves them to be wholly of volcanic + origin.<a name="FNanchor_163_163" id= + "FNanchor_163_163"></a><a href="#Footnote_163_163" class= + "fnanchor">[163]</a> We have, therefore, at the present time, + absolutely no exception whatever to the remarkable fact that all + the oceanic islands of the globe are either of volcanic or coral + formation; and there is, further, good reason to believe that + those of the latter class in every case rest upon a volcanic + foundation.</p> + + <p>In his <i>Origin of Species</i>, Darwin further showed that no + true oceanic island had any native mammals or batrachia <a name= + "Page_343" id="Page_343"></a>when first discovered, this fact + constituting the test of the class to which an island belongs; + whence he argued that none of them had ever been connected with + continents, but all had originated in mid-ocean. These + considerations alone render it almost certain that the areas now + occupied by the great oceans have never, during known geological + time, been occupied by continents, since it is in the highest + degree improbable that every fragment of those continents should + have completely disappeared, and have been replaced by volcanic + islands rising out of profound oceanic abysses; but recent + research into the depth of the oceans and the nature of the + deposits now forming on their floors, adds greatly to the + evidence in this direction, and renders it almost a certainty + that they represent very ancient if not primaeval features of the + earth's surface. A very brief outline of the nature of this + evidence will be now given.</p> + + <p>The researches of the <i>Challenger</i> expedition into the + nature of the sea-bottom show, that the whole of the land debris + brought down by rivers to the ocean (with the exception of pumice + and other floating matter), is deposited comparatively near to + the shores, and that the fineness of the material is an + indication of the distance to which it has been carried. + Everything in the nature of gravel and sand is laid down within a + very few miles of land, only the finer muddy sediments being + carried out for 20 or 50 miles, and the very finest of all, under + the most favourable conditions, rarely extending beyond 150, or + at the utmost, 300 miles from land into the deep ocean.<a name= + "FNanchor_164_164" id="FNanchor_164_164"></a><a href= + "#Footnote_164_164" class="fnanchor">[164]</a> Beyond these + distances, and covering the entire ocean floor, are various oozes + formed wholly from the debris of marine organisms; while + intermingled with these are found various volcanic products which + have been either carried through the air or floated on the + surface, and a small but perfectly recognisable quantity of + meteoric matter. Ice-borne rocks are also found abundantly + scattered over the ocean bottom within a definite distance of the + arctic and antarctic circles, clearly marking out the limit of + floating icebergs in recent geological times.</p> + + <p><a name="Page_344" id="Page_344"></a>Now the whole series of + marine stratified rocks, from the earliest Palaeozoic to the most + recent Tertiary beds, consist of materials closely corresponding + to the land debris now being deposited within a narrow belt round + the shores of all continents; while no rocks have been found + which can be identified with the various oozes now forming in the + deep abysses of the ocean. It follows, therefore, that all the + geological formations have been formed in comparatively shallow + water, and always adjacent to the continental land of the period. + The great thickness of some of the formations is no indication of + a deep sea, but only of slow subsidence during the time that the + deposition was in progress. This view is now adopted by many of + the most experienced geologists, especially by Dr. Archibald + Geikie, Director of the Geological Survey of Great Britain, who, + in his lecture on "Geographical Evolution," says: "From all this + evidence we may legitimately conclude that the present land of + the globe, though consisting in great measure of marine + formations, has never lain under the deep sea; but that its site + must always have been near land. Even its thick marine limestones + are the deposits of comparatively shallow water."<a name= + "FNanchor_165_165" id="FNanchor_165_165"></a><a href= + "#Footnote_165_165" class="fnanchor">[165]</a></p> + + <p>But besides these geological and physical considerations, + there is a mechanical difficulty in the way of repeated change of + position of oceans and continents which has not yet received the + attention it deserves. According to the recent careful estimate + by Mr. John Murray, the land area of the globe is to the water + area as ·28 to ·72. The mean height of the land + above sea-level is 2250 feet, while the mean depth of the ocean + is 14,640 feet. Hence the bulk of dry land is 23,450,000 cubic + miles, and that of the waters of the ocean 323,800,000 cubic + miles; and it follows that if the whole of the solid matter of + the earth's surface were reduced to one level, it would be + everywhere covered by an ocean about two miles deep. The + accompanying diagram will serve to render these figures more + intelligible. The length of the sections of land and ocean are in + the proportion of their respective areas, while the mean height + of the land and the mean depth of the ocean are exhibited on a + greatly increased <a name="Page_345" id="Page_345"></a>vertical + scale. If we considered the continents and their adjacent oceans + separately they would differ a little, but not very materially, + from this diagram; in some cases the proportion of land to ocean + would be a little greater, in others a little less.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig32" id="fig32"></a> <img src="images/fig32.jpg" + width="400" height="184" alt="FIG. 32." title="FIG. 32." /> + <b>FIG. 32.</b> + </div> + + <p>Now, if we try to imagine a process of elevation and + depression by which the sea and land shall completely change + places, we shall be met by insuperable difficulties. We must, in + the first place, assume a general equality between elevation and + subsidence during any given period, because if the elevation over + any extensive continental area were not balanced by some + subsidence of approximately equal amount, an unsupported hollow + would be left under the earth's crust. Let us now suppose a + continental area to sink, and an adjacent oceanic area to rise, + it will be seen that the greater part of the land will disappear + long before the new land has approached the surface of the ocean. + This difficulty will not be removed by supposing a portion of a + continent to subside, and the immediately adjacent portion of the + ocean on the other side of the continent to rise, because in + almost every case we find that within a comparatively short + distance from the shores of all existing continents, the ocean + floor sinks rapidly to a depth of from 2000 to 3000 fathoms, and + maintains a similar depth, generally speaking, over a large + portion of the oceanic areas. In order, therefore, that any area + of continental extent be upraised from the great oceans, there + must be a subsidence of a land area five or six times as great, + unless it can be shown that an extensive elevation of the ocean + floor up to and far <a name="Page_346" id="Page_346"></a>above + the surface could occur without an equivalent depression + elsewhere. The fact that the waters of the ocean are sufficient + to cover the whole globe to a depth of two miles, is alone + sufficient to indicate that the great ocean basins are permanent + features of the earth's surface, since any process of alternation + of these with the land areas would have been almost certain to + result again and again in the total disappearance of large + portions, if not of all, of the dry land of the globe. But the + continuity of terrestrial life since the Devonian and + Carboniferous periods, and the existence of very similar forms in + the corresponding deposits of every continent—as well as + the occurrence of sedimentary rocks, indicating the proximity of + land at the time of their deposit, over a large portion of the + surface of all the continents, and in every geological + period—assure us that no such disappearance has ever + occurred.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Oceanic and Continental Areas.</i></p> + + <p>When we speak of the permanence of oceanic and continental + areas as one of the established facts of modern research, we do + not mean that existing continents and oceans have always + maintained the exact areas and outlines that they now present, + but merely, that while all of them have been undergoing changes + in outline and extent from age to age, they have yet maintained + substantially the same positions, and have never actually changed + places with each other. There are, moreover, certain physical and + biological facts which enable us to mark out these areas with + some confidence.</p> + + <p>We have seen that there are a large number of islands which + may be classed as oceanic, because they have never formed parts + of continents, but have originated in mid-ocean, and have derived + their forms of life by migration across the sea. Their + peculiarities are seen to be very marked in comparison with those + islands which there is good reason to believe are really + fragments of more extensive land areas, and are hence termed + "continental." These continental islands consist in every case of + a variety of stratified rocks of various ages, thus corresponding + closely with the usual structure of continents; although many of + the islands are small like Jersey or the Shetland Islands, or far + from continental land like the Falkland Islands or New Zealand. + They all <a name="Page_347" id="Page_347"></a>contain indigenous + mammalia or batrachia, and generally a much greater variety of + birds, reptiles, insects, and plants, than do the oceanic + islands. From these various characteristics we conclude that they + have all once formed parts of continents, or at all events of + much larger land areas, and have become isolated, either by + subsidence of the intervening land or by the effects of + long-continued marine denudation.</p> + + <p>Now, if we trace the thousand-fathom line around all our + existing continents we find that, with only two exceptions, every + island which can be classed as "continental" falls within this + line, while all that lie beyond it have the undoubted + characteristics of "oceanic" islands. We, therefore, conclude + that the thousand-fathom line marks out, approximately, the + "continental area,"—that is, the limits within which + continental development and change throughout known geological + time have gone on. There may, of course, have been some + extensions of land beyond this limit, while some areas within it + may always have been ocean; but so far as we have any direct + evidence, this line may be taken to mark out, approximately, the + most probable boundary between the "continental area," which has + always consisted of land and shallow sea in varying proportions, + and the great oceanic basins, within the limits of which volcanic + activity has been building up numerous islands, but whose + profound depths have apparently undergone little change.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Madagascar and New Zealand.</i></p> + + <p>The two exceptions just referred to are Madagascar and New + Zealand, and all the evidence goes to show that in these cases + the land connection with the nearest continental area was very + remote in time. The extraordinary isolation of the productions of + Madagascar—almost all the most characteristic forms of + mammalia, birds, and reptiles of Africa being absent from + it—renders it certain that it must have been separated from + that continent very early in the Tertiary, if not as far back as + the latter part of the Secondary period; and this extreme + antiquity is indicated by a depth of considerably more than a + thousand fathoms in the Mozambique Channel, though this deep + portion is less than a hundred miles wide between the Comoro + Islands and the main<a name="Page_348" id= + "Page_348"></a>land.<a name="FNanchor_166_166" id= + "FNanchor_166_166"></a><a href="#Footnote_166_166" class= + "fnanchor">[166]</a> Madagascar is the only island on the globe + with a fairly rich mammalian fauna which is separated from a + continent by a depth greater than a thousand fathoms; and no + other island presents so many peculiarities in these animals, or + has preserved so many lowly organised and archaic forms. The + exceptional character of its productions agrees exactly with its + exceptional isolation by means of a very deep arm of the sea.</p> + + <p>New Zealand possesses no known mammals and only a single + species of batrachian; but its geological structure is perfectly + continental. There is also much evidence that it does possess one + mammal, although no specimens have been yet obtained.<a name= + "FNanchor_167_167" id="FNanchor_167_167"></a><a href= + "#Footnote_167_167" class="fnanchor">[167]</a> Its reptiles and + birds are highly peculiar and more numerous than in any truly + oceanic island. Now the sea which directly separates New Zealand + from Australia is more than 2000 fathoms deep, but in a + north-west direction there is an extensive bank under 1000 + fathoms, extending to and including Lord Howe's Island, while + north of this are other banks of the same depth, approaching + towards a submarine extension of Queensland on the one hand, and + New Caledonia on the other, and altogether suggestive of a land + union with Australia at some very remote period. Now the peculiar + relations of the New Zealand fauna and flora with those of + Australia and of the tropical Pacific Islands to the northward + indicate such a connection, probably during the Cretaceous + period; and here, again, we have the exceptional depth of the + dividing sea and the form of the ocean bottom according well with + the altogether exceptional isolation of New Zealand, an isolation + which has been held by some naturalists to be great enough to + justify its claim to be one of the primary Zoological + Regions.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Teachings of the Thousand-Fathom Line.</i></p> + + <p>If now we accept the annexed map as showing us approximately + how far beyond their present limits our continents may <a name= + "Page_349" id="Page_349"></a>have extended during any portion of + the Tertiary and Secondary periods, we shall obtain a foundation + of inestimable value for our inquiries into those migrations of + animals and plants during past ages which have resulted in their + present peculiarities of distribution. We see, for instance, that + the South American and African continents have always been + separated by nearly as wide an ocean as at present, and that + whatever similarities there may be in their productions must be + due to the similar forms having been derived from a common origin + in one of the great northern continents. The radical difference + between the higher forms of life of the two continents accords + perfectly with their permanent separation. If there had been any + direct connection between them during Tertiary times, we should + hardly have found the deep-seated differences between the + Quadrumana of the two regions—no family even being common + to both; nor the peculiar Insectivora of the one continent, and + the equally peculiar Edentata of the other. The very numerous + families of birds quite peculiar to one or other of these + continents, many of which, by their structural isolation and + varied development of generic and specific forms, indicate a high + antiquity, equally suggest that there has been no near approach + to a land connection during the same epoch.</p> + + <p>Looking to the two great northern continents, we see + indications of a possible connection between them both in the + North Atlantic and the North Pacific oceans; and when we remember + that from middle Tertiary times backward—so far as we know + continuously to the earliest Palaeozoic epoch—a temperate + and equable climate, with abundant woody vegetation, prevailed up + to and within the arctic circle, we see what facilities may have + been afforded for migration from one continent to the other, + sometimes between America and Europe, sometimes between America + and Asia. Admitting these highly probable connections, no + bridging of the Atlantic in more southern latitudes (of which + there is not a particle of evidence) will have been necessary to + account for all the intermigration that has occurred between the + two continents. If, on the other hand, we remember how long must + have been the route, and how diverse must always have been the + conditions between the more northern and the more southern + portions of the American and Euro-Asiatic continents, we shall + not be <a name="Page_350" id="Page_350"></a>surprised that many + widespread forms in either continent have not crossed into the + other; and that while the skunks (Mephitis), the pouched rats + (Saccomyidae), and the turkeys (Meleagris) are confined to + America, the pigs and the hedgehogs, the true flycatchers and the + pheasants are found only in the Euro-Asiatic continent. But, just + as there have been periods which facilitated intermigration + between America and the Old World, there have almost certainly + been periods, perhaps of long duration even geologically, when + these continents have been separated by seas as wide as, or even + wider than, those of the present day; and thus may be explained + such curious anomalies as the origination of the camel-tribe in + America, and its entrance into Asia in comparatively recent + Tertiary times, while the introduction of oxen and bears into + America from the Euro-Asiatic continent appears to have been + equally recent.<a name="FNanchor_168_168" id= + "FNanchor_168_168"></a><a href="#Footnote_168_168" class= + "fnanchor">[168]</a></p> + + <p>We shall find on examination that this view of the general + permanence of the oceanic and continental areas, with constant + minor fluctuations of land and sea over the whole extent of the + latter, enables us to understand, and offer a rational + explanation of, most of the difficult problems of geographical + distribution; and further, that our power of doing this is in + direct proportion to our acquaintance with the distribution of + fossil forms of life during the Tertiary period. We must, also, + take due note of many other facts of almost equal importance for + a due appreciation of the problems presented for solution, the + most essential being, the various powers of dispersal possessed + by the different groups of animals and plants, the geological + antiquity of the species and genera, and the width and depth of + the seas which separate the countries they, inhabit. A few + illustrations will now be given of the way in which these + branches of knowledge enable us to deal with the difficulties and + anomalies that present themselves.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Distribution of Marsupials.</i></p> + + <p>This singular and lowly organised type of mammals constitutes + almost the sole representative of the class in Australia <a name= + "Page_351" id="Page_351"></a>and New Guinea, while it is entirely + unknown in Asia, Africa, or Europe. It reappears in America, + where several species of opossums are found; and it was long + thought necessary to postulate a direct southern connection of + these distant countries, in order to account for this curious + fact of distribution. When, however, we look to what is known of + the geological history of the marsupials the difficulty vanishes. + In the Upper Eocene deposits of Western Europe the remains of + several animals closely allied to the American opossums have been + found; and as, at this period, a very mild climate prevailed far + up into the arctic regions, there is no difficulty in supposing + that the ancestors of the group entered America from Europe or + Northern Asia during early Tertiary times.</p> + + <p>But we must go much further back for the origin of the + Australian marsupials. All the chief types of the higher mammalia + were in existence in the Eocene, if not in the preceding + Cretaceous period, and as we find none of these in Australia, + that country must have been finally separated from the Asiatic + continent during the Secondary or Mesozoic period. Now during + that period, in the Upper and the Lower Oolite and in the still + older Trias, the jaw-bones of numerous small mammalia have been + found, forming eight distinct genera, which are believed to have + been either marsupials or some allied lowly forms. In North + America also, in beds of the Jurassic and Triassic formations, + the remains of an equally great variety of these small mammalia + have been discovered; and from the examination of more than sixty + specimens, belonging to at least six distinct genera, Professor + Marsh is of opinion that they represent a generalised type, from + which the more specialised marsupials and insectivora were + developed.</p> + + <p>From the fact that very similar mammals occur both in Europe + and America at corresponding periods, and in beds which represent + a long succession of geological time, and that during the whole + of this time no fragments of any higher forms have been + discovered, it seems probable that both the northern continents + (or the larger portion of their area) were then inhabited by no + other mammalia than these, with perhaps other equally low types. + It was, probably, not later than the Jurassic age when some of + these primitive marsupials were able to enter Australia, where + they have since <a name="Page_352" id="Page_352"></a>remained + almost completely isolated; and, being free from the competition + of higher forms, they have developed into the great variety of + types we now behold there. These occupy the place, and have to + some extent acquired the form and structure of distinct orders of + the higher mammals—the rodents, the insectivora, and the + carnivora,—while still preserving the essential + characteristics and lowly organisation of the marsupials. At a + much later period—probably in late Tertiary times—the + ancestors of the various species of rats and mice which now + abound in Australia, and which, with the aerial bats, constitute + its only forms of placental mammals, entered the country from + some of the adjacent islands. For this purpose a land connection + was not necessary, as these small creatures might easily be + conveyed among the branches or in the crevices of trees uprooted + by floods and carried down to the sea, and then floated to a + shore many miles distant. That no actual land connection with, or + very close approximation to, an Asiatic island has occurred in + recent times, is sufficiently proved by the fact that no + squirrel, pig, civet, or other widespread mammal of the Eastern + hemisphere has been able to reach the Australian continent.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Distribution of Tapirs.</i></p> + + <p>These curious animals form one of the puzzles of geographical + distribution, being now confined to two very remote regions of + the globe—the Malay Peninsula and adjacent islands of + Sumatra and Borneo, inhabited by one species, and tropical + America, where there are three or four species, ranging from + Brazil to Ecuador and Guatemala. If we considered these living + forms only, we should be obliged to speculate on enormous changes + of land and sea in order that these tropical animals might have + passed from one country to the other. But geological discoveries + have rendered all such hypothetical changes unnecessary. During + Miocene and Pliocene times tapirs abounded over the whole of + Europe and Asia, their remains having been found in the tertiary + deposits of France, India, Burmah, and China. In both North and + South America fossil remains of tapirs occur only in caves and + deposits of Post-Pliocene age, showing that they are + comparatively recent immigrants into that continent. They perhaps + <a name="Page_353" id="Page_353"></a>entered by the route of + Kamchatka and Alaska, where the climate, even now so much milder + and more equable than on the north-east of America, might have + been warm enough in late Pliocene times to have allowed the + migration of these animals. In Asia they were driven southwards + by the competition of numerous higher and more powerful forms, + but have found a last resting-place in the swampy forests of the + Malay region.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>What these Facts Prove.</i></p> + + <p>Now these two cases, of the marsupials and the tapirs, are in + the highest degree instructive, because they show us that, + without any hypothetical bridging of deep oceans, and with only + such changes of sea and land as are indicated by the extent of + the comparatively shallow seas surrounding and connecting the + existing continents, we are able to account for the anomaly of + allied forms occurring only in remote and widely separated areas. + These examples really constitute crucial tests, because, of all + classes of animals, mammalia are least able to surmount physical + barriers. They are obviously unable to pass over wide arms of the + sea, while the necessity for constant supplies of food and water + renders sandy deserts or snow-clad plains equally impassable. + Then, again, the peculiar kinds of food on which alone many of + them can subsist, and their liability to the attacks of other + animals, put a further check upon their migrations. In these + respects almost all other organisms have great advantages over + mammals. Birds can often fly long distances, and can thus cross + arms of the sea, deserts, or mountain ranges; insects not only + fly, but are frequently carried great distances by gales of wind, + as shown by the numerous cases of their visits to ships hundreds + of miles from land. Reptiles, though slow of movement, have + advantages in their greater capacity for enduring hunger or + thirst, their power of resisting cold or drought in a state of + torpidity, and they have also some facilities for migration + across the sea by means of their eggs, which may be conveyed in + crevices of timber or among masses of floating vegetable matter. + And when we come to the vegetable kingdom, the means of transport + are at their maximum, numbers of seeds having special adaptations + <a name="Page_354" id="Page_354"></a>for being carried by + mammalia or birds, and for floating in the water, or through the + air, while many are so small and so light that there is + practically no limit to the distances they may be carried by + gales and hurricanes.</p> + + <p>We may, therefore, feel quite certain that the means of + distribution that have enabled the larger mammalia to reach the + most remote regions from a common starting-point, will be at + least as efficacious, and usually far more efficacious, with all + other land animals and plants; and if in every case the existing + distribution of this class can be explained on the theory of + oceanic and continental permanence, with the limited changes of + sea and land already referred to, no valid objections can be + taken against this theory founded on anomalies of distribution in + other orders. Yet nothing is more common than for students of + this or that group to assort that the theory of oceanic + permanence is quite inconsistent with the distribution of its + various species and genera. Because a few Indian genera and + closely allied species of birds are found in Madagascar, a land + termed "Lemuria" has been supposed to have united the two + countries during a comparatively recent geological epoch; while + the similarity of fossil plants and reptiles, from the Permian + and Miocene formations of India and South Africa, has been + adduced as further evidence of this connection. But there are + also genera of snakes, of insects, and of plants, common to + Madagascar and South America only, which have been held to + necessitate a direct land connection between these countries. + These views evidently refute themselves, because any such land + connections must have led to a far greater similarity in the + productions of the several countries than actually exists, and + would besides render altogether inexplicable the absence of all + the chief types of African and Indian mammalia from Madagascar, + and its marvellous individuality in every department of the + organic world.<a name="FNanchor_169_169" id= + "FNanchor_169_169"></a><a href="#Footnote_169_169" class= + "fnanchor">[169]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Powers of Dispersal as illustrated by Insular + Organisms.</i></p> + + <p>Having arrived at the conclusion that our existing oceans have + remained practically unaltered throughout the Tertiary and + Secondary periods of geology, and that the distribution of the + <a name="Page_355" id="Page_355"></a>mammalia is such as might + have been brought about by their known powers of dispersal, and + by such changes of land and sea as have probably or certainly + occurred, we are, of course, restricted to similar causes to + explain the much wider and sometimes more eccentric distribution + of other classes of animals and of plants. In doing so, we have + to rely partly on direct evidence of dispersal, afforded by the + land organisms that have been observed far out at sea, or which + have taken refuge on ships, as well as by the periodical + visitants to remote islands; but very largely on indirect + evidence, afforded by the frequent presence of certain groups on + remote oceanic islands, which some ancestral forms must, + therefore, have reached by transmission across the ocean from + distant lands.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Birds.</i></p> + + <p>These vary much in their powers of flight, and their + capability of traversing wide seas and oceans. Many swimming and + wading birds can continue long on the wing, fly swiftly, and + have, besides, the power of resting safely on the surface of the + water. These would hardly be limited by any width of ocean, + except for the need of food; and many of them, as the gulls, + petrels, and divers, find abundance of food on the surface of the + sea itself. These groups have a wide distribution <i>across</i> + the oceans; while waders—especially plovers, sandpipers, + snipes, and herons—are equally cosmopolitan, travelling + <i>along</i> the coasts of all the continents, and across the + narrow seas which separate them. Many of these birds seem + unaffected by climate, and as the organisms on which they feed + are equally abundant on arctic, temperate, and tropical shores, + there is hardly any limit to the range even of some of the + species.</p> + + <p>Land-birds are much more restricted in their range, owing to + their usually limited powers of flight, their inability to rest + on the surface of the sea or to obtain food from it, and their + greater specialisation, which renders them less able to maintain + themselves in the new countries they may occasionally reach. Many + of them are adapted to live only in woods, or in marshes, or in + deserts; they need particular kinds of food or a limited range of + temperature; and they are adapted to cope only with the special + enemies or the particular group of <a name="Page_356" id= + "Page_356"></a>competitors among which they have been developed. + Such birds as these may pass again and again to a new country, + but are never able to establish themselves in it; and it is this + organic barrier, as it is termed, rather than any physical + barrier, which, in many cases, determines the presence of a + species in one area and its absence from another. We must always + remember, therefore, that, although the presence of a species in + a remote oceanic island clearly proves that its ancestors must at + one time have found their way there, the absence of a species + does not prove the contrary, since it also may have reached the + island, but have been unable to maintain itself, owing to the + inorganic or organic conditions not being suitable to it. This + general principle applies to all classes of organisms, and there + are many striking illustrations of it. In the Azores there are + eighteen species of land-birds which are permanent residents, but + there are also several others which reach the islands almost + every year after great storms, but have never been able to + establish themselves. In Bermuda the facts are still more + striking, since there are only ten species of resident birds, + while no less than twenty other species of land-birds and more + than a hundred species of waders and aquatics are frequent + visitors, often in great numbers, but are never able to establish + themselves. On the same principle we account for the fact that, + of the many continental insects and birds that have been let + loose, or have escaped from confinement, in this country, hardly + one has been able to maintain itself, and the same phenomenon is + still more striking in the case of plants. Of the thousands of + hardy plants which grow easily in our gardens, very few have ever + run wild, and when the experiment is purposely tried it + invariably fails. Thus A. de Candolle informs us that several + botanists of Paris, Geneva, and especially of Montpellier, have + sown the seeds of many hundreds of species of exotic hardy + plants, in what appeared to be the most favourable situations, + but that in hardly a single case has any one of them become + naturalised.<a name="FNanchor_170_170" id= + "FNanchor_170_170"></a><a href="#Footnote_170_170" class= + "fnanchor">[170]</a> Still more, then, in plants than in animals + the absence of a species does not prove that it has never reached + the locality, but merely that it has not been able to maintain + itself in com<a name="Page_357" id="Page_357"></a>petition with + the native productions. In other cases, as we have seen, facts of + an exactly opposite nature occur. The rat, the pig, and the + rabbit, the water-cress, the clover, and many other plants, when + introduced into New Zealand, nourish exceedingly, and even + exterminate their native competitors; so that in these cases we + may feel sure that the species in question did not exist in New + Zealand simply because they had been unable to reach that country + by their natural means of dispersal. I will now give a few cases, + in addition to those recorded in my previous works, of birds and + insects which have been observed far from any land.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Birds and Insects at Sea.</i></p> + + <p>Captain D. Fullarton of the ship <i>Timaru</i> recorded in his + log the occurrence of a great number of small land-birds about + the ship on 15th March 1886, when in Lat. 48° 31' N., Long. + 8° 16' W. He says: "A great many small land-birds about us; + put about sixty into a coop, evidently tired out." And two days + later, 17th March, "Over fifty of the birds cooped on 15th died, + though fed. Sparrows, finches, water-wagtails, two small birds, + name unknown, one kind like a linnet, and a large bird like a + starling. In all there have been on board over seventy birds, + besides some that hovered about us for some time and then fell + into the sea exhausted." Easterly winds and severe weather were + experienced at the time.<a name="FNanchor_171_171" id= + "FNanchor_171_171"></a><a href="#Footnote_171_171" class= + "fnanchor">[171]</a> The spot where this remarkable flight of + birds was met with is about 160 miles due west of Brest, and this + is the least distance the birds must have been carried. It is + interesting to note that the position of the ship is nearly in + the line from the English and French coasts to the Azores, where, + after great storms, so many bird stragglers arrive annually. + These birds were probably blown out to sea during their spring + migration along the south coast of England to Wales and Ireland. + During the autumnal migration, however, great flocks of + birds—especially starlings, thrushes, and + fieldfares—have been observed every year flying out to sea + from the west coast of Ireland, almost the whole of which must + perish. At the Nash Lighthouse, in the Bristol Channel on the + coast of Glamorganshire, an enormous number of small birds were + observed on 3d September, includ<a name="Page_358" id= + "Page_358"></a>ing nightjars, buntings, white-throats, + willow-wrens, cuckoos, house-sparrows, robins, wheatears, and + blackbirds. These had probably crossed from Somersetshire, and + had they been caught by a storm the larger portion of them must + have been blown out to sea.<a name="FNanchor_172_172" id= + "FNanchor_172_172"></a><a href="#Footnote_172_172" class= + "fnanchor">[172]</a></p> + + <p>These facts enable us to account sufficiently well for the + birds of oceanic islands, the number and variety of which are + seen to be proportionate to their facilities for reaching the + island and maintaining themselves in it. Thus, though more birds + yearly reach Bermuda than the Azores, the number of residents in + the latter islands is much larger, due to the greater extent of + the islands, their number, and their more varied surface. In the + Galapagos the land-birds are still more numerous, due in part to + their larger area and greater proximity to the continent, but + chiefly to the absence of storms, so that the birds which + originally reached the islands have remained long isolated and + have developed into many closely allied species adapted to the + special conditions. All the species of the Galapagos but one are + peculiar to the islands, while the Azores possess only one + peculiar species, and Bermuda none—a fact which is clearly + due to the continual immigration of fresh individuals keeping up + the purity of the breed by intercrossing. In the Sandwich + Islands, which are extremely isolated, being more than 2000 miles + from any continent or large island, we have a condition of things + similar to what prevails in the Galapagos, the land-birds, + eighteen in number, being all peculiar, and belonging, except + one, to peculiar genera. These birds have probably all descended + from three or four original types which reached the islands at + some remote period, probably by means of intervening islets that + have since disappeared. In St. Helena we have a degree of + permanent isolation which has prevented any land-birds from + reaching the island; for although its distance from the + continent, 1100 miles, is not so great as in the case of the + Sandwich Islands, it is situated in an ocean almost entirely + destitute of small islands, while its position within the tropics + renders it free from violent storms. Neither is there, on the + nearest part of the coast of Africa, a perpetual stream of + migrating birds like that which <a name="Page_359" id= + "Page_359"></a>supplies the innumerable stragglers which every + year reach Bermuda and the Azores.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Insects.</i></p> + + <p>Winged insects have been mainly dispersed in the same way as + birds, by their power of flight, aided by violent or + long-continued winds. Being so small, and of such low specific + gravity, they are occasionally carried to still greater + distances; and thus no islands, however remote, are altogether + without them. The eggs of insects, being often deposited in + borings or in crevices of timber, may have been conveyed long + distances by floating trees, as may the larvae of those species + which feed on wood. Several cases have been published of insects + coming on board ships at great distances from land; and Darwin + records having caught a large grasshopper when the ship was 370 + miles from the coast of Africa, whence the insect had probably + come.</p> + + <p>In the <i>Entomologists' Monthly Magazine</i> for June 1885, + Mr. MacLachlan has recorded the occurrence of a swarm of moths in + the Atlantic ocean, from the log of the ship <i>Pleione</i>. The + vessel was homeward bound from New Zealand, and in Lat. 6° + 47' N., Long. 32° 50' W., hundreds of moths appeared about + the ship, settling in numbers on the spars and rigging. The wind + for four days previously had been very light from north, + north-west, or north-east, and sometimes calm. The north-east + trade wind occasionally extends to the ship's position at that + time of year. The captain adds that "frequently, in that part of + the ocean, he has had moths and butterflies come on board." The + position is 960 miles south-west of the Cape Verde Islands, and + about 440 north-east of the South American coast. The specimen + preserved is Deiopeia pulchella, a very common species in dry + localities in the Eastern tropics, and rarely found in Britain, + but, Mr. MacLachlan thinks, not found in South America. They must + have come, therefore, from the Cape Verde Islands, or from some + parts of the African coast, and must have traversed about a + thousand miles of ocean with the assistance, no doubt, of a + strong north-east trade wind for a great part of the distance. In + the British Museum collection there is a specimen of the same + moth caught at sea during the voyage of the <i>Rattlesnake</i>, + <a name="Page_360" id="Page_360"></a>in Lat. 6° N., Long. + 22-1/2° W., being between the former position and Sierra + Leone, thus rendering it probable that the moths came from that + part of the African coast, in which case the swarm encountered by + the <i>Pleione</i> must have travelled more than 1200 miles.</p> + + <p>A similar case was recorded by Mr. F.A. Lucas in the American + periodical <i>Science</i> of 8th April 1887. He states that in + 1870 he met with numerous moths of many species while at sea in + the South Atlantic (Lat. 25° S., Long. 24° W.), about + 1000 miles from the coast of Brazil. As this position is just + beyond the south-east trades, the insects may have been brought + from the land by a westerly gale. In the <i>Zoologist</i> (1864, + p. 8920) is the record of a small longicorn beetle which flew on + board a ship 500 miles off the west coast of Africa. Numerous + other cases are recorded of insects at less distances from land, + and, taken in connection with those already given, they are + sufficient to show that great numbers must be continually carried + out to sea, and that occasionally they are able to reach enormous + distances. But the reproductive powers of insects are so great + that all we require, in order to stock a remote island, is that + some few specimens shall reach it even once in a century, or once + in a thousand years.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Insects at great Altitudes.</i></p> + + <p>Equally important is the proof we possess that insects are + often carried to great altitudes by upward currents of air. + Humboldt noticed them up to heights of 15,000 and 18,000 feet in + South America, and Mr. Albert Müller has collected many + interesting cases of the same character in Europe.<a name= + "FNanchor_173_173" id="FNanchor_173_173"></a><a href= + "#Footnote_173_173" class="fnanchor">[173]</a> A moth (Plusia + gamma) has been found on the summit of Mont Blanc; small + hymenoptera and moths have been seen on the Pyrenees at a height + of 11,000 feet, while numerous flies and beetles, some of + considerable size, have been caught on the glaciers and + snow-fields of various parts of the Alps. Upward currents of air, + whirlwinds and tornadoes, occur in all parts of the world, and + large numbers of insects are thus carried up into the higher + regions of the atmosphere, where they are liable to be caught by + strong winds, and thus conveyed enormous distances over seas or + continents. With such <a name="Page_361" id= + "Page_361"></a>powerful means of dispersal the distribution of + insects over the entire globe, and their presence in the most + remote oceanic islands, offer no difficulties.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Dispersal of Plants.</i></p> + + <p>The dispersal of seeds is effected in a greater variety of + ways than are available in the case of any animals. Some fruits + or seed-vessels, and some seeds, will float for many weeks, and + after immersion in salt water for that period the seeds will + often germinate. Extreme cases are the double cocoa-nut of the + Seychelles, which has been found on the coast of Sumatra, about + 3000 miles distant; the fruits of the Sapindus saponaria + (soap-berry), which has been brought to Bermuda by the Gulf + Stream from the West Indies, and has grown after a journey in the + sea of about 1500 miles; and the West Indian bean, Entada + scandens, which reached the Azores from the West Indies, a + distance of full 3000 miles, and afterwards germinated at Kew. By + these means we can account for the similarity in the shore flora + of the Malay Archipelago and most of the islands of the Pacific; + and from an examination of the fruits and seeds, collected among + drift during the voyage of the <i>Challenger</i>, Mr. Hemsley has + compiled a list of 121 species which are probably widely + dispersed by this means.</p> + + <p>A still larger number of species owe their dispersal to birds + in several distinct ways. An immense number of fruits in all + parts of the world are devoured by birds, and have been + attractively coloured (as we have seen), in order to be so + devoured, because the seeds pass through the birds' bodies and + germinate where they fall. We have seen how frequently birds are + forced by gales of wind across a wide expanse of ocean, and thus + seeds must be occasionally carried. It is a very suggestive fact, + that all the trees and shrubs in the Azores bear berries or small + fruits which are eaten by birds; while all those which bear + larger fruits, or are eaten chiefly by mammals—such as + oaks, beeches, hazels, crabs, etc.—are entirely wanting. + Game-birds and waders often have portions of mud attached to + their feet, and Mr. Darwin has proved by experiment that such mud + frequently contains seeds. One partridge had such a quantity of + mud attached to its foot as to contain seeds from which + eighty-two plants germinated; this proves that <a name="Page_362" + id="Page_362"></a>a very small portion of mud may serve to convey + seeds, and such an occurrence repeated even at long intervals may + greatly aid in stocking remote islands with vegetation. Many + seeds also adhere to the feathers of birds, and thus, again, may + be conveyed as far as birds are ever carried. Dr. Guppy found a + small hard seed in the gizzard of a Cape Petrel, taken about 550 + miles east of Tristan da Cunha.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Dispersal of Seeds by the Wind.</i></p> + + <p>In the preceding cases we have been able to obtain direct + evidence of transportal; but although we know that many seeds are + specially adapted to be dispersed by the wind, we cannot obtain + direct proof that they are so carried for hundreds or thousands + of miles across the sea, owing to the difficulty of detecting + single objects which are so small and inconspicuous. It is + probable, however, that the wind as an agent of dispersal is + really more effective than any of those we have hitherto + considered, because a very large number of plants have seeds + which are very small and light, and are often of such a form as + to facilitate aerial carriage for enormous distances. It is + evident that such seeds are especially liable to be transported + by violent winds, because they become ripe in autumn at the time + when storms are most prevalent, while they either lie upon the + surface of the ground, or are disposed in dry capsules on the + plant ready to be blown away. If inorganic particles comparable + in weight, size, or form with such seeds are carried for great + distances, we may be sure that seeds will also be occasionally + carried in the same way. It will, therefore, be necessary to give + a few examples of wind-carriage of small objects.</p> + + <p>On 27th July 1875 a remarkable shower of small pieces of hay + occurred at Monkstown, near Dublin. They appeared floating slowly + down from a great height, as if falling from a dark cloud which + hung overhead. The pieces picked up were wet, and varied from + single blades of grass to tufts weighing one or two ounces. A + similar shower occurred a few days earlier in Denbighshire, and + was observed to travel in a direction contrary to that of the + wind in the lower atmosphere.<a name="FNanchor_174_174" id= + "FNanchor_174_174"></a><a href="#Footnote_174_174" class= + "fnanchor">[174]</a> There is no evidence of the distance from + which the hay was <a name="Page_363" id="Page_363"></a>brought, + but as it had been carried to a great height, it was in a + position to be conveyed to almost any distance by a violent wind, + had such occurred at the time.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mineral Matter carried by the Wind.</i></p> + + <p>The numerous cases of sand and volcanic dust being carried + enormous distances through the atmosphere sufficiently prove the + importance of wind as a carrier of solid matter, but + unfortunately the matter collected has not been hitherto examined + with a view to determine the maximum size and weight of the + particles. A few facts, however, have been kindly furnished me by + Professor Judd, F.R.S. Some dust which fell at Genoa on 15th + October 1885, and was believed to have been brought from the + African desert, consisted of quartz, hornblende, and other + minerals, and contained particles having a diameter of 1/500 + inch, each weighing 1/200,000 grain. This dust had probably + travelled over 600 miles. In the dust from Krakatoa, which fell + at Batavia, about 100 miles distant, during the great eruption, + there are many solid particles even larger than those mentioned + above. Some of this dust was given me by Professor Judd, and I + found in it several ovoid particles of a much larger size, being + 1/50 inch long, and 1/70 wide and deep. The dust from the same + eruption, which fell on board the ship <i>Arabella</i>, 970 miles + from the volcano, also contained solid particles 1/500 inch + diameter. Mr. John Murray of the <i>Challenger</i> Expedition + writes to me that he finds in the deep sea deposits 500 and even + 700 miles west of the coast of Africa, rounded particles of + quartz, having a diameter of 1/250 inch, and similar particles + are found at equally great distances from the south-west coasts + of Australia; and he considers these to be atmospheric dust + carried to that distance by the wind. Taking the sp. gr. of + quartz at 2.6, these particles would weigh about 1/25,000 grain + each. These interesting facts can, however, by no means be taken + as indicating the extreme limits of the power of wind in carrying + solid particles. During the Krakatoa eruption no gale of special + violence occurred, and the region is one of comparative calms. + The grains of quartz found by Mr. Murray more nearly indicate the + limit, but the very small portions of matter brought up by the + dredge, as com<a name="Page_364" id="Page_364"></a>pared with the + enormous areas of sea-bottom, over which the atmospheric dust + must have been scattered, render it in the highest degree + improbable that the maximum limit either of size of particles, or + of distance from land has been reached.</p> + + <p>Let us, however, assume that the quartz grains, found by Mr. + Murray in the deep-sea ooze 700 miles from land, give us the + extreme limit of the power of the atmosphere as a carrier of + solid particles, and let us compare with these the weights of + some seeds. From a small collection of the seeds of thirty + species of herbaceous plants sent me from Kew, those in the above + table were selected, and small portions of eight of them + carefully weighed in a chemical balance.<a name= + "FNanchor_175_175" id="FNanchor_175_175"></a><a href= + "#Footnote_175_175" class="fnanchor">[175]</a> By counting these + portions I was able to estimate the number of seeds weighing one + grain. The three very minute species, whose numbers are marked + with an asterisk (*), were estimated by the comparison of their + sizes with those of the smaller weighed seeds.</p> + +<pre> +No| Species. |Approximate | Approximate | Remarks. + | |No. of Seeds| Dimensions. | + | |In one Grain| | + | | | in. in. in. | + 1|Draba verna | 1,800 |1/60 x 1/90 x 1/160|Oval, flat. + 2|Hypericum perforatum | 520 | 1/30 x 1/80 |Cylindrical. + 3|Astilbe rivularis | 4,500 | 1/50 x 1/100 |Elongate, flat, tailed, + | | | | wavy. + 4|Saxifraga coriophylla| 750 | 1/40 x 1/75 |Surface rough, adhere + | | | | to the dry capsules. + 5|Oenothera rosea | 640 | 1/40 x 1/80 |Ovate. + 6|Hypericum hirsutum | 700 | 1/30 x 1/100 |Cylindrical, rough. + 7|Mimulus luteus | 2,900 | 1/60 x 1/100 |Oval, minute. + 8|Penthorum sedoides | 8,000* | 1/70 x 1/150 |Flattened, very minute. + 9|Sagina procumbens | 12,000* | 1/120 |Sub-triangular, flat. +10|Orchis maculata | 15,000* | --- |Margined, flat, + | | | | very minute. +11|Gentiana purpurea | 35 | 1/25 |Wavy, rough, with this + | | | | coriaceous margins. +12|Silene alpina | --- | 1/30 |Flat, with fringed + | | | | margins. +13|Adenophora communis | --- | 1/20 x 1/40 |Very thin, wavy, light. + |Quartz grains | 25,000 | 1/250 |Deep sea ... 700 miles. + |Do. |200,000 | 1/500 |Genoa ... 600 miles. + </pre> + + <p>If now we compare the seeds with the quartz grains, we + <a name="Page_365" id="Page_365"></a>find that several are from + twice to three times the weight of the grains found by Mr. + Murray, and others five times, eight times, and fifteen times as + heavy; but they are proportionately very much larger, and, being + usually irregular in shape or compressed, they expose a very much + larger surface to the air. The surface is often rough, and + several have dilated margins or tailed appendages, increasing + friction and rendering the uniform rate of falling through still + air immensely less than in the case of the smooth, rounded, solid + quartz grains. With these advantages it is a moderate estimate + that seeds ten times the weight of the quartz grains could be + carried quite as far through the air by a violent gale and under + the most favourable conditions. These limits will include five of + the seeds here given, as well as hundreds of others which do not + exceed them in weight; and to these we may add some larger seeds + which have other favourable characteristics, as is the case with + numbers 11-13, which, though very much larger than the rest, are + so formed as in all probability to be still more easily carried + great distances by a gale of wind. It appears, therefore, to be + absolutely certain that every autumnal gale capable of conveying + solid mineral particles to great distances, must also carry + numbers of small seeds at least as far; and if this is so, the + wind alone will form one of the most effective agents in the + dispersal of plants.</p> + + <p>Hitherto this mode of conveyance, as applying to the + transmission of seeds for great distances across the ocean, has + been rejected by botanists, for two reasons. In the first place, + there is said to be no direct evidence of such conveyance; and, + secondly, the peculiar plants of remote oceanic islands do not + appear to have seeds specially adapted for aerial transmission. I + will consider briefly each of these objections.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Objection to the Theory of Wind-Dispersal.</i></p> + + <p>To obtain direct evidence of the transmission of such minute + and perishable objects, which do not exist in great quantities, + and are probably carried to the greatest distances but rarely and + as single specimens, is extremely difficult. A bird or insect can + be seen if it comes on board ship, but who would ever detect the + seeds of Mimulus or Orchis even if a score of them fell on a + ship's deck? Yet if but one such seed <a name="Page_366" id= + "Page_366"></a>per century were carried to an oceanic island, + that island might become rapidly overrun by the plant, if the + conditions were favourable to its growth and reproduction. It is + further objected that search has been made for such seeds, and + they have not been found. Professor Kerner of Innsbruck examined + the snow on the surface of glaciers, and assiduously collected + all the seeds he could find, and these were all of plants which + grew in the adjacent mountains or in the same district. In like + manner, the plants growing on moraines were found to be those of + the adjacent mountains, plateaux, or lowlands. Hence he concluded + that the prevalent opinion that seeds may be carried through the + air for very great distances "is not supported by fact."<a name= + "FNanchor_176_176" id="FNanchor_176_176"></a><a href= + "#Footnote_176_176" class="fnanchor">[176]</a> The opinion is + certainly not supported by Kerner's facts, but neither is it + opposed by them. It is obvious that the seeds that would be + carried by the wind to moraines or to the surface of glaciers + would be, first and in the greatest abundance, those of the + immediately surrounding district; then, very much more rarely, + those from more remote mountains; and lastly, in extreme rarity, + those from distant countries or altogether distinct mountain + ranges. Let us suppose the first to be so abundant that a single + seed could be found by industrious search on each square yard of + the surface of the glacier; the second so scarce that only one + could possibly be found in a hundred yards square; while to find + one of the third class it would be necessary exhaustively to + examine a square mile of surface. Should we expect that + <i>one</i> ever to be found, and should the fact that it could + not be found be taken as a proof that it was not there? Besides, + a glacier is altogether in a bad position to receive such remote + wanderers, since it is generally surrounded by lofty mountains, + often range behind range, which would intercept the few air-borne + seeds that might have been carried from a distant land. The + conditions in an oceanic island, on the other hand, are the most + favourable, since the land, especially if high, will intercept + objects carried by the wind, and will thus cause more of the + solid matter to fall on it than on an equal area of ocean. We + know that winds at sea often blow violently for days together, + and the rate of motion is indicated by the fact that 72 miles an + hour was the average velocity <a name="Page_367" id= + "Page_367"></a>of the wind observed during twelve hours at the + Ben Nevis observatory, while the velocity sometimes rises to 120 + miles an hour. A twelve hours' gale might, therefore, carry light + seeds a thousand miles as easily and certainly as it could carry + quartz-grains of much greater specific gravity, rotundity, and + smoothness, 500 or even 100 miles; and it is difficult even to + imagine a sufficient reason why they should not be so + carried—perhaps very rarely and under exceptionally + favourable conditions,—but this is all that is + required.</p> + + <p>As regards the second objection, it has been observed that + orchideae, which have often exceedingly small and light seeds, + are remarkably absent from oceanic islands. This, however, may be + very largely due to their extreme specialisation and dependence + on insect agency for their fertilisation; while the fact that + they do occur in such very remote islands as the Azores, Tahiti, + and the Sandwich Islands, proves that they must have once reached + these localities either by the agency of birds or by transmission + through the air; and the facts I have given above render the + latter mode at least as probable as the former. Sir Joseph Hooker + remarks on the composite plant of Kerguelen Island (Cotula + plumosa) being found also on Lord Auckland and MacQuarrie + Islands, and yet having no pappus, while other species of the + genus possess it. This is certainly remarkable, and proves that + the plant must have, or once have had, some other means of + dispersal across wide oceans.<a name="FNanchor_177_177" id= + "FNanchor_177_177"></a><a href="#Footnote_177_177" class= + "fnanchor">[177]</a> One of the most widely dispersed species in + the whole world (Sonchus oleraceus) possesses pappus, as do four + out of five of the species which are common to Europe and New + Zealand, all of which have a very wide distribution. The same + author remarks on the limited area occupied by most species of + Compositae, notwithstanding their facilities for dispersal by + means of their feathered seeds; but it has been <a name= + "Page_368" id="Page_368"></a>already shown that limitations of + area are almost always due to the competition of allied forms, + facilities for dispersal being only one of many factors in + determining the wide range of species. It is, however, a + specially important factor in the case of the inhabitants of + remote oceanic islands, since, whether they are peculiar species + or not, they or their remote ancestors must at some time or other + have reached their present position by natural means.</p> + + <p>I have already shown elsewhere, that the flora of the Azores + strikingly supports the view of the species having been + introduced by aerial transmission only, that is, by the agency of + birds and the wind, because all plants that could not possibly + have been carried by these means are absent.<a name= + "FNanchor_178_178" id="FNanchor_178_178"></a><a href= + "#Footnote_178_178" class="fnanchor">[178]</a> In the same way we + may account for the extreme rarity of Leguminosae in all oceanic + islands. Mr. Hemsley, in his Report on Insular Floras, says that + they "are wanting in a large number of oceanic islands where + there is no true littoral flora," as St. Helena, Juan Fernandez, + and all the islands of the South Atlantic and South Indian + Oceans. Even in the tropical islands, such as Mauritius and + Bourbon, there are no endemic species, and very few in the + Galapagos and the remoter Pacific Islands. All these facts are + quite in accordance with the absence of facilities for + transmission through the air, either by birds or the wind, owing + to the comparatively large size and weight of the seeds; and an + additional proof is thus afforded of the extreme rarity of the + successful floating of seeds for great distances across the + ocean.<a name="FNanchor_179_179" id= + "FNanchor_179_179"></a><a href="#Footnote_179_179" class= + "fnanchor">[179]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Explanation of North Temperate Plants in the Southern + Hemisphere.</i></p> + + <p>If we now admit that many seeds which are either minute in + size, of thin texture or wavy form, or so fringed or margined as + to afford a good hold to the air, are capable of being carried + for many hundreds of miles by exceptionally <a name="Page_369" + id="Page_369"></a>violent and long-continued gales of wind, we + shall not only be better able to account for the floras of some + of the remotest oceanic islands, but shall also find in the fact + a sufficient explanation of the wide diffusion of many genera, + and even species, of arctic and north temperate plants in the + southern hemisphere or on the summits of tropical mountains. + Nearly fifty of the flowering plants of Tierra-del-Fuego are + found also in North America or Europe, but in no intermediate + country; while fifty-eight species are common to New Zealand and + Northern Europe; thirty-eight to Australia, Northern Europe, and + Asia; and no less than seventy-seven common to New Zealand, + Australia, and South America.<a name="FNanchor_180_180" id= + "FNanchor_180_180"></a><a href="#Footnote_180_180" class= + "fnanchor">[180]</a> On lofty mountains far removed from each + other, identical or closely allied plants often occur. Thus the + fine Primula imperialis of a single mountain peak in Java has + been found (or a closely allied species) in the Himalayas; and + many other plants of the high mountains of Java, Ceylon, and + North India are either identical or closely allied forms. So, in + Africa, some species, found on the summits of the Cameroons and + Fernando Po in West Africa, are closely allied to species in the + Abyssinian highlands and in Temperate Europe; while other + Abyssinian and Cameroons species have recently been found on the + mountains of Madagascar. Some peculiar Australian forms have been + found represented on the summit of Kini Balu in Borneo. Again, on + the summit of the Organ mountains in Brazil there are species + allied to those of the Andes, but not found in the intervening + lowlands.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>No Proof of Recent Lower Temperature in the Tropics.</i></p> + + <p>Now all these facts, and numerous others of like character, + were supposed by Mr. Darwin to be due to a lowering of + temperature during glacial epochs, which allowed these temperate + forms to migrate across the intervening tropical lowlands. But + any such change within the epoch of existing species is almost + inconceivable. In the first place, it would necessitate the + extinction of much of the tropical flora (and with it of the + insect life), because without such extinction alpine herbaceous + plants could certainly never spread over tropical forest + low<a name="Page_370" id="Page_370"></a>lands; and, in the next + place, there is not a particle of direct evidence that any such + lowering of temperature in inter-tropical lowlands ever took + place. The only alleged evidence of the kind is that adduced by + the late Professor Agassiz and Mr. Hartt; but I am informed by my + friend, Mr. J.C. Branner (now State Geologist of Arkansas, U.S.), + who succeeded Mr. Hartt, and spent several years completing the + geological survey of Brazil, that the supposed moraines and + glaciated granite rocks near Rio Janeiro and elsewhere, as well + as the so-called boulder-clay of the same region, are entirely + explicable as the results of sub-aerial denudation and + weathering, and that there is no proof whatever of glaciation in + any part of Brazil.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Lower Temperature not needed to Explain the Facts.</i></p> + + <p>But any such vast physical change as that suggested by Darwin, + involving as it does such tremendous issues as regards its + effects on the tropical fauna and flora of the whole world, is + really quite uncalled for, because the facts to be explained are + of the same essential nature as those presented by remote oceanic + islands, between which and the nearest continents no temperate + land connection is postulated. In proportion to their limited + area and extreme isolation, the Azores, St. Helena, the + Galapagos, and the Sandwich Islands, each possess a fairly + rich—the last a very rich—indigenous flora; and the + means which sufficed to stock them with a great variety of plants + would probably suffice to transmit others from mountain-top to + mountain-top in various parts of the globe. In the case of the + Azores, we have large numbers of species identical with those of + Europe, and others closely allied, forming an exactly parallel + case to the species found on the various mountain summits which + have been referred to. The distances from Madagascar to the South + African mountains and to Kilimandjaro, and from the latter to + Abyssinia, are no greater than from Spain to the Azores, while + there are other equatorial mountains forming stepping-stones at + about an equal distance to the Cameroons. Between Java and the + Himalayas we have the lofty mountains of Sumatra and of + North-western Burma, forming steps at about the same distance + apart; while between Kini Balu and the Australian Alps we + <a name="Page_371" id="Page_371"></a>have the unexplored snow + mountains of New Guinea, the Bellenden Ker mountains in + Queensland, and the New England and Blue Mountains of New South + Wales. Between Brazil and Bolivia the distances are no greater; + while the unbroken range of mountains from Arctic America to + Tierra-del-Fuego offers the greatest facilities for transmission, + the partial gap between the lofty peak of Chiriqui and the high + Andes of New Grenada being far less than from Spain to the + Azores. Thus, whatever means have sufficed for stocking oceanic + islands must have been to some extent effective in transmitting + northern forms from mountain to mountain, across the equator, to + the southern hemisphere; while for this latter form of dispersal + there are special facilities, in the abundance of fresh and + unoccupied surfaces always occurring in mountain regions, owing + to avalanches, torrents, mountain-slides, and rock-falls, thus + affording stations on which air-borne seeds may germinate and + find a temporary home till driven out by the inroads of the + indigenous vegetation. These temporary stations may be at much + lower altitudes than the original habitat of the species, if + other conditions are favourable. Alpine plants often descend into + the valleys on glacial moraines, while some arctic species grow + equally well on mountain summits and on the seashore. The + distances above referred to between the loftier mountains may + thus be greatly reduced by the occurrence of suitable conditions + at lower altitudes, and the facilities for transmission by means + of aerial currents proportionally increased.<a name= + "FNanchor_181_181" id="FNanchor_181_181"></a><a href= + "#Footnote_181_181" class="fnanchor">[181]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Facts Explained by the Wind-Carriage of Seeds.</i></p> + + <p>But if we altogether reject aerial transmission of seeds for + great distances, except by the agency of birds, it will be + difficult, if not impossible, to account for the presence of so + many identical species of plants on remote mountain summits, or + for that "continuous current of vegetation" described by Sir + Joseph Hooker as having apparently long existed from the northern + to the southern hemisphere. It may be admitted that we can, + possibly, account for the greater portion of the floras of remote + oceanic islands by the agency of birds alone; because, when blown + out to sea land-birds must reach some island <a name="Page_372" + id="Page_372"></a>or perish, and all which come within sight of + an island will struggle to reach it as their only refuge. But, + with mountain summits the case is altogether different, because, + being surrounded by land instead of by sea, no bird would need to + fly, or to be carried by the wind, for several hundred miles at a + stretch to another mountain summit, but would find a refuge in + the surrounding uplands, ridges, valleys, or plains. As a rule + the birds that frequent lofty mountain tops are peculiar species, + allied to those of the surrounding district; and there is no + indication whatever of the passage of birds from one remote + mountain to another in any way comparable with the flights of + birds which are known to reach the Azores annually, or even with + the few regular migrants from Australia to New Zealand. It is + almost impossible to conceive that the seeds of the Himalayan + primula should have been thus carried to Java; but, by means of + gales of wind, and intermediate stations from fifty to a few + hundred miles apart, where the seeds might vegetate for a year or + two and produce fresh seed to be again carried on in the same + manner, the transmission might, after many failures, be at last + effected.</p> + + <p>A very important consideration is the vastly larger scale on + which wind-carriage of seeds must act, as compared with + bird-carriage. It can only be a few birds which carry seeds + attached to their feathers or feet. A very small proportion of + these would carry the seeds of Alpine plants; while an almost + infinitesimal fraction of these latter would convey the few seeds + attached to them safely to an oceanic island or remote mountain. + But winds, in the form of whirlwinds or tornadoes, gales or + hurricanes, are perpetually at work over large areas of land and + sea. Insects and light particles of matter are often carried up + to the tops of high mountains; and, from the very nature and + origin of winds, they usually consist of ascending or descending + currents, the former capable of suspending such small and light + objects as are many seeds long enough for them to be carried + enormous distances. For each single seed carried away by external + attachment to the feet or feathers of a bird, countless millions + are probably carried away by violent winds; and the chance of + conveyance to a great distance and in a definite direction must + be many <a name="Page_373" id="Page_373"></a>times greater by the + latter mode than by the former.<a name="FNanchor_182_182" id= + "FNanchor_182_182"></a><a href="#Footnote_182_182" class= + "fnanchor">[182]</a> We have seen that inorganic particles of + much greater specific gravity than seeds, and nearly as heavy as + the smallest kinds, are carried to great distances through the + air, and we can therefore hardly doubt that some seeds are + carried as far. The direct agency of the wind, as a supplement to + bird-transport, will help to explain the presence in oceanic + islands of plants growing in dry or rocky places whose small + seeds are not likely to become attached to birds; while it seems + to be the only effective agency possible in the dispersal of + those species of alpine or sub-alpine plants found on the summits + of distant mountains, or still more widely separated in the + temperate zones of the northern and southern hemispheres.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>On the general principles that have been now laid down, it + will be found that all the chief facts of the geographical + distribution of animals and plants can be sufficiently + understood. There will, of course, be many cases of difficulty + and some seeming anomalies, but these can usually be seen to + depend on our ignorance of some of the essential factors of the + problem. Either we do not know the distribution of the group in + recent geological times, or we are still ignorant of the special + methods by which the organisms are able to cross the sea. The + latter difficulty applies especially to the lizard tribe, which + are found <a name="Page_374" id="Page_374"></a>in almost all the + tropical oceanic islands; but the particular mode in which they + are able to traverse a wide expanse of ocean, which is a perfect + barrier to batrachia and almost so to snakes, has not yet been + discovered. Lizards are found in all the larger Pacific Islands + as far as Tahiti, while snakes do not extend beyond the Fiji + Islands; and the latter are also absent from Mauritius and + Bourbon, where lizards of seven or eight species abound. + Naturalists resident in the Pacific Islands would make a valuable + contribution to our science by studying the life-history of the + native lizards, and endeavouring to ascertain the special + facilities they possess for crossing over wide spaces of + ocean.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_163_163" id= + "Footnote_163_163"></a><a href= + "#FNanchor_163_163"><span class="label">[163]</span></a> See + A. Agassiz, <i>Three Cruises of the Blake</i> (Cambridge, + Mass., 1888), vol. i. p. 127, footnote.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_164_164" id= + "Footnote_164_164"></a><a href= + "#FNanchor_164_164"><span class="label">[164]</span></a> Even + the extremely fine Mississippi mud is nowhere found beyond a + hundred miles from the mouths of the river in the Gulf of + Mexico (A. Agassiz, <i>Three Cruises of the Blake</i>, vol. + i. p. 128).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_165_165" id= + "Footnote_165_165"></a><a href= + "#FNanchor_165_165"><span class="label">[165]</span></a> I + have given a full summary of the evidence for the permanence + of oceanic and continental areas in my <i>Island Life</i>, + chap. vi.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_166_166" id= + "Footnote_166_166"></a><a href= + "#FNanchor_166_166"><span class="label">[166]</span></a> For + a full account of the peculiarities of the Madagascar fauna, + see my <i>Island Life</i>, chap. xix.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_167_167" id= + "Footnote_167_167"></a><a href= + "#FNanchor_167_167"><span class="label">[167]</span></a> See + <i>Island Life</i>, p. 446, and the whole of chaps. xxi. + xxii. More recent soundings have shown that the Map at p. + 443, as well as that of the Madagascar group at p. 387, are + erroneous, the ocean around Norfolk Island and in the Straits + of Mozambique being more than 1000 fathoms deep. The general + argument is, however, unaffected.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_168_168" id= + "Footnote_168_168"></a><a href= + "#FNanchor_168_168"><span class="label">[168]</span></a> For + some details of these migrations, see the author's + <i>Geographical Distribution of Animals</i>, vol. i. p. 140; + also Heilprin's <i>Geographical and Geological Distribution + of Animals</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_169_169" id= + "Footnote_169_169"></a><a href= + "#FNanchor_169_169"><span class="label">[169]</span></a> For + a full discussion of this question, see <i>Island Life</i>, + pp. 390-420.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_170_170" id= + "Footnote_170_170"></a><a href= + "#FNanchor_170_170"><span class="label">[170]</span></a> + <i>Géographie Botanique</i>, p. 798.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_171_171" id= + "Footnote_171_171"></a><a href= + "#FNanchor_171_171"><span class="label">[171]</span></a> + <i>Nature</i>, 1st April 1886.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_172_172" id= + "Footnote_172_172"></a><a href= + "#FNanchor_172_172"><span class="label">[172]</span></a> + Report of the Brit. Assoc. Committee on Migration of Birds + during 1886.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_173_173" id= + "Footnote_173_173"></a><a href= + "#FNanchor_173_173"><span class="label">[173]</span></a> + <i>Trans. Ent. Soc.</i>, 1871, p. 184.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_174_174" id= + "Footnote_174_174"></a><a href= + "#FNanchor_174_174"><span class="label">[174]</span></a> + <i>Nature</i> (1875), vol. xii. pp. 279, 298.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_175_175" id= + "Footnote_175_175"></a><a href= + "#FNanchor_175_175"><span class="label">[175]</span></a> I am + indebted to Professor R. Meldola of the Finsbury Technical + Institute, and Rev. T.D. Titmas of Charterhouse for + furnishing me with the weights required.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_176_176" id= + "Footnote_176_176"></a><a href= + "#FNanchor_176_176"><span class="label">[176]</span></a> See + <i>Nature</i>, vol. vi. p. 164, for a summary of Kerner's + paper.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_177_177" id= + "Footnote_177_177"></a><a href= + "#FNanchor_177_177"><span class="label">[177]</span></a> It + seems quite possible that the absence of pappus in this case + is a recent adaptation, and that it has been brought about by + causes similar to those which have reduced or aborted the + wings of insects in oceanic islands. For when a plant has + once reached one of the storm-swept islands of the southern + ocean, the pappus will be injurious for the same reason that + the wings of insects are injurious, since it will lead to the + seeds being blown out to sea and destroyed. The seeds which + are heaviest and have least pappus will have the best chance + of falling on the ground and remaining there to germinate, + and this process of selection might rapidly lead to the + entire disappearance of the pappus.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_178_178" id= + "Footnote_178_178"></a><a href= + "#FNanchor_178_178"><span class="label">[178]</span></a> See + <i>Island Life</i>, p. 251.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_179_179" id= + "Footnote_179_179"></a><a href= + "#FNanchor_179_179"><span class="label">[179]</span></a> Mr. + Hemsley suggests that it is not so much the difficulty of + transmission by floating, as the bad conditions the seeds are + usually exposed to when they reach land. Many, even if they + germinate, are destroyed by the waves, as Burchell noticed at + St. Helena; while even a flat and sheltered shore would be an + unsuitable position for many inland plants. Air-borne seeds, + on the other hand, may be carried far inland, and so + scattered that some of them are likely to reach suitable + stations.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_180_180" id= + "Footnote_180_180"></a><a href= + "#FNanchor_180_180"><span class="label">[180]</span></a> For + fuller particulars, see Sir J. Hooker's <i>Introduction to + Floras of New Zealand and Australia</i>, and a summary in my + <i>Island Life</i>, chaps. xxii. xxiii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_181_181" id= + "Footnote_181_181"></a><a href= + "#FNanchor_181_181"><span class="label">[181]</span></a> For + a fuller discussion of this subject, see my <i>Island + Life</i>, chap. xxiii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_182_182" id= + "Footnote_182_182"></a><a href= + "#FNanchor_182_182"><span class="label">[182]</span></a> A + very remarkable case of wind conveyance of seeds on a large + scale is described in a letter from Mr. Thomas Hanbury to his + brother, the late Daniel Hanbury, which has been kindly + communicated to me by Mr. Hemsley of Kew. The letter is dated + "Shanghai, 1st May 1856," and the passage referred to is as + follows:—</p> + + <div class="blockquot" style='font-size: 100%;'> + <p>"For the past three days we have had very warm weather + for this time of year, in fact almost as warm as the middle + of summer. Last evening the wind suddenly changed round to + the north and blew all night with considerable violence, + making a great change in the atmosphere.</p> + + <p>"This morning, myriads of small white particles are + floating about in the air; there is not a single cloud and + no mist, yet the sun is quite obscured by this substance, + and it looks like a white fog in England. I enclose thee a + sample, thinking it may interest. It is evidently a + vegetable production; I think, apparently, some kind of + seed."</p> + </div> + + <p>Mr. Hemsley adds, that this substance proves to be the + plumose seeds of a poplar or willow. In order to produce the + effects described—<i>quite obscuring the sun like a + white fog</i>,—the seeds must have filled the air to a + very great height; and they must have been brought from some + district where there were extensive tracts covered with the + tree which produced them.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a><a name= + "Page_375" id="Page_375"></a>CHAPTER XIII</h2> + + <p style='font-weight:bold;'>THE GEOLOGICAL EVIDENCES OF + EVOLUTION</p> + + <div class="blockquot"> + <p>What we may expect—The number of known species of + extinct animals—Causes of the imperfection of the + geological record—Geological evidences of + evolution—Shells—Crocodiles—The rhinoceros + tribe—The pedigree of the horse tribe—Development + of deer's horns—Brain development—Local relations + of fossil and living animals—Cause of extinction of large + animals—Indications of general progress in plants and + animals—The progressive development of + plants—Possible cause of sudden late appearance of + exogens—Geological distribution of + insects—Geological succession of + vertebrata—Concluding remarks.</p> + </div> + + <p>The theory of evolution in the organic world necessarily + implies that the forms of animals and plants have, broadly + speaking, progressed from a more generalised to a more + specialised structure, and from simpler to more complex forms. We + know, however, that this progression has been by no means + regular, but has been accompanied by repeated degradation and + degeneration; while extinction on an enormous scale has again and + again stopped all progress in certain directions, and has often + compelled a fresh start in development from some comparatively + low and imperfect type.</p> + + <p>The enormous extension of geological research in recent times + has made us acquainted with a vast number of extinct organisms, + so vast that in some important groups—such as the + mollusca—the fossil are more numerous than the living + species; while in the mammalia they are not much less numerous, + the preponderance of living species being chiefly in the smaller + and in the arboreal forms which have not been so well preserved + as the members of the larger groups. With such a wealth of + material to illustrate the successive stages <a name="Page_376" + id="Page_376"></a>through which animals have passed, it will + naturally be expected that we should find important evidence of + evolution. We should hope to learn the steps by which some + isolated forms have been connected with their nearest allies, and + in many cases to have the gaps filled up which now separate genus + from genus, or species from species. In some cases these + expectations are fulfilled, but in many other cases we seek in + vain for evidence of the kind we desire; and this absence of + evidence with such an apparent wealth of material is held by many + persons to throw doubt on the theory of evolution itself. They + urge, with much appearance of reason, that all the arguments we + have hitherto adduced fall short of demonstration, and that the + crucial test consists in being able to show, in a great number of + cases, those connecting links which we say must have existed. + Many of the gaps that still remain are so vast that it seems + incredible to these writers that they could ever have been filled + up by a close succession of species, since these must have spread + over so many ages, and have existed in such numbers, that it + seems impossible to account for their total absence from deposits + in which great numbers of species belonging to other groups are + preserved and have been discovered. In order to appreciate the + force, or weakness, of these objections, we must inquire into the + character and completeness of that record of the past life of the + earth which geology has unfolded, and ascertain the nature and + amount of the evidence which, under actual conditions, we may + expect to find.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Number of known Species of Extinct Animals.</i></p> + + <p>When we state that the known fossil mollusca are considerably + more numerous than those which now live on the earth, it appears + at first sight that our knowledge is very complete, but this is + far from being the case. The species have been continually + changing throughout geological time, and at each period have + probably been as numerous as they are now. If we divide the + fossiliferous strata into twelve great divisions—the + Pliocene, Miocene, Eocene, Cretaceous, Oolite, Lias, Trias, + Permian, Carboniferous, Devonian, Silurian, and + Cambrian,—we find not only that each has a very distinct + and characteristic molluscan fauna, but that the different + sub<a name="Page_377" id="Page_377"></a>divisions often present a + widely different series of species; so that although a certain + number of species are common to two or more of the great + divisions, the totality of the species that have lived upon the + earth must be very much more than twelve times—perhaps even + thirty or forty times—the number now living. In like + manner, although the species of fossil mammals now recognised by + more or less fragmentary fossil remains may not be much less + numerous than the living species, yet the duration of existence + of these was comparatively so short that they were almost + completely changed, perhaps six or seven times, during the + Tertiary period; and this is certainly only a fragment of the + geological time during which mammalia existed on the globe.</p> + + <p>There is also reason to believe that the higher animals were + much more abundant in species during past geological epochs than + now, owing to the greater equability of the climate which + rendered even the arctic regions as habitable as the temperate + zones are in our time.</p> + + <p>The same equable climate would probably cause a more uniform + distribution of moisture, and render what are now desert regions + capable of supporting abundance of animal life. This is indicated + by the number and variety of the species of large animals that + have been found fossil in very limited areas which they evidently + inhabited at one period. M. Albert Gaudry found, in the deposits + of a mountain stream at Pikermi in Greece, an abundance of large + mammalia such as are nowhere to be found living together at the + present time. Among them were two species of Mastodon, two + different rhinoceroses, a gigantic wild boar, a camel and a + giraffe larger than those now living, several monkeys, carnivora + ranging from martens and civets to lions and hyaenas of the + largest size, numerous antelopes of at least five distinct + genera, and besides these many forms altogether extinct. Such + were the great herds of Hipparion, an ancestral form of horse; + the Helladotherium, a huge animal bigger than the giraffe; the + Ancylotherium, one of the Edentata; the huge Dinotherium; the + Aceratherium, allied to the rhinoceros; and the monstrous + Chalicotherium, allied to the swine and ruminants, but as large + as a rhinoceros; and to prey upon these, the great Machairodus or + sabre-toothed tiger. And all these remains were <a name= + "Page_378" id="Page_378"></a>found in a space 300 paces long by + 60 paces broad, many of the species existing in enormous + quantities.</p> + + <p>The Pikermi fossils belong to the Upper Miocene formation, but + an equally rich deposit of Upper Eocene age has been discovered + in South-Western France at Quercy, where M. Filhol has determined + the presence of no less than forty-two species of beasts of prey + alone. Equally remarkable are the various discoveries of + mammalian fossils in North America, especially in the old lake + bottoms now forming what are called the "bad lands" of Dakota and + Nebraska, belonging to the Miocene period. Here are found an + enormous assemblage of remains, often perfect skeletons, of + herbivora and carnivora, as varied and interesting as those from + the localities already referred to in Europe; but altogether + distinct, and far exceeding, in number and variety of species of + the larger animals, the whole existing fauna of North America. + Very similar phenomena occur in South America and in Australia, + leading us to the conclusion that the earth at the present time + is impoverished as regards the larger animals, and that at each + successive period of Tertiary time, at all events, it contained a + far greater number of species than now inhabit it. The very + richness and abundance of the remains which we find in limited + areas, serve to convince us how imperfect and fragmentary must be + our knowledge of the earth's fauna at any one past epoch; since + we cannot believe that all, or nearly all, of the animals which + inhabited any district were entombed in a single lake, or + overwhelmed by the floods of a single river.</p> + + <p>But the spots where such rich deposits occur are exceedingly + few and far between when compared with the vast areas of + continental land, and we have every reason to believe that in + past ages, as now, numbers of curious species were rare or local, + the commoner and more abundant species giving a very imperfect + idea of the existing series of animal forms. Yet more important, + as showing the imperfection of our knowledge, is the enormous + lapse of time between the several formations in which we find + organic remains in any abundance, so vast that in many cases we + find ourselves almost in a new world, all the species and most of + the genera of the higher animals having undergone a complete + change.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_379" id="Page_379"></a><i>Causes of the + Imperfection of the Geological Record.</i></p> + + <p>These facts are quite in accordance with the conclusions of + geologists as to the necessary imperfection of the geological + record, since it requires the concurrence of a number of + favourable conditions to preserve any adequate representation of + the life of a given epoch. In the first place, the animals to be + preserved must not die a natural death by disease, or old age, or + by being the prey of other animals, but must be destroyed by some + accident which shall lead to their being embedded in the soil. + They must be either carried away by floods, sink into bogs or + quicksands, or be enveloped in the mud or ashes of a volcanic + eruption; and when thus embedded they must remain undisturbed + amid all the future changes of the earth's surface.</p> + + <p>But the chances against this are enormous, because denudation + is always going on, and the rocks we now find at the earth's + surface are only a small fragment of those which were originally + laid down. The alternations of marine and freshwater deposits, + and the frequent unconformability of strata with those which + overlie them, tell us plainly of repeated elevations and + depressions of the surface, and of denudation on an enormous + scale. Almost every mountain range, with its peaks, ridges, and + valleys, is but the remnant of some vast plateau eaten away by + sub-aerial agencies; every range of sea-cliffs tell us of long + slopes of land destroyed by the waves; while almost all the older + rocks which now form the surface of the earth have been once + covered with newer deposits which have long since disappeared. + Nowhere are the evidences of this denudation more apparent than + in North and South America, where granitic or metamorphic rocks + cover an area hardly less than that of all Europe. The same rocks + are largely developed in Central Africa and Eastern Asia; while, + besides those portions that appear exposed on the surface, areas + of unknown extent are buried under strata which rest on them + uncomformably, and could not, therefore, constitute the original + capping under which the whole of these rocks must once have been + deeply buried; because granite can only be formed, and + metamorphism can only go on, deep down in the crust of the earth. + What an over<a name="Page_380" id="Page_380"></a>whelming idea + does this give us of the destruction of whole piles of rock, + miles in thickness and covering areas comparable with those of + continents; and how great must have been the loss of the + innumerable fossil forms which those rocks contained! In view of + such destruction we are forced to conclude that our + palaeontological collections, rich though they may appear, are + really but small and random samples, giving no adequate idea of + the mighty series of organism which have lived upon the + earth.<a name="FNanchor_183_183" id= + "FNanchor_183_183"></a><a href="#Footnote_183_183" class= + "fnanchor">[183]</a></p> + + <p>Admitting, however, the extreme imperfection of the geological + record as a whole, it may be urged that certain limited portions + of it are fairly complete—as, for example, the various + Miocene deposits of India, Europe, and North America,—and + that in these we ought to find many examples of species and + genera linked together by intermediate forms. It may be replied + that in several cases this really occurs; and the reason why it + does not occur more often is, that the theory of evolution + requires that distinct genera should be linked together, not by a + direct passage, but by the descent of both from a common + ancestor, which may have lived in some much earlier age the + record of which is either wanting or very incomplete. An + illustration given by Mr. Darwin will make this more clear to + those who have not studied the subject. The fantail and pouter + pigeons are two very distinct and unlike breeds, which we yet + know to have been both derived from the common wild rock-pigeon. + Now, if we had every variety of living pigeon before us, or even + all those which have lived during the present century, we should + find no intermediate types between these two—none combining + in any degree the characters of the pouter with that of the + fantail. Neither should we ever find such an intermediate form, + even had there been preserved a specimen of every breed of pigeon + since the ancestral rock-pigeon was first tamed by man—a + period of probably several thousand years. We thus see that a + complete passage from one very distinct species to another could + not be expected even had we a complete record of the life of any + one period. What we require is a complete <a name="Page_381" id= + "Page_381"></a>record of all the species that have existed since + the two forms began to diverge from their common ancestor, and + this the known imperfection of the record renders it almost + impossible that we should ever attain. All that we have a right + to expect is, that, as we multiply the fossil forms in any group, + the gaps that at first existed in that group shall become less + wide and less numerous; and also that, in some cases, a tolerably + direct series shall be found, by which the more specialised forms + of the present day shall be connected with more generalised + ancestral types. We might also expect that when a country is now + characterised by special groups of animals, the fossil forms that + immediately preceded them shall, for the most part, belong to the + same groups; and further, that, comparing the more ancient with + the more modern types, we should find indications of progression, + the earlier forms being, on the whole, lower in organisation, and + less specialised in structure than the later. Now evidence of + evolution of these varied kinds is what we do find, and almost + every fresh discovery adds to their number and cogency. In order, + therefore, to show that the testimony given by geology is + entirely in favour of the theory of descent with modification, + some of the more striking of the facts will now be given.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Geological Evidences of Evolution.</i></p> + + <p>In an article in <i>Nature</i> (vol. xiv. p. 275), Professor + Judd calls attention to some recent discoveries in the Hungarian + plains, of fossil lacustrine shells, and their careful study by + Dr. Neumayr and M. Paul of the Austrian Geological Survey. The + beds in which they occur have accumulated to the thickness of + 2000 feet, containing throughout abundance of fossils, and + divisible into eight zones, each of which exhibits a well-marked + and characteristic fauna. Professor Judd then describes the + bearing of these discoveries as follows—</p> + + <div class="blockquot"> + <p>"The group of shells which affords the most interesting + evidence of the origin of new forms through descent with + modification is that of the genus Vivipara or Paludina, which + occurs in prodigious abundance throughout the whole series of + freshwater strata. We shall not, of course, attempt in this + place to enter into any details concerning the forty distinct + <i>forms</i> of this genus (Dr. Neumayr very properly hesitates + to call them all <a name="Page_382" id= + "Page_382"></a><i>species</i>), which are named and described + in this monograph, and between which, as the authors show, so + many connecting links, clearly illustrating the derivation of + the newer from the older types, have been detected. On the + minds of those who carefully examine the admirably engraved + figures given in the plates accompanying this valuable memoir, + or still better, the very large series of specimens from among + which the subjects of these figures are selected, and which are + now in the museum of the Reichsanstalt of Vienna, but little + doubt will, we suspect, remain that the authors have fully made + out their case, and have demonstrated that, beyond all + controversy, the series with highly complicated ornamentation + were variously derived by descent—the lines of which are + in most cases perfectly clear and obvious—from the simple + and unornamented Vivipara achatinoides of the + Congerien-Schichten (the lower division of the series of + strata). It is interesting to notice that a large portion of + these unquestionably derived forms depart so widely from the + type of the genus Vivipara, that they have been separated on so + high an authority as that of Sandberger, as a new genus, under + the name of Tulotoma. And hence we are led to the conclusion + that a vast number of forms, certainly exhibiting specific + distinctions, and according to some naturalists, differences + even entitled to be regarded of generic value, have all a + common ancestry."</p> + </div> + + <p>It is, as Professor Judd remarks, owing to the exceptionally + favourable circumstances of a long-continued and unbroken series + of deposits being formed under physical conditions either + identical or very slowly changing, that we owe so complete a + record of the process of organic change. Usually, some disturbing + elements, such as a sudden change of physical conditions, or the + immigration of new sets of forms from other areas and the + consequent retreat or partial extinction of the older fauna, + interferes with the continuity of organic development, and + produces those puzzling discordances so generally met with in + geological formations of marine origin. While a case of the kind + now described affords evidence of the origin of species complete + and conclusive, though on a necessarily very limited scale, the + very rarity of the conditions which are essential to such + completeness serves to explain why it is that in most cases the + direct evidence of evolution is not to be obtained.</p> + + <p><a name="Page_383" id="Page_383"></a>Another illustration of + the filling up of gaps between existing groups is afforded by + Professor Huxley's researches on fossil crocodiles. The gap + between the existing crocodiles and the lizards is very wide, but + as we go back in geological time we meet with fossil forms which + are to some extent intermediate and form a connected series. The + three living genera—Crocodilus, Alligator, and + Gavialis—are found in the Eocene formation, and allied + forms of another genus, Holops, in the Chalk. From the Chalk + backward to the Lias another group of genera occurs, having + anatomical characteristics intermediate between the living + crocodiles and the most ancient forms. These, forming two genera + Belodon and Stagonolepis, are found in a still older formation, + the Trias. They have characters resembling some lizards, + especially the remarkable Hatteria of New Zealand, and have also + some resemblances to the Dinosaurians—reptiles which in + some respects approach birds. Considering how comparatively few + are the remains of this group of animals, the evidence which it + affords of progressive development is remarkably clear.<a name= + "FNanchor_184_184" id="FNanchor_184_184"></a><a href= + "#Footnote_184_184" class="fnanchor">[184]</a></p> + + <p>Among the higher animals the rhinoceros, the horse, and the + deer afford good evidence of advance in organisation and of the + filling up of the gaps which separate the living forms from their + nearest allies. The earliest ancestral forms of the rhinoceroses + occur in the Middle Eocene of the United States, and were to some + extent intermediate between the rhinoceros and tapir families, + having like the latter four toes to the front feet, and three to + those behind. These are followed in the Upper Eocene by the genus + Amynodon, in which the skull assumes more distinctly the + rhinocerotic type. Following this in the Lower Miocene we have + the Aceratherium, like the last in its feet, but still more + decidedly a rhinoceros in its general structure. From this there + are two diverging lines—one in the Old World, the other in + the New. In the former, to which the Aceratherium is supposed to + have migrated in early Miocene times, when a mild climate and + luxuriant vegetation prevailed far within the arctic circle, it + gave rise to the Ceratorhinus and the various horned rhinoceroses + of late Tertiary times and of those now living. In America a + <a name="Page_384" id="Page_384"></a>number of large hornless + rhinoceroses were developed—they are found in the Upper + Miocene, Pliocene, and Post-Pliocene formations—and then + became extinct. The true rhinoceroses have three toes on all the + feet.<a name="FNanchor_185_185" id= + "FNanchor_185_185"></a><a href="#Footnote_185_185" class= + "fnanchor">[185]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Pedigree of the Horse Tribe.</i></p> + + <p>Yet more remarkable is the evidence afforded by the ancestral + forms of the horse tribe which have been discovered in the + American tertiaries. The family Equidae, comprising the living + horse, asses, and zebras, differ widely from all other mammals in + the peculiar structure of the feet, all of which terminate in a + single large toe forming the hoof. They have forty teeth, the + molars being formed of hard and soft material in crescentic + folds, so as to be a powerful agent in grinding up hard grasses + and other vegetable food. The former peculiarities depend upon + modifications of the skeleton, which have been thus described by + Professor Huxley:—</p> + + <div class="blockquot"> + <p>"Let us turn in the first place to the fore-limb. In most + quadrupeds, as in ourselves, the fore-arm contains distinct + bones, called the radius and the ulna. The corresponding region + in the horse seems at first to possess but one bone. Careful + observation, however, enables us to distinguish in this bone a + part which clearly answers to the upper end of the ulna. This + is closely united with the chief mass of the bone which + represents the radius, and runs out into a slender shaft, which + may be traced for some distance downwards upon the back of the + radius, and then in most cases thins out and vanishes. It takes + still more trouble to make sure of what is nevertheless the + fact, that a small part of the lower end of the bone of a + horse's fore-arm, which is only distinct in a very young foal, + is really the lower extremity of the ulna.</p> + + <p>"What is commonly called the knee of a horse is its wrist. + The 'cannon bone' answers to the middle bone of the five + metacarpal bones which support the palm of the hand in + ourselves. The pastern, coronary, and coffin bones of + veterinarians answer to the joints of our middle fingers, while + the hoof is simply a greatly enlarged and thickened nail. But + if <a name="Page_385" id="Page_385"></a>what lies below the + horse's 'knee' thus corresponds to the middle finger in + ourselves, what has become of the four other fingers or digits? + We find in the places of the second and fourth digits only two + slender splintlike bones, about two-thirds as long as the + cannon bone, which gradually taper to their lower ends and bear + no finger joints, or, as they are termed, phalanges. Sometimes, + small bony or gristly nodules are to be found at the bases of + these two metacarpal splints, and it is probable that these + represent rudiments of the first and fifth toes. Thus, the part + of the horse's skeleton which corresponds with that of the + human hand, contains one overgrown middle digit, and at least + two imperfect lateral digits; and these answer, respectively, + to the third, the second, and the fourth fingers in man.</p> + + <p>"Corresponding modifications are found in the hind limb. In + ourselves, and in most quadrupeds, the leg contains two + distinct bones, a large bone, the tibia, and a smaller and more + slender bone, the fibula. But, in the horse, the fibula seems, + at first, to be reduced to its upper end; a short slender bone + united with the tibia, and ending in a point below, occupying + its place. Examination of the lower end of a young foal's + shin-bone, however, shows a distinct portion of osseous matter + which is the lower end of the fibula; so that the, apparently + single, lower end of the shin-bone is really made up of the + coalesced ends of the tibia and fibula, just as the, apparently + single, lower end of the fore-arm bone is composed of the + coalesced radius and ulna.</p> + + <p>"The heel of the horse is the part commonly known as the + hock. The hinder cannon bone answers to the middle metatarsal + bone of the human foot, the pastern, coronary, and coffin + bones, to the middle toe bones; the hind hoof to the nail; as + in the forefoot. And, as in the forefoot, there are merely two + splints to represent the second and the fourth toes. Sometimes + a rudiment of a fifth toe appears to be traceable.</p> + + <p>"The teeth of a horse are not less peculiar than its limbs. + The living engine, like all others, must be well stoked if it + is to do its work; and the horse, if it is to make good its + wear and tear, and to exert the enormous amount of force + required for its propulsion, must be well and rapidly fed. To + this end, <a name="Page_386" id="Page_386"></a>good cutting + instruments and powerful and lasting crushers are needful. + Accordingly, the twelve cutting teeth of a horse are close-set + and concentrated in the forepart of its mouth, like so many + adzes or chisels. The grinders or molars are large, and have an + extremely complicated structure, being composed of a number of + different substances of unequal hardness. The consequence of + this is that they wear away at different rates; and, hence, the + surface of each grinder is always as uneven as that of a good + millstone."<a name="FNanchor_186_186" id= + "FNanchor_186_186"></a><a href="#Footnote_186_186" class= + "fnanchor">[186]</a></p> + </div> + + <p>We thus see that the Equidae differ very widely in structure + from most other mammals. Assuming the truth of the theory of + evolution, we should expect to find traces among extinct animals + of the steps by which this great modification has been effected; + and we do really find traces of these steps, imperfectly among + European fossils, but far more completely among those of + America.</p> + + <p>It is a singular fact that, although no horse inhabited + America when discovered by Europeans, yet abundance of remains of + extinct horses have been found both in North and South America in + Post-Tertiary and Upper Pliocene deposits; and from these an + almost continuous series of modified forms can be traced in the + Tertiary formation, till we reach, at the very base of the + series, a primitive form so unlike our perfected animal, that, + had we not the intermediate links, few persons would believe that + the one was the ancestor of the other. The tracing out of this + marvellous history we owe chiefly to Professor Marsh of Yale + College, who has himself discovered no less than thirty species + of fossil Equidae; and we will allow him to tell the story of the + development of the horse from a humble progenitor in his own + words.</p> + + <div class="blockquot"> + <p>"The oldest representative of the horse at present known is + the diminutive Eohippus from the Lower Eocene. Several species + have been found, all about the size of a fox. Like most of the + early mammals, these ungulates had forty-four teeth, the molars + with short crowns and quite distinct in form from the + premolars. The ulna and fibula were entire and distinct, and + there were four well-developed toes and a rudiment of another + on the forefeet, and three toes behind. In the structure of the + feet and teeth, the Eohippus unmistak<a name="Page_387" id= + "Page_387"></a>ably indicates that the direct ancestral line to + the modern horse has already separated from the other + perissodactyles, or odd-toed ungulates.</p> + + <p>"In the next higher division of the Eocene another genus, + Orohippus, makes its appearance, replacing Eohippus, and + showing a greater, though still distant, resemblance to the + equine type. The rudimentary first digit of the forefoot has + disappeared, and the last premolar has gone over to the molar + series. Orohippus was but little larger than Eohippus, and in + most other respects very similar. Several species have been + found, but none occur later than the Upper Eocene.</p> + + <p>"Near the base of the Miocene, we find a third closely + allied genus, Mesohippus, which is about as large as a sheep, + and one stage nearer the horse. There are only three toes and a + rudimentary splint on the forefeet, and three toes behind. Two + of the premolar teeth are quite like the molars. The ulna is no + longer distinct or the fibula entire, and other characters show + clearly that the transition is advancing.</p> + + <p>"In the Upper Miocene Mesohippus is not found, but in its + place a fourth form, Miohippus, continues the line. This genus + is near the Anchitherium of Europe, but presents several + important differences. The three toes in each foot are more + nearly of a size, and a rudiment of the fifth metacarpal bone + is retained. All the known species of this genus are larger + than those of Mesohippus, and none of them pass above the + Miocene formation.</p> + + <p>"The genus Protohippus of the Lower Pliocene is yet more + equine, and some of its species equalled the ass in size. There + are still three toes on each foot, but only the middle one, + corresponding to the single toe of the horse, comes to the + ground. This genus resembles most nearly the Hipparion of + Europe.</p> + + <p>"In the Pliocene we have the last stage of the series before + reaching the horse, in the genus Pliohippus, which has lost the + small hooflets, and in other respects is very equine. Only in + the Upper Pliocene does the true Equus appear and complete the + genealogy of the horse, which in the Post-Tertiary roamed over + the whole of North and South America, and soon after became + extinct. This occurred long before the discovery of the + continent by Europeans, and no satisfactory <a name="Page_388" + id="Page_388"></a><a name="Page_389" id="Page_389"></a>reason + for the extinction has yet been given. Besides the characters I + have mentioned, there are many others in the skeleton, skull, + teeth, and brain of the forty or more intermediate species, + which show that the transition from the Eocene Eohippus to the + modern Equus has taken place in the order indicated"<a name= + "FNanchor_187_187" id="FNanchor_187_187"></a><a href= + "#Footnote_187_187" class="fnanchor">[187]</a> (see Fig. + 33).</p> + </div> + + <div class="figcenter" style="width: 400px;"> + <a name="fig33" id="fig33"></a> <img src="images/fig33.jpg" + width="400" height="664" alt= + "FIG. 33.—Geological development of the horse tribe (Eohippus since discovered)." + title= + "FIG. 33.—Geological development of the horse tribe (Eohippus since discovered)." /> + <b>FIG. 33.—Geological development of the horse tribe + (Eohippus since discovered).</b> + </div> + + <p>Well may Professor Huxley say that this is demonstrative + evidence of evolution; the doctrine resting upon exactly as + secure a foundation as did the Copernican theory of the motions + of the heavenly bodies at the time of its promulgation. Both have + the same basis—the coincidence of the observed facts with + the theoretical requirements.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Development of Deer's Horns.</i></p> + + <p>Another clear and unmistakable proof of evolution is afforded + by one of the highest and latest developed tribes of + mammals—the true deer. These differ from all other + ruminants in possessing solid deciduous horns which are always + more or less branched. They first appear in the Middle Miocene + formation, and continue down to our time; and their development + has been carefully traced by Professor Boyd Dawkins, who thus + summarises his results:—</p> + + <div class="blockquot"> + <p>"In the middle stage of the Miocene the cervine antler + consists merely of a simple forked crown (as in Cervus + dicroceros), which increases in size in the Upper Miocene, + although it still remains small and erect, like that of the + roe. In Cervus Matheroni it measures 11·4 inches, and + throws off not more than four tines, all small. The deer living + in Auvergne in the succeeding or Pliocene age, present us with + another stage in the history of antler development. There, for + the first time, we see antlers of the Axis and Rusa type, + larger and longer, and more branching than any antlers were + before, and possessing three or more well-developed tines. Deer + of this type abounded in Pliocene Europe. They belong to the + Oriental division of the Cervidae, and their presence in Europe + confirms the evidence of the flora, brought forward by the + Comte de Saporta, that the Pliocene climate was warm. They have + probably disappeared from Europe in consequence <a name= + "Page_390" id="Page_390"></a>of the lowering of the temperature + in the Pleistocene age, while their descendants have found a + congenial home in the warmer regions of Eastern Asia.</p> + + <p>"In the latest stage of the Pliocene—the Upper + Pliocene of the Val d'Arno—the Cervus dicranios of Nesti + presents us with antlers much smaller than those of the Irish + elk, but very complicated in their branching. This animal + survived into the succeeding age, and is found in the + pre-glacial forest bed of Norfolk, being described by Dr. + Falconer under the name of Sedgwick's deer. The Irish elk, + moose, stag, reindeer, and fallow deer appear in Europe in the + Pleistocene age, all with highly complicated antlers in the + adult, and the first possessing the largest antlers yet known. + Of these the Irish elk disappeared in the Prehistoric age, + after having lived in countless herds in Ireland, while the + rest have lived on into our own times in Euro-Asia, and, with + the exception of the last, also in North America.</p> + + <p>"From this survey it is obvious that the cervine antlers + have increased in size and complexity from the Mid-Miocene to + the Pleistocene age, and that their successive changes are + analogous to those which are observed in the development of + antlers in the living deer, which begin with a simple point, + and increase in number of tines till their limit of growth be + reached. In other words, the development of antlers indicated + at successive and widely-separated pages of the geological + record is the same as that observed in the history of a single + living species. It is also obvious that the progressive + diminution of size and complexity in the antlers, from the + present time back into the early Tertiary age, shows that we + are approaching the zero of antler development in the + Mid-Miocene. No trace of any antler-bearing ruminant has been + met with in the lower Miocenes, either of Europe or the United + States."<a name="FNanchor_188_188" id= + "FNanchor_188_188"></a><a href="#Footnote_188_188" class= + "fnanchor">[188]</a></p> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Progressive Brain-Development.</i></p> + + <p>The three illustrations now given sufficiently prove that, + whenever the geological record approaches to completeness, we + have evidence of the progressive change of species in definite + directions, and from less developed to more de<a name="Page_391" + id="Page_391"></a>veloped types—exactly such a change as we + may expect to find if the evolution theory be the true one. Many + other illustrations of a similar change could be given, but the + animal groups in which they occur being less familiar, the + details would be less interesting, and perhaps hardly + intelligible. There is, however, one very remarkable proof of + development that must be briefly noticed—that afforded by + the steady increase in the size of the brain. This may be best + stated in the words of Professor Marsh:—</p> + + <div class="blockquot"> + <p>"The real progress of mammalian life in America, from the + beginning of the Tertiary to the present, is well illustrated + by the brain-growth, in which we have the key to many other + changes. The earliest known Tertiary mammals all had very small + brains, and in some forms this organ was proportionally less + than in certain reptiles. There was a gradual increase in the + size of the brain during this period, and it is interesting to + find that this growth was mainly confined to the cerebral + hemispheres, or higher portion of the brain. In most groups of + mammals the brain has gradually become more convoluted, and + thus increased in quality as well as quantity. In some also the + cerebellum and olfactory lobes, the lower parts of the brain, + have even diminished in size. In the long struggle for + existence during Tertiary time the big brains won, then as now; + and the increasing power thus gained rendered useless many + structures inherited from primitive ancestors, but no longer + adapted to new conditions."</p> + </div> + + <p>This remarkable proof of development in the organ of the + mental faculties, forms a fitting climax to the evidence already + adduced of the progressive evolution of the general structure of + the body, as illustrated by the bony skeleton. We now pass on to + another class of facts equally suggestive of evolution.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Local Relations of Fossil and Living Animals.</i></p> + + <p>If all existing animals have been produced from ancestral + forms—mostly extinct—under the law of variation and + natural selection, we may expect to find in most cases a close + relation between the living forms of each country and those which + inhabited it in the immediately preceding epoch. But if species + have originated in some quite different way, either by <a name= + "Page_392" id="Page_392"></a>any kind of special creation, or by + sudden advances of organisation in the offspring of preceding + types, such close relationship would not be found; and facts of + this kind become, therefore, to some extent a test of evolution + under natural selection or some other law of gradual change. Of + course the relationship will not appear when extensive migration + has occurred, by which the inhabitants of one region have been + able to take possession of another region, and destroy or drive + out its original inhabitants, as has sometimes happened. But such + cases are comparatively rare, except where great changes of + climate are known to have occurred; and we usually do find a + remarkable continuity between the existing fauna and flora of a + country and those of the immediately preceding age. A few of the + more remarkable of these cases will now be briefly noticed.</p> + + <p>The mammalian fauna of Australia consists, as is well known, + wholly of the lowest forms—the Marsupials and + Monotremata—except only a few species of mice. This is + accounted for by the complete isolation of the country from the + Asiatic continent during the whole period of the development of + the higher animals. At some earlier epoch the ancestral + marsupials, which abounded both in Europe and North America in + the middle of the Secondary period, entered the country, and have + since remained there, free from the competition of higher forms, + and have undergone a special development in accordance with the + peculiar conditions of a limited area. While in the large + continents higher forms of mammalia have been developed, which + have almost or wholly exterminated the less perfect marsupials, + in Australia these latter have become modified into such varied + forms as the leaping kangaroos, the burrowing wombats, the + arboreal phalangers, the insectivorous bandicoots, and the + carnivorous Dasyuridae or native cats, culminating in the + Thylacinus or "tiger-wolf" of Tasmania—animals as unlike + each other as our sheep, rabbits, squirrels, and dogs, but all + retaining the characteristic features of the marsupial type.</p> + + <p>Now in the caves and late Tertiary or Post-Tertiary deposits + of Australia the remains of many extinct mammalia have been + found, but all are marsupials. There are many kangaroos, some + larger than any living species, and others more allied to + <a name="Page_393" id="Page_393"></a>the tree-kangaroos of New + Guinea; a large wombat as large as a tapir; the Diprotodon, a + thick-limbed kangaroo the size of a rhinoceros or small elephant; + and a quite different animal, the Nototherium, nearly as large. + The carnivorous Thylacinus of Tasmania is also found fossil; and + a huge phalanger, Thylacoleo, the size of a lion, believed by + Professor Owen and by Professor Oscar Schmidt to have been + equally carnivorous and destructive.<a name="FNanchor_189_189" + id="FNanchor_189_189"></a><a href="#Footnote_189_189" class= + "fnanchor">[189]</a> Besides these, there are many other species + more resembling the living forms both in size and structure, of + which they may be, in some cases, the direct ancestors. Two + species of extinct Echidna, belonging to the very low + Monotremata, have also been found in New South Wales.</p> + + <p>Next to Australia, South America possesses the most remarkable + assemblage of peculiar mammals, in its numerous + Edentata—the sloths, ant-eaters, and armadillos; its + rodents, such as the cavies and chinchillas; its marsupial + opossums, and its quadrumana of the family Cebidae. Remains of + extinct species of all these have been found in the caves of + Brazil, of Post-Pliocene age; while in the earlier Pliocene + deposits of the pampas many distinct genera of these groups have + been found, some of gigantic size and extraordinary form. There + are armadillos of many types, some being as large as elephants; + gigantic sloths of the genera Megatherium, Megalonyx, Mylodon, + Lestodon, and many others; rodents belonging to the American + families Cavidae and Chinchillidae; and ungulates allied to the + llama; besides many other extinct forms of intermediate types or + of uncertain affinities.<a name="FNanchor_190_190" id= + "FNanchor_190_190"></a><a href="#Footnote_190_190" class= + "fnanchor">[190]</a> The extinct Moas of New Zealand—huge + wingless birds allied to the living Apteryx—illustrate the + same general law.</p> + + <p>The examples now quoted, besides illustrating and enforcing + the general fact of evolution, throw some light on the usual + character of the modification and progression of animal forms. In + the cases where the geological record is tolerably complete, we + find a continuous development of some kind—either in + complexity of ornamentation, as in the fossil Paludinas of the + Hungarian lake-basins; in size and in the specialisation of the + <a name="Page_394" id="Page_394"></a>feet and teeth, as in the + American fossil horses; or in the increased development of the + branching horns, as in the true deer. In each of these cases + specialisation and adaptation to the conditions of the + environment appear to have reached their limits, and any change + of these conditions, especially if it be at all rapid or + accompanied by the competition of less developed but more + adaptable forms, is liable to cause the extinction of the most + highly developed groups. Such we know was the case with the horse + tribe in America, which totally disappeared in that continent at + an epoch so recent that we cannot be sure that the disappearance + was not witnessed, perhaps caused, by man; while even in the + Eastern hemisphere it is the smaller species—the asses and + the zebras—that have persisted, while the larger and more + highly developed true horses have almost, if not quite, + disappeared in a state of nature. So we find, both in Australia + and South America, that in a quite recent period many of the + largest and most specialised forms have become extinct, while + only the smaller types have survived to our day; and a similar + fact is to be observed in many of the earlier geological epochs, + a group progressing and reaching a maximum of size or complexity + and then dying out, or leaving at most but few and pigmy + representatives.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Cause of Extinction of Large Animals.</i></p> + + <p>Now there are several reasons for the repeated extinction of + large rather than of small animals. In the first place, animals + of great bulk require a proportionate supply of food, and any + adverse change of conditions would affect them more seriously + than it would smaller animals. In the next place, the extreme + specialisation of many of these large animals would render it + less easy for them to be modified in any new direction suited to + changed conditions. Still more important, perhaps, is the fact + that very large animals always increase slowly as compared with + small ones—the elephant producing a single young one every + three years, while a rabbit may have a litter of seven or eight + young two or three times a year. Now the probability of + favourable variations will be in direct proportion to the + population of the species, and as the smaller animals are not + only many hundred times more numerous than the largest, but also + increase perhaps a hundred times as <a name="Page_395" id= + "Page_395"></a>rapidly, they are able to become quickly modified + by variation and natural selection in harmony with changed + conditions, while the large and bulky species, being unable to + vary quickly enough, are obliged to succumb in the struggle for + existence. As Professor Marsh well observes: "In every vigorous + primitive type which was destined to survive many geological + changes, there seems to have been a tendency to throw off lateral + branches, which became highly specialised and soon died out, + because they were unable to adapt themselves to new conditions." + And he goes on to show how the whole narrow path of the + persistent Suilline type, throughout the entire series of the + American tertiaries, is strewed with the remains of such + ambitious offshoots, many of them attaining the size of a + rhinoceros; "while the typical pig, with an obstinacy never lost, + has held on in spite of catastrophes and evolution, and still + lives in America to-day."</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Indications of General Progression in Plants and + Animals.</i></p> + + <p>One of the most powerful arguments formerly adduced against + evolution was, that geology afforded no evidence of the gradual + development of organic forms, but that whole tribes and classes + appeared suddenly at definite epochs, and often in great variety + and exhibiting a very perfect organisation. The mammalia, for + example, were long thought to have first appeared in Tertiary + times, where they are represented in some of the earlier deposits + by all the great divisions of the class fully + developed—carnivora, rodents, insectivora, marsupials, and + even the perissodactyle and artiodactyle divisions of the + ungulata—as clearly defined as at the present day. The + discovery in 1818 of a single lower jaw in the Stonesfield Slate + of Oxfordshire hardly threw doubt on the generalisation, since + either its mammalian character was denied, or the geological + position of the strata, in which it was found, was held to have + been erroneously determined. But since then, at intervals of many + years, other remains of mammalia have been discovered in the + Secondary strata, ranging from the Upper Oolite to the Upper + Trias both in Europe and the United States, and one even + (Tritylodon) in the Trias of South Africa. All these are either + marsupials, or of some still lower type of mammalia; but they + consist of many distinct forms classed in <a name="Page_396" id= + "Page_396"></a>about twenty genera. Nevertheless, a great gap + still exists between these mammals and those of the Tertiary + strata, since no mammal of any kind has been found in any part of + the Cretaceous formation, although in several of its subdivisions + abundance of land plants, freshwater shells, and air-breathing + reptiles have been discovered. So with fishes. In the last + century none had been obtained lower than the Carboniferous + formation; thirty years later they were found to be very abundant + in the Devonian rocks, and later still they were discovered in + the Upper Ludlow and Lower Ludlow beds of the Silurian + formation.</p> + + <p>We thus see that such sudden appearances are deceptive, and + are, in fact, only what we ought to expect from the known + imperfection of the geological record. The conditions favourable + to the fossilisation of any group of animals occur comparatively + rarely, and only in very limited areas; while the conditions + essential for their permanent preservation in the rocks, amid all + the destruction caused by denudation or metamorphism, are still + more exceptional. And when they are thus preserved to our day, + the particular part of the rocks in which they lie hidden may not + be on the surface but buried down deep under other strata, and + may thus, except in the case of mineral-bearing deposits, be + altogether out of our reach. Then, again, how large a proportion + of the earth consists of wild and uncivilised regions in which no + exploration of the rocks has been yet made, so that whether we + shall find the fossilised remains of any particular group of + animals which lived during a limited period of the earth's + history, and in a limited area, depends upon at least a fivefold + combination of chances. Now, if we take each of these chances + separately as only ten to one against us (and some are certainly + more than this), then the actual chance against our finding the + fossil remains, say of any one order of mammalia, or of land + plants, at any particular geological horizon, will be about a + hundred thousand to one.</p> + + <p>It may be said, if the chances are so great, how is it that we + find such immense numbers of fossil species exceeding in number, + in some groups, all those that are now living? But this is + exactly what we should expect, because the number of species of + organisms that have ever lived upon the earth, since <a name= + "Page_397" id="Page_397"></a>the earliest geological times, will + probably be many hundred times greater than those now existing of + which we have any knowledge; and hence the enormous gaps and + chasms in the geological record of extinct forms is not to be + wondered at. Yet, notwithstanding these chasms in our knowledge, + if evolution is true, there ought to have been, on the whole, + progression in all the chief types of life. The higher and more + specialised forms should have come into existence later than the + lower and more generalised forms; and however fragmentary the + portions we possess of the whole tree of life upon the earth, + they ought to show us broadly that such a progressive evolution + has taken place. We have seen that in some special groups, + already referred to, such a progression is clearly visible, and + we will now cast a hasty glance over the entire series of fossil + forms, in order to see if a similar progression is manifested by + them as a whole.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Progressive Development of Plants.</i></p> + + <p>Ever since fossil plants have been collected and studied, the + broad fact has been apparent that the early plants—those of + the Coal formation—were mainly cryptogamous, while in the + Tertiary deposits the higher flowering plants prevailed. In the + intermediate secondary epoch the gymnosperms—cycads and + coniferae—formed a prominent part of the vegetation, and as + these have usually been held to be a kind of transition form + between the flowerless and flowering plants, the geological + succession has always, broadly speaking, been in accordance with + the theory of evolution. Beyond this, however, the facts were + very puzzling. The highest cryptogams—ferns, lycopods, and + equisetaceae—appeared suddenly, and in immense profusion in + the Coal formation, at which period they attained a development + they have never since surpassed or even equalled; while the + highest plants—the dicotyledonous and monocotyledonous + angiosperms—which now form the bulk of the vegetation of + the world, and exhibit the most wonderful modifications of form + and structure, were almost unknown till the Tertiary period, when + they suddenly appeared in full development, and, for the most + part, under the same generic forms as now exist.</p> + + <p>During the latter half of the present century, however, great + additions have been made to our knowledge of fossil <a name= + "Page_398" id="Page_398"></a>plants; and although there are still + indications of vast gaps in our knowledge, due, no doubt, to the + very exceptional conditions required for the preservation of + plant remains, we now possess evidence of a more continuous + development of the various types of vegetation. According to Mr. + Lester F. Ward, between 8000 and 9000 species of fossil plants + have been described or indicated; and, owing to the careful study + of the nervation of leaves, a large number of these are referable + to their proper orders or genera, and therefore give us some + notion—which, though very imperfect, is probably accurate + in its main outlines—of the progressive development of + vegetation on the earth.<a name="FNanchor_191_191" id= + "FNanchor_191_191"></a><a href="#Footnote_191_191" class= + "fnanchor">[191]</a> The following is a summary of the facts as + given by Mr. Ward:—</p> + + <p>The lowest forms of vegetable life—the cellular + plants—have been found in Lower Silurian deposits in the + form of three species of marine algae; and in the whole Silurian + formation fifty species have been recognised. We cannot for a + moment suppose, however, that this indicates the first appearance + of vegetable life upon the earth, for in these same Lower + Silurian beds the more highly organised vascular cryptogams + appear in the form of rhizocarps—plants allied to Marsilea + and Azolla,—and a very little higher, ferns, lycopods, and + even conifers appear. We have indications, however, of a still + more ancient vegetation, in the carbonaceous shales and thick + beds of graphite far down in the Middle Laurentian, since there + is no other known agency than the vegetable cell by means of + which carbon can be extracted from the atmo<a name="Page_399" id= + "Page_399"></a>sphere and fixed in the solid state. These great + beds of graphite, therefore, imply the existence of abundance of + vegetable life at the very commencement of the era of which we + have any geological record.<a name="FNanchor_192_192" id= + "FNanchor_192_192"></a><a href="#Footnote_192_192" class= + "fnanchor">[192]</a></p> + + <p>Ferns, as already stated, begin in the Middle Silurian + formation with the Eopteris Morrieri. In the Devonian, we have 79 + species, in the Carboniferous 627, and in the Permian 186 + species; after which fossil ferns diminish greatly, though they + are found in every formation; and the fact that fully 3000 living + species are known, while the richest portion of the Tertiary in + fossil plants—the Miocene—- has only produced 87 + species, will serve to indicate the extreme imperfection of the + geological record.</p> + + <p>The Equisetaceae(horsetails) which also first appear in the + Silurian and reach their maximum development in the Coal + formation, are, in all succeeding formations, far less numerous + than ferns, and only thirty living species are known. + Lycopodiaceae, though still more abundant in the Coal formation, + are very rarely found in any succeeding deposit, though the + living species are tolerably numerous, about 500 having been + described. As we cannot suppose them to have really diminished + and then increased again in this extraordinary manner, we have + another indication of the exceptional nature of plant + preservation and the extreme and erratic character of the + imperfection of the record.</p> + + <p>Passing now to the next higher division of plants—the + gymnosperms—we find Coniferae appearing in the Upper + Silurian, becoming tolerably abundant in the Devonian, and + reaching a maximum in the Carboniferous, from which formation + more than 300 species are known, equal to the number recorded as + now living. They occur in all succeeding formations, being + abundant in the Oolite, and excessively so in the Miocene, from + which 250 species have been described. The allied family of + gymnosperms, the Cycadaceae, first appear in the Carboniferous + era, but very scantily; are most abundant in the Oolite, from + which formation 116 species are known, and then steadily diminish + to the Tertiary, although there are seventy-five living + species.</p> + + <p>We now come to the true flowering plants, and we first + <a name="Page_400" id="Page_400"></a>meet with monocotyledons in + the Carboniferous and Permian formations. The character of these + fossils was long disputed, but is now believed to be well + established; and the sub-class continues to be present in small + numbers in all succeeding deposits, becoming rather plentiful in + the Upper Cretaceous, and very abundant in the Eocene and + Miocene. In the latter formation 272 species have been + discovered; but the 116 species in the Eocene form a larger + proportion of the total vegetation of the period.</p> + + <p>True dicotyledons appear very much later, in the Cretaceous + period, and only in its upper division, if we except a single + species from the Urgonian beds of Greenland. The remarkable thing + is that we here find the sub-class fully developed and in great + luxuriance of types, all the three divisions—Apetalae, + Polypetalae, and Gamopetalae—being represented, with a + total of no less than 770 species. Among them are such familiar + forms as the poplar, the birch, the beech, the sycamore, and the + oak; as well as the fig, the true laurel, the sassafras, the + persimmon, the maple, the walnut, the magnolia, and even the + apple and the plum tribes. Passing on to the Tertiary period the + numbers increase, till they reach their maximum in the Miocene, + where more than 2000 species of dicotyledons have been + discovered. Among these the proportionate number of the higher + gamopetalae has slightly increased, but is considerably less than + at the present day.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Possible Cause of sudden late Appearance of Exogens.</i></p> + + <p>The sudden appearance of fully developed exogenous flowering + plants in the Cretaceous period is very analogous to the equally + sudden appearance of all the chief types of placental mammalia in + the Eocene; and in both cases we must feel sure that this + suddenness is only apparent, due to unknown conditions which have + prevented their preservation (or their discovery) in earlier + formations. The case of the dicotyledonous plants is in some + respects the most extraordinary, because in the earlier Mesozoic + formations we appear to have a fair representation of the flora + of the period, including such varied forms as ferns, equisetums, + cycads, conifers, and monocotyledons. The only hint at an + explanation of this anomaly has been given by Mr. Ball, who + supposes <a name="Page_401" id="Page_401"></a>that all these + groups inhabited the lowlands, where there was not only excessive + heat and moisture, but also a superabundance of carbonic acid in + the atmosphere—conditions under which these groups had been + developed, but which were prejudicial to the dicotyledons. These + latter are supposed to have originated on the high table-lands + and mountain ranges, in a rarer and drier atmosphere in which the + quantity of carbonic acid gas was much less; and any deposits + formed in lake beds at high altitudes and at such a remote epoch + have been destroyed by denudation, and hence we have no record of + their existence.<a name="FNanchor_193_193" id= + "FNanchor_193_193"></a><a href="#Footnote_193_193" class= + "fnanchor">[193]</a></p> + + <p>During a few weeks spent recently in the Rocky Mountains, I + was struck by the great scarcity of monocotyledons and ferns in + comparison with dicotyledons—a scarcity due apparently to + the dryness and rarity of the atmosphere favouring the higher + groups. If we compare Coulter's <i>Rocky Mountain Botany</i> with + Gray's <i>Botany of the Northern (East) United States</i>, we + have two areas which differ chiefly in the points of altitude and + atmospheric moisture. Unfortunately, in neither of these works + are the species consecutively numbered; but by taking the pages + occupied by the two divisions of dicotyledons on the one hand, + monocotyledons and ferns on the other, we can obtain a good + approximation. In this way we find that in the flora of the + North-Eastern States the monocotyledons and ferns are to the + dicotyledons in the proportion of 45 to 100; in the Rocky + Mountains they are in the proportion of only 34 to 100; while if + we take an exclusively Alpine flora, as given by Mr. Ball, there + are not one-fifth as many monocotyledons as dicotyledons. These + facts show that even at the present day elevated plateaux and + mountains are more favourable to dicotyledons than to + monocotyledons, and we may, therefore, well suppose that the + former originated within such elevated areas, and were for long + ages confined to them. It is interesting to note that their + richest early remains have been found in the central regions of + the North American continent, where they now, proportionally, + most abound, and where the conditions of altitude and a dry + atmosphere were probably present at a very early period.</p> + + <p><a name="Page_402" id="Page_402"></a></p> + + <div class="figcenter" style="width: 500px;"> + <a name="fig34" id="fig34"></a> <img src="images/fig34.jpg" + width="500" height="358" alt= + "FIG. 34.—Diagram illustrating the Geological Distribution of Plants." + title= + "FIG. 34.—Diagram illustrating the Geological Distribution of Plants." /> + <b>FIG. 34.—Diagram illustrating the Geological + Distribution of Plants.</b> + </div> + + <p>The diagram (Fig. 34), slightly modified from one given by Mr. + Ward, will illustrate our present knowledge of the development of + the vegetable kingdom in geological time. <a name="Page_403" id= + "Page_403"></a>The shaded vertical bands exhibit the proportions + of the fossil forms actually discovered, while the outline + extensions are intended to show what we may fairly presume to + have been the approximate periods of origin, and progressive + increase of the number of species, of the chief divisions of the + vegetable kingdom. These seem to accord fairly well with their + respective grades of development, and thus offer no obstacle to + the acceptance of the belief in their progressive evolution.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Geological Distribution of Insects.</i></p> + + <p>The marvellous development of insects into such an endless + variety of forms, their extreme specialisation, and their + adaptation to almost every possible condition of life, would + almost necessarily imply an extreme antiquity. Owing, however, to + their small size, their lightness, and their usually aerial + habits, no class of animals has been so scantily preserved in the + rocks; and it is only recently that the whole of the scattered + material relating to fossil insects and their allies have been + brought together by Mr. Samuel H. Scudder of Boston, and we have + thus learned their bearing on the theory of evolution.<a name= + "FNanchor_194_194" id="FNanchor_194_194"></a><a href= + "#Footnote_194_194" class="fnanchor">[194]</a></p> + + <p>The most striking fact which presents itself on a glance at + the distribution of fossil insects, is the completeness of the + representation of all the chief types far back in the Secondary + period, at which time many of the existing families appear to + have been perfectly differentiated. Thus in the Lias we find + dragonflies "apparently as highly specialised as to-day, no less + than four tribes being present." Of beetles we have undoubted + Curculionidae from the Lias and Trias; Chrysomelidae in the same + deposits; Cerambycidae in the Oolites; Scarabaeidae in the Lias; + Buprestidae in the Trias; Elateridae, Trogositidae, and + Nitidulidae in the Lias; Staphylinidae in the English Purbecks; + while Hydrophilidae, Gyrinidae, and Carabidae occur in the Lias. + All these forms are well represented, but there are many other + families doubtfully identified in equally ancient rocks. Diptera + of the families Empidae, Asilidae, and Tipulidae have been found + as far back as the Lias. Of Lepidoptera, Sphingidae and Tineidae + have been found <a name="Page_404" id="Page_404"></a>in the + Oolite; while ants, representing the highly specialised + Hymenoptera, have occurred in the Purbeck and Lias.</p> + + <p>This remarkable identity of the families of very ancient with + those of existing insects is quite comparable with the apparently + sudden appearance of existing genera of trees in the Cretaceous + epoch. In both cases we feel certain that we must go very much + farther back in order to find the ancestral forms from which they + were developed, and that at any moment some fresh discovery may + revolutionise our ideas as to the antiquity of certain groups. + Such a discovery was made while Mr. Scudder's work was passing + through the press. Up to that date all the existing orders of + true insects appeared to have originated in the Trias, the + alleged moth and beetle of the Coal formation having been + incorrectly determined. But now, undoubted remains of beetles + have been found in the Coal measures of Silesia, thus supporting + the interpretation of the borings in carboniferous trees as + having been made by insects of this order, and carrying back this + highly specialised form of insect life well into Palaeozoic + times. Such a discovery renders all speculation as to the origin + of true insects premature, because we may feel sure that all the + other orders of insects, except perhaps hymenoptera and + lepidoptera, were contemporaneous with the highly specialised + beetles.</p> + + <p>The less highly organised terrestrial arthropoda—the + Arachnida and Myriapoda—are, as might be expected, much + more ancient. A fossil spider has been found in the + Carboniferous, and scorpions in the Upper Silurian rocks of + Scotland, Sweden, and the United States. Myriapoda have been + found abundantly in the Carboniferous and Devonian formations; + but all are of extinct orders, exhibiting a more generalised + structure than living forms.</p> + + <p>Much more extraordinary, however, is the presence in the + Palaeozoic formations of ancestral forms of true insects, termed + by Mr. Scudder Palaeodictyoptera. They consist of generalised + cockroaches and walking-stick insects (Orthopteroidea); ancient + mayflies and allied forms, of which there are six families and + more than thirty genera (Neuropteroidea); three genera of + Hemipteroidea resembling various Homoptera and Hemiptera, mostly + from the Carboniferous formation, a few from the Devonian, and + one ancestral cockroach (Palaeoblattina) <a name="Page_405" id= + "Page_405"></a>from the Middle Silurian sandstone of France. If + this occurrence of a true hexapod insect from the Middle Silurian + be really established, taken in connection with the well-defined + Coleoptera from the Carboniferous, the origin of the entire group + of terrestrial arthropoda is necessarily thrown back into the + Cambrian epoch, if not earlier. And this cannot be considered + improbable in view of the highly differentiated land + plants—ferns, equisetums, and lycopods—in the Middle + or Lower Silurian, and even a conifer (Cordaites Robbii) in the + Upper Silurian; while the beds of graphite in the Laurentian were + probably formed from terrestrial vegetation.</p> + + <p>On the whole, then, we may affirm that, although the + geological record of the insect life of the earth is + exceptionally imperfect, it yet decidedly supports the evolution + hypothesis. The most specialised order, Lepidoptera, is the most + recent, only dating back to the Oolite; the Hymenoptera, Diptera, + and Homoptera go as far as the Lias; while the Orthoptera and + Neuroptera extend to the Trias. The recent discovery of + Coleoptera in the Carboniferous shows, however, that the + preceding limits are not absolute, and will probably soon be + overpassed. Only the more generalised ancestral forms of winged + insects have been traced back to Silurian time, and along with + them the less highly organised scorpions; facts which serve to + show us the extreme imperfection of our knowledge, and indicate + possibilities of a world of terrestrial life in the remotest + Palaeozoic times.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Geological Succession of Vertebrata.</i></p> + + <p>The lowest forms of vertebrates are the fishes, and these + appear first in the geological record in the Upper Silurian + formation. The most ancient known fish is a Pteraspis, one of the + bucklered ganoids or plated fishes—by no means a very low + type—allied to the sturgeon (Accipenser) and alligator-gar + (Lepidosteus), but, as a group, now nearly extinct. Almost + equally ancient are the sharks, which under various forms still + abound in our seas. We cannot suppose these to be nearly the + earliest fishes, especially as the two lowest orders, now + represented by the Amphioxus or lancelet and the lampreys, have + not yet been found fossil. The ganoids were greatly developed in + the Devonian era, and continued till the <a name="Page_406" id= + "Page_406"></a>Cretaceous, when they gave way to the true osseous + fishes, which had first appeared in the Jurassic period, and have + continued to increase till the present day. This much later + appearance of the higher osseous fishes is quite in accordance + with evolution, although some of the very lowest forms, the + lancelet and the lampreys, together with the archaic ceratodus, + have survived to our time.</p> + + <p>The Amphibia, represented by the extinct labyrinthodons, + appear first in the Carboniferous rocks, and these peculiar forms + became extinct early in the Secondary period. The labyrinthodons + were, however, highly specialised, and do not at all indicate the + origin of the class, which may be as ancient as the lower forms + of fishes. Hardly any recognisable remains of our existing + groups—the frogs, toads, and salamanders—are found + before the Tertiary period, a fact which indicates the extreme + imperfection of the record as regards this class of animals.</p> + + <p>True reptiles have not been found till we reach the Permian + where Prohatteria and Proterosaurus occur, the former closely + allied to the lizard-like Sphenodon of New Zealand, the latter + having its nearest allies in the same group of + reptiles—Rhyncocephala, other forms of which occur in the + Trias. In this last-named formation the earliest + crocodiles—Phytosaurus (Belodon) and Stagonolepis occur, as + well as the earliest tortoises—Chelytherium, Proganochelys, + and Psephoderma.<a name="FNanchor_195_195" id= + "FNanchor_195_195"></a><a href="#Footnote_195_195" class= + "fnanchor">[195]</a> Fossil serpents have been first found in the + Cretaceous formation, but the conditions for the preservation of + these forms have evidently been unfavourable, and the record is + correspondingly incomplete. The marine Plesiosauri and + Ichthyosauri, the flying Pterodactyles, the terrestrial Iguanodon + of Europe, and the huge Atlantosaurus of Colorado—the + largest land animal that has ever lived upon the earth<a name= + "FNanchor_196_196" id="FNanchor_196_196"></a><a href= + "#Footnote_196_196" class="fnanchor">[196]</a>—all belong + to special developments of the reptilian type which flourished + during the Secondary epoch, and then became extinct.</p> + + <p><a name="Page_407" id="Page_407"></a>Birds are among the + rarest of fossils, due, no doubt, to their aerial habits removing + them from the ordinary dangers of flood, bog, or ice which + overwhelm mammals and reptiles, and also to their small specific + gravity which keeps them floating on the surface of water till + devoured. Their remains were long confined to Tertiary deposits, + where many living genera and a few extinct forms have been found. + The only birds yet known from the older rocks are the toothed + birds (Odontornithes) of the Cretaceous beds of the United + States, belonging to two distinct families and many genera; a + penguin-like form (Enaliornis) from the Upper Greensand of + Cambridge; and the well-known long-tailed Archaeopteryx from the + Upper Oolite of Bavaria. The record is thus imperfect and + fragmentary in the extreme; but it yet shows us, in the few birds + discovered in the older rocks, more primitive and generalised + types, while the Tertiary birds had already become specialised + like those living, and had lost both the teeth and the long + vertebral tail, which indicate reptilian affinities in the + earlier</p> + + <p>Mammalia have been found, as already stated, as far back as + the Trias formation, in Europe in the United States and in South + Africa, all being very small, and belonging either to the + Marsupial order, or to some still lower and more generalised + type, out of which both Marsupials and Insectivora were + developed. Other allied forms have been found in the Lower and + Upper Oolite both of Europe and the United States. But there is + then a great gap in the whole Cretaceous formation, from which no + mammal has been obtained, although both in the Wealden and the + Upper Chalk in Europe, and in the Upper Cretaceous deposits of + the United States an abundant and well-preserved terrestrial + flora has been discovered. Why no mammals have left their remains + here it is impossible to say. We can only suppose that the + limited areas in which land plants have been so abundantly + preserved, did not present the conditions which are needed for + the fossilisation and preservation of mammalian remains.</p> + + <p>When we come to the Tertiary formation, we find mammals in + abundance; but a wonderful change has taken place. The obscure + early types have disappeared, and we discover in their place a + whole series of forms belonging to existing orders, <a name= + "Page_408" id="Page_408"></a>and even sometimes to existing + families. Thus, in the Eocene we have remains of the opossum + family; bats apparently belonging to living genera; rodents + allied to the South American cavies and to dormice and squirrels; + hoofed animals belonging to the odd-toed and even-toed groups; + and ancestral forms of cats, civets, dogs, with a number of more + generalised forms of carnivora. Besides these there are whales, + lemurs, and many strange ancestral forms of proboscidea.<a name= + "FNanchor_197_197" id="FNanchor_197_197"></a><a href= + "#Footnote_197_197" class="fnanchor">[197]</a></p> + + <p>The great diversity of forms and structures at so remote an + epoch would require for their development an amount of time, + which, judging by the changes that have occurred in other groups, + would carry us back far into the Mesozoic period. In order to + understand why we have no record of these changes in any part of + the world, we must fall back upon some such supposition as we + made in the case of the dicotyledonous plants. Perhaps, indeed, + the two cases are really connected, and the upland regions of the + primeval world, which saw the development of our higher + vegetation, may have also afforded the theatre for the gradual + development of the varied mammalian types which surprise us by + their sudden appearance in Tertiary times.</p> + + <div class="figcenter" style="width: 400px;"> + <img src="images/p408.jpg" width="400" height="209" alt= + "GEOLOGICAL DISTRIBUTION OF MAMMALIA." title= + "GEOLOGICAL DISTRIBUTION OF MAMMALIA." /> <b>GEOLOGICAL + DISTRIBUTION OF MAMMALIA.</b> + </div> + + <p>Notwithstanding these irregularities and gaps in the record, + the accompanying table, summarising our actual knowledge of the + geological distribution of the five classes of vertebrata, + <a name="Page_409" id="Page_409"></a>exhibits a steady + progression from lower to higher types, excepting only the + deficiency in the bird record which is easily explained. The + comparative perfection of type in which each of these classes + first appears, renders it certain that the origin of each and all + of them must be sought much farther back than any records which + have yet been discovered. The researches of palaeontologists and + embryologists indicate a reptilian origin for birds and mammals, + while reptiles and amphibia arose, perhaps independently, from + fishes.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>The brief review we have now taken of the more suggestive + facts presented by the geological succession of organic forms, is + sufficient to show that most, if not all, of the supposed + difficulties which it presents in the way of evolution, are due + either to imperfections in the geological record itself, or to + our still very incomplete knowledge of what is really recorded in + the earth's crust. We learn, however, that just as discovery + progresses, gaps are filled up and difficulties disappear; while, + in the case of many individual groups, we have already obtained + all the evidence of progressive development that can reasonably + be expected. We conclude, therefore, that the geological + difficulty has now disappeared; and that this noble science, when + properly understood, affords clear and weighty evidence of + evolution.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_183_183" id= + "Footnote_183_183"></a><a href= + "#FNanchor_183_183"><span class="label">[183]</span></a> The + reader who desires to understand this subject more fully, + should study chap. x. of the <i>Origin of Species</i>, and + chap. xiv. of Sir Charles Lyell's <i>Principles of + Geology</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_184_184" id= + "Footnote_184_184"></a><a href= + "#FNanchor_184_184"><span class="label">[184]</span></a> On + "Stagonolepis Robertsoni and on the Evolution of the + Crocodilia," in <i>Q.J. of Geological Society</i>, 1875; and + abstract in <i>Nature</i>, vol. xii. p. 38.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_185_185" id= + "Footnote_185_185"></a><a href= + "#FNanchor_185_185"><span class="label">[185]</span></a> From + a paper by Messrs. Scott and Osborne, "On the Origin and + Development of the Rhinoceros Group," read before the British + Association in 1883.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_186_186" id= + "Footnote_186_186"></a><a href= + "#FNanchor_186_186"><span class="label">[186]</span></a> + American Addresses, pp. 73-76.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_187_187" id= + "Footnote_187_187"></a><a href= + "#FNanchor_187_187"><span class="label">[187]</span></a> + Lecture on the Introduction and Succession of Vertebrate Life + in America, <i>Nature</i>, vol. xvi. p. 471.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_188_188" id= + "Footnote_188_188"></a><a href= + "#FNanchor_188_188"><span class="label">[188]</span></a> + <i>Nature</i>, vol. xxv. p. 84.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_189_189" id= + "Footnote_189_189"></a><a href= + "#FNanchor_189_189"><span class="label">[189]</span></a> See + <i>The Mammalia in their Relation to Primeval Times</i>, p. + 102.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_190_190" id= + "Footnote_190_190"></a><a href= + "#FNanchor_190_190"><span class="label">[190]</span></a> For + a brief enumeration and description of these fossils, see the + author's <i>Geographical Distribution of Animals</i>, vol. i. + p. 146.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_191_191" id= + "Footnote_191_191"></a><a href= + "#FNanchor_191_191"><span class="label">[191]</span></a> + Sketch of Palaeobotany in Fifth Annual Report of U.S. + Geological Survey, 1883-84, pp. 363-452, with diagrams. Sir + J. William Dawson, speaking of the value of leaves for the + determination of fossil plants, says: "In my own experience I + have often found determinations of the leaves of trees + confirmed by the discovery of their fruits or of the + structure of their stems. Thus, in the rich cretaceous + plant-beds of the Dunvegan series, we have beech-nuts + associated in the same bed with leaves referred to + <i>Fagus</i>. In the Laramie beds I determined many years ago + nuts of the <i>Trapa</i> or water-chestnut, and subsequently + Lesquereux found in beds in the United States leaves which he + referred to the same genus. Later, I found in collections + made on the Red Deer River of Canada my fruits and + Lesquereux's leaves on the same slab. The presence of trees + of the genera <i>Carya</i> and <i>Juglans</i> in the same + formation was inferred from their leaves, and specimens have + since been obtained of silicified wood with the microscopic + structure of the modern butternut. Still we are willing to + admit that determinations from leaves alone are liable to + doubt."—<i>The Geological History of Plants</i>, p. + 196.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_192_192" id= + "Footnote_192_192"></a><a href= + "#FNanchor_192_192"><span class="label">[192]</span></a> Sir + J. William Dawson's <i>Geological History of Plants</i>, p. + 18.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_193_193" id= + "Footnote_193_193"></a><a href= + "#FNanchor_193_193"><span class="label">[193]</span></a> "On + the Origin of the Flora of the European Alps," <i>Proc. of + Roy. Geog. Society</i>, vol. i. (1879), pp. 564-588.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_194_194" id= + "Footnote_194_194"></a><a href= + "#FNanchor_194_194"><span class="label">[194]</span></a> + Systematic Review of our Present Knowledge of Fossil Insects, + including Myriapods and Arachnids (<i>Bull. of U.S. Geol. + Survey</i>, No. 31, Washington, 1886).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_195_195" id= + "Footnote_195_195"></a><a href= + "#FNanchor_195_195"><span class="label">[195]</span></a> For + the facts as to the early appearance of the above named + groups of reptiles I am indebted to Mr. E. Lydekker of the + Geological Department of the Natural History Museum.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_196_196" id= + "Footnote_196_196"></a><a href= + "#FNanchor_196_196"><span class="label">[196]</span></a> + According to Professor Marsh this creature was 50 or 60 feet + long, and when erect, at least 30 feet in height. It fed upon + the foliage of the mountain forests of the Cretaceous epoch, + the remains of which are preserved with it.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_197_197" id= + "Footnote_197_197"></a><a href= + "#FNanchor_197_197"><span class="label">[197]</span></a> For + fuller details, see the author's <i>Geographical Distribution + of Animals</i>, and Heilprin's <i>Geographical and Geological + Distribution of Animals</i>.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a><a name="Page_410" + id="Page_410"></a>CHAPTER XIV</h2> + + <p style='font-weight:bold;'>FUNDAMENTAL PROBLEMS IN RELATION TO + VARIATION AND HEREDITY</p> + + <div class="blockquot"> + <p>Fundamental difficulties and objections—Mr. Herbert + Spencer's factors of organic evolution—Disuse and effects + of withdrawal of natural selection—Supposed effects of + disuse among wild animals—Difficulty as to co-adaptation + of parts by variation and selection—Direct action of the + environment—The American school of + evolutionists—Origin of the feet of the + ungulates—Supposed action of animal + intelligence—Semper on the direct influence of the + environment—Professor Geddes's theory of variation in + plants—Objections to the theory—On the origin of + spines—Variation and selection overpower the effects of + use and disuse—Supposed action of the environment in + imitating variations—Weismann's theory of + heredity—The cause of variation—The non-heredity of + acquired characters—The theory of + instinct—Concluding remarks.</p> + </div> + + <p>Having now set forth and illustrated at some length the most + important of the applications of the development hypothesis in + the explanation of the broader and more generally interesting + phenomena presented by the organic world, we propose to discuss + some of the more fundamental problems and difficulties which have + recently been adduced by eminent naturalists. It is the more + necessary to do this, because there is now a tendency to minimise + the action of natural selection in the production of organic + forms, and to set up in its place certain fundamental principles + of variation or laws of growth, which it is urged are the real + originators of the several lines of development, and of most of + the variety of form and structure in the vegetable and animal + kingdoms. These views have, moreover, been seized upon by popular + writers to throw doubt and discredit on the whole theory of + <a name="Page_411" id="Page_411"></a>evolution, and especially on + Darwin's presentation of that theory, to the bewilderment of the + general public, who are quite unable to decide how far the new + views, even if well established, tend to subvert the Darwinian + theory, or whether they are really more than subsidiary parts of + it, and quite powerless without it to produce any effect + whatever.</p> + + <p>The writers whose special views we now propose to consider + are: (1) Mr. Herbert Spencer, on modification of structures + arising from modification of functions, as set forth in his + <i>Factors of Organic Evolution</i>. (2) Dr. E.D. Cope, who + advocates similar views in detail, in his work entitled <i>The + Origin of the Fittest</i>, and may be considered the head of a + school of American naturalists who minimise the agency of natural + selection. (3) Dr. Karl Semper, who has especially studied the + direct influence of the environment in the whole animal kingdom, + and has set forth his views in a volume on <i>The Natural + Conditions of Existence as they Affect Animal Life</i>. (4) Mr. + Patrick Geddes, who urges that fundamental laws of growth, and + the antagonism of vegetative and reproductive forces, account for + much that has been imputed to natural selection.</p> + + <p>We will now endeavour to ascertain what are the more important + facts and arguments adduced by each of the above writers, and how + far they offer a substitute for the action of natural selection; + having done which, a brief account will be given of the views of + Dr. Aug. Weismann, whose theory of heredity will, if established, + strike at the very root of the arguments of the first three of + the writers above referred to.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Mr. Herbert Spencer's Factors of Organic Evolution.</i></p> + + <p>Mr. Spencer, while fully recognising the importance and wide + range of the principle of natural selection, thinks that + sufficient weight has not been given to the effects of use and + disuse as a factor in evolution, or to the direct action of the + environment in determining or modifying organic structures. As + examples of the former class of actions, he adduces the decreased + size of the jaws in the civilised races of mankind, the + inheritance of nervous disease produced by overwork, the great + and inherited development of the udders in cows and goats, and + the shortened legs, jaws, and snout in <a name="Page_412" id= + "Page_412"></a>improved races of pigs—the two latter + examples being quoted from Mr. Darwin,—and other cases of + like nature. As examples of the latter, Mr. Darwin is again + quoted as admitting that there are many cases in which the action + of similar conditions appears to have produced corresponding + changes in different species; and we have a very elaborate + discussion of the direct action of the medium in modifying the + protoplasm of simple organisms, so as to bring about the + difference between the outer surface and the inner part that + characterises the cells or other units of which they are + formed.</p> + + <p>Now, although this essay did little more than bring together + facts which had been already adduced by Mr. Darwin or by Mr. + Spencer himself, and lay stress upon their importance, its + publication in a popular review was immediately seized upon as + "an avowed and definite declaration against some of the leading + ideas on which the Mechanical Philosophy depends," and as being + "fatal to the adequacy of the Mechanical Philosophy as any + explanation of organic evolution,"<a name="FNanchor_198_198" id= + "FNanchor_198_198"></a><a href="#Footnote_198_198" class= + "fnanchor">[198]</a>—an expression of opinion which would + be repudiated by every Darwinian. For, even admitting the + interpretation which Mr. Spencer puts on the facts he adduces, + they are all included in the causes which Darwin himself + recognised as having acted in bringing about the infinitude of + forms in the organic world. In the concluding chapter of the + <i>Origin of Species</i> he says: "I have now recapitulated the + facts and considerations which have thoroughly convinced me that + species have been modified during a long course of descent. This + has been effected chiefly through the natural selection of + numerous successive, slight, favourable variations; aided in an + important manner by the inherited effects of the use and disuse + of parts; and in an unimportant manner—that is, in relation + to adaptive structures whether past or present, by the direct + action of external conditions, and by variations which seem to + us, in our ignorance, to arise spontaneously." This passage, + summarising Darwin's whole inquiry, and explaining his final + point of view, shows how very inaccurate may be the popular + notion, as expressed by the Duke of Argyll, of any supposed + additions to the causes of change of species as recognised by + Darwin.</p> + + <p><a name="Page_413" id="Page_413"></a>But, as we shall see + presently, there is now much reason to believe that the supposed + inheritance of acquired modifications—that is, of the + effects of use and disuse, or of the direct influence of the + environment—is not a fact; and if so, the very foundation + is taken away from the whole class of objections on which so much + stress is now laid. It therefore becomes important to inquire + whether the facts adduced by Darwin, Spencer, and others, do + really necessitate such inheritance, or whether any other + interpretation of them is possible. I believe there is such an + interpretation; and we will first consider the cases of disuse on + which Mr. Spencer lays most stress.</p> + + <p>The cases Mr. Spencer adduces as demonstrating the effects of + disuse in diminishing the size and strength of organs are, the + diminished size of the jaws in the races of civilised men, and + the diminution of the muscles used in closing the jaws in the + case of pet-dogs fed for generations on soft food. He argues that + the minute reduction in any one generation could not possibly + have been useful, and, therefore, not the subject of natural + selection; and against the theory of correlation of the + diminished jaw with increased brain in man, he urges that there + are cases of large brain development, accompanied by jaws above + the average size. Against the theory of economy of nutrition in + the case of the pet-dogs, he places the abundant food of these + animals which would render such economy needless.</p> + + <p>But neither he nor Mr. Darwin has considered the effects of + the withdrawal of the action of natural selection in keeping up + the parts in question to their full dimensions, which, of itself, + seems to me quite adequate to produce the results observed. + Recurring to the evidence, adduced in Chapter III, of the + constant variation occurring in all parts of the organism, while + selection is constantly acting on these variations in eliminating + all that fall below the best working standard, and preserving + only those that are fully up to it; and, remembering further, + that, of the whole number of the increase produced annually, only + a small percentage of the best adapted can be preserved, we shall + see that every useful organ will be kept up nearly to its higher + limit of size and efficiency. Now Mr. Galton has proved + experimentally that, when any part has <a name="Page_414" id= + "Page_414"></a>thus been increased (or diminished) by selection, + there is in the offspring a strong tendency to revert to a mean + or average size, which tends to check further increase. And this + mean appears to be, not the mean of the actual existing + individuals but a lower mean, or that from which they had been + recently raised by selection.<a name="FNanchor_199_199" id= + "FNanchor_199_199"></a><a href="#Footnote_199_199" class= + "fnanchor">[199]</a> He calls this the law of "Regression towards + Mediocrity," and it has been proved by experiments with + vegetables and by observations on mankind. This regression, in + every generation, takes place even when both parents have been + selected for their high development of the organ in question; but + when there is no such selection, and crosses are allowed among + individuals of every grade of development, the deterioration will + be very rapid; and after a time not only will the average size of + the part be greatly reduced, but the instances of full + development will become very rare. Thus what Weismann terms + "panmixia," or free intercrossing, will co-operate with Galton's + law of "regression towards mediocrity," and the result will be + that, whenever selection ceases to act on any part or organ which + has heretofore been kept up to a maximum of size and efficiency, + the organ in question will rapidly decrease till it reaches a + mean value considerably below the mean of the progeny that has + usually been produced each year, and very greatly below the mean + of that portion which has survived annually; and this will take + place by the general law of heredity, and quite irrespective of + any <i>use</i> or <i>disuse</i> of the part in question. Now, no + observations have been adduced by Mr. Spencer or others, showing + that the average amount of change supposed to be due to + <i>disuse</i> is greater than that due to the law of regression + towards mediocrity; while even if it were somewhat greater, we + can see many possible contributory causes to its production. In + the case of civilised man's diminished jaw, there may well be + some correlation between the jaw and the brain, seeing that + increased mental activity would lead to the withdrawal of blood + and of nervous energy from adjacent parts, and might thus lead to + diminished growth of those parts in the individual. And in the + case of pet-dogs, the selection of small or short-headed + individuals would imply the unconscious selection of those with + less massive temporal muscles, and thus lead to the concomitant + <a name="Page_415" id="Page_415"></a>reduction of those muscles. + The amount of reduction observed by Darwin in the wing-bones of + domestic ducks and poultry, and in the hind legs of tame rabbits, + is very small, and is certainly no greater than the above causes + will well account for; while so many of the external characters + of all our domestic animals have been subject to long-continued + artificial selection, and we are so ignorant of the possible + correlations of different parts, that the phenomena presented by + them seem sufficiently explained without recurrence to the + assumption that any changes in the individual, due to disuse, are + inherited by the offspring.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Supposed Effects of Disuse among Wild Animals.</i></p> + + <p>It may be urged, however, that among wild animals we have many + undoubted results of disuse much more pronounced than those among + domestic kinds, results which cannot be explained by the causes + already adduced. Such are the reduced size of the wings of many + birds on oceanic islands; the abortion of the eyes in many cave + animals, and in some which live underground; and the loss of the + hind limbs in whales and in some lizards. These cases differ + greatly in the amount of the reduction of parts which has taken + place, and may be due to different causes. It is remarkable that + in some of the birds of oceanic islands the reduction is little + if at all greater than in domestic birds, as in the water-hen of + Tristan d'Acunha. Now if the reduction of wing were due to the + hereditary effects of disuse, we should expect a very much + greater effect in a bird inhabiting an oceanic island than in a + domestic bird, where the disuse has been in action for an + indefinitely shorter period. In the case of many other birds, + however—as some of the New Zealand rails and the extinct + dodo of Mauritius—the wings have been reduced to a much + more rudimentary condition, though it is still obvious that they + were once organs of flight; and in these cases we certainly + require some other causes than those which have reduced the wings + of our domestic fowls. One such cause may have been of the same + nature as that which has been so efficient in reducing the wings + of the insects of oceanic islands—the destruction of those + which, during the occasional use of their wings, were carried out + to sea. This form of natural selection may well have acted in the + case of <a name="Page_416" id="Page_416"></a>birds whose powers + of flight were already somewhat reduced, and to whom, there being + no enemies to escape from, their use was only a source of danger. + We may thus, perhaps, account for the fact that many of these + birds retain small but useless wings with which they never fly; + for, the wings having been reduced to this functionless + condition, no power could reduce them further except correlation + of growth or economy of nutrition, causes which only rarely come + into play.</p> + + <p>The complete loss of eyes in some cave animals may, perhaps, + be explained in a somewhat similar way. Whenever, owing to the + total darkness, they became useless, they might also become + injurious, on account of their delicacy of organisation and + liability to accidents and disease; in which case natural + selection would begin to act to reduce, and finally abort them; + and this explains why, in some cases, the rudimentary eye + remains, although completely covered by a protective outer skin. + Whales, like moas and cassowaries, carry us back to a remote + past, of whose conditions we know too little for safe + speculation. We are quite ignorant of the ancestral forms of + either of these groups, and are therefore without the materials + needful for determining the steps by which the change took place, + or the causes which brought it about.<a name="FNanchor_200_200" + id="FNanchor_200_200"></a><a href="#Footnote_200_200" class= + "fnanchor">[200]</a></p> + + <p>On a review of the various examples that have been given by + Mr. Darwin and others of organs that have been reduced or + aborted, there seems too much diversity in the results for all to + be due to so direct and uniform a cause as the individual effects + of disuse accumulated by heredity. For if that were the only or + chief efficient cause, and a cause capable of producing a decided + effect during the comparatively short period <a name="Page_417" + id="Page_417"></a>of the existence of animals in a state of + domestication, we should expect to find that, in wild species, + all unused parts or organs had been reduced to the smallest + rudiments, or had wholly disappeared. Instead of this we find + various grades of reduction, indicating the probable result of + several distinct causes, sometimes acting separately, sometimes + in combination, such as those we have already pointed out.</p> + + <p>And if we find no positive evidence of <i>disuse</i>, acting + by its direct effect on the individual, being transmitted to the + offspring, still less can we find such evidence in the case of + the <i>use</i> of organs. For here the very fact of <i>use</i>, + in a wild state, implies <i>utility</i>, and utility is the + constant subject for the action of natural selection; while among + domestic animals those parts which are exceptionally used are so + used in the service of man, and have thus become the subjects of + artificial selection. Thus "the great and inherited development + of the udders in cows and goats," quoted by Spencer from Darwin, + really affords no proof of inheritance of the increase due to + use, because, from the earliest period of the domestication of + these animals, abundant milk-production has been highly esteemed, + and has thus been the subject of selection; while there are no + cases among wild animals that may not be better explained by + variation and natural selection.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Difficulty as to Co-adaptation of Parts by Variation and + Selection.</i></p> + + <p>Mr. Spencer again brings forward this difficulty, as he did in + his <i>Principles of Biology</i> twenty-five years ago, and urges + that all the adjustments of bones, muscles, blood-vessels, and + nerves which would be required during, for example, the + development of the neck and fore-limbs of the giraffe, could + <a name="Page_418" id="Page_418"></a>not have been effected by + "simultaneous fortunate spontaneous variations." But this + difficulty is fully disposed of by the facts of simultaneous + variation adduced in our third chapter, and has also been + specially considered in Chapter VI, p. 127. The best answer to + this objection may, perhaps, be found in the fact that the very + thing said to be impossible by variation and natural selection + has been again and again effected by variation and artificial + selection. During the process of formation of such breeds as the + greyhound or the bulldog, of the race-horse and carthorse, of the + fantail pigeon or the otter-sheep, many co-ordinate adjustments + have been produced; and no difficulty has occurred, whether the + change has been effected by a single variation—as in the + last case named—or by slow steps, as in all the others. It + seems to be forgotten that most animals have such a surplus of + vitality and strength for all the ordinary occasions of life that + any slight superiority in one part can be at once utilised; while + the moment any want of balance occurs, variations in the + insufficiently developed parts will be selected to bring back the + harmony of the whole organisation. The fact that, in all domestic + animals, variations do occur, rendering them swifter or stronger, + larger or smaller, stouter or slenderer, and that such variations + can be separately selected and accumulated for man's purposes, is + sufficient to render it certain that similar or even greater + changes may be effected by natural selection, which, as Darwin + well remarks, "acts on every internal organ, on every shade of + constitututional difference, on the whole machinery of life." The + difficulty as to co-adaptation of parts by variation and natural + selection appears to me, therefore, to be a wholly imaginary + difficulty which has no place whatever in the operations of + nature.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Direct Action of the Environment.</i></p> + + <p>Mr. Spencer's last objection to the wide scope given by + Darwinians to the agency of natural selection is, that organisms + are acted upon by the environment, which produces in them + definite changes, and that these changes in the individual are + transmitted by inheritance, and thus become increased in + successive generations. That such changes are produced in the + individual there is ample evidence, but that they are in<a name= + "Page_419" id="Page_419"></a>herited independently of any form of + selection or of reversion is exceedingly doubtful, and Darwin + nowhere expresses himself as satisfied with the evidence. The two + very strongest cases he mentions are the twenty-nine species of + American trees which all differed in a corresponding way from + their nearest European allies; and the American maize which + became changed after three generations in Europe. But in the case + of the trees the differences alleged may be partly due to + correlation with constitutional peculiarities dependent on + climate, especially as regards the deeper tint of the fading + leaves and the smaller size of the buds and seeds in America than + in Europe; while the less deeply toothed or serrated leaves in + the American species are, in our present complete ignorance of + the causes and uses of serration, quite as likely to be due to + some form of adaptation as to any direct action of the climate. + Again, we are not told how many of the allied species do not vary + in this particular manner, and this is certainly an important + factor in any conclusion we may form on the question.</p> + + <p>In the case of the maize it appears that one of the more + remarkable and highly selected American varieties was cultivated + in Germany, and in three years nearly all resemblance to the + original parent was lost; and in the sixth year it closely + resembled a common European variety, but was of somewhat more + vigorous growth. In this case no selection appears to have been + practised, and the effects may have been due to that "reversion + to mediocrity" which invariably occurs, and is more especially + marked in the case of varieties which have been rapidly produced + by artificial selection. It may be considered as a partial + reversion to the wild or unimproved stock; and the same thing + would probably have occurred, though perhaps less rapidly, in + America itself. As this is stated by Darwin to be the most + remarkable case known to him "of the direct and prompt action of + climate on a plant," we must conclude that such direct effects + have not been proved to be accumulated by inheritance, + independently of reversion or selection.</p> + + <p>The remaining part of Mr. Spencer's essay is devoted to a + consideration of the hypothetical action of the environment on + the lower organisms which consist of simple cells or formless + masses of protoplasm; and he shows with great <a name="Page_420" + id="Page_420"></a>elaboration that the outer and inner parts of + these are necessarily subject to different conditions; and that + the outer actions of air or water lead to the formation of + integuments, and sometimes to other definite modifications of the + surface, whence arise permanent differences of structure. + Although in these cases also it is very difficult to determine + how much is due to direct modification by external agencies + transmitted and accumulated by inheritance, and how much to + spontaneous variations accumulated by natural selection, the + probabilities in favour of the former mode of action are here + greater, because there is no differentiation of nutritive and + reproductive cells in these simple organisms; and it can be + readily seen that any change produced in the latter will almost + certainly affect the next generation.<a name="FNanchor_201_201" + id="FNanchor_201_201"></a><a href="#Footnote_201_201" class= + "fnanchor">[201]</a> We are thus carried back almost to the + origin of life, and can only vaguely speculate on what took place + under conditions of which we know so little.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The American School of Evolutionists.</i></p> + + <p>The tentative views of Mr. Spencer which we have just + discussed, are carried much further, and attempts have been made + to work them out in great detail, by many American naturalists, + whose best representative is Dr. E.D. Cope of + Philadelphia.<a name="FNanchor_202_202" id= + "FNanchor_202_202"></a><a href="#Footnote_202_202" class= + "fnanchor">[202]</a> This school endeavours to explain all the + chief modifications of form in the animal kingdom by fundamental + laws of growth and the inherited effects of use and effort, + returning, in fact, to the teachings of Lamarck as being at least + equally important with those of Darwin.</p> + + <p>The following extract will serve to show the high position + claimed by this school as original discoverers, and as having + made important additions to the theory of evolution:</p> + + <p>"Wallace and Darwin have propounded as the cause of + modification in descent their law of natural selection. This law + has been epitomised by Spencer as the 'survival of the fittest.' + This neat expression no doubt covers the case, but it leaves the + origin of the fittest entirely untouched. Darwin assumes a + 'tendency to variation' in nature, and it is plainly <a name= + "Page_421" id="Page_421"></a>necessary to do this, in order that + materials for the exercise of a selection should exist. Darwin + and Wallace's law is then only restrictive, directive, + conservative, or destructive of something already created. I + propose, then, to seek for the originative laws by which these + subjects are furnished; in other words, for the causes of the + origin of the fittest."<a name="FNanchor_203_203" id= + "FNanchor_203_203"></a><a href="#Footnote_203_203" class= + "fnanchor">[203]</a></p> + + <p>Mr. Cope lays great stress on the existence of a special + developmental force termed "bathmism" or growth-force, which acts + by means of retardation and acceleration "without any reference + to fitness at all;" that "instead of being controlled by fitness + it is the controller of fitness." He argues that "all the + characteristics of generalised groups from genera up (excepting, + perhaps, families) have been evolved under the law of + acceleration and retardation," combined with some intervention of + natural selection; and that specific characters, or species, have + been evolved by natural selection with some assistance from the + higher law. He, therefore, makes species and genera two + absolutely distinct things, the latter not developed out of the + former; generic characters and specific characters are, in his + opinion, fundamentally different, and have had different origins, + and whole groups of species have been simultaneously modified, so + as to belong to another genus; whence he thinks it "highly + probable that the same specific form has existed through a + succession of genera, and perhaps in different epochs of geologic + time."</p> + + <p>Useful characters, he concludes, have been produced by the + special location of growth-force by use; useless ones have been + produced by location of growth-force without the influence of + use. Another element which determines the direction of + growth-force, and which precedes use, is effort; and "it is + thought that effort becomes incorporated into the metaphysical + acquisitions of the parent, and is inherited with other + metaphysical qualities by the young, which, during the period of + growth, is much more susceptible to modifying influences, and is + likely to exhibit structural change in consequence."<a name= + "FNanchor_204_204" id="FNanchor_204_204"></a><a href= + "#Footnote_204_204" class="fnanchor">[204]</a></p> + + <p>From these few examples of their teachings, it is clear that + <a name="Page_422" id="Page_422"></a>these American evolutionists + have departed very widely from the views of Mr. Darwin, and in + place of the well-established causes and admitted laws to which + he appeals have introduced theoretical conceptions which have not + yet been tested by experiments or facts, as well as metaphysical + conceptions which are incapable of proof. And when they come to + illustrate these views by an appeal to palaeontology or + morphology, we find that a far simpler and more complete + explanation of the facts is afforded by the established + principles of variation and natural selection. The confidence + with which these new ideas are enunciated, and the repeated + assertion that without them Darwinism is powerless to explain the + origin of organic forms, renders it necessary to bestow a little + more time on the explanations they give us of well-known + phenomena with which, they assert, other theories are incompetent + to grapple.</p> + + <p>As examples of use producing structural change, Mr. Cope + adduces the hooked and toothed beaks of the falcons and the + butcher-birds, and he argues that the fact of these birds + belonging to widely different groups proves that similarity of + use has produced a similar structural result. But no attempt is + made to show any direct causal connection between the use of a + bill to cut or tear flesh and the development of a tooth on the + mandible. Such use might conceivably strengthen the bill or + increase its size, but not cause a special tooth-like outgrowth + which was not present in the ancestral thrush-like forms of the + butcher-bird. On the other hand, it is clear that any variations + of the bill tending towards a hook or tooth would give the + possessor some advantage in seizing and tearing its prey, and + would thus be preserved and increased by natural selection. + Again, Mr. Cope urges the effects of a supposed "law of polar or + centrifugal growth" to counteract a tendency to unsymmetrical + growth, where one side of the body is used more than the other. + But the undoubted hurtfulness of want of symmetry in many + important actions or functions would rapidly eliminate any such + tendency. When, however, it has <a name="Page_423" id= + "Page_423"></a>become useful, as in the case of the single + enlarged claw of many Crustacea, it has been preserved by natural + selection.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Origin of the Feet of the Ungulates.</i></p> + + <p>Perhaps the most original and suggestive of Mr. Cope's + applications of the theory of use and effort in modifying + structure are, his chapters "On the Origin of the Foot-Structure + of the Ungulates;" and that "On the Effect of Impacts and Strains + on the Feet of Mammalia;" and they will serve also to show the + comparative merits of this theory and that of natural selection + in explaining a difficult case of modification, especially as it + is an explanation claimed as new and original when first + enunciated in 1881. Let us, then, see how he deals with the + problem.</p> + + <p>The remarkable progressive change of a four or five-toed + ancestor into the one-toed horse, and the equally remarkable + division of the whole group of ungulate animals into the odd-toed + and even-toed divisions, Mr. Cope attempts to explain by the + effects of impact and use among animals which frequented hard or + swampy ground respectively. On hard ground, it is urged, the long + middle toe would be most used and subjected to the greatest + strains, and would therefore acquire both strength and + development. It would then be still more exclusively used, and + the extra nourishment required by it would be drawn from the + adjacent less-used toes, which would accordingly diminish in + size, till, after a long series of changes, the records of which + are so well preserved in the American tertiary rocks, the true + one-toed horse was developed. In soft or swampy ground, on the + other hand, the tendency would be to spread out the foot so that + there were two toes on each side. The two middle toes would thus + be most used and most subject to strains, and would, therefore, + increase at the expense of the lateral toes. There would be, no + doubt, an advantage in these two functional toes being of equal + size, so as to prevent twisting of the foot while walking; and + variations tending to bring this about would be advantageous, and + would therefore be preserved. Thus, by a parallel series of + changes in another direction, adapted to a distinct set of + conditions, we should arrive at the symmetrical divided hoofs of + our deer and cattle. The fact <a name="Page_424" id= + "Page_424"></a>that sheep and goats are specially mountain and + rock-loving animals may be explained by their being a later + modification, since the divided hoof once formed is evidently + well adapted to secure a firm footing on rugged and precipitous + ground, although it could hardly have been first developed in + such localities. Mr. Cope thus concludes: "Certain it is that the + length of the bones in the feet of the ungulate orders has a + direct relation to the dryness of the ground they inhabit, and + the possibility of speed which their habit permits them or + necessarily imposes on them."<a name="FNanchor_205_205" id= + "FNanchor_205_205"></a><a href="#Footnote_205_205" class= + "fnanchor">[205]</a></p> + + <p>If there is any truth in the explanation here briefly + summarised, it must entirely depend on the fact of individual + modifications thus produced being hereditary, and we yet await + the proof of this. In the meantime it is clear that the very same + results could have been brought about by variation and natural + selection. For the toes, like all other organs, vary in size and + proportions, and in their degree of union or separation; and if + in one group of animals it was beneficial to have the middle toe + larger and longer, and in another set to have the two middle toes + of the same size, nothing can be more certain than that these + particular modifications would be continuously preserved, and the + very results we see ultimately produced.</p> + + <p>The oft-repeated objections that the cause of variations is + unknown, that there must be something to determine variations in + the right direction; that "natural selection includes no actively + progressive principle, but must wait for the development of + variation, and then, after securing the survival of the best, + wait again for the best to project its own variations for + selection," we have already sufficiently answered by showing that + variation—in abundant or typical species—is always + present in ample amount; that it exists in all parts and organs; + that these vary, for the most part, independently, so that any + required combination of variations can be secured; and finally, + that all variation is necessarily either in excess or defect of + the mean condition, and that, consequently, the right or + favourable variations are so frequently present that the unerring + power of natural selection never wants materials to work + upon.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_425" id="Page_425"></a><i>Supposed Action of Animal + Intelligence.</i></p> + + <p>The following passage briefly summarises Mr. Cope's position: + "Intelligence is a conservative principle, and will always direct + effort and use into lines which will be beneficial to its + possessor. Here we have the source of the fittest, <i>i.e.</i> + addition of parts by increase and location of growth-force, + directed by the influence of various kinds of compulsion in the + lower, and intelligent option among higher animals. Thus + intelligent choice, taking advantage of the successive evolution + of physical conditions, may be regarded as the <i>originator of + the fittest</i>, while natural selection is the tribunal to which + all results of accelerated growth are submitted. This preserves + or destroys them, and determines the new points of departure on + which accelerated growth shall build."<a name="FNanchor_206_206" + id="FNanchor_206_206"></a><a href="#Footnote_206_206" class= + "fnanchor">[206]</a></p> + + <p>This notion of "intelligence"—the intelligence of the + animal itself—determining its own variation, is so + evidently a very partial theory, inapplicable to the whole + vegetable kingdom, and almost so to all the lower forms of + animals, amongst which, nevertheless, there is the very same + adaptation and co-ordination of parts and functions as among the + highest, that it is strange to see it put forward with such + confidence as necessary for the completion of Darwin's theory. If + "the various kinds of compulsion"—by which are apparently + meant the laws of variation, growth, and reproduction, the + struggle for existence, and the actions necessary to preserve + life under the conditions of the animal's environment—are + sufficient to have developed the varied forms of the lower + animals and of plants, we can see no reason why the same + "compulsion" should not have carried on the development of the + higher animals also. The action of this "intelligent option" is + altogether unproved; while the acknowledgment that natural + selection is the tribunal which either preserves or destroys the + variations submitted to it, seems quite inconsistent with the + statement that intelligent choice is the "orginator of the + fittest," since whatever is really "the fittest" can never be + destroyed by natural selection, which is but another name for the + survival of the fittest. If "the fittest" is always definitely + <a name="Page_426" id="Page_426"></a>produced by some other + power, then natural selection is not wanted. If, on the other + hand, both fit and unfit are produced, and natural selection + decides between them, that is pure Darwinism, and Mr. Cope's + theories have added nothing to it.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig35" id="fig35"></a> <img src="images/fig35.jpg" + width="400" height="494" alt= + "FIG. 35.—Transformation of Artemia salina to A. Milhausenii; 1, tail-lobe of A. salina, and its transition through 2,3,4,5, to 6, into that of A. Milhausenii; 7, post-abdomen of A. salina; 8, post-abdomen of a form bred in brackish water; 9, gill of A. Milhausenii; 10, gill of A. salina. (From Schmankewitsch.)" + title= + "FIG. 35.—Transformation of Artemia salina to A. Milhausenii; 1, tail-lobe of A. salina, and its transition through 2,3,4,5, to 6, into that of A. Milhausenii; 7, post-abdomen of A. salina; 8, post-abdomen of a form bred in brackish water; 9, gill of A. Milhausenii; 10, gill of A. salina. (From Schmankewitsch.)" /> + <b>FIG. 35.—Transformation of Artemia salina to A. + Milhausenii; 1, tail-lobe of A. salina, and its transition + through 2,3,4,5, to 6, into that of A. Milhausenii; 7, + post-abdomen of A. salina; 8, post-abdomen of a form bred in + brackish water; 9, gill of A. Milhausenii; 10, gill of A. + salina. (From Schmankewitsch.)</b> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Semper on the Direct Influence of the Environment.</i></p> + + <p>Another eminent naturalist, Professor Karl Semper of + Würzburg, also adopts the view of the direct transforming + power of the environment, and has brought together an <a name= + "Page_427" id="Page_427"></a>immense body of interesting facts + showing the influence of food, of light, of temperature, of still + water and moving water, of the atmosphere and its currents, of + gravitation, and of other organisms, in modifying the forms and + other characteristics of animals.<a name="FNanchor_207_207" id= + "FNanchor_207_207"></a><a href="#Footnote_207_207" class= + "fnanchor">[207]</a> He believes that these various influences + produce a direct and important effect, and that this effect is + accumulated by inheritance; yet he acknowledges that we have no + direct evidence of this, and there is hardly a single case + adduced in the book which is not equally well explained by + adaptation, brought about by the survival of beneficial + variations. Perhaps the most remarkable case he has brought + forward is that of the transformation of species of crustaceans + by a change in the saltness of the water (see Fig. 35). Artemia + salina lives in brackish water, while A. Milhausenii inhabits + water which is much salter. They differ greatly in the form of + the tail-lobes, and in the presence or absence of spines upon the + tail, and had always been considered perfectly distinct species. + Yet either was transformed into the other in a few generations, + during which the saltness of the water was gradually altered. Yet + more, A. salina was gradually accustomed to fresher water, and in + the course of a few generations, when the water had become + perfectly fresh, the species was changed into Branchipus + stagnalis, which had always been considered to belong to a + different genus on account of differences in the form of the + antennae and of the posterior segments of the body (see Fig. 36). + This certainly appears to be a proof of change of conditions + producing a change of form independently of selection, and of + that change of form, while remaining under the same conditions, + being inherited. Yet there is this peculiarity in the case, that + there is a chemical change in the water, and that this water + permeates the whole body, and must be absorbed by the tissues, + and thus affect the ova and even the reproductive <a name= + "Page_428" id="Page_428"></a>elements, and in this way may + profoundly modify the whole organisation. Why and how the + external effects are limited to special details of the structure + we do not know; but it does not seem as if any far-reaching + conclusions as to the cumulative effect of external conditions on + the higher terrestrial animals and plants, can be drawn from such + an exceptional phenomenon. It seems rather analogous to those + effects of external influences on the very lowest organisms in + which the vegetative and reproductive organs are hardly + differentiated, in which case such effects are doubtless + inherited.<a name="FNanchor_208_208" id= + "FNanchor_208_208"></a><a href="#Footnote_208_208" class= + "fnanchor">[208]</a></p> + + <div class="figcenter" style="width: 414px;"> + <a name="fig36" id="fig36"></a> <img src="images/fig36.jpg" + width="414" height="586" alt= + "FIG. 36. a. Branchipus stagnalis. b. Artemia salina." title= + "FIG. 36. a. Branchipus stagnalis. b. Artemia salina." /> + <b>FIG. 36. a. Branchipus stagnalis. b. Artemia salina.</b> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Professor Geddes's Theory of Variation in Plants.</i></p> + + <p>In a paper read before the Edinburgh Botanical Society in 1886 + Mr. Patrick Geddes laid down the outlines of a fundamental theory + of plant variation, which he has further extended in the article + "Variation and Selection" in the <i>Encydopaedia Britannica</i>, + and in a paper read before the Linnaean Society but not yet + published.</p> + + <p>A theory of variation should deal alike with the origin of + specific distinctions and with those vaster differences which + characterise the larger groups, and he thinks it should answer + such questions as—How an axis comes to be arrested to form + a flower? how the various forms of inflorescence were evolved? + how did perigynous or epigynous flowers arise from hypogynous + flowers? and many others equally fundamental. Natural selection + acting upon numerous accidental variations will not, he urges, + account for such general facts as these, which must depend on + some constant law of variation. This law he believes to be the + well-known antagonism of vegetative and reproductive growth + acting throughout the whole course of plant development; and he + uses it to explain many of the most characteristic features of + the structure of flowers and fruits.</p> + + <p><a name="Page_429" id="Page_429"></a>Commencing with the + origin of the flower, which all botanists agree in regarding as a + shortened branch, he explains this shortening as an inevitable + physiological fact, since the cost of the development of the + reproductive elements is so great as necessarily to check + vegetative growth. In the same manner the shortening of the + inflorescence from raceme to spike or umbel, and thence to the + capitulum or dense flower-head of the composite plants is brought + about. This shortening, carried still further, produces the + flattened leaf-like receptacle of Dorstenia, and further still + the deeply hollowed fruity receptacle of the fig.</p> + + <p>The flower itself undergoes a parallel modification due to a + similar cause. It is formed by a series of modified leaves + arranged round a shortened axis. In its earlier stages the number + of these modified leaves is indefinite, as in many Ranunculaceae; + and the axis itself is not greatly shortened, as in Myosurus. The + first advance is to a definite number of parts and a permanently + shortened axis, in the arrangement termed hypogynous, in which + all the whorls are quite distinct from each other. In the next + stage there is a further shortening of the central axis, leaving + the outer portion as a ring on which the petals are inserted, + producing the arrangement termed perigynous. A still further + advance is made by the contraction of the axis, so as to leave + the central part forming the ovary quite below the flower, which + is then termed epigynous.</p> + + <p>These several modifications are said to be parallel and + definite, and to be determined by the continuous checking of + vegetation by reproduction along what is an absolute groove of + progressive change. This being the case, the importance of + natural selection is greatly diminished. Instead of selecting and + accumulating spontaneous indefinite variations, its function is + to retard them after the stage of maximum utility has been + independently reached. The same simple conception is said to + unlock innumerable problems of vegetable morphology, large and + small alike. It explains the inevitable development of gymnosperm + into angiosperm by the checked vegetative growth of the + ovule-bearing leaf or carpel; while such minor adaptations as the + splitting fruit of the geranium or the cupped stigma of the + pansy, can be no longer looked upon as achievements <a name= + "Page_430" id="Page_430"></a>of natural selection, but must be + regarded as naturally traceable to the vegetative checking of + their respective types of leaf organ. Again, a detailed + examination of spiny plants practically excludes the hypothesis + of mammalian selection altogether, and shows spines to arise as + an expression of the diminishing vegetativeness—in fact, + the ebbing vitality of a species.<a name="FNanchor_209_209" id= + "FNanchor_209_209"></a><a href="#Footnote_209_209" class= + "fnanchor">[209]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Objections to the Theory.</i></p> + + <p>The theory here sketched out is enticing, and at first sight + seems calculated to throw much light on the history of plant + development; but on further consideration, it seems wanting in + definiteness, while it is beset with difficulties at every step. + Take first the shortening of the raceme into the umbel and the + capitulum, said to be caused by arrest of vegetative growth, due + to the antagonism of reproduction. If this were the whole + explanation of the phenomenon, we should expect the quantity of + seed to increase as this vegetative growth diminished, since the + seed is the product of the reproductive energy of the plant, and + its quantity the best measure of that energy. But is this the + case? The ranunculus has comparatively few seeds, and the flowers + are not numerous; while in the same order the larkspur and the + columbine have far more seeds as well as more flowers, but there + is no shortening of the raceme or diminution of the foliage, + although the flowers are large and complex. So, the extremely + shortened and compressed flower-heads of the compositae produce + comparatively few seeds—one only to each flower; while the + foxglove, with its long spike of showy flowers, produces an + enormous number.</p> + + <p>Again, if the shortening of the central axis in the successive + stages of hypogynous, perigynous, and epigynous flowers were an + indication of preponderant reproduction and diminished + vegetation, we should find everywhere some clear indications of + this fact. The plants with hypogynous flowers should, as a rule, + have less seed and more vigorous and abundant foliage than those + at the other extreme with epigynous flowers. But the <a name= + "Page_431" id="Page_431"></a>hypogynous poppies, pinks, and St. + John's worts have abundance of seed and rather scanty foliage; + while the epigynous dogwoods and honeysuckles have few seeds and + abundant foliage. If, instead of the number of the seeds, we take + the size of the fruit as an indication of reproductive energy, we + find this at a maximum in the gourd family, yet their rapid and + luxuriant growth shows no diminution of vegetative power. So that + the statement that plant modifications proceed "along an absolute + groove of progressive change" is contradicted by innumerable + facts indicating advance and regression, improvement or + degradation, according as the ever-changing environment renders + one form more advantageous than the other. As one instance I may + mention the Anonaceae or custard-apple tribe, which are certainly + an advance from the Ranunculaceae; yet in the genus Polyalthea + the fruit consists of a number of separate carpels, each borne on + a long stalk, as if reverting to the primitive stalked carpellary + leaves.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>On the Origin of Spines.</i></p> + + <p>But perhaps the most extraordinary application of the theory + is that which considers spines to be an indication of the "ebbing + vitality of a species," and which excludes "mammalian selection + altogether." If this were true, spines should occur mainly in + feeble, rare, and dying-out species, instead of which we have the + hawthorn, one of our most vigorous shrubs or trees, with abundant + vitality and an extensive range over the whole Palaearctic + region, showing that it is really a dominant species. In North + America the numerous thorny species of Crataegus are equally + vigorous, as are the false acacia (Robinia) and the honey-locust + (Gleditschia). Neither have the numerous species of very spiny + Acacias been noticed to be rarer or less vigorous than the + unarmed kinds.</p> + + <p>On the other point—that spines are not due to mammalian + selection—we are able to adduce what must be considered + direct and conclusive evidence. For if spines, admittedly + produced by aborted branches, petioles, or peduncles, are due + solely or mainly to diminished vegetativeness or ebbing vitality, + they ought to occur in all countries alike, or at all events in + all whose similar conditions tend to check vegetation; whereas, + if they are, solely or mainly, developed as a protection against + the attacks <a name="Page_432" id="Page_432"></a>of herbivorous + mammals, they ought to be most abundant where these are + plentiful, and rare or absent where indigenous mammalia are + wanting. Oceanic islands, as compared with continents, would thus + furnish a crucial test of the two theories; and Mr. Hemsley of + Kew, who has specially studied insular floras, has given me some + valuable information on this point. He says: "There are no spiny + or prickly plants in the indigenous element of the St. Helena + flora. The relatively rich flora of the Sandwich Isles is not + absolutely without a prickly plant, but almost so. All the + endemic genera are unarmed, and the endemic species of almost + every other genus. Even such genera as Zanthoxylon, Acacia, + Xylosoma, Lycium, and Solanum, of which there are many armed + species in other countries, are only represented by unarmed + species. The two endemic Rubi have the prickles reduced to the + setaceous condition, and the two palms are unarmed.</p> + + <p>"The flora of the Galapagos includes a number of prickly + plants, among them several cacti (these have not been + investigated and may be American species), but I do not think one + of the known endemic species of any family is prickly or + spiny.</p> + + <p>"Spiny and prickly plants are also rare in New Zealand, but + there are the formidably armed species of wild Spaniard + (Aciphylla), one species of Rubus, the pungent-leaved Epacrideae + and a few others."</p> + + <p>Mr. J.G. Baker of Kew, who has specially studied the flora of + Mauritius and the adjacent islands, also writes me on this point. + He says: "Taking Mauritius alone, I do not call to mind a single + species that is a spinose endemic tree or shrub. If you take the + whole group of islands (Mauritius, Bourbon, Seychelles, and + Rodriguez), there will be about a dozen species, but then nine of + these are palms. Leaving out palms, the trees and shrubs of that + part of the world are exceptionally non-spinose."</p> + + <p>These are certainly remarkable facts, and quite inexplicable + on the theory of spines being caused solely by checked vegetative + growth, due to weakness of constitution or to an arid soil and + climate. For the Galapagos and many parts of the Sandwich Islands + are very arid, as is a considerable part of the North Island of + New Zealand. Yet in our own moist climate <a name="Page_433" id= + "Page_433"></a>and with our very limited number of trees and + shrubs we have about eighteen spiny or prickly species, more, + apparently, than in the whole endemic floras of the Mauritius, + Sandwich Islands, and Galapagos, though these are all especially + rich in shrubby and arboreal species. In New Zealand the prickly + Rubus is a leafless trailing plant, and its prickles are probably + a protection against the large snails of the country, several of + which have shells from two to three and a half inches + long.<a name="FNanchor_210_210" id= + "FNanchor_210_210"></a><a href="#Footnote_210_210" class= + "fnanchor">[210]</a> The "wild Spaniards" are very spiny + herbaceous Umbelliferae, and may have gained their spines to + preserve them from being trodden down or eaten by the Moas, + which, for countless ages, took the place of mammals in New + Zealand. The exact use or meaning of the spines in palms is more + doubtful, though they are, no doubt, protective against some + animals; but it is certainly an extraordinary fact that in the + entire flora of the Mauritius, so largely consisting of trees and + shrubs, not a single endemic species should be thorny or + spiny.</p> + + <p>If now we consider that every continental flora produces a + considerable proportion of spiny and thorny species, and that + these rise to a maximum in South Africa, where herbivorous + mammalia were (before the settlement of the country), perhaps, + more abundant and varied than in any other part of the world; + while another district, remarkable for well-armed vegetation, is + Chile, where the camel-like vicugnas, llamas, and alpacas, and an + abundance of large rodents wage perpetual war against shrubby + vegetation, we shall see the full significance of the almost + total absence of thorny and spiny plants in the chief oceanic + islands; and so far from "excluding the hypothesis of mammalian + selection altogether," we shall find in this hypothesis the only + satisfactory explanation of the facts.</p> + + <p>From the brief consideration of Professor Geddes's theory now + given, we conclude that, although the antagonism between + vegetative and reproductive growth is a real agency, and must be + taken account of in our endeavour to explain many of the + fundamental facts in the structure and form of plants, yet it is + so overpowered and directed at every step by the natural + selection of favourable variations, that the results of its + <a name="Page_434" id="Page_434"></a>exclusive and unmodified + action are nowhere to be found in nature. It may be allowed to + rank as one of those "laws of growth," of which so many have now + been indicated, and which were always recognised by Darwin as + underlying all variation; but unless we bear in mind that its + action must always be subordinated to natural selection, and that + it is continually checked, or diverted, or even reversed by the + necessity of adaptation to the environment, we shall be liable to + fall into such glaring errors as the imputing to "ebbing + vitality" alone such a widespread phenomenon as the occurrence of + spines and thorns, while ignoring altogether the influence of the + organic environment in their production.<a name= + "FNanchor_211_211" id="FNanchor_211_211"></a><a href= + "#Footnote_211_211" class="fnanchor">[211]</a></p> + + <p>The sketch now given of the chief attempts that have been made + to prove that either the direct action of the environment or + certain fundamental laws of variation are independent causes of + modification of species, shows us that their authors have, in + every case, failed to establish their contention. Any direct + action of the environment, or any characters acquired by use or + disuse, can have no effect whatever upon the race unless they are + inherited; and that they are inherited in any case, <a name= + "Page_435" id="Page_435"></a>except when they directly affect the + reproductive cells, has not been proved. On the other hand, as we + shall presently show, there is much reason for believing that + such acquired characters are in their nature non-heritable.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Variation and Selection Overpower the Effects of Use and + Disuse.</i></p> + + <p>But there is another objection to this theory arising from the + very nature of the effects produced. In each generation the + effects of use or disuse, or of effort, will certainly be very + small, while of this small effect it is not maintained that the + whole will be always inherited by the next generation. How small + the effect is we have no means of determining, except in the case + of disuse, which Mr. Darwin investigated carefully. He found that + in twelve fancy breeds of pigeons, which are often kept in + aviaries, or if free fly but little, the sternum had been reduced + by about one-seventh or one-eighth of its entire length, and that + of the scapula about one-ninth. In domestic ducks the weight of + the wing-bones in proportion to that of the whole skeleton had + decreased about one-tenth. In domestic rabbits the bones of the + legs were found to have increased in weight in due proportion to + the increased weight of the body, but those of the hind legs were + rather less in proportion to those of the fore legs than in the + wild animal, a difference which may be imputed to their being + less used in rapid motion. The pigeons, therefore, afford the + greatest amount of reduction by disuse—one-seventh of the + length of the sternum. But the pigeon has certainly been + domesticated four or five thousand years; and if the reduction of + the wings by disuse has only been going on for the last thousand + years, the amount of reduction in each generation would be + absolutely imperceptible, and quite within the limits of the + reduction due to the absence of selection, as already explained. + But, as we have seen in Chapter III, the fortuitous variation of + every part or organ usually amounts to one-tenth, and often to + one-sixth of the average dimensions—that is, the fortuitous + variation in one generation among a limited number of the + individuals of a species is as great as the cumulative effects of + disuse in a thousand generations! If we assume that the effects + of use or of effort in the individual are equal to the effects of + disuse, or even ten or a hundred times greater, they <a name= + "Page_436" id="Page_436"></a>will even then not equal, in each + generation, the amount of the fortuitous variations of the same + part. If it be urged that the effects of use would modify all the + individuals of a species, while the fortuitous variations to the + amount named only apply to a portion of them, it may be replied, + that that portion is sufficiently large to afford ample materials + for selection, since it often equals the numbers that can + annually survive; while the recurrence in each successive + generation of a like amount of variation would render possible + such a rapid adjustment to new conditions that the effects of use + or disuse would be as nothing in comparison. It follows, that + even admitting the modifying effects of the environment, and that + such modifications are inherited, they would yet be entirely + swamped by the greater effects of fortuitous variation, and the + far more rapid cumulative results of the selection of such + variations.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Supposed Action of the Environment in Initiating + Variations.</i></p> + + <p>It is, however, urged that the reaction of the environment + initiates variations, which without it would never arise; such, + for instance, as the origin of horns through the pressures and + irritations caused by butting, or otherwise using the head as a + weapon or for defence. Admitting, for the sake of argument, that + this is so, all the evidence we possess shows that, from the very + first appearance of the rudiment of such an organ, it would vary + to a greater extent than the amount of growth directly produced + by use; and these variations would be subject to selection, and + would thus modify the organ in ways which use alone would never + bring about. We have seen that this has been the case with the + branching antlers of the stag, which have been modified by + selection, so as to become useful in other ways than as a mere + weapon; and the same has almost certainly been the case with the + variously curved and twisted horns of antelopes. In like manner, + every conceivable rudiment would, from its first appearance, be + subject to the law of variation and selection, to which, + thenceforth, the direct effect of the environment would be + altogether subordinate.</p> + + <p>A very similar mode of reasoning will apply to the other + branch of the subject—the initiation of structures and + organs <a name="Page_437" id="Page_437"></a>by the action of the + fundamental laws of growth. Admitting that such laws have + determined some of the main divisions of the animal and vegetable + kingdom, have originated certain important organs, and have been + the fundamental cause of certain lines of development, yet at + every step of the process these laws must have acted in entire + subordination to the law of natural selection. No modification + thus initiated could have advanced a single step, unless it were, + on the whole, a useful modification; while its entire future + course would be necessarily subject to the laws of variation and + selection, by which it would be sometimes checked, sometimes + hastened on, sometimes diverted to one purpose, sometimes to + another, according as the needs of the organism, under the + special conditions of its existence, required such modification. + We need not deny that such laws and influences may have acted in + the manner suggested, but what we do deny is that they could + possibly escape from the ever-present and all-powerful modifying + effects of variation and natural selection.<a name= + "FNanchor_212_212" id="FNanchor_212_212"></a><a href= + "#Footnote_212_212" class="fnanchor">[212]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Weismann's Theory of Heredity.</i></p> + + <p>Professor August Weismann has put forth a new theory of + heredity founded upon the "continuity of the germ-plasm," one of + the logical consequences of which is, that acquired characters of + whatever kind are not transmitted from parent to offspring. As + this is a matter of vital importance to the theory of natural + selection, and as, if well founded, it strikes away the + foundations of most of the theories discussed in the present + chapter, a brief outline of Weismann's views must be attempted, + <a name="Page_438" id="Page_438"></a>although it is very + difficult to make them intelligible to persons unfamiliar with + the main facts of modern embryology.<a name="FNanchor_213_213" + id="FNanchor_213_213"></a><a href="#Footnote_213_213" class= + "fnanchor">[213]</a></p> + + <p>The problem is thus stated by Weismann: "How is it that in the + case of all higher animals and plants a single cell is able to + separate itself from amongst the millions of most various kinds + of which an organism is composed, and by division and complicated + differentiation to reconstruct a new individual with marvellous + likeness, unchanged in many cases even throughout whole + geological periods?" Darwin attempted to solve the problem by his + theory of "Pangenesis," which supposed that every individual cell + in the body gave off gemmules or germs capable of reproducing + themselves, and that portions of these germs of each of the + almost infinite number of cells permeate the whole body and + become collected in the generative cells, and are thus able to + reproduce the whole organism. This theory is felt to be so + ponderously complex and difficult that it has met with no general + acceptance among physiologists.</p> + + <p>The fact that the germ-cells <i>do</i> reproduce with + wonderful accuracy not only the general characters of the + species, but many of the individual characteristics of the + parents or more remote ancestors, and that this process is + continued from generation to generation, can be accounted for, + Weismann thinks, only on two suppositions which are + physiologically possible. Either the substance of the parent + germ-cell, after passing through a cycle of changes required for + the construction of a new individual, possesses the capability of + producing anew germ-cells identical with those from which that + individual was developed, or <i>the new germ-cells arise, as far + as their essential and characteristic substance is concerned, not + at all out of the body of the individual, but direct from the + parent germ-cell</i>. This latter view Weismann holds to be the + correct one, and, on this theory, heredity depends on the fact + that a substance of special molecular composition passes over + from one generation to another. This is the "germ-plasm," the + power of which to develop itself into a perfect organism depends + on the extraordinary complication of its minutest structure. At + every new birth a portion <a name="Page_439" id="Page_439"></a>of + the specific germ-plasm, which the parent egg-cell contains, is + not used up in producing the offspring, but is reserved unchanged + to produce the germ-cells of the following generation. Thus the + germ-cells—so far as regards their essential part the + germ-plasm—are not a product of the body itself, but are + related to one another in the same way as are a series of + generations of unicellular organisms derived from one another by + a continuous course of simple division. Thus the question of + heredity is reduced to one of growth. A minute portion of the + very same germ-plasm from which, first the germ-cell, and then + the whole organism of the parent, were developed, becomes the + starting-point of the growth of the child.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Cause of Variation.</i></p> + + <p>But if this were all, the offspring would reproduce the parent + exactly, in every detail of form and structure; and here we see + the importance of sex, for each new germ grows out of the united + germ-plasms of two parents, whence arises a mingling of their + characters in the offspring. This occurs in each generation; + hence every individual is a complex result reproducing in + ever-varying degrees the diverse characteristics of his two + parents, four grandparents, eight great-grandparents, and other + more remote ancestors; and that ever-present individual variation + arises which furnishes the material for natural selection to act + upon. Diversity of sex becomes, therefore, of primary importance + as <i>the cause of variation</i>. Where asexual generation + prevails, the characteristics of the individual alone are + reproduced, and there are thus no means of effecting the change + of form or structure required by changed conditions of existence. + Under such changed conditions a complex organism, if only + asexually propagated, would become extinct. But when a complex + organism is sexually propagated, there is an ever-present cause + of change which, though slight in any one generation, is + cumulative, and under the influence of selection is sufficient to + keep up the harmony between the organism and its slowly changing + environment.<a name="FNanchor_214_214" id= + "FNanchor_214_214"></a><a href="#Footnote_214_214" class= + "fnanchor">[214]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_440" id="Page_440"></a><i>The Non-Heredity of + Acquired Characters.</i></p> + + <p>Certain observations on the embryology of the lower animals + are held to afford direct proof of this theory of heredity, but + they are too technical to be made clear to ordinary readers. A + logical result of the theory is the impossibility of the + transmission of acquired characters, since the molecular + structure of the germ-plasm is already determined within the + embryo; and Weismann holds that there are no facts which really + prove that acquired characters can be inherited, although their + inheritance has, by most writers, been considered so probable as + hardly to stand in need of direct proof.</p> + + <p>We have already shown, in the earlier part of this chapter, + that many instances of change, imputed to the inheritance of + acquired variations, are really cases of selection; while the + very fact that <i>use</i> implies <i>usefulness</i> renders it + almost impossible to eliminate the action of selection in a state + of nature. As regards mutilations, it is generally admitted that + they are not hereditary, and there is ample evidence on this + point. When it was the fashion to dock horses' tails, it was not + found that horses were born with short tails; nor are Chinese + women born with distorted feet; nor are any of the numerous forms + of racial mutilation in man, which have in some cases been + carried on for hundreds of generations, inherited. Nevertheless, + a few cases of apparent inheritance of mutilations have been + recorded,<a name="FNanchor_215_215" id= + "FNanchor_215_215"></a><a href="#Footnote_215_215" class= + "fnanchor">[215]</a> and these, if trustworthy, are difficulties + in the way of the theory. The undoubted inheritance of disease is + hardly a difficulty, because the predisposition to disease is a + congenital, not an acquired character, and as such would be the + subject of inheritance. The often-quoted case of a disease + induced by mutilation being inherited (Brown-Sequard's epileptic + guinea-pigs) has been discussed by Professor Weismann, and shown + to be not conclusive. The mutilation itself—a section of + certain nerves—was never inherited, but <a name="Page_441" + id="Page_441"></a>the resulting epilepsy, or a general state of + weakness, deformity, or sores, was sometimes inherited. It is, + however, possible that the mere injury introduced and encouraged + the growth of certain microbes, which, spreading through the + organism, sometimes reached the germ-cells, and thus transmitted + a diseased condition to the offspring. Such a transference of + microbes is believed to occur in syphilis and tuberculosis, and + has been ascertained to occur in the case of the muscardine + silkworm disease.<a name="FNanchor_216_216" id= + "FNanchor_216_216"></a><a href="#Footnote_216_216" class= + "fnanchor">[216]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Theory of Instinct.</i></p> + + <p>The theory now briefly outlined cannot be said to be proved, + but it commends itself to many physiologists as being inherently + probable, and as furnishing a good working hypothesis till + displaced by a better. We cannot, therefore, accept any arguments + against the agency of natural selection which are based upon the + opposite and equally unproved theory that acquired characters are + inherited; and as this applies to the whole school of what may be + termed Neo-Lamarckians, their speculations cease to have any + weight.</p> + + <p>The same remark applies to the popular theory of instincts as + being inherited habits; though Darwin gave very little weight to + this, but derived almost all instincts from spontaneous useful + variations which, like other spontaneous variations, are of + course inherited. At first sight it appears as if the acquired + habits of our trained dogs—pointers, retrievers, + etc.—are certainly inherited; but this need not be the + case, because there must be some structural or psychical + peculiarities, such as modifications in the attachments of + muscles, increased delicacy of smell or sight, or peculiar likes + and dislikes, which are inherited; and from these, peculiar + habits follow as a natural consequence, or are easily acquired. + Now, as selection has been constantly at work in improving all + our domestic animals, we have unconsciously modified the + structure, while preserving only those animals which best served + our purpose in their peculiar faculties, instincts, or + habits.</p> + + <p><a name="Page_442" id="Page_442"></a>Much of the mystery of + instinct arises from the persistent refusal to recognise the + agency of imitation, memory, observation, and reason as often + forming part of it. Yet there is ample evidence that such agency + must be taken into account. Both Wilson and Leroy state that + young birds build inferior nests to old ones, and the latter + author observes that the best nests are made by birds whose young + remain longest in the nest. So, migration is now well ascertained + to be effected by means of vision, long flights being made on + bright moonlight nights when the birds fly very high, while on + cloudy nights they fly low, and then often lose their way. + Thousands annually fly out to sea and perish, showing that the + instinct to migrate is imperfect, and is not a good substitute + for reason and observation.</p> + + <p>Again, much of the perfection of instinct is due to the + extreme severity of the selection during its development, any + failure involving destruction. The chick which cannot break the + eggshell, the caterpillar that fails to suspend itself properly + or to spin a safe cocoon, the bees that lose their way or that + fail to store honey, inevitably perish. So the birds that fail to + feed and protect their young, or the butterflies that lay their + eggs on the wrong food-plant, leave no offspring, and the race + with imperfect instincts perishes. Now, during the long and very + slow course of development of each organism, this rigid selection + at every step of progress has led to the preservation of every + detail of structure, faculty, or habit that has been necessary + for the preservation of the race, and has thus gradually built up + the various instincts which seem so marvellous to us, but which + can yet be shown to be in many cases still imperfect. Here, as + everywhere else in nature, we find comparative, not absolute + perfection, with every gradation from what is clearly due to + imitation or reason up to what seems to us perfect + instinct—that in which a complex action is performed + without any previous experience or instruction.<a name= + "FNanchor_217_217" id="FNanchor_217_217"></a><a href= + "#Footnote_217_217" class="fnanchor">[217]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_443" id="Page_443"></a><i>Concluding + Remarks.</i></p> + + <p>Having now passed in review the more important of the recent + objections to, or criticisms of, the theory of natural selection, + we have arrived at the conclusion that in no one case have the + writers in question been able materially to diminish its + importance, or to show that any of the laws or forces to which + they appeal can act otherwise than in strict subordination to it. + The direct action of the environment as set forth by Mr. Herbert + Spencer, Dr. Cope, and Dr. Karl Semper, even if we admit that its + effects on the individual are transmitted by inheritance, are so + small in comparison with the amount of spontaneous variation of + every part of the organism that they must be quite overshadowed + by the latter. And if such direct action may, in some cases, have + initiated certain organs or outgrowths, these must from their + very first beginnings have been subject to variation and natural + selection, and their further development have been almost wholly + due to these ever-present and powerful causes. <a name="Page_444" + id="Page_444"></a>The same remark applies to the views of + Professor Geddes on the laws of growth which have determined + certain essential features in the morphology of plants and + animals. The attempt to substitute these laws for those of + variation and natural selection has failed in cases where we can + apply a definite test, as in that of the origin of spines on + trees and shrubs; while the extreme diversity of vegetable + structure and form among the plants of the same country and of + the same natural order, of itself affords a proof of the + preponderating influence of variation and natural selection in + keeping the many diverse forms in harmony with the highly complex + and ever-changing environment.</p> + + <p>Lastly, we have seen that Professor Weismann's theory of the + continuity of the germ-plasm and the consequent non-heredity of + acquired characters, while in perfect harmony with all the + well-ascertained facts of heredity and development, adds greatly + to the importance of natural selection as the one invariable and + ever-present factor in all organic change, and that which can + alone have produced the temporary fixity combined with the + secular modification of species. While admitting, as Darwin + always admitted, the co-operation of the fundamental laws of + growth and variation, of correlation and heredity, in determining + the direction of lines of variation or in the initiation of + peculiar organs, we find that variation and natural selection are + ever-present agencies, which take possession, as it were, of + every minute change originated by these fundamental causes, check + or favour their further development, or modify them in countless + varied ways according to the varying needs of the organism. + Whatever other causes have been at work, Natural Selection is + supreme, to an extent which even Darwin himself hesitated to + claim for it. The more we study it the more we are convinced of + its overpowering importance, and the more confidently we claim, + in Darwin's own words, that it "has been the most important, but + not the exclusive, means of modification."</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_198_198" id= + "Footnote_198_198"></a><a href= + "#FNanchor_198_198"><span class="label">[198]</span></a> See + the Duke of Argyll's letter in <i>Nature</i>, vol. xxxiv. p. + 336.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_199_199" id= + "Footnote_199_199"></a><a href= + "#FNanchor_199_199"><span class="label">[199]</span></a> + <i>Journal of the Anthropological Institute,</i> vol. xv. pp. + 246-260.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_200_200" id= + "Footnote_200_200"></a><a href= + "#FNanchor_200_200"><span class="label">[200]</span></a> The + idea of the non-heredity of acquired variations was suggested + by the summary of Professor Weismann's views, in + <i>Nature</i>, referred to later on. But since this chapter + was written I have, through the kindness of Mr. E.B. Poulton, + seen some of the proofs of the forthcoming translation of + Weismann's Essays on Heredity, in which he sets forth an + explanation very similar to that here given. On the difficult + question of the almost entire disappearance of organs, as in + the limbs of snakes and of some lizards, he adduces "a + certain form of correlation, which Roux calls 'the struggle + of the parts in the organism,'" as playing an important part. + Atrophy following disuse is nearly always attended by the + corresponding increase of other organs: blind animals possess + more developed organs of touch, hearing, and smell; the loss + of power in the wings is accompanied by increased strength of + the legs, etc. Now as these latter characters, being useful, + will be selected, it is easy to understand that a congenital + increase of these will be accompanied by a corresponding + congenital diminution of the unused organ; and in cases where + the means of nutrition are deficient, every diminution of + these useless parts will be a gain to the whole organism, and + thus their complete disappearance will, in some cases, be + brought about directly by natural selection. This corresponds + with what we know of these rudimentary organs.</p> + + <p>It must, however, be pointed out that the non-heredity of + acquired characters was maintained by Mr. Francis Galton more + than twelve years ago, on theoretical considerations almost + identical with those urged by Professor Weismann; while the + insufficiency of the evidence for their hereditary + transmission was shown, by similar arguments to those used + above and in the work of Professor Weismann already referred + to (see "A Theory of Heredity," in <i>Journ. Anthrop. + Instit.</i>, vol. v. pp. 343-345).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_201_201" id= + "Footnote_201_201"></a><a href= + "#FNanchor_201_201"><span class="label">[201]</span></a> This + explanation is derived from Weismann's Theory of the + Continuity of the Germ-Plasm as summarised in + <i>Nature</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_202_202" id= + "Footnote_202_202"></a><a href= + "#FNanchor_202_202"><span class="label">[202]</span></a> See + a collection of his essays under the title, <i>The Origin of + the Fittest: Essays on Evolution</i>, D. Appleton and Co. New + York. 1887.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_203_203" id= + "Footnote_203_203"></a><a href= + "#FNanchor_203_203"><span class="label">[203]</span></a> + <i>Origin of the Fittest</i>, p. 174.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_204_204" id= + "Footnote_204_204"></a><a href= + "#FNanchor_204_204"><span class="label">[204]</span></a> + <i>Ibid.</i> p. 29. It may be here noted that Darwin found + these theories unintelligible. In a letter to Professor E.T. + Morse in 1877, he writes: "There is one point which I regret + you did not make clear in your Address, namely, what is the + meaning and importance of Professors Cope and Hyatt's views + on acceleration and retardation? I have endeavoured, and + given up in despair, the attempt to grasp their meaning" + (<i>Life and Letters</i>, vol. iii. p. 233).</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_205_205" id= + "Footnote_205_205"></a><a href= + "#FNanchor_205_205"><span class="label">[205]</span></a> + <i>Origin of the Fittest</i>, p. 374.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_206_206" id= + "Footnote_206_206"></a><a href= + "#FNanchor_206_206"><span class="label">[206]</span></a> + <i>Origin of the Fittest</i>, p. 40.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_207_207" id= + "Footnote_207_207"></a><a href= + "#FNanchor_207_207"><span class="label">[207]</span></a> + <i>The Natural Conditions of Existence as they Affect Animal + Life.</i> London, 1883.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_208_208" id= + "Footnote_208_208"></a><a href= + "#FNanchor_208_208"><span class="label">[208]</span></a> In + Dr. Weismann's essay on "Heredity," already referred to, he + considers it not improbable that changes in organisms + produced by climatic influences may be inherited, because, as + these changes do not affect the external parts of an organism + only, but often, as in the case of warmth or moisture + permeate the whole structure, they may possibly modify the + germ-plasm itself, and thus induce variations in the next + generation. In this way, he thinks, may possibly be explained + the climatic varieties of certain butterflies, and some other + changes which seem to be effected by change of climate in a + few generations.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_209_209" id= + "Footnote_209_209"></a><a href= + "#FNanchor_209_209"><span class="label">[209]</span></a> This + brief indication of Professor Geddes's views is taken from + the article "Variation and Selection" in the <i>Encyclopedia + Britannica</i>, and a paper "On the Nature and Causes of + Variation in Plants" in <i>Trans. and Proc. of the Edinburgh + Botanical Society</i>, 1886; and is, for the most part, + expressed in his own words.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_210_210" id= + "Footnote_210_210"></a><a href= + "#FNanchor_210_210"><span class="label">[210]</span></a> + Placostylis bovinus, 3½ inches long; Paryphanta + Busbyi, 3 in. diam.; P. Hochstetteri, 2¾ in. diam.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_211_211" id= + "Footnote_211_211"></a><a href= + "#FNanchor_211_211"><span class="label">[211]</span></a> The + general arguments and objections here set forth will apply + with equal force to Professor G. Henslow's theory of the + origin of the various forms and structures of flowers as due + to "the responsive actions of the protoplasm in consequence + of the irritations set up by the weights, pressures, thrusts, + tensions, etc., of the insect visitors" (<i>The Origin of + Floral Structures through Insect and other Agencies</i>, p. + 340). On the assumption that acquired characters are + inherited, such irritations may have had something to do with + the initiation of variations and with the production of + certain details of structure, but they are clearly + incompetent to have brought about the more important + structural and functional modifications of flowers. Such are, + the various adjustments of length and position of the stamens + to bring the pollen to the insect and from the insect to the + stigma; the various motions of stamens and styles at the + right time and the right direction; the physiological + adjustments bringing about fertility or sterility in + heterostyled plants; the traps, springs, and complex + movements of various parts of orchids; and innumerable other + remarkable phenomena.</p> + + <p>For the explanation of these we have no resource but + variation and selection, to the effects of which, acting + alternately with regression or degradation as above explained + (p. 328) must be imputed the development of the countless + floral structures we now behold. Even the primitive flowers, + whose initiation may, perhaps, have been caused, or rendered + possible, by the irritation set up by insects' visits, must, + from their very origin, have been modified, in accordance + with the supreme law of utility, by means of variation and + survival of the fittest.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_212_212" id= + "Footnote_212_212"></a><a href= + "#FNanchor_212_212"><span class="label">[212]</span></a> In + an essay on "The Duration of Life," forming part of the + translation of Dr. Weismann's papers already referred to, the + author still further extends the sphere of natural selection + by showing that the average duration of life in each species + has been determined by it. A certain length of life is + essential in order that the species may produce offspring + sufficient to ensure its continuance under the most + unfavourable conditions; and it is shown that the remarkable + inequalities of longevity in different species and groups may + be thus accounted for. Yet more, the occurrence of death in + the higher organisms, in place of the continued survival of + the unicellular organisms however much they may increase by + subdivision, may be traced to the same great law of utility + for the race and survival of the fittest. The whole essay is + of exceeding interest, and will repay a careful perusal. A + similar idea occurred to the present writer about twenty + years back, and was briefly noted down at the time, but + subsequently forgotten.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_213_213" id= + "Footnote_213_213"></a><a href= + "#FNanchor_213_213"><span class="label">[213]</span></a> The + outline here given is derived from two articles in + <i>Nature</i>, vol. xxxiii. p. 154, and vol. xxxiv. p. 629, + in which Weismann's papers are summarised and partly + translated.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_214_214" id= + "Footnote_214_214"></a><a href= + "#FNanchor_214_214"><span class="label">[214]</span></a> + There are many indications that this explanation of the cause + of variation is the true one. Mr. E.B. Poulton suggests one, + in the fact that parthenogenetic reproduction only occurs in + isolated species, not in groups of related species; as this + shows that parthenogenesis cannot lead to the evolution of + new forms. Again, in parthenogenetic females the complete + apparatus for fertilisation remains unreduced; but if these + varied as do sexually produced animals, the organs referred + to, being unused, would become rudimentary.</p> + + <p>Even more important is the significance of the "polar + bodies," as explained by Weismann in one of his + <i>Essays</i>; since, if his interpretation of them be + correct, variability is a necessary consequence of sexual + generation.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_215_215" id= + "Footnote_215_215"></a><a href= + "#FNanchor_215_215"><span class="label">[215]</span></a> + Darwin's <i>Animals and Plants</i>, vol. ii. pp. 23, 24.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_216_216" id= + "Footnote_216_216"></a><a href= + "#FNanchor_216_216"><span class="label">[216]</span></a> In + his essay on "Heredity," Dr. Weismann discusses many other + cases of supposed inheritance of acquired characters, and + shows that they can all be explained in other ways. + Shortsightedness among civilised nations, for example, is due + partly to the absence of selection and consequent regression + towards a mean, and partly to its individual production by + constant reading.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_217_217" id= + "Footnote_217_217"></a><a href= + "#FNanchor_217_217"><span class="label">[217]</span></a> + Weismann explains instinct on similar lines, and gives many + interesting illustrations (see <i>Essays on Heredity</i>). He + holds "that all instinct is entirely due to the operation of + natural selection, and has its foundation, not upon inherited + experiences, but upon variations of the germ." Many + interesting and difficult cases of instinct are discussed by + Darwin in Chapter VIII of the <i>Origin of Species</i>, which + should be read in connection with the above remarks.</p> + + <p>Since this chapter was written my attention has been + directed to Mr. Francis Galton's <i>Theory of Heredity</i> + (already referred to at p. 417) which was published thirteen + years ago as an alternative for Darwin's theory of + pangenesis.</p> + + <p>Mr. Galton's theory, although it attracted little + attention, appears to me to be substantially the same as that + of Professor Weismann. Galton's "stirp" is Weismann's + "germ-plasm." Galton supposes the sexual elements in the + offspring to be directly formed from the residue of the + <i>stirp</i> not used up in the development of the body of + the parent—Weismann's "continuity of the germ-plasm." + Galton also draws many of the same conclusions from his + theory. He maintains that characters acquired by the + individual as the result of external influences cannot be + inherited, unless such influences act directly on the + reproductive elements—instancing the possible heredity + of alcoholism, because the alcohol permeates the tissues and + may reach the sexual elements. He discusses the supposed + heredity of effects produced by use or disuse, and explains + them much in the same manner as does Weismann. Galton is an + anthropologist, and applies the theory, mainly, to explain + the peculiarities of hereditary transmission in man, many of + which peculiarities he discusses and elucidates. Weismann is + a biologist, and is mostly concerned with the application of + the theory to explain variation and instinct, and to the + further development of the theory of evolution. He has worked + it out more thoroughly, and has adduced embryological + evidence in its support; but the views of both writers are + substantially the same, and their theories were arrived at + quite independently. The names of Galton and Weismann should + therefore be associated as discoverers of what may be + considered (if finally established) the most important + contribution to the evolution theory since the appearance of + the <i>Origin of Species</i>.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a><a name="Page_445" + id="Page_445"></a>CHAPTER XV</h2> + + <p style='font-weight:bold;'>DARWINISM APPLIED TO MAN</p> + + <div class="blockquot"> + <p>General identity of human and animal + structure—Rudiments and variations showing relation of + man to other mammals—The embryonic development of man and + other mammalia—Diseases common to man and the lower + animals—The animals most nearly allied to man—The + brains of man and apes—External differences of man and + apes—Summary of the animal characteristics of + man—The geological antiquity of man—The probable + birthplace of man—The origin of the moral and + intellectual nature of man—The argument from + continuity—The origin of the mathematical + faculty—The origin of the musical and artistic + faculties—Independent proof that these faculties have not + been developed by natural selection—The interpretation of + the facts—Concluding remarks.</p> + </div> + + <p>Our review of modern Darwinism might fitly have terminated + with the preceding chapter; but the immense interest that + attaches to the origin of the human race, and the amount of + misconception which prevails regarding the essential teachings of + Darwin's theory on this question, as well as regarding my own + special views upon it, induce me to devote a final chapter to its + discussion.</p> + + <p>To any one who considers the structure of man's body, even in + the most superficial manner, it must be evident that it is the + body of an animal, differing greatly, it is true, from the bodies + of all other animals, but agreeing with them in all essential + features. The bony structure of man classes him as a vertebrate; + the mode of suckling his young classes him as a mammal; his + blood, his muscles, and his nerves, the structure of his heart + with its veins and arteries, his lungs and his whole respiratory + and circulatory systems, all closely correspond to those of other + mammals, and are often almost identical with <a name="Page_446" + id="Page_446"></a>them. He possesses the same number of limbs + terminating in the same number of digits as belong fundamentally + to the mammalian class. His senses are identical with theirs, and + his organs of sense are the same in number and occupy the same + relative position. Every detail of structure which is common to + the mammalia as a class is found also in man, while he only + differs from them in such ways and degrees as the various species + or groups of mammals differ from each other. If, then, we have + good reason to believe that every existing group of mammalia has + descended from some common ancestral form—as we saw to be + so completely demonstrated in the case of the horse + tribe,—and that each family, each order, and even the whole + class must similarly have descended from some much more ancient + and more generalised type, it would be in the highest degree + improbable—so improbable as to be almost + inconceivable—that man, agreeing with them so closely in + every detail of his structure, should have had some quite + distinct mode of origin. Let us, then, see what other evidence + bears upon the question, and whether it is sufficient to convert + the probability of his animal origin into a practical + certainty.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Rudiments and Variations as Indicating the Relation of Man to + other Mammals.</i></p> + + <p>All the higher animals present rudiments of organs which, + though useless to them, are useful in some allied group, and are + believed to have descended from a common ancestor in which they + were useful. Thus there are in ruminants rudiments of incisor + teeth which, in some species, never cut through the gums; many + lizards have external rudimentary legs; while many birds, as the + Apteryx, have quite rudimentary wings. Now man possesses similar + rudiments, sometimes constantly, sometimes only occasionally + present, which serve intimately to connect his bodily structure + with that of the lower animals. Many animals, for example, have a + special muscle for moving or twitching the skin. In man there are + remnants of this in certain parts of the body, especially in the + forehead, enabling us to raise our eyebrows; but some persons + have it in other parts. A few persons are able to move the whole + scalp so as to throw off any object placed on the head, <a name= + "Page_447" id="Page_447"></a>and this property has been proved, + in one case, to be inherited. In the outer fold of the ear there + is sometimes a projecting point, corresponding in position to the + pointed ear of many animals, and believed to be a rudiment of it. + In the alimentary canal there is a rudiment—the vermiform + appendage of the caecum—which is not only useless, but is + sometimes a cause of disease and death in man; yet in many + vegetable feeding animals it is very long, and even in the + orang-utan it is of considerable length and convoluted. So, man + possesses rudimentary bones of a tail concealed beneath the skin, + and, in some rare cases, this forms a minute external tail.</p> + + <p>The variability of every part of man's structure is very + great, and many of these variations tend to approximate towards + the structure of other animals. The courses of the arteries are + eminently variable, so that for surgical purposes it has been + necessary to determine the probable proportion of each variation. + The muscles are so variable that in fifty cases the muscles of + the foot were found to be not strictly alike in any two, and in + some the deviations were considerable; while in thirty-six + subjects Mr. J. Wood observed no fewer than 558 muscular + variations. The same author states that in a single male subject + there were no fewer than seven muscular variations, all of which + plainly represented muscles proper to various kinds of apes. The + muscles of the hands and arms—parts which are so eminently + characteristic of man—are extremely liable to vary, so as + to resemble the corresponding muscles of the lower animals. That + such variations are due to reversion to a former state of + existence Mr. Darwin thinks highly probable, and he adds: "It is + quite incredible that a man should, through mere accident, + abnormally resemble certain apes in no less than seven of his + muscles, if there had been no genetic connection between them. On + the other hand, if man is descended from some ape-like creature, + no valid reason can be assigned why certain muscles should not + suddenly reappear after an interval of many thousand generations, + in the same manner as, with horses, asses, and mules, dark + coloured stripes suddenly reappear on the legs and shoulders, + after an interval of hundreds, or more probably of thousands of + generations."<a name="FNanchor_218_218" id= + "FNanchor_218_218"></a><a href="#Footnote_218_218" class= + "fnanchor">[218]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_448" id="Page_448"></a><i>The Embryonic Development + of Man and other Mammalia.</i></p> + + <p>The progressive development of any vertebrate from the ovum or + minute embryonic egg affords one of the most marvellous chapters + in Natural History. We see the contents of the ovum undergoing + numerous definite changes, its interior dividing and subdividing + till it consists of a mass of cells, then a groove appears + marking out the median line or vertebral column of the future + animal, and thereafter are slowly developed the various essential + organs of the body. After describing in some detail what takes + place in the case of the ovum of the dog, Professor Huxley + continues: "The history of the development of any other + vertebrate animal, lizard, snake, frog, or fish tells the same + story. There is always to begin with, an egg having the same + essential structure as that of the dog; the yelk of that egg + undergoes division or segmentation, as it is called, the ultimate + products of that segmentation constitute the building materials + for the body of the young animal; and this is built up round a + primitive groove, in the floor of which a notochord is developed. + Furthermore, there is a period in which the young of all these + animals resemble one another, not merely in outward form, but in + all essentials of structure, so closely, that the differences + between them are inconsiderable, while in their subsequent course + they diverge more and more widely from one another. And it is a + general law that the more closely any animals resemble one + another in adult structure, the larger and the more intimately do + their embryos resemble one another; so that, for example, the + embryos of a snake and of a lizard remain like one another longer + than do those of a snake and a bird; and the embryos of a dog and + of a cat remain like one another for a far longer period than do + those of a dog and a bird, or of a dog and an opossum, or even + than those of a dog and a monkey."<a name="FNanchor_219_219" id= + "FNanchor_219_219"></a><a href="#Footnote_219_219" class= + "fnanchor">[219]</a></p> + + <p>We thus see that the study of development affords a test of + affinity in animals that are externally very much unlike each + other; and we naturally ask how this applies to man. Is he + developed in a different way from other mammals, as we should + certainly expect if he has had a distinct and <a name="Page_449" + id="Page_449"></a>altogether different origin? "The reply," says + Professor Huxley, "is not doubtful for a moment. Without + question, the mode of origin and the early stages of the + development of man are identical with those of the animals + immediately below him in the scale." And again he tells us: "It + is very long before the body of the young human being can be + readily discriminated from that of the young puppy; but at a + tolerably early period the two become distinguishable by the + different forms of their adjuncts, the yelk-sac and the + allantois;" and after describing these differences he continues: + "But exactly in those respects in which the developing man + differs from the dog, he resembles the ape.... So that it is only + quite in the latter stages of development that the young human + being presents marked differences from the young ape, while the + latter departs as much from the dog in its development as the man + does. Startling as this last assertion may appear to be, it is + demonstrably true, and it alone appears to me sufficient to place + beyond all doubt the structural unity of man with the rest of the + animal world, and more particularly and closely with the + apes."<a name="FNanchor_220_220" id= + "FNanchor_220_220"></a><a href="#Footnote_220_220" class= + "fnanchor">[220]</a></p> + + <p>A few of the curious details in which man passes through + stages common to the lower animals may be mentioned. At one stage + the os coccyx projects like a true tail, extending considerably + beyond the rudimentary legs. In the seventh month the + convolutions of the brain resemble those of an adult baboon. The + great toe, so characteristic of man, forming the fulcrum which + most assists him in standing erect, in an early stage of the + embryo is much shorter than the other toes, and instead of being + parallel with them, projects at an angle from the side of the + foot, thus corresponding with its permanent condition in the + quadrumana. Numerous other examples might be quoted, all + illustrating the same general law.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Diseases Common to Man and the Lower Animals.</i></p> + + <p>Though the fact is so well known, it is certainly one of + profound significance that many animal diseases can be + communicated to man, since it shows similarity, if not identity, + in <a name="Page_450" id="Page_450"></a>the minute structure of + the tissues, the nature of the blood, the nerves, and the brain. + Such diseases as hydrophobia, variola, the glanders, cholera, + herpes, etc., can be transmitted from animals to man or the + reverse; while monkeys are liable to many of the same + non-contagious diseases as we are. Rengger, who carefully + observed the common monkey (Cebus Azarae) in Paraguay, found it + liable to catarrh, with the usual symptoms, terminating sometimes + in consumption. These monkeys also suffered from apoplexy, + inflammation of the bowels, and cataract in the eye. Medicines + produced the same effect upon them as upon us. Many kinds of + monkeys have a strong taste for tea, coffee, spirits, and even + tobacco. These facts show the similarity of the nerves of taste + in monkeys and in ourselves, and that their whole nervous system + is affected in a similar way. Even the parasites, both external + and internal, that affect man are not altogether peculiar to him, + but belong to the same families or genera as those which infest + animals, and in one case, scabies, even the same species.<a name= + "FNanchor_221_221" id="FNanchor_221_221"></a><a href= + "#Footnote_221_221" class="fnanchor">[221]</a> These curious + facts seem quite inconsistent with the idea that man's bodily + structure and nature are altogether distinct from those of + animals, and have had a different origin; while the facts are + just what we should expect if he has been produced by descent + with modification from some common ancestor.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Animals most nearly Allied to Man.</i></p> + + <p>By universal consent we see in the monkey tribe a caricature + of humanity. Their faces, their hands, their actions and + expressions present ludicrous resemblances to our own. But there + is one group of this great tribe in which this resemblance is + greatest, and they have hence been called the anthropoid or + man-like apes. These are few in number, and inhabit only the + equatorial regions of Africa and Asia, countries where the + climate is most uniform, the forests densest, and the supply of + fruit abundant throughout the year. These animals are now + comparatively well known, consisting of the orang-utan of Borneo + and Sumatra, the chimpanzee and the gorilla of West Africa, and + the group of gibbons or long-armed apes, consisting of many + species and inhabiting South-Eastern <a name="Page_451" id= + "Page_451"></a>Asia and the larger Malay Islands. These last are + far less like man than the other three, one or other of which has + at various times been claimed to be the most man-like of the apes + and our nearest relations in the animal kingdom. The question of + the degree of resemblance of these animals to ourselves is one of + great interest, leading, as it does, to some important + conclusions as to our origin and geological antiquity, and we + will therefore briefly consider it.</p> + + <p>If we compare the skeletons of the orang or chimpanzee with + that of man, we find them to be a kind of distorted copy, every + bone corresponding (with very few exceptions), but altered + somewhat in size, proportions, and position. So great is this + resemblance that it led Professor Owen to remark: "I cannot shut + my eyes to the significance of that all-pervading similitude of + structure—every tooth, every bone, strictly + homologous—which makes the determination of the difference + between <i>Homo</i> and <i>Pithecus</i> the anatomist's + difficulty."</p> + + <p>The actual differences in the skeletons of these apes and that + of man—that is, differences dependent on the presence or + absence of certain bones, and not on their form or + position—have been enumerated by Mr. Mivart as + follows:—(1) In the breast-bone consisting of but two + bones, man agrees with the gibbons; the chimpanzee and gorilla + having this part consisting of seven bones in a single series, + while in the orang they are arranged in a double series of ten + bones. (2) The normal number of the ribs in the orang and some + gibbons is twelve pairs, as in man, while in the chimpanzee and + gorilla there are thirteen pairs. (3) The orang and the gibbons + also agree with man in having five lumbar vertebrae, while in the + gorilla and the chimpanzee there are but four, and sometimes only + three. (4) The gorilla and chimpanzee agree with man in having + eight small bones in the wrist, while the orang and the gibbons, + as well as all other monkeys, have nine.<a name= + "FNanchor_222_222" id="FNanchor_222_222"></a><a href= + "#Footnote_222_222" class="fnanchor">[222]</a></p> + + <p>The differences in the form, size, and attachments of the + various bones, muscles, and other organs of these apes and + <a name="Page_452" id="Page_452"></a>man are very numerous and + exceedingly complex, sometimes one species, sometimes another + agreeing most nearly with ourselves, thus presenting a tangled + web of affinities which it is very difficult to unravel. + Estimated by the skeleton alone, the chimpanzee and gorilla seem + nearer to man than the orang, which last is also inferior as + presenting certain aberrations in the muscles. In the form of the + ear the gorilla is more human than any other ape, while in the + tongue the orang is the more man-like. In the stomach and liver + the gibbons approach nearest to man, then come the orang and + chimpanzee, while the gorilla has a degraded liver more + resembling that of the lower monkeys and baboons.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Brains of Man and Apes.</i></p> + + <p>We come now to that part of his organisation in which man is + so much higher than all the lower animals—the brain; and + here, Mr. Mivart informs us, the orang stands highest in rank. + The height of the orang's cerebrum in front is greater in + proportion than in either the chimpanzee or the gorilla. "On + comparing the brain of man with the brains of the orang, + chimpanzee, and baboon, we find a successive decrease in the + frontal lobe, and a successive and very great increase in the + relative size of the occipital lobe. Concomitantly with this + increase and decrease, certain folds of brain substance, called + 'bridging convolutions,' which in man are conspicuously + interposed between the parietal and occipital lobes, seem as + utterly to disappear in the chimpanzee, as they do in the baboon. + In the orang, however, though much reduced, they are still to be + distinguished.... The actual and absolute mass of the brain is, + however, slightly greater in the chimpanzee than in the orang, as + is the relative vertical extent of the middle part of the + cerebrum, although, as already stated, the frontal portion is + higher in the orang; while, according to M. Gratiolet, the + gorilla is not only inferior to the orang in cerebral + development, but even to his smaller African congener, the + chimpanzee."<a name="FNanchor_223_223" id= + "FNanchor_223_223"></a><a href="#Footnote_223_223" class= + "fnanchor">[223]</a></p> + + <p>On the whole, then, we find that no one of the great apes can + be positively asserted to be nearest to man in structure. Each of + them approaches him in certain characteristics, while <a name= + "Page_453" id="Page_453"></a>in others it is widely removed, + giving the idea, so consonant with the theory of evolution as + developed by Darwin, that all are derived from a common ancestor, + from which the existing anthropoid apes as well as man have + diverged. When, however, we turn from the details of anatomy to + peculiarities of external form and motions, we find that, in a + variety of characters, all these apes resemble each other and + differ from man, so that we may fairly say that, while they have + diverged somewhat from each other, they have diverged much more + widely from ourselves. Let us briefly enumerate some of these + differences.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>External Differences of Man and Apes.</i></p> + + <p>All apes have large canine teeth, while in man these are no + longer than the adjacent incisors or premolars, the whole forming + a perfectly even series. In apes the arms are proportionately + much longer than in man, while the thighs are much shorter. No + ape stands really erect, a posture which is natural in man. The + thumb is proportionately larger in man, and more perfectly + opposable than in that of any ape. The foot of man differs + largely from that of all apes, in the horizontal sole, the + projecting heel, the short toes, and the powerful great toe + firmly attached parallel to the other toes; all perfectly adapted + for maintaining the erect posture, and for free motion without + any aid from the arms or hands. In apes the foot is formed almost + exactly like our hand, with a large thumb-like great toe quite + free from the other toes, and so articulated as to be opposable + to them; forming with the long finger-like toes a perfect + grasping hand. The sole cannot be placed horizontally on the + ground; but when standing on a level surface the animal rests on + the outer edge of the foot with the finger and thumb-like toes + partly closed, while the hands are placed on the ground resting + on the knuckles. The illustration on the next page (Fig. 37) + shows, fairly well, the peculiarities of the hands and feet of + the chimpanzee, and their marked differences, both in form and + use, from those of man.</p> + + <p>The four limbs, with the peculiarly formed feet and hands, are + those of arboreal animals which only occasionally and awkwardly + move on level ground. The arms are used in pro<a name="Page_454" + id="Page_454"></a>gression equally with the feet, and the hands + are only adapted for uses similar to those of our hands when the + animal is at rest, and then but clumsily. Lastly, the apes are + all hairy animals, like the majority of other mammals, man alone + having a smooth and almost naked skin. These numerous and + striking differences, even more than those of the skeleton and + internal anatomy, point to an enormously remote epoch when the + race that was ultimately to develop into man diverged from that + other stock which continued the animal type and ultimately + produced the existing varieties of anthropoid apes.</p> + + <div class="figcenter" style="width: 400px;"> + <a name="fig37" id="fig37"></a> <img src="images/fig37.jpg" + width="400" height="455" alt= + "FIG. 37.—Chimpanzee (Troglodytes niger)." title= + "FIG. 37.—Chimpanzee (Troglodytes niger)." /> <b>FIG. + 37.—Chimpanzee (Troglodytes niger).</b> + </div> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Summary of the Animal Characteristics of Man.</i></p> + + <p>The facts now very briefly summarised amount almost to a + demonstration that man, in his bodily structure, has been derived + from the lower animals, of which he is the culminating + development. In his possession of rudimentary structures <a name= + "Page_455" id="Page_455"></a>which are functional in some of the + mammalia; in the numerous variations of his muscles and other + organs agreeing with characters which are constant in some apes; + in his embryonic development, absolutely identical in character + with that of mammalia in general, and closely resembling in its + details that of the higher quadrumana; in the diseases which he + has in common with other mammalia; and in the wonderful + approximation of his skeleton to those of one or other of the + anthropoid apes, we have an amount of evidence in this direction + which it seems impossible to explain away. And this evidence will + appear more forcible if we consider for a moment what the + rejection of it implies. For the only alternative supposition is, + that man has been specially created—that is to say, has + been produced in some quite different way from other animals and + altogether independently of them. But in that case the + rudimentary structures, the animal-like variations, the identical + course of development, and all the other animal characteristics + he possesses are deceptive, and inevitably lead us, as thinking + beings making use of the reason which is our noblest and most + distinctive feature, into gross error.</p> + + <p>We cannot believe, however, that a careful study of the facts + of nature leads to conclusions directly opposed to the truth; + and, as we seek in vain, in our physical structure and the course + of its development, for any indication of an origin independent + of the rest of the animal world, we are compelled to reject the + idea of "special creation" for man, as being entirely unsupported + by facts as well as in the highest degree improbable.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Geological Antiquity of Man.</i></p> + + <p>The evidence we now possess of the exact nature of the + resemblance of man to the various species of anthropoid apes, + shows us that he has little special affinity for any one rather + than another species, while he differs from them all in several + important characters in which they agree with each other. The + conclusion to be drawn from these facts is, that his points of + affinity connect him with the whole group, while his special + peculiarities equally separate him from the whole group, and that + he must, therefore, have diverged from the common ancestral form + before the existing types of anthropoid apes <a name="Page_456" + id="Page_456"></a>had diverged from each other. Now, this + divergence almost certainly took place as early as the Miocene + period, because in the Upper Miocene deposits of Western Europe + remains of two species of ape have been found allied to the + gibbons, one of them, Dryopithecus, nearly as large as a man, and + believed by M. Lartet to have approached man in its dentition + more than the existing apes. We seem hardly, therefore, to have + reached, in the Upper Miocene, the epoch of the common ancestor + of man and the anthropoids.</p> + + <p>The evidence of the antiquity of man himself is also scanty, + and takes us but very little way back into the past. We have + clear proof of his existence in Europe in the latter stages of + the glacial epoch, with many indications of his presence in + interglacial or even pre-glacial times; while both the actual + remains and the works of man found in the auriferous gravels of + California deep under lava-flows of Pliocene age, show that he + existed in the New World at least as early as in the Old.<a name= + "FNanchor_224_224" id="FNanchor_224_224"></a><a href= + "#Footnote_224_224" class="fnanchor">[224]</a> These earliest + remains of man have been received with doubt, and even with + ridicule, as if there were some extreme improbability in them. + But, in point of fact, the wonder is that human remains have not + been found more frequently in pre-glacial deposits. Referring to + the most ancient fossil remains found in Europe—the Engis + and Neanderthal crania,—Professor Huxley makes the + following weighty remark: "In conclusion, I may say, that the + fossil remains of Man hitherto discovered do not seem to me to + take us appreciably nearer to that lower pithecoid form, by the + modification of which he has, probably, become what he is." The + Californian remains and works of art, above referred to, give no + indication of a specially low form of man; and it remains an + unsolved problem why no traces of the long line of man's + ancestors, back to the remote period when he first branched off + from the pithecoid type, have yet been discovered.</p> + + <p>It has been objected by some writers—notably by + Professor Boyd Dawkins—that man did not probably exist in + Pliocene times, because almost all the known mammalia of that + epoch are distinct species from those now living on the earth, + and that the same changes of the environment which led to + <a name="Page_457" id="Page_457"></a>the modification of other + mammalian species would also have led to a change in man. But + this argument overlooks the fact that man differs essentially + from all other mammals in this respect, that whereas any + important adaptation to new conditions can be effected in them + only by a change in bodily structure, man is able to adapt + himself to much greater changes of conditions by a mental + development leading him to the use of fire, of tools, of + clothing, of improved dwellings, of nets and snares, and of + agriculture. By the help of these, without any change whatever in + his bodily structure, he has been able to spread over and occupy + the whole earth; to dwell securely in forest, plain, or mountain; + to inhabit alike the burning desert or the arctic wastes; to cope + with every kind of wild beast, and to provide himself with food + in districts where, as an animal trusting to nature's unaided + productions, he would have starved.<a name="FNanchor_225_225" id= + "FNanchor_225_225"></a><a href="#Footnote_225_225" class= + "fnanchor">[225]</a></p> + + <p>It follows, therefore, that from the time when the ancestral + man first walked erect, with hands freed from any active part in + locomotion, and when his brain-power became sufficient to cause + him to use his hands in making weapons and tools, houses and + clothing, to use fire for cooking, and to plant seeds or roots to + supply himself with stores of food, the power of natural + selection would cease to act in producing modifications of his + body, but would continuously advance his mind through the + development of its organ, the brain. Hence man may have become + truly man—the species, Homo sapiens—even in the + Miocene period; and while all other mammals were becoming + modified from age to age under the influence of ever-changing + physical and biological conditions, he would be advancing mainly + in intelligence, but perhaps also in stature, and by that advance + alone would be able to maintain himself as the master of all + other animals and as the most widespread occupier of the earth. + It is quite in accordance with this view that we find the most + pronounced distinction between man and the anthropoid apes in the + size and complexity of his brain. Thus, Professor Huxley tells us + that "it may be doubted whether a healthy human adult brain ever + weighed <a name="Page_458" id="Page_458"></a>less than 31 or 32 + ounces, or that the heaviest gorilla brain has exceeded 20 + ounces," although "a full-grown gorilla is probably pretty nearly + twice as heavy as a Bosjes man, or as many an European + woman."<a name="FNanchor_226_226" id= + "FNanchor_226_226"></a><a href="#Footnote_226_226" class= + "fnanchor">[226]</a> The average human brain, however, weighs 48 + or 49 ounces, and if we take the average ape brain at only 2 + ounces less than the very largest gorilla's brain, or 18 ounces, + we shall see better the enormous increase which has taken place + in the brain of man since the time when he branched off from the + apes; and this increase will be still greater if we consider that + the brains of apes, like those of all other mammals, have also + increased from earlier to later geological times.</p> + + <p>If these various considerations are taken into account, we + must conclude that the essential features of man's structure as + compared with that of apes—his erect posture and free + hands—were acquired at a comparatively early period, and + were, in fact, the characteristics which gave him his superiority + over other mammals, and started him on the line of development + which has led to his conquest of the world. But during this long + and steady development of brain and intellect, mankind must have + continuously increased in numbers and in the area which they + occupied—they must have formed what Darwin terms a + "dominant race." For had they been few in numbers and confined to + a limited area, they could hardly have successfully struggled + against the numerous fierce carnivora of that period, and against + those adverse influences which led to the extinction of so many + more powerful animals. A large population spread over an + extensive area is also needed to supply an adequate number of + brain variations for man's progressive improvement. But this + large population and long-continued development in a single line + of advance renders it the more difficult to account for the + complete absence of human or pre-human remains in all those + deposits which have furnished, in such rich abundance, the + remains of other land animals. It is true that the remains of + apes are also very rare, and we may well suppose that the + superior intelligence of man led him to avoid that extensive + destruction by flood or in morass which seems to have often + overwhelmed other animals. Yet, when <a name="Page_459" id= + "Page_459"></a>we consider that, even in our own day, men are not + unfrequently overwhelmed by volcanic eruptions, as in Java and + Japan, or carried away in vast numbers by floods, as in Bengal + and China, it seems impossible but that ample remains of Miocene + and Pliocene man do exist buried in the most recent layers of the + earth's crust, and that more extended research or some fortunate + discovery will some day bring them to light.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Probable Birthplace of Man.</i></p> + + <p>It has usually been considered that the ancestral form of man + originated in the tropics, where vegetation is most abundant and + the climate most equable. But there are some important objections + to this view. The anthropoid apes, as well as most of the monkey + tribe, are essentially arboreal in their structure, whereas the + great distinctive character of man is his special adaptation to + terrestrial locomotion. We can hardly suppose, therefore, that he + originated in a forest region, where fruits to be obtained by + climbing are the chief vegetable food. It is more probable that + he began his existence on the open plains or high plateaux of the + temperate or sub-tropical zone, where the seeds of indigenous + cereals and numerous herbivora, rodents, and game-birds, with + fishes and molluscs in the lakes, rivers, and seas supplied him + with an abundance of varied food. In such a region he would + develop skill as a hunter, trapper, or fisherman, and later as a + herdsman and cultivator,—a succession of which we find + indications in the palaeolithic and neolithic races of + Europe.</p> + + <p>In seeking to determine the particular areas in which his + earliest traces are likely to be found, we are restricted to some + portion of the Eastern hemisphere, where alone the anthropoid + apes exist, or have apparently ever existed.</p> + + <p>There is good reason to believe, also, that Africa must be + excluded, because it is known to have been separated from the + northern continent in early tertiary times, and to have acquired + its existing fauna of the higher mammalia by a later union with + that continent after the separation from it of Madagascar, an + island which has preserved for us a sample, as it were, of the + early African mammalian fauna, from which not only the anthropoid + apes, but all the higher quadrumana <a name="Page_460" id= + "Page_460"></a>are absent.<a name="FNanchor_227_227" id= + "FNanchor_227_227"></a><a href="#Footnote_227_227" class= + "fnanchor">[227]</a> There remains only the great Euro-Asiatic + continent; and its enormous plateaux, extending from Persia right + across Tibet and Siberia to Manchuria, afford an area, some part + or other of which probably offered suitable conditions, in late + Miocene or early Pliocene times, for the development of ancestral + man.</p> + + <p>It is in this area that we still find that type of + mankind—the Mongolian—which retains a colour of the + skin midway between the black or brown-black of the negro, and + the ruddy or olive-white of the Caucasian types, a colour which + still prevails over all Northern Asia, over the American + continents, and over much of Polynesia. From this primary tint + arose, under the influence of varied conditions, and probably in + correlation with constitutional changes adapted to peculiar + climates, the varied tints which still exist among mankind. If + the reasoning by which this conclusion is reached be sound, and + all the earlier stages of man's development from an animal form + occurred in the area now indicated, we can better understand how + it is that we have as yet met with no traces of the missing + links, or even of man's existence during late tertiary times, + because no part of the world is so entirely unexplored by the + geologist as this very region. The area in question is + sufficiently extensive and varied to admit of primeval man having + attained to a considerable population, and having developed his + full human characteristics, both physical and mental, before + there was any need for him to migrate beyond its limits. One of + his earliest important migrations was probably into Africa, + where, spreading westward, he became modified in colour and hair + in correlation with physiological changes adapting him to the + climate of the equatorial lowlands. Spreading north-westward into + Europe the moist and cool climate led to a modification of an + opposite character, and thus may have arisen the three great + human types which still exist. Somewhat later, probably, he + spread eastward into North-West America and soon scattered + himself over the whole continent; and all this may well have + occurred in early or middle Pliocene times. Thereafter, at very + long intervals, successive waves of migration carried him into + every <a name="Page_461" id="Page_461"></a>part of the habitable + world, and by conquest and intermixture led ultimately to that + puzzling gradation of types which the ethnologist in vain seeks + to unravel.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Origin of the Moral and Intellectual Nature of + Man.</i></p> + + <p>From the foregoing discussion it will be seen that I fully + accept Mr. Darwin's conclusion as to the essential identity of + man's bodily structure with that of the higher mammalia, and his + descent from some ancestral form common to man and the anthropoid + apes. The evidence of such descent appears to me to be + overwhelming and conclusive. Again, as to the cause and method of + such descent and modification, we may admit, at all events + provisionally, that the laws of variation and natural selection, + acting through the struggle for existence and the continual need + of more perfect adaptation to the physical and biological + environments, may have brought about, first that perfection of + bodily structure in which he is so far above all other animals, + and in co-ordination with it the larger and more developed brain, + by means of which he has been able to utilise that structure in + the more and more complete subjection of the whole animal and + vegetable kingdoms to his service.</p> + + <p>But this is only the beginning of Mr. Darwin's work, since he + goes on to discuss the moral nature and mental faculties of man, + and derives these too by gradual modification and development + from the lower animals. Although, perhaps, nowhere distinctly + formulated, his whole argument tends to the conclusion that man's + entire nature and all his faculties, whether moral, intellectual, + or spiritual, have been derived from their rudiments in the lower + animals, in the same manner and by the action of the same general + laws as his physical structure has been derived. As this + conclusion appears to me not to be supported by adequate + evidence, and to be directly opposed to many well-ascertained + facts, I propose to devote a brief space to its discussion.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Argument from Continuity.</i></p> + + <p>Mr. Darwin's mode of argument consists in showing that the + rudiments of most, if not of all, the mental and moral faculties + of man can be detected in some animals. The <a name="Page_462" + id="Page_462"></a>manifestations of intelligence, amounting in + some cases to distinct acts of reasoning, in many animals, are + adduced as exhibiting in a much less degree the intelligence and + reason of man. Instances of curiosity, imitation, attention, + wonder, and memory are given; while examples are also adduced + which may be interpreted as proving that animals exhibit kindness + to their fellows, or manifest pride, contempt, and shame. Some + are said to have the rudiments of language, because they utter + several different sounds, each of which has a definite meaning to + their fellows or to their young; others the rudiments of + arithmetic, because they seem to count and remember up to three, + four, or even five. A sense of beauty is imputed to them on + account of their own bright colours or the use of coloured + objects in their nests; while dogs, cats, and horses are said to + have imagination, because they appear to be disturbed by dreams. + Even some distant approach to the rudiments of religion is said + to be found in the deep love and complete submission of a dog to + his master.<a name="FNanchor_228_228" id= + "FNanchor_228_228"></a><a href="#Footnote_228_228" class= + "fnanchor">[228]</a></p> + + <p>Turning from animals to man, it is shown that in the lowest + savages many of these faculties are very little advanced from the + condition in which they appear in the higher animals; while + others, although fairly well exhibited, are yet greatly inferior + to the point of development they have reached in civilised races. + In particular, the moral sense is said to have been developed + from the social instincts of savages, and to depend mainly on the + enduring discomfort produced by any action which excites the + general disapproval of the tribe. Thus, every act of an + individual which is believed to be contrary to the interests of + the tribe, excites its unvarying disapprobation and is held to be + immoral; while every act, on the other hand, which is, as a rule, + beneficial to the tribe, is warmly and constantly approved, and + is thus considered to be right or moral. From the mental + struggle, when an act that would benefit self is injurious to the + tribe, there arises conscience; and thus the social instincts are + the foundation of the moral sense and of the fundamental + principles of morality.<a name="FNanchor_229_229" id= + "FNanchor_229_229"></a><a href="#Footnote_229_229" class= + "fnanchor">[229]</a></p> + + <p>The question of the origin and nature of the moral sense and + of conscience is far too vast and complex to be discussed + <a name="Page_463" id="Page_463"></a>here, and a reference to it + has been introduced only to complete the sketch of Mr. Darwin's + view of the continuity and gradual development of all human + faculties from the lower animals up to savages, and from savage + up to civilised man. The point to which I wish specially to call + attention is, that to prove continuity and the progressive + development of the intellectual and moral faculties from animals + to man, is not the same as proving that these faculties have been + developed by natural selection; and this last is what Mr. Darwin + has hardly attempted, although to support his theory it was + absolutely essential to prove it. Because man's physical + structure has been developed from an animal form by natural + selection, it does not necessarily follow that his mental nature, + even though developed <i>pari passu</i> with it, has been + developed by the same causes only. To illustrate by a physical + analogy. Upheaval and depression of land, combined with + sub-aerial denudation by wind and frost, rain and rivers, and + marine denudation on coastlines, were long thought to account for + all the modelling of the earth's surface not directly due to + volcanic action; and in the early editions of Lyell's + <i>Principles of Geology</i> these are the sole causes appealed + to. But when the action of glaciers was studied and the recent + occurrence of a glacial epoch demonstrated as a fact, many + phenomena—such as moraines and other gravel deposits, + boulder clay, erratic boulders, grooved and rounded rocks, and + Alpine lake basins—were seen to be due to this altogether + distinct cause. There was no breach of continuity, no sudden + catastrophe; the cold period came on and passed away in the most + gradual manner, and its effects often passed insensibly into + those produced by denudation or upheaval; yet none the less a new + agency appeared at a definite time, and new effects were produced + which, though continuous with preceding effects, were not due to + the same causes. It is not, therefore, to be assumed, without + proof or against independent evidence, that the later stages of + an apparently continuous development are necessarily due to the + same causes only as the earlier stages. Applying this argument to + the case of man's intellectual and moral nature, I propose to + show that certain definite portions of it could not have been + developed by variation and natural selection alone, and that, + therefore, some other influence, law, or agency is <a name= + "Page_464" id="Page_464"></a>required to account for them. If + this can be clearly shown for any one or more of the special + faculties of intellectual man, we shall be justified in assuming + that the same unknown cause or power may have had a much wider + influence, and may have profoundly influenced the whole course of + his development.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Origin of the Mathematical Faculty.</i></p> + + <p>We have ample evidence that, in all the lower races of man, + what may be termed the mathematical faculty is, either absent, + or, if present, quite unexercised. The Bushmen and the Brazilian + Wood-Indians are said not to count beyond two. Many Australian + tribes only have words for one and two, which are combined to + make three, four, five, or six, beyond which they do not count. + The Damaras of South Africa only count to three; and Mr. Galton + gives a curious description of how one of them was hopelessly + puzzled when he had sold two sheep for two sticks of tobacco + each, and received four sticks in payment. He could only find out + that he was correctly paid by taking two sticks and then giving + one sheep, then receiving two sticks more and giving the other + sheep. Even the comparatively intellectual Zulus can only count + up to ten by using the hands and fingers. The Ahts of North-West + America count in nearly the same manner, and most of the tribes + of South America are no further advanced.<a name= + "FNanchor_230_230" id="FNanchor_230_230"></a><a href= + "#Footnote_230_230" class="fnanchor">[230]</a> The Kaffirs have + great herds of cattle, and if one is lost they miss it + immediately, but this is not by counting, but by noticing the + absence of one they know; just as in a large family or a school a + boy is missed without going through the process of counting. + Somewhat higher races, as the Esquimaux, can count up to twenty + by using the hands and the feet; and other races get even further + than this by saying "one man" for twenty, "two men" for forty, + and so on, equivalent to our rural mode of reckoning by scores. + From the fact that so many of the existing savage races can only + count to four or five, Sir John Lubbock thinks it improbable that + our earliest ancestors could have counted as high as ten.<a name= + "FNanchor_231_231" id="FNanchor_231_231"></a><a href= + "#Footnote_231_231" class="fnanchor">[231]</a></p> + + <p><a name="Page_465" id="Page_465"></a>When we turn to the more + civilised races, we find the use of numbers and the art of + counting greatly extended. Even the Tongas of the South Sea + islands are said to have been able to count as high as 100,000. + But mere counting does not imply either the possession or the use + of anything that can be really called the mathematical faculty, + the exercise of which in any broad sense has only been possible + since the introduction of the decimal notation. The Greeks, the + Romans, the Egyptians, the Jews, and the Chinese had all such + cumbrous systems, that anything like a science of arithmetic, + beyond very simple operations, was impossible; and the Roman + system, by which the year 1888 would be written MDCCCLXXXVIII, + was that in common use in Europe down to the fourteenth or + fifteenth centuries, and even much later in some places. Algebra, + which was invented by the Hindoos, from whom also came the + decimal notation, was not introduced into Europe till the + thirteenth century, although the Greeks had some acquaintance + with it; and it reached Western Europe from Italy only in the + sixteenth century.<a name="FNanchor_232_232" id= + "FNanchor_232_232"></a><a href="#Footnote_232_232" class= + "fnanchor">[232]</a> It was, no doubt, owing to the absence of a + sound system of numeration that the mathematical talent of the + Greeks was directed chiefly to geometry, in which science Euclid, + Archimedes, and others made such brilliant discoveries. It is, + however, during the last three centuries only that the civilised + world appears to have become conscious of the possession of a + marvellous faculty which, when supplied with the necessary tools + in the decimal notation, the elements of algebra and geometry, + and the power of rapidly communicating discoveries and ideas by + the art of printing, has developed to an extent, the full + grandeur of which can be appreciated only by those who have + devoted some time (even if unsuccessfully) to the study.</p> + + <p>The facts now set forth as to the almost total absence of + mathematical faculty in savages and its wonderful development in + quite recent times, are exceedingly suggestive, and in regard + <a name="Page_466" id="Page_466"></a>to them we are limited to + two possible theories. Either prehistoric and savage man did not + possess this faculty at all (or only in its merest rudiments); or + they did possess it, but had neither the means nor the + incitements for its exercise. In the former case we have to ask + by what means has this faculty been so rapidly developed in all + civilised races, many of which a few centuries back were, in this + respect, almost savages themselves; while in the latter case the + difficulty is still greater, for we have to assume the existence + of a faculty which had never been used either by the supposed + possessors of it or by their ancestors.</p> + + <p>Let us take, then, the least difficult supposition—that + savages possessed only the mere rudiments of the faculty, such as + their ability to count, sometimes up to ten, but with an utter + inability to perform the very simplest processes of arithmetic or + of geometry—and inquire how this rudimentary faculty became + rapidly developed into that of a Newton, a La Place, a Gauss, or + a Cayley. We will admit that there is every possible gradation + between these extremes, and that there has been perfect + continuity in the development of the faculty; but we ask, What + motive power caused its development?</p> + + <p>It must be remembered we are here dealing solely with the + capability of the Darwinian theory to account for the origin of + the <i>mind</i>, as well as it accounts for the origin of the + <i>body</i> of man, and we must, therefore, recall the essential + features of that theory. These are, the preservation of useful + variations in the struggle for life; that no creature can be + improved beyond its necessities for the time being; that the law + acts by life and death, and by the survival of the fittest. We + have to ask, therefore, what relation the successive stages of + improvement of the mathematical faculty had to the life or death + of its possessors; to the struggles of tribe with tribe, or + nation with nation; or to the ultimate survival of one race and + the extinction of another. If it cannot possibly have had any + such effects, then it cannot have been produced by natural + selection.</p> + + <p>It is evident that in the struggles of savage man with the + elements and with wild beasts, or of tribe with tribe, this + faculty can have had no influence. It had nothing to do with + <a name="Page_467" id="Page_467"></a>the early migrations of man, + or with the conquest and extermination of weaker by more powerful + peoples. The Greeks did not successfully resist the Persian + invaders by any aid from their few mathematicians, but by + military training, patriotism, and self-sacrifice. The barbarous + conquerors of the East, Timurlane and Gengkhis Khan, did not owe + their success to any superiority of intellect or of mathematical + faculty in themselves or their followers. Even if the great + conquests of the Romans were, in part, due to their systematic + military organisation, and to their skill in making roads and + encampments, which may, perhaps, be imputed to some exercise of + the mathematical faculty, that did not prevent them from being + conquered in turn by barbarians, in whom it was almost entirely + absent. And if we take the most civilised peoples of the ancient + world—the Hindoos, the Arabs, the Greeks, and the Romans, + all of whom had some amount of mathematical talent—we find + that it is not these, but the descendants of the barbarians of + those days—the Celts, the Teutons, and the Slavs—who + have proved themselves the fittest to survive in the great + struggle of races, although we cannot trace their steadily + growing success during past centuries either to the possession of + any exceptional mathematical faculty or to its exercise. They + have indeed proved themselves, to-day, to be possessed of a + marvellous endowment of the mathematical faculty; but their + success at home and abroad, as colonists or as conquerors, as + individuals or as nations, can in no way be traced to this + faculty, since they were almost the last who devoted themselves + to its exercise. We conclude, then, that the present gigantic + development of the mathematical faculty is wholly unexplained by + the theory of natural selection, and must be due to some + altogether distinct cause.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>The Origin of the Musical and Artistic Faculties.</i></p> + + <p>These distinctively human faculties follow very closely the + lines of the mathematical faculty in their progressive + development, and serve to enforce the same argument. Among the + lower savages music, as we understand it, hardly exists, though + they all delight in rude musical sounds, as of drums, tom-toms, + or gongs; and they also sing in monotonous chants. Almost exactly + as they advance in general intellect, and in the arts <a name= + "Page_468" id="Page_468"></a>of social life, their appreciation + of music appears to rise in proportion; and we find among them + rude stringed instruments and whistles, till, in Java, we have + regular bands of skilled performers probably the successors of + Hindoo musicians of the age before the Mahometan conquest. The + Egyptians are believed to have been the earliest musicians, and + from them the Jews and the Greeks, no doubt, derived their + knowledge of the art; but it seems to be admitted that neither + the latter nor the Romans knew anything of harmony or of the + essential features of modern music.<a name="FNanchor_233_233" id= + "FNanchor_233_233"></a><a href="#Footnote_233_233" class= + "fnanchor">[233]</a> Till the fifteenth century little progress + appears to have been made in the science or the practice of + music; but since that era it has advanced with marvellous + rapidity, its progress being curiously parallel with that of + mathematics, inasmuch as great musical geniuses appeared suddenly + among different nations, equal in their possession of this + special faculty to any that have since arisen.</p> + + <p>As with the mathematical, so with the musical faculty, it is + impossible to trace any connection between its possession and + survival in the struggle for existence. It seems to have arisen + as a <i>result</i> of social and intellectual advancement, not as + a <i>cause</i>; and there is some evidence that it is latent in + the lower races, since under European training native military + bands have been formed in many parts of the world, which have + been able to perform creditably the best modern music.</p> + + <p>The artistic faculty has run a somewhat different course, + though analogous to that of the faculties already discussed. Most + savages exhibit some rudiments of it, either in drawing or + carving human or animal figures; but, almost without exception, + these figures are rude and such as would be executed by the + ordinary inartistic child. In fact, modern savages are, in this + respect hardly equal to those prehistoric men who represented the + mammoth and the reindeer on pieces of horn or bone. With any + advance in the arts of social life, we have a corresponding + advance in artistic skill and taste, rising very high in the art + of Japan and India, but culminating in the marvellous sculpture + of the best period of Grecian history. In the Middle Ages art was + chiefly manifested in <a name="Page_469" id= + "Page_469"></a>ecclesiastical architecture and the illumination + of manuscripts, but from the thirteenth to the fifteenth + centuries pictorial art revived in Italy and attained to a degree + of perfection which has never been surpassed. This revival was + followed closely by the schools of Germany, the Netherlands, + Spain, France, and England, showing that the true artistic + faculty belonged to no one nation, but was fairly distributed + among the various European races.</p> + + <p>These several developments of the artistic faculty, whether + manifested in sculpture, painting, or architecture, are evidently + outgrowths of the human intellect which have no immediate + influence on the survival of individuals or of tribes, or on the + success of nations in their struggles for supremacy or for + existence. The glorious art of Greece did not prevent the nation + from falling under the sway of the less advanced Roman; while we + ourselves, among whom art was the latest to arise, have taken the + lead in the colonisation of the world, thus proving our mixed + race to be the fittest to survive.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Independent Proof that the Mathematical, Musical, and Artistic + Faculties have not been Developed under the Law of Natural + Selection.</i></p> + + <p>The law of Natural Selection or the survival of the fittest + is, as its name implies, a rigid law, which acts by the life or + death of the individuals submitted to its action. From its very + nature it can act only on useful or hurtful characteristics, + eliminating the latter and keeping up the former to a fairly + general level of efficiency. Hence it necessarily follows that + the characters developed by its means will be present in all the + individuals of a species, and, though varying, will not vary very + widely from a common standard. The amount of variation we found, + in our third chapter, to be about one-fifth or one-sixth of the + mean value—that is, if the mean value were taken at 100, + the variations would reach from 80 to 120, or somewhat more, if + very large numbers were compared. In accordance with this law we + find, that all those characters in man which were certainly + essential to him during his early stages of development, exist in + all savages with some approach to equality. In the speed of + running, in bodily strength, in skill with weapons, in acuteness + of vision, or in power of <a name="Page_470" id= + "Page_470"></a>following a trail, all are fairly proficient, and + the differences of endowment do not probably exceed the limits of + variation in animals above referred to. So, in animal instinct or + intelligence, we find the same general level of development. + Every wren makes a fairly good nest like its fellows; every fox + has an average amount of the sagacity of its race; while all the + higher birds and mammals have the necessary affections and + instincts needful for the protection and bringing-up of their + offspring.</p> + + <p>But in those specially developed faculties of civilised man + which we have been considering, the case is very different. They + exist only in a small proportion of individuals, while the + difference of capacity between these favoured individuals and the + average of mankind is enormous. Taking first the mathematical + faculty, probably fewer than one in a hundred really possess it, + the great bulk of the population having no natural ability for + the study, or feeling the slightest interest in it.<a name= + "FNanchor_234_234" id="FNanchor_234_234"></a><a href= + "#Footnote_234_234" class="fnanchor">[234]</a> And if we attempt + to measure the amount of variation in the faculty itself between + a first-class mathematician and the ordinary run of people who + find any kind of calculation confusing and altogether devoid of + interest, it is probable that the former could not be estimated + at less than a hundred times the latter, and perhaps a thousand + times would more nearly measure the difference between them.</p> + + <p>The artistic faculty appears to agree pretty closely with the + mathematical in its frequency. The boys and girls who, going + beyond the mere conventional designs of children, draw what they + <i>see</i>, not what they <i>know</i> to be the shape of things; + who naturally sketch in perspective, because it is thus they see + objects; who see, and represent in their sketches, the light and + shade as well as the mere outlines of objects; and who can draw + recognisable sketches of every one they know, are certainly very + few compared with those who are totally incap<a name="Page_471" + id="Page_471"></a>able of anything of the kind. From some + inquiries I have made in schools, and from my own observation, I + believe that those who are endowed with this natural artistic + talent do not exceed, even if they come up to, one per cent of + the whole population.</p> + + <p>The variations in the amount of artistic faculty are certainly + very great, even if we do not take the extremes. The gradations + of power between the ordinary man or woman "who does not draw," + and whose attempts at representing any object, animate or + inanimate, would be laughable, and the average good artist who, + with a few bold strokes, can produce a recognisable and even + effective sketch of a landscape, a street, or an animal, are very + numerous; and we can hardly measure the difference between them + at less than fifty or a hundred fold.</p> + + <p>The musical faculty is undoubtedly, in its lower forms, less + uncommon than either of the preceding, but it still differs + essentially from the necessary or useful faculties in that it is + almost entirely wanting in one-half even of civilised men. For + every person who draws, as it were instinctively, there are + probably five or ten who sing or play without having been taught + and from mere innate love and perception of melody and + harmony.<a name="FNanchor_235_235" id= + "FNanchor_235_235"></a><a href="#Footnote_235_235" class= + "fnanchor">[235]</a> On the other hand, there are probably about + as many who seem absolutely deficient in musical perception, who + take little pleasure in it, who cannot perceive discords or + remember tunes, and who could not learn to sing or play with any + amount of study. The gradations, too, are here quite as great as + in mathematics or pictorial art, and the special faculty of the + great musical composer must be reckoned many hundreds or perhaps + thousands of times greater than that of the ordinary "unmusical" + person above referred to.</p> + + <p>It appears then, that, both on account of the limited number + of persons gifted with the mathematical, the artistic, or the + musical faculty, as well as from the enormous variations in its + development, these mental powers differ widely from those which + are essential to man, and are, for the most part, common to him + and the lower animals; and that they could <a name="Page_472" id= + "Page_472"></a>not, therefore, possibly have been developed in + him by means of the law of natural selection.</p> + <hr style='width: 45%;' /> + + <p>We have thus shown, by two distinct lines of argument, that + faculties are developed in civilised man which, both in their + mode of origin, their function, and their variations, are + altogether distinct from those other characters and faculties + which are essential to him, and which have been brought to their + actual state of efficiency by the necessities of his existence. + And besides the three which have been specially referred to, + there are others which evidently belong to the same class. Such + is the metaphysical faculty, which enables us to form abstract + conceptions of a kind the most remote from all practical + applications, to discuss the ultimate causes of things, the + nature and qualities of matter, motion, and force, of space and + time, of cause and effect, of will and conscience. Speculations + on these abstract and difficult questions are impossible to + savages, who seem to have no mental faculty enabling them to + grasp the essential ideas or conceptions; yet whenever any race + attains to civilisation, and comprises a body of people who, + whether as priests or philosophers, are relieved from the + necessity of labour or of taking an active part in war or + government, the metaphysical faculty appears to spring suddenly + into existence, although, like the other faculties we have + referred to, it is always confined to a very limited proportion + of the population.</p> + + <p>In the same class we may place the peculiar faculty of wit and + humour, an altogether natural gift whose development appears to + be parallel with that of the other exceptional faculties. Like + them, it is almost unknown among savages, but appears more or + less frequently as civilisation advances and the interests of + life become more numerous and more complex. Like them, too, it is + altogether removed from utility in the struggle for life, and + appears sporadically in a very small percentage of the + population; the majority being, as is well known, totally unable + to say a witty thing or make a pun even to save their + lives.<a name="FNanchor_236_236" id= + "FNanchor_236_236"></a><a href="#Footnote_236_236" class= + "fnanchor">[236]</a></p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <a name="Page_473" id="Page_473"></a><i>The Interpretation of the + Facts.</i></p> + + <p>The facts now set forth prove the existence of a number of + mental faculties which either do not exist at all or exist in a + very rudimentary condition in savages, but appear almost suddenly + and in perfect development in the higher civilised races. These + same faculties are further distinguished by their sporadic + character, being well developed only in a very small proportion + of the community; and by the enormous amount of variation in + their development, the higher manifestations of them being many + times—perhaps a hundred or a thousand times—stronger + than the lower. Each of these characteristics is totally + inconsistent with any action of the law of natural selection in + the production of the faculties referred to; and the facts, taken + in their entirety, compel us to recognise some origin for them + wholly distinct from that which has served to account for the + animal characteristics—whether bodily or mental—of + man.</p> + + <p><a name="Page_474" id="Page_474"></a>The special faculties we + have been discussing clearly point to the existence in man of + something which he has not derived from his animal + progenitors—something which we may best refer to as being + of a spiritual essence or nature, capable of progressive + development under favourable conditions. On the hypothesis of + this spiritual nature, superadded to the animal nature of man, we + are able to understand much that is otherwise mysterious or + unintelligible in regard to him, especially the enormous + influence of ideas, principles, and beliefs over his whole life + and actions. Thus alone we can understand the constancy of the + martyr, the unselfishness of the philanthropist, the devotion of + the patriot, the enthusiasm of the artist, and the resolute and + persevering search of the scientific worker after nature's + secrets. Thus we may perceive that the love of truth, the delight + in beauty, the passion for justice, and the thrill of exultation + with which we hear of any act of courageous self-sacrifice, are + the workings within us of a higher nature which has not been + developed by means of the struggle for material existence.</p> + + <p>It will, no doubt, be urged that the admitted continuity of + man's progress from the brute does not admit of the introduction + of new causes, and that we have no evidence of the sudden change + of nature which such introduction would bring about. The fallacy + as to new causes involving any breach of continuity, or any + sudden or abrupt change, in the effects, has already been shown; + but we will further point out that there are at least three + stages in the development of the organic world when some new + cause or power must necessarily have come into action.</p> + + <p>The first stage is the change from inorganic to organic, when + the earliest vegetable cell, or the living protoplasm out of + which it arose, first appeared. This is often imputed to a mere + increase of complexity of chemical compounds; but increase of + complexity, with consequent instability, even if we admit that it + may have produced protoplasm as a chemical compound, could + certainly not have produced <i>living</i> + protoplasm—protoplasm which has the power of growth and of + reproduction, and of that continuous process of development which + has resulted in the marvellous variety and complex organisation + of the whole vegetable kingdom. There is in all this something + <a name="Page_475" id="Page_475"></a>quite beyond and apart from + chemical changes, however complex; and it has been well said that + the first vegetable cell was a new thing in the world, possessing + altogether new powers—that of extracting and fixing carbon + from the carbon-dioxide of the atmosphere, that of indefinite + reproduction, and, still more marvellous, the power of variation + and of reproducing those variations till endless complications of + structure and varieties of form have been the result. Here, then, + we have indications of a new power at work, which we may term + <i>vitality</i>, since it gives to certain forms of matter all + those characters and properties which constitute Life.</p> + + <p>The next stage is still more marvellous, still more completely + beyond all possibility of explanation by matter, its laws and + forces. It is the introduction of sensation or consciousness, + constituting the fundamental distinction between the animal and + vegetable kingdoms. Here all idea of mere complication of + structure producing the result is out of the question. We feel it + to be altogether preposterous to assume that at a certain stage + of complexity of atomic constitution, and as a necessary result + of that complexity alone, an <i>ego</i> should start into + existence, a thing that <i>feels</i>, that is <i>conscious</i> of + its own existence. Here we have the certainty that something new + has arisen, a being whose nascent consciousness has gone on + increasing in power and definiteness till it has culminated in + the higher animals. No verbal explanation or attempt at + explanation—such as the statement that life is the result + of the molecular forces of the protoplasm, or that the whole + existing organic universe from the amaeba up to man was latent in + the fire-mist from which the solar system was developed—can + afford any mental satisfaction, or help us in any way to a + solution of the mystery.</p> + + <p>The third stage is, as we have seen, the existence in man of a + number of his most characteristic and noblest faculties, those + which raise him furthest above the brutes and open up + possibilities of almost indefinite advancement. These faculties + could not possibly have been developed by means of the same laws + which have determined the progressive development of the organic + world in general, and also of man's physical organism.<a name= + "FNanchor_237_237" id="FNanchor_237_237"></a><a href= + "#Footnote_237_237" class="fnanchor">[237]</a></p> + + <p><a name="Page_476" id="Page_476"></a>These three distinct + stages of progress from the inorganic world of matter and motion + up to man, point clearly to an unseen universe—to a world + of spirit, to which the world of matter is altogether + subordinate. To this spiritual world we may refer the + marvellously complex forces which we know as gravitation, + cohesion, chemical force, radiant force, and electricity, without + which the material universe could not exist for a moment in its + present form, and perhaps not at all, since without these forces, + and perhaps others which may be termed atomic, it is doubtful + whether matter itself could have any existence. And still more + surely can we refer to it those progressive manifestations of + Life in the vegetable, the animal, and man—which we may + classify as unconscious, conscious, and intellectual + life,—and which probably depend upon different degrees of + spiritual influx. I have already shown that this involves no + necessary infraction of the law of continuity in physical or + mental evolution; whence it follows that any difficulty we may + find in discriminating the inorganic from the organic, the lower + vegetable from the lower animal organisms, or the higher animals + from the lowest types of man, has no bearing at all upon the + question. This is to be decided by showing that a change in + essential nature (due, probably, to causes of a higher order than + those of the material universe) took place at the several stages + of progress which I have indicated; a change which may be none + the less real because absolutely imperceptible at its point of + origin, as is the change that takes place in the curve in which a + body is moving when the application of some new force causes the + curve to be slightly altered.</p> + + <p style='text-align:center; font-weight:bold; margin-top:1.5em'> + <i>Concluding Remarks.</i></p> + + <p>Those who admit my interpretation of the evidence now + adduced—strictly scientific evidence in its appeal to facts + which are clearly what ought <i>not</i> to be on the + materialistic theory—will be able to accept the spiritual + nature of man, as not in any way inconsistent with the theory of + evolution, but as dependent on those fundamental laws and causes + which furnish the very materials for evolution to work with. They + will also be relieved from the crushing mental burthen imposed + upon those who—maintaining that we, in common with the + <a name="Page_477" id="Page_477"></a>rest of nature, are but + products of the blind eternal forces of the universe, and + believing also that the time must come when the sun will lose his + heat and all life on the earth necessarily cease—have to + contemplate a not very distant future in which all this glorious + earth—which for untold millions of years has been slowly + developing forms of life and beauty to culminate at last in + man—shall be as if it had never existed; who are compelled + to suppose that all the slow growths of our race struggling + towards a higher life, all the agony of martyrs, all the groans + of victims, all the evil and misery and undeserved suffering of + the ages, all the struggles for freedom, all the efforts towards + justice, all the aspirations for virtue and the wellbeing of + humanity, shall absolutely vanish, and, "like the baseless fabric + of a vision, leave not a wrack behind."</p> + + <p>As contrasted with this hopeless and soul-deadening belief, + we, who accept the existence of a spiritual world, can look upon + the universe as a grand consistent whole adapted in all its parts + to the development of spiritual beings capable of indefinite life + and perfectibility. To us, the whole purpose, the only <i>raison + d'être</i> of the world—with all its complexities of + physical structure, with its grand geological progress, the slow + evolution of the vegetable and animal kingdoms, and the ultimate + appearance of man—was the development of the human spirit + in association with the human body. From the fact that the spirit + of man—the man himself—<i>is</i> so developed, we may + well believe that this is the only, or at least the best, way for + its development; and we may even see in what is usually termed + "evil" on the earth, one of the most efficient means of its + growth. For we know that the noblest faculties of man are + strengthened and perfected by struggle and effort; it is by + unceasing warfare against physical evils and in the midst of + difficulty and danger that energy, courage, self-reliance, and + industry have become the common qualities of the northern races; + it is by the battle with moral evil in all its hydra-headed + forms, that the still nobler qualities of justice and mercy and + humanity and self-sacrifice have been steadily increasing in the + world. Beings thus trained and strengthened by their + surroundings, and possessing latent faculties capable of such + noble development, are surely destined for a higher and more + permanent exist<a name="Page_478" id="Page_478"></a>ence; and we + may confidently believe with our greatest living poet—</p> + + <p><span style="margin-left: 2em;">That life is not as idle + ore,</span><br /> + <br /> + <span style="margin-left: 2em;">But iron dug from central + gloom,</span><br /> + <span style="margin-left: 3em;">And heated hot with burning + fears,</span><br /> + <span style="margin-left: 3em;">And dipt in baths of hissing + tears,</span><br /> + <span style="margin-left: 2em;">And batter'd with the shocks of + doom</span><br /> + <br /> + <span style="margin-left: 2em;">To shape and + use.</span><br /></p> + + <p>We thus find that the Darwinian theory, even when carried out + to its extreme logical conclusion, not only does not oppose, but + lends a decided support to, a belief in the spiritual nature of + man. It shows us how man's body may have been developed from that + of a lower animal form under the law of natural selection; but it + also teaches us that we possess intellectual and moral faculties + which could not have been so developed, but must have had another + origin; and for this origin we can only find an adequate cause in + the unseen universe of Spirit.</p> + + <div class="footnotes"> + <h3>FOOTNOTES:</h3> + + <div class="footnote"> + <p><a name="Footnote_218_218" id= + "Footnote_218_218"></a><a href= + "#FNanchor_218_218"><span class="label">[218]</span></a> + <i>Descent of Man</i>, pp. 41-43; also pp. 13-15.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_219_219" id= + "Footnote_219_219"></a><a href= + "#FNanchor_219_219"><span class="label">[219]</span></a> + <i>Man's Place in Nature</i>, p. 64.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_220_220" id= + "Footnote_220_220"></a><a href= + "#FNanchor_220_220"><span class="label">[220]</span></a> + <i>Man's Place in Nature</i>, p. 67. See Figs. of Embryos of + Man and Dog in Darwin's <i>Descent of Man</i>, p. 10.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_221_221" id= + "Footnote_221_221"></a><a href= + "#FNanchor_221_221"><span class="label">[221]</span></a> + <i>The Descent of Man</i>, pp. 7, 8.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_222_222" id= + "Footnote_222_222"></a><a href= + "#FNanchor_222_222"><span class="label">[222]</span></a> + <i>Man and Apes.</i> By St. George Mivart, F.R.S., 1873. It + is an interesting fact (for which I am indebted to Mr. E.B. + Poulton) that the human embryo possesses the extra rib and + wrist-bone referred to above in (2) and (4) as occurring in + some of the apes.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_223_223" id= + "Footnote_223_223"></a><a href= + "#FNanchor_223_223"><span class="label">[223]</span></a> + <i>Man and Apes</i>, pp. 138, 144.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_224_224" id= + "Footnote_224_224"></a><a href= + "#FNanchor_224_224"><span class="label">[224]</span></a> For + a sketch of the evidence of Man's Antiquity in America, see + <i>The Nineteenth Century</i> for November 1887.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_225_225" id= + "Footnote_225_225"></a><a href= + "#FNanchor_225_225"><span class="label">[225]</span></a> This + subject was first discussed in an article in the + <i>Anthropological Review</i>, May 1864, and republished in + my <i>Contributions to Natural Selection</i>, chap, ix, in + 1870.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_226_226" id= + "Footnote_226_226"></a><a href= + "#FNanchor_226_226"><span class="label">[226]</span></a> + <i>Man's Place in Nature</i>, p. 102.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_227_227" id= + "Footnote_227_227"></a><a href= + "#FNanchor_227_227"><span class="label">[227]</span></a> For + a full discussion of this question, see the author's + <i>Geographical Distribution of Animals</i>, vol. i. p. + 285.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_228_228" id= + "Footnote_228_228"></a><a href= + "#FNanchor_228_228"><span class="label">[228]</span></a> For + a full discussion of all these points, see <i>Descent of + Man</i>, chap. iii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_229_229" id= + "Footnote_229_229"></a><a href= + "#FNanchor_229_229"><span class="label">[229]</span></a> + <i>Descent of Man</i>, chap. iv.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_230_230" id= + "Footnote_230_230"></a><a href= + "#FNanchor_230_230"><span class="label">[230]</span></a> + Lubbock's <i>Origin of Civilisation</i>, fourth edition, pp. + 434-440; Tylor's <i>Primitive Culture</i>, chap. vii.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_231_231" id= + "Footnote_231_231"></a><a href= + "#FNanchor_231_231"><span class="label">[231]</span></a> It + has been recently stated that some of these facts are + erroneous, and that some Australians can keep accurate + reckoning up to 100, or more, when required. But this does + not alter the general fact that many low races, including the + Australians, have no words for high numbers and never require + to use them. If they are now, with a little practice, able to + count much higher, this indicates the possession of a faculty + which could not have been developed under the law of utility + only, since the absence of words for such high numbers shows + that they were neither used nor required.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_232_232" id= + "Footnote_232_232"></a><a href= + "#FNanchor_232_232"><span class="label">[232]</span></a> + Article Arithmetic in <i>Eng. Cyc. of Arts and + Sciences</i>.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_233_233" id= + "Footnote_233_233"></a><a href= + "#FNanchor_233_233"><span class="label">[233]</span></a> See + "History of Music," in <i>Eng. Cyc.</i>, Science and Arts + Division.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_234_234" id= + "Footnote_234_234"></a><a href= + "#FNanchor_234_234"><span class="label">[234]</span></a> This + is the estimate furnished me by two mathematical masters in + one of our great public schools of the proportion of boys who + have any special taste or capacity for mathematical studies. + Many more, of course, can be drilled into a fair knowledge of + elementary mathematics, but only this small proportion + possess the natural faculty which renders it possible for + them ever to rank high as mathematicians, to take any + pleasure in it, or to do any original mathematical work.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_235_235" id= + "Footnote_235_235"></a><a href= + "#FNanchor_235_235"><span class="label">[235]</span></a> I am + informed, however, by a music master in a large school that + only about one per cent have real or decided musical talent, + corresponding curiously with the estimate of the + mathematicians.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_236_236" id= + "Footnote_236_236"></a><a href= + "#FNanchor_236_236"><span class="label">[236]</span></a> In + the latter part of his essay on Heredity (pp. 91-93 of the + volume of <i>Essays</i>), Dr. Weismann refers to this + question of the origin of "talents" in man, and, like myself, + comes to the conclusion that they could not be developed + under the law of natural selection. He says: "It may be + objected that, in man, in addition to the instincts inherent + in every individual, special individual predispositions are + also found, of such a nature that it is impossible they can + have arisen by individual variations of the germ-plasm. On + the other hand, these predispositions—which we call + talents—cannot have arisen through natural selection, + because life is in no way dependent on their presence, and + there seems to be no way of explaining their origin except by + an assumption of the summation of the skill attained by + exercise in the course of each single life. In this case, + therefore, we seem at first sight to be compelled to accept + the transmission of acquired characters." Weismann then goes + on to show that the facts do not support this view; that the + mathematical, musical, or artistic faculties often appear + suddenly in a family whose other members and ancestors were + in no way distinguished; and that even when hereditary in + families, the talent often appears at its maximum at the + commencement or in the middle of the series, not increasing + to the end, as it should do if it depended in any way on the + transmission of acquired skill. Gauss was not the son of a + mathematician, nor Handel of a musician, nor Titian of a + painter, and there is no proof of any special talent in the + ancestors of these men of genius, who at once developed the + most marvellous pre-eminence in their respective talents. And + after showing that such great men only appear at certain + stages of human development, and that two or more of the + special talents are not unfrequently combined in one + individual, he concludes thus—</p> + + <div class="blockquot" style='font-size: 100%;'> + <p>"Upon this subject I only wish to add that, in my + opinion, talents do not appear to depend upon the + improvement of any special mental quality by continued + practice, but they are the expression, and to a certain + extent the bye-product, of the human mind, which is so + highly developed in all directions."</p> + </div> + + <p>It will, I think, be admitted that this view hardly + accounts for the existence of the highly peculiar human + faculties in question.</p> + </div> + + <div class="footnote"> + <p><a name="Footnote_237_237" id= + "Footnote_237_237"></a><a href= + "#FNanchor_237_237"><span class="label">[237]</span></a> For + an earlier discussion of this subject, with some wider + applications, see the author's <i>Contributions to the Theory + of Natural Selection</i>, chap. x.</p> + </div> + </div> + <hr style="width: 65%;" /> + + <h2><a name="INDEX" id="INDEX"></a><a name="Page_479" id= + "Page_479"></a>INDEX</h2> + + <p><span style="margin-left: 1em;"><b>A</b> </span><br /> + <br /> + <span style="margin-left: 1em;">Abbott, Dr. C.C., instability of + habits of birds, <a href='#Page_76'>76</a></span><br /> + <span style="margin-left: 2em;">on American water-thrushes + (Seiurus), <a href='#Page_117'>117</a></span><br /> + <span style="margin-left: 2em;">Mr., drawings of caterpillars and + their food plants, <a href='#Page_203'>203</a></span><br /> + <br /> + <span style="margin-left: 1em;">Accessory plumes, development and + display of, <a href='#Page_293'>293</a></span><br /> + <br /> + <span style="margin-left: 1em;">Acclimatisation, <a href= + '#Page_94'>94</a></span><br /> + <br /> + <span style="margin-left: 1em;">Achatinellidae, Gulick on + variations in, <a href='#Page_147'>147</a></span><br /> + <br /> + <span style="margin-left: 1em;">Acquired characters, non-heredity + of, <a href='#Page_440'>440</a></span><br /> + <br /> + <span style="margin-left: 1em;">Acraeidae, mimicry of, <a href= + '#Page_247'>247</a></span><br /> + <br /> + <span style="margin-left: 1em;">Adaptation to conditions at + various periods of life, <a href='#Page_112'>112</a></span><br /> + <br /> + <span style="margin-left: 1em;">Adolias dirtea, sexual diversity + of, <a href='#Page_271'>271</a></span><br /> + <br /> + <span style="margin-left: 1em;">Aegeriidae, mimicry by, <a href= + '#Page_240'>240</a></span><br /> + <br /> + <span style="margin-left: 1em;">Agaristidae, mimicry of, <a href= + '#Page_246'>246</a></span><br /> + <br /> + <span style="margin-left: 1em;">Agassiz, on species, <a href= + '#Page_5'>5</a></span><br /> + <span style="margin-left: 2em;">on North American weeds, <a href= + '#Page_15'>15</a></span><br /> + <br /> + <span style="margin-left: 1em;">Agelaeus phoeniceus, diagram + showing variations of, <a href='#Page_56'>56</a>;</span><br /> + <span style="margin-left: 2em;">proportionate numbers which vary, + <a href='#Page_64'>64</a></span><br /> + <br /> + <span style="margin-left: 1em;">Albatross, courtship of great, + <a href='#Page_287'>287</a></span><br /> + <br /> + <span style="margin-left: 1em;">Allen, Mr. Grant, on forms of + leaves, <a href='#Page_133'>133</a></span><br /> + <span style="margin-left: 2em;">on degradation of wind-fertilised + from insect-fertilised flowers, <a href='#Page_325'>325</a> + (note)</span><br /> + <span style="margin-left: 2em;">on insects and flowers, <a href= + '#Page_332'>332</a></span><br /> + <span style="margin-left: 2em;">on production of colour through + the agency of the colour sense, <a href= + '#Page_334'>334</a></span><br /> + <span style="margin-left: 2em;">Mr. J.A., on the variability of + birds, <a href='#Page_50'>50</a></span><br /> + <br /> + <span style="margin-left: 1em;">Allen, Mr. J.A., on colour + as influenced by climate, <a href= + '#Page_228'>228</a></span><br /> + <br /> + <span style="margin-left: 1em;">Alluring coloration, <a href= + '#Page_210'>210</a></span><br /> + <br /> + <span style="margin-left: 1em;">American school of evolutionists, + <a href='#Page_420'>420</a></span><br /> + <br /> + <span style="margin-left: 1em;">Anemone nemorosa, variability of, + <a href='#Page_78'>78</a></span><br /> + <br /> + <span style="margin-left: 1em;">Animal coloration, a theory of, + <a href='#Page_288'>288</a></span><br /> + <span style="margin-left: 2em;">general laws of, <a href= + '#Page_296'>296</a></span><br /> + <span style="margin-left: 2em;">intelligence, supposed action of, + <a href='#Page_425'>425</a></span><br /> + <span style="margin-left: 2em;">characteristics of man, <a href= + '#Page_454'>454</a></span><br /> + <br /> + <span style="margin-left: 1em;">Animals, the struggle among, + <a href='#Page_18'>18</a></span><br /> + <span style="margin-left: 2em;">wild, their enjoyment of life, + <a href='#Page_39'>39</a></span><br /> + <span style="margin-left: 2em;">usually die painless deaths, + <a href='#Page_38'>38</a></span><br /> + <span style="margin-left: 2em;">constitutional variation of, + <a href='#Page_94'>94</a></span><br /> + <span style="margin-left: 2em;">uses of colours of, <a href= + '#Page_134'>134</a></span><br /> + <span style="margin-left: 2em;">supposed effects of disuse in + wild, <a href='#Page_415'>415</a></span><br /> + <span style="margin-left: 2em;">most allied to man, <a href= + '#Page_450'>450</a></span><br /> + <br /> + <span style="margin-left: 1em;">Antelopes, recognition marks of, + <a href='#Page_219'>219</a></span><br /> + <br /> + <span style="margin-left: 1em;">Anthrocera filipendula inedible, + <a href='#Page_235'>235</a></span><br /> + <br /> + <span style="margin-left: 1em;">Apples, variations of, <a href= + '#Page_87'>87</a></span><br /> + <br /> + <span style="margin-left: 1em;">Arctic animals, supposed causes + of white colour of, <a href='#Page_191'>191</a></span><br /> + <br /> + <span style="margin-left: 1em;">Argyll, Duke of, on goose reared + by a golden eagle, <a href='#Page_75'>75</a></span><br /> + <br /> + <span style="margin-left: 1em;">Artemia salina and A. + milhausenii, <a href='#Page_426'>426</a></span><br /> + <br /> + <span style="margin-left: 1em;">Asclepias curassavica, spread of, + <a href='#Page_28'>28</a></span><br /> + <br /> + <span style="margin-left: 1em;">Asses running wild in Quito, + <a href='#Page_28'>28</a></span><br /> + <br /> + <span style="margin-left: 1em;">Attractive fruits, <a href= + '#Page_306'>306</a></span><br /> + <br /> + <span style="margin-left: 1em;">Australia, spread of the + Cape-weed in, <a href='#Page_29'>29</a></span><br /> + <span style="margin-left: 2em;">fossil and recent mammals of, + <a href='#Page_392'>392</a></span><br /> + <br /> + <span style="margin-left: 1em;">Azara, on cause of horses and + cattle not running wild in Paraguay, <a href= + '#Page_19'>19</a></span><br /> + <br /> + <span style="margin-left: 1em;">Azores, flora of, supports aerial + transmission of seeds, <a href='#Page_368'>368</a></span><br /> + <br /> + <a name="Page_480" id="Page_480"></a><br /> + <span style="margin-left: 1em;"><b>B</b></span><br /> + <br /> + <span style="margin-left: 1em;">Baker, Mr. J.G., on rarity of + spiny plants in Mauritius, <a href= + '#Page_432'>432</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ball, Mr., on cause of late + appearance of exogens, <a href='#Page_400'>400</a></span><br /> + <br /> + <span style="margin-left: 1em;">Barber, Mrs., on variable + colouring of pupae of Papilio nireus, <a href= + '#Page_197'>197</a></span><br /> + <span style="margin-left: 2em;">on protective colours of African + sun-birds, <a href='#Page_200'>200</a></span><br /> + <br /> + <span style="margin-left: 1em;">Barbs, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Barriers, importance of, in + questions of distribution, <a href= + '#Page_341'>341</a></span><br /> + <br /> + <span style="margin-left: 1em;">Bates, Mr. H.W., on varieties of + butterflies, <a href='#Page_44'>44</a></span><br /> + <span style="margin-left: 2em;">on inedibility of Heliconidae, + <a href='#Page_234'>234</a></span><br /> + <span style="margin-left: 2em;">on a conspicuous caterpillar, + <a href='#Page_236'>236</a></span><br /> + <span style="margin-left: 2em;">on mimicry, <a href= + '#Page_240'>240</a>, <a href='#Page_243'>243</a>, <a href= + '#Page_249'>249</a></span><br /> + <br /> + <span style="margin-left: 1em;">Bathmism or growth-force, Cope + on, <a href='#Page_421'>421</a></span><br /> + <br /> + <span style="margin-left: 1em;">Beddard, Mr. F.E., variations of + earthworms, <a href='#Page_67'>67</a></span><br /> + <span style="margin-left: 2em;">on plumes of bird of paradise, + <a href='#Page_292'>292</a></span><br /> + <br /> + <span style="margin-left: 1em;">Beech trees, aggressive in + Denmark, <a href='#Page_21'>21</a></span><br /> + <br /> + <span style="margin-left: 1em;">Beetle and wasp (figs.), <a href= + '#Page_259'>259</a></span><br /> + <br /> + <span style="margin-left: 1em;">Beetle, fossil in coal measures + of Silesia, <a href='#Page_404'>404</a></span><br /> + <br /> + <span style="margin-left: 1em;">Beginnings of important organs, + <a href='#Page_128'>128</a></span><br /> + <br /> + <span style="margin-left: 1em;">Belt, Mr., on leaf-like locust, + <a href='#Page_203'>203</a></span><br /> + <span style="margin-left: 2em;">on birds avoiding Heliconidae, + <a href='#Page_234'>234</a></span><br /> + <br /> + <span style="margin-left: 1em;">Belt's frog, <a href= + '#Page_266'>266</a></span><br /> + <br /> + <span style="margin-left: 1em;">Birds, rate of increase of, + <a href='#Page_25'>25</a></span><br /> + <span style="margin-left: 2em;">how destroyed, <a href= + '#Page_26'>26</a></span><br /> + <span style="margin-left: 2em;">variation among, <a href= + '#Page_49'>49</a></span><br /> + <span style="margin-left: 2em;">variation of markings of, + <a href='#Page_52'>52</a></span><br /> + <span style="margin-left: 2em;">variation of wings and tails of, + <a href='#Page_53'>53</a></span><br /> + <span style="margin-left: 2em;">diagram showing variation of + tarsus and toes, <a href='#Page_60'>60</a></span><br /> + <span style="margin-left: 2em;">use of structural peculiarities + of, <a href='#Page_135'>135</a></span><br /> + <span style="margin-left: 2em;">eggs, coloration of, <a href= + '#Page_212'>212</a></span><br /> + <span style="margin-left: 2em;">recognition marks of, <a href= + '#Page_222'>222</a></span><br /> + <span style="margin-left: 2em;">and butterflies, white in + tropical islands, <a href='#Page_230'>230</a></span><br /> + <span style="margin-left: 2em;">sometimes seize inedible + butterflies, <a href='#Page_255'>255</a></span><br /> + <span style="margin-left: 2em;">mimicry among, <a href= + '#Page_263'>263</a></span><br /> + <br /> + <span style="margin-left: 1em;">Birds, sexual coloration of, + <a href='#Page_275'>275</a></span><br /> + <span style="margin-left: 2em;">cause of dull colour of female, + <a href='#Page_277'>277</a></span><br /> + <span style="margin-left: 2em;">choice of female not known to be + determined by colour, etc., <a href= + '#Page_285'>285</a></span><br /> + <span style="margin-left: 2em;">decorative plumage of, <a href= + '#Page_285'>285</a></span><br /> + <span style="margin-left: 2em;">antics of unornamented, <a href= + '#Page_287'>287</a></span><br /> + <span style="margin-left: 2em;">which fertilise flowers, <a href= + '#Page_319'>319</a></span><br /> + <span style="margin-left: 2em;">colours of, not dependent on the + colours of flowers, <a href='#Page_336'>336</a></span><br /> + <span style="margin-left: 2em;">no proof of aesthetic tastes in, + <a href='#Page_336'>336</a></span><br /> + <span style="margin-left: 2em;">dispersal of, <a href= + '#Page_355'>355</a></span><br /> + <span style="margin-left: 2em;">and insects at sea, <a href= + '#Page_357'>357</a></span><br /> + <span style="margin-left: 2em;">of oceanic islands, <a href= + '#Page_358'>358</a></span><br /> + <span style="margin-left: 2em;">carrying seeds on their feet, + <a href='#Page_361'>361</a></span><br /> + <span style="margin-left: 2em;">ancestral forms of, <a href= + '#Page_407'>407</a></span><br /> + <br /> + <span style="margin-left: 1em;">Birthplace, probable, of man, + <a href='#Page_459'>459</a></span><br /> + <br /> + <span style="margin-left: 1em;">Bombyx regia, protective form of + larva of, <a href='#Page_210'>210</a></span><br /> + <br /> + <span style="margin-left: 1em;">Boyd Dawkins, on development of + deer's horns, <a href='#Page_389'>389</a></span><br /> + <span style="margin-left: 2em;">on origin of man, <a href= + '#Page_456'>456</a></span><br /> + <br /> + <span style="margin-left: 1em;">Brady, Mr. George, on protective + colouring of starfishes, <a href='#Page_209'>209</a></span><br /> + <br /> + <span style="margin-left: 1em;">Brain development, progressive, + <a href='#Page_390'>390</a></span><br /> + <br /> + <span style="margin-left: 1em;">Brains of man and apes, <a href= + '#Page_452'>452</a></span><br /> + <br /> + <span style="margin-left: 1em;">Branner, Mr. J.C., on supposed + proofs of glaciation in Brazil, <a href= + '#Page_370'>370</a></span><br /> + <br /> + <span style="margin-left: 1em;">Brazil, supposed proof of + glaciation in, <a href='#Page_370'>370</a></span><br /> + <br /> + <span style="margin-left: 1em;">Brewer, Professor W.H., on want + of symmetry in colours of animals, <a href= + '#Page_217'>217</a></span><br /> + <br /> + <span style="margin-left: 1em;">Bromelia, animals inhabiting + leaves of, <a href='#Page_118'>118</a></span><br /> + <br /> + <span style="margin-left: 1em;">Bronn, Professor, on supposed + uselessness of variations of ears and tails, <a href= + '#Page_136'>136</a></span><br /> + <br /> + <span style="margin-left: 1em;">Butler, Mr. A.G., on inedibility + of conspicuous caterpillars, <a href= + '#Page_237'>237</a></span><br /> + <br /> + <span style="margin-left: 1em;">Butterflies, varieties of, + <a href='#Page_44'>44</a></span><br /> + <span style="margin-left: 2em;">small, of Isle of Man, <a href= + '#Page_106'>106</a></span><br /> + <span style="margin-left: 2em;">special protective colouring of, + <a href='#Page_206'>206</a></span><br /> + <span style="margin-left: 2em;">recognition by, <a href= + '#Page_226'>226</a></span><br /> + <span style="margin-left: 2em;">inedibility of some, <a href= + '#Page_234'>234</a></span><br /> + <span style="margin-left: 2em;">mimicry among, <a href= + '#Page_240'>240</a>, <a href='#Page_249'>249</a></span><br /> + <span style="margin-left: 2em;">colour development of, <a href= + '#Page_274'>274</a></span><br /> + <span style="margin-left: 2em;">sexual coloration of, <a href= + '#Page_271'>271</a></span><br /> + <br /> + <a name="Page_481" id="Page_481"></a><br /> + <span style="margin-left: 1em;"><b>C</b></span><br /> + <br /> + <span style="margin-left: 1em;">Caddis-fly larvae inhabiting + bromelia leaves, <a href='#Page_118'>118</a></span><br /> + <br /> + <span style="margin-left: 1em;">Callophis, harmless mimicking + poisonous species, <a href='#Page_262'>262</a></span><br /> + <br /> + <span style="margin-left: 1em;">Candolle, Alp. de, on variation + in oaks, <a href='#Page_77'>77</a></span><br /> + <span style="margin-left: 2em;">on variability of Papaver + bracteatum, <a href='#Page_79'>79</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cardinalis virginianus, diagram + showing proportionate numbers which vary, <a href= + '#Page_65'>65</a>;</span><br /> + <span style="margin-left: 2em;">variations of, <a href= + '#Page_58'>58</a></span><br /> + <br /> + <span style="margin-left: 1em;">Carpenter, Dr. W.B., on variation + in the Foraminifera, <a href='#Page_43'>43</a></span><br /> + <br /> + <span style="margin-left: 1em;">Carriers, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Caterpillars, resemblance of, to + their food plants, <a href='#Page_203'>203</a>-<a href= + '#Page_205'>205</a></span><br /> + <span style="margin-left: 2em;">inedible, <a href= + '#Page_236'>236</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cattle, how they prevent the + growth of trees, <a href='#Page_18'>18</a></span><br /> + <span style="margin-left: 2em;">increase of, in St. Domingo, + Mexico, and the pampas, <a href='#Page_27'>27</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ceylon, spread of Lantana mixta + in, <a href='#Page_29'>29</a></span><br /> + <br /> + <span style="margin-left: 1em;">Chaffinch, change of habit of, in + New Zealand, <a href='#Page_76'>76</a></span><br /> + <br /> + <span style="margin-left: 1em;">Chambers, Robert, on origin of + species, <a href='#Page_3'>3</a></span><br /> + <br /> + <span style="margin-left: 1em;">Chance rarely determines + survival, <a href='#Page_123'>123</a></span><br /> + <br /> + <span style="margin-left: 1em;">Change of conditions, utility of, + <a href='#Page_326'>326</a></span><br /> + <br /> + <span style="margin-left: 1em;">Characters, non-adaptive, + <a href='#Page_131'>131</a></span><br /> + <span style="margin-left: 2em;">transferred from useless to + useful class, <a href='#Page_132'>132</a></span><br /> + <br /> + <span style="margin-left: 1em;">Charaxes psaphon persecuted by a + bird, <a href='#Page_235'>235</a></span><br /> + <br /> + <span style="margin-left: 1em;">Chile, numerous red tubular + flowers in, <a href='#Page_320'>320</a></span><br /> + <br /> + <span style="margin-left: 1em;">Chimpanzee, figure of, <a href= + '#Page_454'>454</a></span><br /> + <br /> + <span style="margin-left: 1em;">Clark, Mr. Edwin, on cause of + absence of forests on the pampas, <a href= + '#Page_23'>23</a></span><br /> + <span style="margin-left: 2em;">on the struggle for life in the + South American valleys, <a href='#Page_24'>24</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cleistogamous flowers, <a href= + '#Page_322'>322</a></span><br /> + <br /> + <span style="margin-left: 1em;">Close interbreeding, supposed + evil results of, <a href='#Page_326'>326</a></span><br /> + <br /> + <span style="margin-left: 1em;">Clover, white, spread of, in New + Zealand, <a href='#Page_28'>28</a></span><br /> + <br /> + <span style="margin-left: 1em;">Co-adaptation of parts by + variation, no real difficulty, <a href= + '#Page_418'>418</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cobra, use of hood of, <a href= + '#Page_262'>262</a></span><br /> + <br /> + <span style="margin-left: 1em;">Coccinella mimicked by + grasshopper, (figure), <a href='#Page_260'>260</a></span><br /> + <br /> + <span style="margin-left: 1em;">Collingwood, Mr., on butterflies + recognising their kind, <a href='#Page_226'>226</a></span><br /> + <br /> + <span style="margin-left: 1em;">Coloration, alluring, <a href= + '#Page_210'>210</a></span><br /> + <span style="margin-left: 2em;">of birds' eggs, <a href= + '#Page_212'>212</a></span><br /> + <span style="margin-left: 2em;">a theory of animal, <a href= + '#Page_288'>288</a></span><br /> + <br /> + <span style="margin-left: 1em;">Colour correlated with sterility, + <a href='#Page_169'>169</a></span><br /> + <span style="margin-left: 2em;">correlated with constitutional + peculiarities, <a href='#Page_170'>170</a></span><br /> + <span style="margin-left: 2em;">in nature, the problem to be + solved, <a href='#Page_188'>188</a></span><br /> + <span style="margin-left: 2em;">constancy, in animals indicates + utility, <a href='#Page_189'>189</a></span><br /> + <span style="margin-left: 2em;">and environment, <a href= + '#Page_190'>190</a></span><br /> + <span style="margin-left: 2em;">general theories of animal, + <a href='#Page_193'>193</a></span><br /> + <span style="margin-left: 2em;">animal, supposed causes of, + <a href='#Page_193'>193</a></span><br /> + <span style="margin-left: 2em;">obscure, of many tropical + animals, <a href='#Page_194'>194</a></span><br /> + <span style="margin-left: 2em;">produced by surrounding objects, + <a href='#Page_195'>195</a></span><br /> + <span style="margin-left: 2em;">adaptations, local, <a href= + '#Page_199'>199</a></span><br /> + <span style="margin-left: 2em;">for recognition, <a href= + '#Page_217'>217</a></span><br /> + <span style="margin-left: 2em;">of wild animals not quite + symmetrical, <a href='#Page_217'>217</a> (note)</span><br /> + <span style="margin-left: 2em;">as influenced by locality or + climate, <a href='#Page_228'>228</a></span><br /> + <span style="margin-left: 2em;">development in butterflies, + <a href='#Page_274'>274</a></span><br /> + <span style="margin-left: 2em;">more variable than habits, + <a href='#Page_278'>278</a></span><br /> + <span style="margin-left: 2em;">and nerve distribution, <a href= + '#Page_290'>290</a></span><br /> + <span style="margin-left: 2em;">and tegumentary appendages, + <a href='#Page_291'>291</a></span><br /> + <span style="margin-left: 2em;">of flowers, <a href= + '#Page_308'>308</a></span><br /> + <span style="margin-left: 2em;">change of, in flowers when + fertilised, <a href='#Page_317'>317</a></span><br /> + <span style="margin-left: 2em;">in nature, concluding remarks on, + <a href='#Page_299'>299</a>, <a href= + '#Page_333'>333</a></span><br /> + <span style="margin-left: 2em;">of fruits, <a href= + '#Page_304'>304</a></span><br /> + <span style="margin-left: 2em;">of flowers growing together + contrasted, <a href='#Page_318'>318</a></span><br /> + <br /> + <span style="margin-left: 1em;">Complexity of flowers due to + alternate adaptation to insect and self-fertilisation, <a href= + '#Page_328'>328</a></span><br /> + <br /> + <span style="margin-left: 1em;">Composite, a, widely dispersed + without pappus, <a href='#Page_367'>367</a></span><br /> + <br /> + <span style="margin-left: 1em;">Confinement, affecting fertility, + <a href='#Page_154'>154</a></span><br /> + <br /> + <span style="margin-left: 1em;">Continental and oceanic areas, + <a href='#Page_346'>346</a></span><br /> + <br /> + <span style="margin-left: 1em;">Continents and oceans cannot have + changed places, <a href='#Page_345'>345</a></span><br /> + <span style="margin-left: 2em;">possible connections between, + <a href='#Page_349'>349</a></span><br /> + <br /> + <span style="margin-left: 1em;">Continuity does not prove + identity of origin, <a href='#Page_463'>463</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cope, Dr. E.D., on non-adaptive + characters, <a href='#Page_131'>131</a></span><br /> + <a name="Page_482" id="Page_482"></a> <span style= + "margin-left: 2em;">on fundamental laws of growth, <a href= + '#Page_420'>420</a></span><br /> + <span style="margin-left: 2em;">on bathmism or growth-force, + <a href='#Page_421'>421</a></span><br /> + <span style="margin-left: 2em;">on use producing structural + change, <a href='#Page_422'>422</a></span><br /> + <span style="margin-left: 2em;">on law of centrifugal growth, + <a href='#Page_422'>422</a></span><br /> + <span style="margin-left: 2em;">on origin of the feet of + ungulates, <a href='#Page_423'>423</a></span><br /> + <span style="margin-left: 2em;">on action of animal intelligence, + <a href='#Page_425'>425</a></span><br /> + <br /> + <span style="margin-left: 1em;">Correlations in pigeons, horses, + etc., <a href='#Page_140'>140</a></span><br /> + <br /> + <span style="margin-left: 1em;">Corvus frugilegus, <a href= + '#Page_2'>2</a></span><br /> + <span style="margin-left: 2em;">corone, <a href= + '#Page_2'>2</a></span><br /> + <br /> + <span style="margin-left: 1em;">Coursers, figures of secondary + quills, <a href='#Page_224'>224</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cowslip, two forms of, <a href= + '#Page_157'>157</a></span><br /> + <br /> + <span style="margin-left: 1em;">Crab, sexual diversity of colour + of, <a href='#Page_269'>269</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cretaceous period, dicotyledons + of, <a href='#Page_400'>400</a></span><br /> + <br /> + <span style="margin-left: 1em;">Crisp, Dr., on variations of gall + bladder and alimentary canal, <a href= + '#Page_69'>69</a></span><br /> + <br /> + <span style="margin-left: 1em;">Crosses, a cause of variation, + <a href='#Page_99'>99</a></span><br /> + <span style="margin-left: 2em;">reciprocal, <a href= + '#Page_155'>155</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cross-fertilisation, modes of + securing, <a href='#Page_310'>310</a></span><br /> + <span style="margin-left: 2em;">difference in, <a href= + '#Page_155'>155</a></span><br /> + <br /> + <span style="margin-left: 1em;">Crossing and changed + conditions,</span><br /> + <span style="margin-left: 2em;">parallelism of, <a href= + '#Page_166'>166</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cruciferae, variations of + structure in, <a href='#Page_80'>80</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cuckoo, eggs of, <a href= + '#Page_216'>216</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cuckoos mimick hawks, <a href= + '#Page_263'>263</a></span><br /> + <br /> + <span style="margin-left: 1em;">Cultivated plants, origin of + useful, <a href='#Page_97'>97</a></span><br /> + <br /> + <span style="margin-left: 1em;">Curculionidae mimicked by various + insects (figs.), <a href='#Page_260'>260</a></span><br /> + <br /> + <span style="margin-left: 1em;">Curves of variation, <a href= + '#Page_64'>64</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>D</b></span><br /> + <br /> + <span style="margin-left: 1em;">Dana, Professor, on the + permanence of continents, <a href= + '#Page_342'>342</a></span><br /> + <br /> + <span style="margin-left: 1em;">Danaidae little attacked by + mites, <a href='#Page_235'>235</a></span><br /> + <span style="margin-left: 2em;">mimicry of, <a href= + '#Page_246'>246</a></span><br /> + <br /> + <span style="margin-left: 1em;">Darwin, change of opinion + effected by, <a href='#Page_8'>8</a></span><br /> + <span style="margin-left: 2em;">the Newton of Natural History, + <a href='#Page_9'>9</a></span><br /> + <span style="margin-left: 2em;">his view of his own work, + <a href='#Page_10'>10</a></span><br /> + <span style="margin-left: 2em;">on the enemies of plants, + <a href='#Page_16'>16</a></span><br /> + <span style="margin-left: 2em;">on fir-trees destroyed by cattle, + <a href='#Page_17'>17</a></span><br /> + <span style="margin-left: 2em;">on change of plants and animals + caused by planting, <a href='#Page_18'>18</a></span><br /> + <span style="margin-left: 2em;">on absence of wild cattle in + Paraguay, <a href='#Page_19'>19</a></span><br /> + <span style="margin-left: 2em;">on cats and red clover, <a href= + '#Page_20'>20</a></span><br /> + <span style="margin-left: 2em;">on variety of plants in old turf, + <a href='#Page_35'>35</a></span><br /> + <span style="margin-left: 2em;">on the beneficent action of the + struggle for existence, <a href='#Page_40'>40</a></span><br /> + <span style="margin-left: 2em;">on variability of wild geraniums, + <a href='#Page_79'>79</a></span><br /> + <span style="margin-left: 2em;">on variability of common species, + <a href='#Page_80'>80</a></span><br /> + <span style="margin-left: 2em;">his non-recognition of extreme + variability of wild species, <a href= + '#Page_82'>82</a></span><br /> + <span style="margin-left: 2em;">on races of domestic pigeon, + <a href='#Page_90'>90</a></span><br /> + <span style="margin-left: 2em;">on constitutional variation in + plants, <a href='#Page_95'>95</a></span><br /> + <span style="margin-left: 2em;">on unconscious selection, + <a href='#Page_96'>96</a></span><br /> + <span style="margin-left: 2em;">on a case of divergence, <a href= + '#Page_105'>105</a></span><br /> + <span style="margin-left: 2em;">on advantage of diversification + of structure in inhabitants of one region, <a href= + '#Page_110'>110</a></span><br /> + <span style="margin-left: 2em;">on species of plants in turf, + <a href='#Page_110'>110</a></span><br /> + <span style="margin-left: 2em;">on isolation, <a href= + '#Page_119'>119</a></span><br /> + <span style="margin-left: 2em;">on origin of mammary glands, + <a href='#Page_129'>129</a></span><br /> + <span style="margin-left: 2em;">on eyes of flatfish, <a href= + '#Page_129'>129</a></span><br /> + <span style="margin-left: 2em;">on origin of the eye, <a href= + '#Page_130'>130</a></span><br /> + <span style="margin-left: 2em;">on useless characters, <a href= + '#Page_131'>131</a></span><br /> + <span style="margin-left: 2em;">on use of ears and tails, + <a href='#Page_136'>136</a></span><br /> + <span style="margin-left: 2em;">on disappearance of sports, + <a href='#Page_140'>140</a></span><br /> + <span style="margin-left: 2em;">on tendency to vary in one + direction, <a href='#Page_141'>141</a></span><br /> + <span style="margin-left: 2em;">on rare perpetuation of sports, + <a href='#Page_142'>142</a></span><br /> + <span style="margin-left: 2em;">on utility of specific + characters, <a href='#Page_142'>142</a> (note)</span><br /> + <span style="margin-left: 2em;">on importance of biological + environment, <a href='#Page_148'>148</a></span><br /> + <span style="margin-left: 2em;">on variable fertility of plants, + <a href='#Page_155'>155</a></span><br /> + <span style="margin-left: 2em;">on fertile hybrids among plants, + <a href='#Page_164'>164</a></span><br /> + <br /> + <span style="margin-left: 1em;">Darwin, on correlation of + sterility and colour, <a href='#Page_169'>169</a></span><br /> + <a name="Page_483" id="Page_483"></a> <span style= + "margin-left: 2em;">on selective association, <a href= + '#Page_172'>172</a></span><br /> + <span style="margin-left: 2em;">on infertility and natural + selection, <a href='#Page_174'>174</a></span><br /> + <span style="margin-left: 2em;">on cause of infertility of + hybrids, <a href='#Page_185'>185</a></span><br /> + <span style="margin-left: 2em;">on white tail of rabbit, <a href= + '#Page_218'>218</a></span><br /> + <span style="margin-left: 2em;">on conspicuous caterpillars, + <a href='#Page_236'>236</a></span><br /> + <span style="margin-left: 2em;">on sexual selection in insects, + <a href='#Page_274'>274</a></span><br /> + <span style="margin-left: 2em;">on decorative plumage of male + birds, <a href='#Page_285'>285</a></span><br /> + <span style="margin-left: 2em;">on development of ocelli, + <a href='#Page_290'>290</a></span><br /> + <span style="margin-left: 2em;">on value of cross-fertilisation, + <a href='#Page_309'>309</a></span><br /> + <span style="margin-left: 2em;">on limits to + utility of intercrossing, <a href= + '#Page_326'>326</a></span><br /> + <span style="margin-left: 2em;">on flowers due to insects, + <a href='#Page_332'>332</a></span><br /> + <span style="margin-left: 2em;">on oceanic islands, <a href= + '#Page_342'>342</a></span><br /> + <span style="margin-left: 2em;">on effects of disuse in domestic + animals, <a href='#Page_415'>415</a>, <a href= + '#Page_435'>435</a></span><br /> + <span style="margin-left: 2em;">on direct action of environment, + <a href='#Page_419'>419</a></span><br /> + <span style="margin-left: 2em;">on unintelligibility of theory of + retardation and acceleration, <a href='#Page_421'>421</a> + (note)</span><br /> + <span style="margin-left: 2em;">on origin of man's moral nature, + <a href='#Page_461'>461</a></span><br /> + <span style="margin-left: 2em;">Mr. George, on intermarriages of + British aristocracy, <a href='#Page_326'>326</a></span><br /> + <br /> + <span style="margin-left: 1em;">Darwinian theory, statement of, + <a href='#Page_10'>10</a></span><br /> + <span style="margin-left: 2em;">not opposed to spiritual nature + of man, <a href='#Page_478'>478</a></span><br /> + <span style="margin-left: 1em;">Dawkins, Professor Boyd, on + development of deer's horns, <a href= + '#Page_389'>389</a></span><br /> + <span style="margin-left: 2em;">on recent origin of man, <a href= + '#Page_456'>456</a></span><br /> + <span style="margin-left: 1em;">Dawson, Sir W., on determination + of fossil plants by leaves, <a href='#Page_398'>398</a> + (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Death of wild animals usually + painless, <a href='#Page_38'>38</a></span><br /> + <br /> + <span style="margin-left: 1em;">De Candolle, definition of + species, <a href='#Page_1'>1</a></span><br /> + <span style="margin-left: 2em;">on difficulty of naturalising + plants, <a href='#Page_15'>15</a></span><br /> + <span style="margin-left: 2em;">on war between plants, <a href= + '#Page_16'>16</a></span><br /> + <span style="margin-left: 2em;">on origin of useful cultivated + plants, <a href='#Page_97'>97</a></span><br /> + <br /> + <span style="margin-left: 1em;">Deer's horns, development of, + <a href='#Page_389'>389</a></span><br /> + <br /> + <span style="margin-left: 1em;">Degeneration, <a href= + '#Page_121'>121</a></span><br /> + <br /> + <span style="margin-left: 1em;">Delboeuf's law of variation, + <a href='#Page_141'>141</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dendraeca coronata, variation of + wing-feathers of, <a href='#Page_51'>51</a></span><br /> + <br /> + <span style="margin-left: 1em;">Denmark, struggle between trees + in, <a href='#Page_20'>20</a></span><br /> + <br /> + <span style="margin-left: 1em;">Denudation, evidences of, + <a href='#Page_379'>379</a></span><br /> + <br /> + <span style="margin-left: 1em;">Desert animals, colour of, + <a href='#Page_192'>192</a></span><br /> + <br /> + <span style="margin-left: 1em;">Deserts, effect of goats and + camels in destroying vegetation in, <a href= + '#Page_17'>17</a></span><br /> + <br /> + <span style="margin-left: 1em;">Development and display of + accessory plumes, <a href='#Page_293'>293</a></span><br /> + <br /> + <span style="margin-left: 1em;">Diadema anomala, <a href= + '#Page_271'>271</a></span><br /> + <span style="margin-left: 2em;">misippus, great diversity of + sexes in, <a href='#Page_271'>271</a></span><br /> + <br /> + <span style="margin-left: 1em;">Diaphora mendica mimics Spilosoma + menthrasti, <a href='#Page_249'>249</a></span><br /> + <br /> + <span style="margin-left: 1em;">Difficulties in the facts of + fertilisation of flowers, <a href= + '#Page_325'>325</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dimorphism and trimorphism, + <a href='#Page_156'>156</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dippers, probable origin of, + <a href='#Page_116'>116</a></span><br /> + <br /> + <span style="margin-left: 1em;">Disease and markings, <a href= + '#Page_290'>290</a></span><br /> + <br /> + <span style="margin-left: 1em;">Diseases common to man and + animals, <a href='#Page_449'>449</a></span><br /> + <br /> + <span style="margin-left: 1em;">Display of decorative plumage, + <a href='#Page_287'>287</a></span><br /> + <br /> + <span style="margin-left: 1em;">Distribution of organisms should + be explained by theory of descent, <a href= + '#Page_338'>338</a></span><br /> + <span style="margin-left: 2em;">conditions which have determined + the, <a href='#Page_341'>341</a></span><br /> + <span style="margin-left: 2em;">of marsupials, <a href= + '#Page_350'>350</a></span><br /> + <span style="margin-left: 2em;">of tapirs, <a href= + '#Page_352'>352</a></span><br /> + <br /> + <span style="margin-left: 1em;">Disuse, effects of, among wild + animals, <a href='#Page_415'>415</a></span><br /> + <span style="margin-left: 2em;">no proof that the effects of, are + inherited, <a href='#Page_417'>417</a></span><br /> + <br /> + <span style="margin-left: 1em;">Divergence of character, <a href= + '#Page_105'>105</a>-<a href='#Page_109'>109</a></span><br /> + <span style="margin-left: 2em;">leads to maximum of forms of life + in each area, <a href='#Page_109'>109</a></span><br /> + <br /> + <span style="margin-left: 1em;">Diversity of fauna and flora with + geographical proximity, <a href='#Page_339'>339</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dixon, Mr. C, changed habits of + chaffinch in New Zealand, <a href='#Page_76'>76</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dogs, origin of, <a href= + '#Page_88'>88</a></span><br /> + <span style="margin-left: 2em;">varieties of, <a href= + '#Page_89'>89</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dolichonyx oryzivorus, diagram + showing variations of, <a href='#Page_55'>55</a></span><br /> + <br /> + <span style="margin-left: 1em;">Domestic animals, varieties of, + <a href='#Page_88'>88</a></span><br /> + <br /> + <span style="margin-left: 1em;">Draba verna, varieties of, + <a href='#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dress of men not determined by + female choice, <a href='#Page_286'>286</a></span><br /> + <br /> + <span style="margin-left: 1em;">Dust from Krakatoa, size of + particles of, <a href='#Page_363'>363</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>E</b></span><br /> + <br /> + <span style="margin-left: 1em;">Eastern butterflies, variation + of, <a href='#Page_45'>45</a></span><br /> + <br /> + <span style="margin-left: 1em;">Eaton, Rev. A.E., on Kerguelen + insects, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Edwards, Mr. W.H., on dark forms + of Papilio turnus, <a href='#Page_248'>248</a></span><br /> + <a name="Page_484" id="Page_484"></a><br /> + <span style="margin-left: 1em;">Eggs protectively coloured, + <a href='#Page_214'>214</a>, <a href= + '#Page_215'>215</a></span><br /> + <span style="margin-left: 2em;">theory of varied colours of, + <a href='#Page_216'>216</a></span><br /> + <br /> + <span style="margin-left: 1em;">Elaps mimicked by harmless + snakes, <a href='#Page_261'>261</a></span><br /> + <br /> + <span style="margin-left: 1em;">Embryonic development of man and + other mammalia, <a href='#Page_448'>448</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ennis, Mr. John, on willows + driving out watercresses from rivers of New Zealand, <a href= + '#Page_24'>24</a></span><br /> + <br /> + <span style="margin-left: 1em;">Entomostraca, in bromelia leaves, + <a href='#Page_118'>118</a></span><br /> + <br /> + <span style="margin-left: 1em;">Environment never identical for + two species, <a href='#Page_149'>149</a></span><br /> + <span style="margin-left: 2em;">direct action of, <a href= + '#Page_418'>418</a></span><br /> + <span style="margin-left: 2em;">direct influence of, <a href= + '#Page_426'>426</a></span><br /> + <span style="margin-left: 2em;">as initiator of variations, + <a href='#Page_436'>436</a></span><br /> + <span style="margin-left: 2em;">action of, overpowered by natural + selection, <a href='#Page_437'>437</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ethical aspect of the struggle + for existence, <a href='#Page_36'>36</a></span><br /> + <br /> + <span style="margin-left: 1em;">Euchelia jacobeae inedible, + <a href='#Page_235'>235</a></span><br /> + <br /> + <span style="margin-left: 1em;">Everett, Mr. A., on a caterpillar + resembling moss, <a href='#Page_205'>205</a></span><br /> + <br /> + <span style="margin-left: 1em;">Evidence of evolution that may be + expected among fossil forms, <a href= + '#Page_380'>380</a></span><br /> + <br /> + <span style="margin-left: 1em;">Evolutionists, American school + of, <a href='#Page_420'>420</a></span><br /> + <br /> + <span style="margin-left: 1em;">Exogens, possible cause of sudden + late appearance of, <a href='#Page_400'>400</a></span><br /> + <br /> + <span style="margin-left: 1em;">External differences of man and + apes, <a href='#Page_453'>453</a></span><br /> + <br /> + <span style="margin-left: 1em;">Extinct animals, number of + species of, <a href='#Page_376'>376</a></span><br /> + <br /> + <span style="margin-left: 1em;">Extinction of large animals, + cause of, <a href='#Page_394'>394</a></span><br /> + <br /> + <span style="margin-left: 1em;">Eye, origin of, <a href= + '#Page_130'>130</a></span><br /> + <br /> + <span style="margin-left: 1em;">Eyes, explanation of loss of in + cave animals, <a href='#Page_416'>416</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>F</b></span><br /> + <br /> + <span style="margin-left: 1em;">Facts of natural selection, + summary of, <a href='#Page_122'>122</a></span><br /> + <br /> + <span style="margin-left: 1em;">Falcons illustrating divergence, + <a href='#Page_108'>108</a></span><br /> + <span style="margin-left: 2em;">and butcher birds, hooked and + toothed beaks of, <a href='#Page_422'>422</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fantails, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Female birds, why often dull + coloured, <a href='#Page_277'>277</a></span><br /> + <br /> + <span style="margin-left: 1em;">Female birds, what their choice + of mates is determined by, <a href= + '#Page_286'>286</a></span><br /> + <span style="margin-left: 2em;">butterflies, why dull coloured, + <a href='#Page_272'>272</a></span><br /> + <span style="margin-left: 2em;">brighter than male bird, <a href= + '#Page_281'>281</a></span><br /> + <span style="margin-left: 2em;">choice a doubtful agent in + selection, <a href='#Page_283'>283</a></span><br /> + <span style="margin-left: 2em;">preference neutralised by natural + selection, <a href='#Page_294'>294</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fertility of domestic animals, + <a href='#Page_154'>154</a></span><br /> + <br /> + <span style="margin-left: 1em;">Flatfish, eyes of, <a href= + '#Page_129'>129</a></span><br /> + <br /> + <span style="margin-left: 1em;">Flesh-fly, enormous increase of, + <a href='#Page_25'>25</a></span><br /> + <br /> + <span style="margin-left: 1em;">Floral structure, great + differences of, in allied genera and species, <a href= + '#Page_329'>329</a></span><br /> + <br /> + <span style="margin-left: 1em;">Flowers, variations of, <a href= + '#Page_88'>88</a></span><br /> + <span style="margin-left: 2em;">colours of, <a href= + '#Page_308'>308</a></span><br /> + <span style="margin-left: 2em;">with sham nectaries, <a href= + '#Page_317'>317</a></span><br /> + <span style="margin-left: 2em;">changing colour when fertilised, + <a href='#Page_317'>317</a></span><br /> + <span style="margin-left: 2em;">adapted to bees or to + butterflies, <a href='#Page_318'>318</a></span><br /> + <span style="margin-left: 2em;">contrasted colours of, at same + season and locality, <a href='#Page_318'>318</a></span><br /> + <span style="margin-left: 2em;">fertilisation of, by birds, + <a href='#Page_319'>319</a></span><br /> + <span style="margin-left: 2em;">self-fertilisation of, <a href= + '#Page_321'>321</a></span><br /> + <span style="margin-left: 2em;">once insect-fertilised now + self-fertile, <a href='#Page_323'>323</a></span><br /> + <span style="margin-left: 2em;">how the struggle for existence + acts among, <a href='#Page_328'>328</a></span><br /> + <span style="margin-left: 2em;">repeatedly modified during whole + Tertiary period, <a href='#Page_331'>331</a></span><br /> + <span style="margin-left: 2em;">the product of insect agency, + <a href='#Page_332'>332</a></span><br /> + <br /> + <span style="margin-left: 1em;">Forbes, Mr. H.O., on protective + colour of a pigeon, <a href='#Page_200'>200</a></span><br /> + <span style="margin-left: 2em;">on spider imitating birds' + dropping, <a href='#Page_211'>211</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fossil shells, complete series of + transitional forms of, <a href='#Page_381'>381</a></span><br /> + <span style="margin-left: 2em;">crocodiles afford evidence of + evolution, <a href='#Page_383'>383</a></span><br /> + <span style="margin-left: 2em;">horses in America, <a href= + '#Page_386'>386</a></span><br /> + <span style="margin-left: 2em;">and living animals, local + relations of, <a href='#Page_391'>391</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fowl, early domestication of, + <a href='#Page_97'>97</a></span><br /> + <br /> + <span style="margin-left: 1em;">Frill-back, Indian, <a href= + '#Page_93'>93</a></span><br /> + <br /> + <span style="margin-left: 1em;">Frog inhabiting bromelia leaves, + <a href='#Page_118'>118</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fruits, use of characters of, + <a href='#Page_133'>133</a></span><br /> + <span style="margin-left: 2em;">colours of, <a href= + '#Page_304'>304</a></span><br /> + <span style="margin-left: 2em;">edible or attractive, <a href= + '#Page_306'>306</a></span><br /> + <span style="margin-left: 2em;">poisonous, <a href= + '#Page_307'>307</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fulica atra, protectively + coloured eggs of, <a href='#Page_215'>215</a></span><br /> + <br /> + <span style="margin-left: 1em;">Fulmar petrel, abundance of, + <a href='#Page_30'>30</a></span><br /> + <br /> + <br /> + <a name="Page_485" id="Page_485"></a> <span style= + "margin-left: 1em;"><b>G</b></span><br /> + <br /> + <span style="margin-left: 1em;">Gallinaceae, ornamental plumes + of, <a href='#Page_292'>292</a></span><br /> + <br /> + <span style="margin-left: 1em;">Galton, Mr. F., diagrams of + variability used by, <a href='#Page_74'>74</a></span><br /> + <span style="margin-left: 2em;">on markings of zebra, <a href= + '#Page_220'>220</a> (note)</span><br /> + <span style="margin-left: 2em;">on regression towards + mediocrity, <a href='#Page_414'>414</a></span><br /> + <span style="margin-left: 2em;">theory of heredity by, <a href= + '#Page_443'>443</a> (note)</span><br /> + <span style="margin-left: 2em;">on imperfect counting of the + Damaras, <a href='#Page_464'>464</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gaudry on extinct animals at + Pikermi, <a href='#Page_377'>377</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gay, Mons. T., on variations of + structure in Cruciferae, <a href='#Page_80'>80</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gazella soemmerringi (figure), + <a href='#Page_219'>219</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gazelles, recognition marks of, + <a href='#Page_218'>218</a></span><br /> + <br /> + <span style="margin-left: 1em;">Geddes, Professor, on variation + in plants, <a href='#Page_428'>428</a></span><br /> + <span style="margin-left: 2em;">objection to theory of, <a href= + '#Page_430'>430</a></span><br /> + <br /> + <span style="margin-left: 1em;">Geikie, Dr. Archibald, on + formation of marine stratified rocks, <a href= + '#Page_344'>344</a></span><br /> + <br /> + <span style="margin-left: 1em;">Geoffroy St. Hilaire, on species, + <a href='#Page_6'>6</a></span><br /> + <br /> + <span style="margin-left: 1em;">Geological evidences of + evolution, <a href='#Page_376'>376</a>, <a href= + '#Page_381'>381</a></span><br /> + <span style="margin-left: 2em;">record, causes of imperfection + of, <a href='#Page_379'>379</a></span><br /> + <span style="margin-left: 2em;">distribution of insects, <a href= + '#Page_403'>403</a></span><br /> + <span style="margin-left: 2em;">antiquity of man, <a href= + '#Page_455'>455</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ghost-moth, colours of, <a href= + '#Page_270'>270</a></span><br /> + <br /> + <span style="margin-left: 1em;">Glaciation, no proofs of, in + Brazil, <a href='#Page_370'>370</a></span><br /> + <br /> + <span style="margin-left: 1em;">Glow-worm, light a warning of + inedibility, <a href='#Page_287'>287</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gomphia oleaefolia, variability + of, <a href='#Page_79'>79</a></span><br /> + <br /> + <span style="margin-left: 1em;">Goose eating flesh, <a href= + '#Page_75'>75</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gosse, Mr. P.H., on variation in + the sea-anemones, <a href='#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">on sea-anemone and bullhead, + <a href='#Page_265'>265</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gould, Mr., on colours of coast + and inland birds, <a href='#Page_228'>228</a></span><br /> + <br /> + <span style="margin-left: 1em;">Grant Allen, on forms of leaves, + <a href='#Page_133'>133</a></span><br /> + <span style="margin-left: 2em;">on insects and flowers, <a href= + '#Page_332'>332</a></span><br /> + <br /> + <span style="margin-left: 1em;">Graphite in Laurentian implies + abundant plant life, <a href='#Page_398'>398</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gray, Dr. Asa, on naturalised + plants in the United States, <a href= + '#Page_110'>110</a></span><br /> + <span style="margin-left: 2em;">Dr. J.E., on variation of skulls + of mammalia, <a href='#Page_71'>71</a></span><br /> + <br /> + <span style="margin-left: 1em;">Great fertility not essential to + rapid increase, <a href='#Page_30'>30</a></span><br /> + <br /> + <span style="margin-left: 1em;">Great powers of increase of + animals, <a href='#Page_27'>27</a></span><br /> + <br /> + <span style="margin-left: 1em;">Green colour of birds in tropical + forests, <a href='#Page_192'>192</a></span><br /> + <br /> + <span style="margin-left: 1em;">Grouse, red, recent divergence + of, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Gulick, Rev. J.T., on variation + of land-shells, <a href='#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">on isolation and variation, + <a href='#Page_147'>147</a>, <a href= + '#Page_150'>150</a></span><br /> + <span style="margin-left: 2em;">on divergent evolution, <a href= + '#Page_148'>148</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>H</b></span><br /> + <br /> + <span style="margin-left: 1em;">Habits of animals, + variability of, <a href='#Page_74'>74</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hairy caterpillars inedible, + <a href='#Page_237'>237</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hanbury, Mr. Thomas, on a + remarkable case of wind conveyance of seed, <a href= + '#Page_373'>373</a> (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Hansten-Blangsted, on succession + of trees in Denmark, <a href='#Page_21'>21</a></span><br /> + <br /> + <span style="margin-left: 1em;">Harvest mice, prehensile tails of + young, <a href='#Page_136'>136</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hawkweed, species and varieties + of British, <a href='#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hector, Sir James, use of horns + of deer, <a href='#Page_137'>137</a></span><br /> + <br /> + <span style="margin-left: 1em;">Heliconidae, warning colours of, + <a href='#Page_234'>234</a></span><br /> + <span style="margin-left: 2em;">mimicry of, <a href= + '#Page_240'>240</a></span><br /> + <br /> + <span style="margin-left: 1em;">Helix nemoralis, varieties of, + <a href='#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">hortensis, varieties of, <a href= + '#Page_43'>43</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hemsley, Mr., on rarity of spines + in oceanic islands, <a href='#Page_432'>432</a></span><br /> + <br /> + <span style="margin-left: 1em;">Henslow, Professor G., on vigour + of self-fertilised plants, <a href= + '#Page_323'>323</a></span><br /> + <span style="margin-left: 2em;">on wind-fertilised as + degradations from insect-fertilised flowers, <a href= + '#Page_324'>324</a></span><br /> + <span style="margin-left: 2em;">on origin of forms and structures + of flowers, 434 (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Herbert, Dean, on species, + <a href='#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">on plant hybrids, <a href= + '#Page_164'>164</a></span><br /> + <br /> + <span style="margin-left: 1em;">Herbivora, recognition marks of, + <a href='#Page_218'>218</a></span><br /> + <br /> + <span style="margin-left: 1em;">Heredity, <a href= + '#Page_11'>11</a></span><br /> + <span style="margin-left: 2em;">Weismann's theory of, <a href= + '#Page_437'>437</a></span><br /> + <br /> + <span style="margin-left: 1em;">Herschel, Sir John, on species, + <a href='#Page_3'>3</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hooker, Sir Joseph, on attempts + at naturalising Australian plants in New Zealand, <a href= + '#Page_16'>16</a></span><br /> + <br /> + <span style="margin-left: 1em;">Home, Mr. C, on inedibility of an + Indian locust, <a href='#Page_267'>267</a></span><br /> + <br /> + <span style="margin-left: 1em;">Horns of deer, uses of, <a href= + '#Page_136'>136</a></span><br /> + <br /> + <span style="margin-left: 1em;">Horse tribe, pedigree of, + <a href='#Page_384'>384</a></span><br /> + <a name="Page_486" id="Page_486"></a> <span style= + "margin-left: 2em;">ancestral forms of, <a href= + '#Page_386'>386</a></span><br /> + <br /> + <span style="margin-left: 1em;">Humming-birds, recognition marks + of, <a href='#Page_226'>226</a></span><br /> + <br /> + <span style="margin-left: 1em;">Huth, Mr., on close + interbreeding, <a href='#Page_160'>160</a></span><br /> + <br /> + <span style="margin-left: 1em;">Huxley, Professor on the struggle + for existence, <a href='#Page_37'>37</a></span><br /> + <span style="margin-left: 2em;">on fossil crocodiles, <a href= + '#Page_383'>383</a></span><br /> + <span style="margin-left: 2em;">on anatomical peculiarities of + the horse tribe, <a href='#Page_384'>384</a></span><br /> + <span style="margin-left: 2em;">on development of vertebrates, + <a href='#Page_448'>448</a></span><br /> + <span style="margin-left: 2em;">on early man, <a href= + '#Page_456'>456</a></span><br /> + <span style="margin-left: 2em;">on brains of man and the gorilla, + <a href='#Page_457'>457</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hybridity, remarks on facts of, + <a href='#Page_166'>166</a></span><br /> + <span style="margin-left: 2em;">summary on, <a href= + '#Page_184'>184</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hybrids, infertility of, supposed + test of distinct species, <a href= + '#Page_152'>152</a></span><br /> + <span style="margin-left: 2em;">fertility of, <a href= + '#Page_159'>159</a></span><br /> + <span style="margin-left: 2em;">fertile among animals, <a href= + '#Page_162'>162</a></span><br /> + <span style="margin-left: 2em;">between sheep and goat, <a href= + '#Page_162'>162</a></span><br /> + <span style="margin-left: 2em;">fertile between distinct species + of moths, <a href='#Page_163'>163</a></span><br /> + <span style="margin-left: 2em;">fertile among plants, <a href= + '#Page_163'>163</a></span><br /> + <br /> + <span style="margin-left: 1em;">Hymenopus bicornis, resembling + flower, <a href='#Page_212'>212</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>I</b></span><br /> + <br /> + <span style="margin-left: 1em;">Icterus Baltimore, diagram + showing proportionate numbers which</span><br /> + <span style="margin-left: 1em;">vary, <a href= + '#Page_63'>63</a></span><br /> + <br /> + <span style="margin-left: 1em;">Imitative resemblances, how + produced, <a href='#Page_205'>205</a></span><br /> + <br /> + <span style="margin-left: 1em;">Increase of organisms in a + geometrical ratio, <a href='#Page_25'>25</a></span><br /> + <br /> + <span style="margin-left: 1em;">Inedible fruits rarely coloured, + <a href='#Page_308'>308</a></span><br /> + <br /> + <span style="margin-left: 1em;">Insect and self-fertilisation, + alternation of, in flowers, <a href= + '#Page_328'>328</a></span><br /> + <br /> + <span style="margin-left: 1em;">Insect-fertilisation, facts + relating to, <a href='#Page_316'>316</a></span><br /> + <br /> + <span style="margin-left: 1em;">Insects, coloured for + recognition, <a href='#Page_226'>226</a></span><br /> + <span style="margin-left: 2em;">warning colours of, <a href= + '#Page_233'>233</a></span><br /> + <span style="margin-left: 2em;">sexual coloration of, <a href= + '#Page_269'>269</a></span><br /> + <span style="margin-left: 2em;">importance of dull colours to + female, <a href='#Page_272'>272</a></span><br /> + <span style="margin-left: 2em;">visiting one kind of flower at a + time, <a href='#Page_318'>318</a></span><br /> + <span style="margin-left: 2em;">and flowers, the most brilliant + not found together, <a href='#Page_335'>335</a></span><br /> + <br /> + <span style="margin-left: 1em;">Insects, no proof of love of + colour by, <a href='#Page_336'>336</a></span><br /> + <span style="margin-left: 2em;">and birds at sea, <a href= + '#Page_357'>357</a></span><br /> + <span style="margin-left: 2em;">in mid-ocean, <a href= + '#Page_359'>359</a></span><br /> + <span style="margin-left: 2em;">at great altitudes, <a href= + '#Page_360'>360</a></span><br /> + <span style="margin-left: 2em;">geological distribution of, + <a href='#Page_403'>403</a></span><br /> + <span style="margin-left: 2em;">ancestral in Silurian, <a href= + '#Page_405'>405</a></span><br /> + <span style="margin-left: 2em;">fossil support evolution, + <a href='#Page_405'>405</a></span><br /> + <br /> + <span style="margin-left: 1em;">Instability of useless + characters, <a href='#Page_138'>138</a></span><br /> + <br /> + <span style="margin-left: 1em;">Instinct, the theory of, <a href= + '#Page_441'>441</a></span><br /> + <br /> + <span style="margin-left: 1em;">Insular organisms illustrate + powers of dispersal, <a href='#Page_354'>354</a></span><br /> + <br /> + <span style="margin-left: 1em;">Interbreeding, close, injurious + effects of, <a href='#Page_160'>160</a></span><br /> + <span style="margin-left: 2em;">supposed evil results of close, + <a href='#Page_326'>326</a></span><br /> + <br /> + <span style="margin-left: 1em;">Intercrossing, swamping effects + of, <a href='#Page_142'>142</a></span><br /> + <span style="margin-left: 2em;">not necessarily useful, <a href= + '#Page_325'>325</a></span><br /> + <br /> + <span style="margin-left: 1em;">Intermediate forms, why not + found, <a href='#Page_380'>380</a></span><br /> + <br /> + <span style="margin-left: 1em;">Islands, all oceanic are volcanic + or coralline, <a href='#Page_342'>342</a></span><br /> + <br /> + <span style="margin-left: 1em;">Isle of Man, small butterflies + of, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Isolation, the importance of, + <a href='#Page_119'>119</a></span><br /> + <span style="margin-left: 2em;">to prevent intercrossing, + <a href='#Page_144'>144</a></span><br /> + <span style="margin-left: 2em;">by variations of habits, etc., + <a href='#Page_145'>145</a></span><br /> + <span style="margin-left: 2em;">Rev. J.G. Gulick on, <a href= + '#Page_147'>147</a></span><br /> + <span style="margin-left: 2em;">when ineffective, <a href= + '#Page_150'>150</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ituna Ilione and Thyridia + megisto, figures of wings of, <a href= + '#Page_251'>251</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>J</b></span><br /> + <br /> + <span style="margin-left: 1em;">Jacobin, <a href= + '#Page_93'>93</a></span><br /> + <br /> + <span style="margin-left: 1em;">Jenyns, Rev. L., on internal + variations of mammalia, <a href='#Page_69'>69</a></span><br /> + <br /> + <span style="margin-left: 1em;">Jordan, Mons. A., on varieties of + Draba verna, <a href='#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Judd, Professor, on dust fallen + at Genoa, <a href='#Page_363'>363</a></span><br /> + <span style="margin-left: 2em;">on Hungarian fossil lacustrine + shells, <a href='#Page_381'>381</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>K</b></span><br /> + <br /> + <span style="margin-left: 1em;">Kerguelen Island, wingless + insects of, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Kerivoula picta, protective + colour of, <a href='#Page_201'>201</a></span><br /> + <br /> + <span style="margin-left: 1em;">Kerner, Professor, on use of + external characters of plants, <a href= + '#Page_133'>133</a></span><br /> + <a name="Page_487" id="Page_487"></a> <span style= + "margin-left: 2em;">on seeds found on glaciers, <a href= + '#Page_366'>366</a></span><br /> + <br /> + <span style="margin-left: 1em;">Kingfishers illustrating + divergence of character, <a href='#Page_109'>109</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>L</b></span><br /> + <br /> + <span style="margin-left: 1em;">Lacerta muralis, diagram of + variation of, <a href='#Page_47'>47</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lagopus scoticus, origin of, + <a href='#Page_107'>107</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lamarck, on origin of species, + <a href='#Page_3'>3</a></span><br /> + <br /> + <span style="margin-left: 1em;">Land debris deposited near + coasts, <a href='#Page_343'>343</a></span><br /> + <span style="margin-left: 2em;">and ocean, diagram showing + comparative height and depth of, <a href= + '#Page_345'>345</a></span><br /> + <br /> + <span style="margin-left: 1em;">Large animals, cause of + extinction of, <a href='#Page_394'>394</a></span><br /> + <br /> + <span style="margin-left: 1em;">Larvae of moths, variability of, + <a href='#Page_46'>46</a></span><br /> + <br /> + <span style="margin-left: 1em;">Laughers, Frill-backs, Nuns, + Spots, and Swallows, <a href='#Page_93'>93</a></span><br /> + <br /> + <span style="margin-left: 1em;">Law of relation of colour and + nest, <a href='#Page_278'>278</a>, <a href= + '#Page_279'>279</a></span><br /> + <br /> + <span style="margin-left: 1em;">Laws of animal coloration, + <a href='#Page_296'>296</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lawson Tait, on uses of tails, + <a href='#Page_136'>136</a></span><br /> + <br /> + <span style="margin-left: 1em;">Leaf-butterflies, <a href= + '#Page_207'>207</a></span><br /> + <br /> + <span style="margin-left: 1em;">Leguminosae, rare in oceanic + islands, <a href='#Page_368'>368</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lemuria, an unsound hypothesis, + <a href='#Page_354'>354</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lepidoptera, variation of, + <a href='#Page_44'>44</a></span><br /> + <br /> + <span style="margin-left: 1em;">Leyden Museum, diagram showing + variability of birds in, <a href='#Page_61'>61</a></span><br /> + <br /> + <span style="margin-left: 1em;">Life, Weismann on duration of, + 437 (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Limenitis misippus mimics Danais + archippus, <a href='#Page_248'>248</a></span><br /> + <span style="margin-left: 2em;">ursula mimics Papilio philenor, + <a href='#Page_248'>248</a></span><br /> + <br /> + <span style="margin-left: 1em;">Linnaeus, on rapid increase of + the flesh-fly, <a href='#Page_25'>25</a></span><br /> + <br /> + <span style="margin-left: 1em;">Livingstone, his sensations when + seized by a lion, <a href='#Page_38'>38</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lizards, variation among, + <a href='#Page_46'>46</a></span><br /> + <span style="margin-left: 2em;">diagram of variation of, <a href= + '#Page_48'>48</a></span><br /> + <span style="margin-left: 2em;">sexual colours of, <a href= + '#Page_281'>281</a></span><br /> + <br /> + <span style="margin-left: 1em;">Local colour adaptations, + <a href='#Page_199'>199</a></span><br /> + <br /> + <span style="margin-left: 1em;">Locusts with warning colours + inedible, <a href='#Page_267'>267</a></span><br /> + <br /> + <span style="margin-left: 1em;">Longicorns mimic Malacoderms, + <a href='#Page_257'>257</a></span><br /> + <br /> + <span style="margin-left: 1em;">Low, Mr., on effects of close + interbreeding, <a href='#Page_160'>160</a></span><br /> + <br /> + <span style="margin-left: 1em;">Low, Mr., on fertile crosses + between sheep and goat, <a href='#Page_162'>162</a></span><br /> + <span style="margin-left: 2em;">on selective association, + <a href='#Page_172'>172</a></span><br /> + <br /> + <span style="margin-left: 1em;">Low forms of life, continued + existence of, explained, <a href='#Page_114'>114</a></span><br /> + <span style="margin-left: 2em;">forms, persistence of, <a href= + '#Page_121'>121</a></span><br /> + <span style="margin-left: 2em;">temperature of tropics not needed + to explain plant dispersal, <a href= + '#Page_370'>370</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lower types, extinction of, among + the higher animals, <a href='#Page_114'>114</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lubbock, Sir John, on forms of + leaves, <a href='#Page_133'>133</a></span><br /> + <span style="margin-left: 2em;">on imperfect counting of early + man, <a href='#Page_464'>464</a></span><br /> + <br /> + <span style="margin-left: 1em;">Lyell, Sir Charles, on variation + of species, <a href='#Page_4'>4</a></span><br /> + <span style="margin-left: 2em;">on the shifting of continents, + <a href='#Page_342'>342</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>M</b></span><br /> + <br /> + <span style="margin-left: 1em;">Madagascar and New Zealand, + <a href='#Page_347'>347</a></span><br /> + <br /> + <span style="margin-left: 1em;">Madeira, wingless beetles of, + <a href='#Page_105'>105</a></span><br /> + <br /> + <span style="margin-left: 1em;">Maize, origin of, <a href= + '#Page_98'>98</a></span><br /> + <br /> + <span style="margin-left: 1em;">Male rivalry, a real cause of + selection, <a href='#Page_283'>283</a></span><br /> + <br /> + <span style="margin-left: 1em;">Males of many animals fights + together, <a href='#Page_282'>282</a></span><br /> + <br /> + <span style="margin-left: 1em;">Malm, on eyes of flatfish, + <a href='#Page_129'>129</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mammalia, variation of, <a href= + '#Page_65'>65</a></span><br /> + <span style="margin-left: 2em;">sexual colours of, <a href= + '#Page_281'>281</a>, <a href='#Page_282'>282</a></span><br /> + <span style="margin-left: 2em;">afford crucial tests of theories + of distribution, <a href='#Page_353'>353</a></span><br /> + <span style="margin-left: 2em;">early forms of, <a href= + '#Page_407'>407</a></span><br /> + <span style="margin-left: 2em;">geological distribution of, + <a href='#Page_408'>408</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mammary glands, supposed origin + of, <a href='#Page_129'>129</a></span><br /> + <br /> + <span style="margin-left: 1em;">Man, summary of animal + characteristics of, <a href='#Page_454'>454</a></span><br /> + <span style="margin-left: 2em;">geological antiquity of, <a href= + '#Page_455'>455</a></span><br /> + <span style="margin-left: 2em;">early remains of, in California, + <a href='#Page_456'>456</a></span><br /> + <span style="margin-left: 2em;">probably as old as the Miocene, + <a href='#Page_457'>457</a></span><br /> + <span style="margin-left: 2em;">probable birthplace of, <a href= + '#Page_459'>459</a></span><br /> + <span style="margin-left: 2em;">origin of moral and intellectual + nature of, <a href='#Page_461'>461</a></span><br /> + <span style="margin-left: 2em;">possesses mental qualities not + derived exclusively</span><br /> + <span style="margin-left: 6em;">from his animal progenitors, + <a href='#Page_474'>474</a></span><br /> + <br /> + <span style="margin-left: 1em;">Man's body that of an animal, + <a href='#Page_444'>444</a></span><br /> + <a name="Page_488" id="Page_488"></a> <span style= + "margin-left: 2em;">development similar to that of animals, + <a href='#Page_449'>449</a></span><br /> + <span style="margin-left: 2em;">structure compared with that of + the anthropoid apes, <a href='#Page_451'>451</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mania typica refused by lizards, + <a href='#Page_238'>238</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mantidae resembling flowers, + <a href='#Page_212'>212</a></span><br /> + <br /> + <span style="margin-left: 1em;">Marcgravia nepenthoides + fertilised by birds (woodcut), <a href= + '#Page_320'>320</a></span><br /> + <br /> + <span style="margin-left: 1em;">Marine animals, protective + resemblance among, <a href='#Page_208'>208</a></span><br /> + <span style="margin-left: 2em;">with warning colours, <a href= + '#Page_266'>266</a></span><br /> + <br /> + <span style="margin-left: 1em;">Marsh, Mr., on destructiveness to + vegetation of goats and camels, <a href= + '#Page_17'>17</a></span><br /> + <span style="margin-left: 2em;">Professor O., on the development + of the horse tribe, <a href='#Page_386'>386</a></span><br /> + <span style="margin-left: 2em;">on brain development of Tertiary + mammals, <a href='#Page_391'>391</a></span><br /> + <span style="margin-left: 2em;">on specialised forms dying out, + <a href='#Page_395'>395</a></span><br /> + <br /> + <span style="margin-left: 1em;">Marsupials, distribution of, + <a href='#Page_350'>350</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mathematical faculty, the origin + of the, <a href='#Page_464'>464</a></span><br /> + <span style="margin-left: 2em;">how developed, <a href= + '#Page_466'>466</a></span><br /> + <span style="margin-left: 2em;">not developed by law of natural + selection, <a href='#Page_469'>469</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mathematics, late development of, + <a href='#Page_465'>465</a></span><br /> + <br /> + <span style="margin-left: 1em;">Meldola, Professor R., on + variable protective colouring, <a href= + '#Page_196'>196</a></span><br /> + <span style="margin-left: 2em;">on mimicry among British moths, + 249 (note)</span><br /> + <span style="margin-left: 2em;">on an extension of the theory of + mimicry, <a href='#Page_255'>255</a> (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Melons, variations of, <a href= + '#Page_87'>87</a></span><br /> + <br /> + <span style="margin-left: 1em;">Methona psidii and Leptalis orise + (figs.), <a href='#Page_241'>241</a></span><br /> + <br /> + <span style="margin-left: 1em;">Meyer, Dr. A.B., on mimicry of + snakes, <a href='#Page_262'>262</a></span><br /> + <br /> + <span style="margin-left: 1em;">Milne Edwards, on variation of + lizards, <a href='#Page_46'>46</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mimicking birds deceive + naturalists, <a href='#Page_264'>264</a></span><br /> + <span style="margin-left: 2em;">butterfly, figure of, <a href= + '#Page_241'>241</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mimicry, <a href= + '#Page_239'>239</a></span><br /> + <span style="margin-left: 2em;">how it has been produced, + <a href='#Page_242'>242</a></span><br /> + <span style="margin-left: 2em;">among protected genera, <a href= + '#Page_249'>249</a></span><br /> + <span style="margin-left: 2em;">extension of, <a href= + '#Page_255'>255</a></span><br /> + <span style="margin-left: 2em;">in various orders of insects, + <a href='#Page_257'>257</a></span><br /> + <span style="margin-left: 2em;">among vertebrata, <a href= + '#Page_261'>261</a></span><br /> + <span style="margin-left: 2em;">among birds, <a href= + '#Page_263'>263</a></span><br /> + <span style="margin-left: 2em;">objections to theory of, <a href= + '#Page_264'>264</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mineral particles carried by + wind, <a href='#Page_363'>363</a></span><br /> + <br /> + <span style="margin-left: 1em;">Miocene fossils of North America, + <a href='#Page_378'>378</a></span><br /> + <br /> + <span style="margin-left: 1em;">Missing links, character of, + <a href='#Page_380'>380</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mivart, Dr. St. George, on + variation of ribs and dorsal vertebrae, <a href= + '#Page_69'>69</a></span><br /> + <span style="margin-left: 2em;">on supposed useless characters, + <a href='#Page_138'>138</a> (note)</span><br /> + <span style="margin-left: 2em;">on resemblance of man and apes, + <a href='#Page_451'>451</a></span><br /> + <br /> + <span style="margin-left: 1em;">Modifications for special + purposes, <a href='#Page_113'>113</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mongrels, sterility of, <a href= + '#Page_165'>165</a></span><br /> + <br /> + <span style="margin-left: 1em;">Monkeys affected by medicines as + are men, <a href='#Page_450'>450</a></span><br /> + <br /> + <span style="margin-left: 1em;">Monocotyledons degradations from + dicotyledons, <a href='#Page_325'>325</a> (note)</span><br /> + <span style="margin-left: 2em;">scarcity of, in Rocky Mountains, + <a href='#Page_401'>401</a></span><br /> + <span style="margin-left: 2em;">scarcity of, in Alpine flora, + <a href='#Page_401'>401</a></span><br /> + <br /> + <span style="margin-left: 1em;">Moral nature of man, origin of, + <a href='#Page_461'>461</a></span><br /> + <br /> + <span style="margin-left: 1em;">Morse, Professor E.T., on + protective colouring of marine mollusca, <a href= + '#Page_209'>209</a></span><br /> + <br /> + <span style="margin-left: 1em;">Moseley, Professor, on protective + resemblance among marine</span><br /> + <span style="margin-left: 1em;">animals, <a href= + '#Page_208'>208</a></span><br /> + <span style="margin-left: 2em;">on courtship of Great Albatross, + <a href='#Page_287'>287</a></span><br /> + <br /> + <span style="margin-left: 1em;">Moths, protected groups of, + <a href='#Page_235'>235</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mountains, remote, with identical + plants, <a href='#Page_369'>369</a></span><br /> + <br /> + <span style="margin-left: 1em;">Müller, Dr. Fritz, on + inhabitants of bromelia leaves, <a href= + '#Page_118'>118</a></span><br /> + <span style="margin-left: 2em;">on butterfly, deceived by its + mimic, <a href='#Page_245'>245</a></span><br /> + <span style="margin-left: 2em;">his explanation of mimicry among + protected genera, <a href='#Page_252'>252</a></span><br /> + <span style="margin-left: 2em;">Dr. Hermann, on variability of + Myosurus minimus, <a href='#Page_78'>78</a></span><br /> + <br /> + <span style="margin-left: 1em;">Murray, Mr. John, on bulk of land + and ocean, <a href='#Page_344'>344</a></span><br /> + <span style="margin-left: 2em;">on quartz particles on ocean + floor, <a href='#Page_363'>363</a></span><br /> + <span style="margin-left: 2em;">Rev. R.P., variation in the + neuration of butterflies' wings, <a href= + '#Page_45'>45</a></span><br /> + <br /> + <span style="margin-left: 1em;">Musical and artistic faculties, + origin of, <a href='#Page_467'>467</a></span><br /> + <br /> + <span style="margin-left: 1em;">Myosurns minimus, variability of, + <a href='#Page_78'>78</a></span><br /> + <br /> + <a name="Page_489" id="Page_489"></a><br /> + <span style="margin-left: 1em;"><b>N</b></span><br /> + <br /> + <span style="margin-left: 1em;">Natural selection with changed + and unchanged conditions, <a href= + '#Page_103'>103</a></span><br /> + <span style="margin-left: 2em;">and sterility, <a href= + '#Page_173'>173</a></span><br /> + <span style="margin-left: 2em;">overpowers effects of use and + disuse, <a href='#Page_435'>435</a></span><br /> + <span style="margin-left: 2em;">the most important agency in + modifying species, <a href='#Page_444'>444</a></span><br /> + <br /> + <span style="margin-left: 1em;">Naturalist deceived by a + mimicking insect, <a href='#Page_259'>259</a></span><br /> + <span style="margin-left: 2em;">by mimicking birds, <a href= + '#Page_264'>264</a></span><br /> + <br /> + <span style="margin-left: 1em;">Naudin, M., on varieties of + melons, <a href='#Page_87'>87</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nectarinea amethystina, + protective colouring of, <a href='#Page_201'>201</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nestor notabilis, variation of + habits of, <a href='#Page_75'>75</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nests of birds influence the + colour of females, <a href='#Page_278'>278</a></span><br /> + <br /> + <span style="margin-left: 1em;">New species, conditions + favourable to origin of, <a href='#Page_115'>115</a></span><br /> + <br /> + <span style="margin-left: 1em;">Newton, Professor A., on fertile + hybrid ducks, <a href='#Page_162'>162</a></span><br /> + <br /> + <span style="margin-left: 1em;">New Zealand, European plants in, + <a href='#Page_15'>15</a></span><br /> + <span style="margin-left: 2em;">spread of white clover in, + <a href='#Page_28'>28</a></span><br /> + <span style="margin-left: 2em;">effects of introduced plants in, + <a href='#Page_29'>29</a></span><br /> + <span style="margin-left: 2em;">native rat and fly exterminated + by European species, <a href='#Page_34'>34</a></span><br /> + <span style="margin-left: 2em;">many plants of, incapable of + self-fertilisation, <a href='#Page_321'>321</a></span><br /> + <span style="margin-left: 2em;">fauna of, <a href= + '#Page_348'>348</a></span><br /> + <span style="margin-left: 2em;">few spiny plants in, <a href= + '#Page_433'>433</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nocturnal animals, colours of, + <a href='#Page_193'>193</a></span><br /> + <br /> + <span style="margin-left: 1em;">Non-adaptive characters, + instability of, <a href='#Page_138'>138</a></span><br /> + <br /> + <span style="margin-left: 1em;">Normandy pigs, fleshy appendages + to jaws of, <a href='#Page_139'>139</a></span><br /> + <br /> + <span style="margin-left: 1em;">North America, Miocene fossils + of, <a href='#Page_378'>378</a></span><br /> + <br /> + <span style="margin-left: 1em;">Northern plants in southern + hemisphere, <a href='#Page_368'>368</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nostus Borbonicus, variability + of, <a href='#Page_80'>80</a></span><br /> + <br /> + <span style="margin-left: 1em;">Number of individuals which vary, + <a href='#Page_62'>62</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nutmeg, how dispersed, <a href= + '#Page_307'>307</a></span><br /> + <br /> + <span style="margin-left: 1em;">Nuts, not meant to be eaten, + <a href='#Page_305'>305</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>O</b></span><br /> + <br /> + <span style="margin-left: 1em;">Oaks, great variability of, + <a href='#Page_78'>78</a></span><br /> + <br /> + <span style="margin-left: 1em;">Objections to Darwin's theory, + <a href='#Page_126'>126</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ocean floor, deposits on, + <a href='#Page_343'>343</a></span><br /> + <br /> + <span style="margin-left: 1em;">Oceanic animals, colours of, + <a href='#Page_193'>193</a></span><br /> + <span style="margin-left: 2em;">and continental areas, <a href= + '#Page_346'>346</a></span><br /> + <span style="margin-left: 2em;">islands have no mammals or + batrachia, <a href='#Page_342'>342</a></span><br /> + <br /> + <span style="margin-left: 1em;">Oceans, the permanence of, + <a href='#Page_341'>341</a></span><br /> + <br /> + <span style="margin-left: 1em;">Oedicnemus, figures of wings of, + <a href='#Page_223'>223</a></span><br /> + <br /> + <span style="margin-left: 1em;">Opthalmis lincea and Artaxa + simulans (figs.), <a href='#Page_247'>247</a></span><br /> + <br /> + <span style="margin-left: 1em;">Orang-utans, variations of skull + of, <a href='#Page_69'>69</a></span><br /> + <br /> + <span style="margin-left: 1em;">Orchideae, why scarce on oceanic + islands, <a href='#Page_367'>367</a></span><br /> + <br /> + <span style="margin-left: 1em;">Orchis pyramidalis, mode of + fertilisation of, <a href='#Page_314'>314</a></span><br /> + <span style="margin-left: 2em;">figures illustrating + fertilisation of, <a href='#Page_315'>315</a></span><br /> + <br /> + <span style="margin-left: 1em;">Organic development, three stages + of, involving new cause or power, <a href= + '#Page_474'>474</a></span><br /> + <span style="margin-left: 2em;">world, the development of, + implies a spiritual world, <a href= + '#Page_476'>476</a></span><br /> + <br /> + <span style="margin-left: 1em;">Organisation, advance of, by + natural selection, <a href='#Page_120'>120</a></span><br /> + <span style="margin-left: 2em;">degradation in, <a href= + '#Page_121'>121</a></span><br /> + <br /> + <span style="margin-left: 1em;">Origin of species, objections, + <a href='#Page_7'>7</a></span><br /> + <span style="margin-left: 2em;">of accessory plumes, <a href= + '#Page_291'>291</a></span><br /> + <br /> + <span style="margin-left: 1em;">Orioles mimicking honey-suckers, + <a href='#Page_263'>263</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ornamental plumes and vitality, + <a href='#Page_293'>293</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>P</b></span><br /> + <br /> + <span style="margin-left: 1em;">Pachyrhynchi subjects of mimicry, + <a href='#Page_261'>261</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pampas, effects of drought in, + <a href='#Page_23'>23</a></span><br /> + <br /> + <span style="margin-left: 1em;">Papaver bracteatum, variability + of, <a href='#Page_79'>79</a></span><br /> + <br /> + <span style="margin-left: 1em;">Papilio, use of forked tentacle + of larva of, <a href='#Page_210'>210</a></span><br /> + <span style="margin-left: 2em;">protected groups of, <a href= + '#Page_235'>235</a></span><br /> + <span style="margin-left: 2em;">mimicry of, <a href= + '#Page_247'>247</a></span><br /> + <br /> + <span style="margin-left: 1em;">Paraguay, absence of wild cattle + and horses, <a href='#Page_19'>19</a></span><br /> + <br /> + <span style="margin-left: 1em;">Parnassia palustris, sham + nectaries of, <a href='#Page_317'>317</a></span><br /> + <br /> + <span style="margin-left: 1em;">Parrot, change of habits of New + Zealand, <a href='#Page_75'>75</a></span><br /> + <br /> + <span style="margin-left: 1em;">Parus, species of, illustrate + divergence, of character, <a href= + '#Page_107'>107</a></span><br /> + <br /> + <span style="margin-left: 1em;">Passenger-pigeon, account of its + breeding-places and numbers, <a href= + '#Page_31'>31</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pelagic animals, colours of, + <a href='#Page_193'>193</a></span><br /> + <a name="Page_490" id="Page_490"></a><br /> + <span style="margin-left: 1em;">Phasmidae, resemblance of, to + sticks and leaves, <a href='#Page_203'>203</a></span><br /> + <br /> + <span style="margin-left: 1em;">Physiological selection, <a href= + '#Page_180'>180</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pickard-Cambridge, Rev. O., on + sexual selection, <a href='#Page_296'>296</a> (note)</span><br /> + <br /> + <span style="margin-left: 1em;">Pieridae, sexual diversity among, + <a href='#Page_271'>271</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pigeons, varieties of, <a href= + '#Page_89'>89</a></span><br /> + <span style="margin-left: 2em;">domestic, derived from wild + rock-pigeons, <a href='#Page_90'>90</a></span><br /> + <span style="margin-left: 2em;">curious correlations in, <a href= + '#Page_140'>140</a></span><br /> + <span style="margin-left: 2em;">white eggs of, protective, + <a href='#Page_213'>213</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pigs, great increase of, in South + America and New Zealand, <a href='#Page_28'>28</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pikermi, extinct animals of, + <a href='#Page_377'>377</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pipits as illustrating + divergence, <a href='#Page_108'>108</a></span><br /> + <br /> + <span style="margin-left: 1em;">Planorbidae, variations of, + <a href='#Page_44'>44</a></span><br /> + <br /> + <span style="margin-left: 1em;">Plants, the enemies of, <a href= + '#Page_16'>16</a></span><br /> + <span style="margin-left: 2em;">variability of, <a href= + '#Page_76'>76</a></span><br /> + <span style="margin-left: 2em;">constitutional variation of, + <a href='#Page_94'>94</a></span><br /> + <span style="margin-left: 2em;">colour relations of, <a href= + '#Page_302'>302</a></span><br /> + <span style="margin-left: 2em;">true mimicry rare in, <a href= + '#Page_303'>303</a></span><br /> + <span style="margin-left: 2em;">exotic rarely naturalised in + Europe, <a href='#Page_356'>356</a></span><br /> + <span style="margin-left: 2em;">dispersal of, <a href= + '#Page_361'>361</a></span><br /> + <span style="margin-left: 2em;">northern, in southern hemisphere, + <a href='#Page_368'>368</a></span><br /> + <span style="margin-left: 2em;">identical on summits of remote + mountains, <a href='#Page_369'>369</a></span><br /> + <span style="margin-left: 2em;">progressive development of, + <a href='#Page_397'>397</a></span><br /> + <span style="margin-left: 2em;">geological development of + (diagram), <a href='#Page_402'>402</a></span><br /> + <br /> + <span style="margin-left: 1em;">Plovers, recognition marks of + (figure), <a href='#Page_221'>221</a></span><br /> + <br /> + <span style="margin-left: 1em;">Plumes, origin of accessory, + <a href='#Page_291'>291</a></span><br /> + <span style="margin-left: 2em;">muscular relation of ornamental, + <a href='#Page_292'>292</a></span><br /> + <br /> + <span style="margin-left: 1em;">Poisonous fruits, <a href= + '#Page_307'>307</a></span><br /> + <br /> + <span style="margin-left: 1em;">Porto Santo, rabbits of, <a href= + '#Page_326'>326</a></span><br /> + <br /> + <span style="margin-left: 1em;">Poulton, Mr. E.B., on variable + colours of larvae and pupae, <a href='#Page_196'>196</a>, + <a href='#Page_198'>198</a></span><br /> + <span style="margin-left: 2em;">on concealments of insects by + resemblance to environment, <a href= + '#Page_202'>202</a></span><br /> + <span style="margin-left: 2em;">on protective form of Notodonta + ziczac, <a href='#Page_210'>210</a></span><br /> + <span style="margin-left: 2em;">on inedibility of conspicuous + larvae, <a href='#Page_237'>237</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pouters, <a href= + '#Page_90'>90</a></span><br /> + <br /> + <span style="margin-left: 1em;">Primulaceae, variations of + structure in, <a href='#Page_79'>79</a></span><br /> + <br /> + <span style="margin-left: 1em;">Problem, the, before Darwin, + <a href='#Page_6'>6</a></span><br /> + <br /> + <span style="margin-left: 1em;">Problems in variation and + heredity, <a href='#Page_410'>410</a></span><br /> + <br /> + <span style="margin-left: 1em;">Progression in plants and + animals, <a href='#Page_395'>395</a></span><br /> + <br /> + <span style="margin-left: 1em;">Protection by terrifying enemies, + <a href='#Page_209'>209</a></span><br /> + <br /> + <span style="margin-left: 1em;">Protective colouring, variable, + <a href='#Page_195'>195</a></span><br /> + <span style="margin-left: 2em;">of white-headed fruit-pigeon, + <a href='#Page_200'>200</a></span><br /> + <span style="margin-left: 2em;">of African sun-birds, <a href= + '#Page_200'>200</a></span><br /> + <span style="margin-left: 2em;">of Kerivoula picta, <a href= + '#Page_201'>201</a></span><br /> + <span style="margin-left: 2em;">of sloths, <a href= + '#Page_201'>201</a></span><br /> + <span style="margin-left: 2em;">of larva of Sphinx ligustri, + <a href='#Page_202'>202</a></span><br /> + <span style="margin-left: 2em;">of stick and leaf insects, + <a href='#Page_203'>203</a></span><br /> + <span style="margin-left: 2em;">of caterpillars, <a href= + '#Page_203'>203</a>, <a href='#Page_205'>205</a></span><br /> + <span style="margin-left: 2em;">of butterflies, <a href= + '#Page_206'>206</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ptilopus cinctus, protective + colour of, <a href='#Page_200'>200</a></span><br /> + <br /> + <span style="margin-left: 1em;">Pugnacity of birds with accessory + plumes, <a href='#Page_294'>294</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>R</b></span><br /> + <br /> + <span style="margin-left: 1em;">Rabbit, use of white tail of, + <a href='#Page_218'>218</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rapid increase of plants, + <a href='#Page_28'>28</a></span><br /> + <br /> + <span style="margin-left: 1em;">Raspail, M., on variability in a + grass, <a href='#Page_80'>80</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rat, black, spread of, <a href= + '#Page_34'>34</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rattlesnake, use of rattle of, + <a href='#Page_262'>262</a></span><br /> + <br /> + <span style="margin-left: 1em;">Raven, why black in arctic + regions, <a href='#Page_191'>191</a></span><br /> + <br /> + <span style="margin-left: 1em;">Reciprocal crosses, <a href= + '#Page_155'>155</a></span><br /> + <br /> + <span style="margin-left: 1em;">Recognition marks of herbivora, + <a href='#Page_218'>218</a></span><br /> + <span style="margin-left: 2em;">of birds, <a href= + '#Page_222'>222</a></span><br /> + <span style="margin-left: 2em;">of tropical forest birds, + <a href='#Page_224'>224</a></span><br /> + <span style="margin-left: 2em;">of insects, <a href= + '#Page_226'>226</a></span><br /> + <br /> + <span style="margin-left: 1em;">Reproductive functions, + susceptibility of, <a href='#Page_153'>153</a></span><br /> + <br /> + <span style="margin-left: 1em;">Reptiles, geological distribution + of, <a href='#Page_406'>406</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rhinoceroses, evidence of + evolution afforded by fossil, <a href= + '#Page_383'>383</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rocks, all stratified formed in + shallow water, <a href='#Page_344'>344</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rocky Mountains, scarcity of + monocotyledons in, <a href='#Page_401'>401</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rodents, prevent woody vegetation + in the pampas, <a href='#Page_23'>23</a></span><br /> + <br /> + <span style="margin-left: 1em;">Romanes, Professor G.J., on + useless characters, <a href='#Page_131'>131</a>, <a href= + '#Page_139'>139</a></span><br /> + <span style="margin-left: 2em;">on meaningless peculiarities of + structure, <a href='#Page_140'>140</a></span><br /> + <span style="margin-left: 2em;">on supposed absence of + simultaneous variations, <a href='#Page_142'>142</a></span><br /> + <span style="margin-left: 2em;">on physiological selection, + <a href='#Page_180'>180</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rook and crow, <a href= + '#Page_2'>2</a></span><br /> + <a name="Page_491" id="Page_491"></a><br /> + <span style="margin-left: 1em;">Roses, Mr. Baker on varieties of, + <a href='#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rubus, Bentham and Babington on + species and varieties of, <a href='#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rudiments and variations in man, + <a href='#Page_446'>446</a></span><br /> + <br /> + <span style="margin-left: 1em;">Runts, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Rutaceae, variation of structure + in, <a href='#Page_79'>79</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>S</b></span><br /> + <br /> + <span style="margin-left: 1em;">St. Helena, destruction of + forests by goats, <a href='#Page_17'>17</a></span><br /> + <br /> + <span style="margin-left: 1em;">St. Hilaire, M. Aug., variability + of Gomphia oleaefolia, <a href='#Page_79'>79</a></span><br /> + <br /> + <span style="margin-left: 1em;">Saxicola, divergence of character + in species of, <a href='#Page_108'>108</a></span><br /> + <span style="margin-left: 2em;">recognition marks of, <a href= + '#Page_222'>222</a></span><br /> + <br /> + <span style="margin-left: 1em;">Scientific opinion before Darwin, + <a href='#Page_4'>4</a></span><br /> + <br /> + <span style="margin-left: 1em;">Scolopax, figures of tails of, + <a href='#Page_225'>225</a></span><br /> + <br /> + <span style="margin-left: 1em;">Scudder, Mr. S.H., on inedibility + of Danais archippus, <a href='#Page_238'>238</a></span><br /> + <span style="margin-left: 2em;">on fossil insects, <a href= + '#Page_403'>403</a></span><br /> + <br /> + <span style="margin-left: 1em;">Seebohm, Mr., on swamping effects + of intercrossing, <a href='#Page_143'>143</a></span><br /> + <br /> + <span style="margin-left: 1em;">Seeds, how dispersed, <a href= + '#Page_306'>306</a></span><br /> + <span style="margin-left: 2em;">how protected, <a href= + '#Page_307'>307</a></span><br /> + <span style="margin-left: 2em;">floating great distances, + <a href='#Page_361'>361</a></span><br /> + <span style="margin-left: 2em;">dispersal of, by wind, <a href= + '#Page_362'>362</a></span><br /> + <span style="margin-left: 2em;">weight and dimensions of, + <a href='#Page_364'>364</a></span><br /> + <span style="margin-left: 2em;">importance of wind-carriage of, + <a href='#Page_372'>372</a></span><br /> + <span style="margin-left: 2em;">remarkable case of wind-carriage + of, <a href='#Page_373'>373</a></span><br /> + <br /> + <span style="margin-left: 1em;">Seiurus carolinensis, diagram of + variation, <a href='#Page_67'>67</a></span><br /> + <span style="margin-left: 2em;">sp., habits of, <a href= + '#Page_117'>117</a></span><br /> + <br /> + <span style="margin-left: 1em;">Selection, artificial, <a href= + '#Page_84'>84</a></span><br /> + <span style="margin-left: 2em;">by man, circumstances favourable + to, <a href='#Page_96'>96</a></span><br /> + <span style="margin-left: 2em;">unconscious, <a href= + '#Page_96'>96</a></span><br /> + <br /> + <span style="margin-left: 1em;">Selective association, isolation + by, <a href='#Page_171'>171</a></span><br /> + <br /> + <span style="margin-left: 1em;">Self-fertilisation of flowers, + <a href='#Page_321'>321</a></span><br /> + <br /> + <span style="margin-left: 1em;">Semper, Professor, on casting + hairs of reptiles and Crustacea, <a href='#Page_137'>137</a> + (note)</span><br /> + <span style="margin-left: 2em;">on direct influence of + environment, <a href='#Page_426'>426</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sesiidae, mimicry by, <a href= + '#Page_240'>240</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sex colour and nests of birds, + <a href='#Page_277'>277</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sex, colours characteristic of, + <a href='#Page_269'>269</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sexual colours of insects, + probable causes of, <a href='#Page_273'>273</a></span><br /> + <span style="margin-left: 2em;">of birds, <a href= + '#Page_275'>275</a></span><br /> + <span style="margin-left: 2em;">characters due to natural + selection, <a href='#Page_283'>283</a></span><br /> + <span style="margin-left: 2em;">diversity the cause of variation, + <a href='#Page_439'>439</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sexual selection and colour, + <a href='#Page_274'>274</a></span><br /> + <span style="margin-left: 2em;">by struggles of males, <a href= + '#Page_282'>282</a></span><br /> + <span style="margin-left: 2em;">neutralised by natural selection, + <a href='#Page_294'>294</a>-<a href= + '#Page_296'>296</a></span><br /> + <span style="margin-left: 2em;">restricted to male struggles, + <a href='#Page_296'>296</a></span><br /> + <br /> + <span style="margin-left: 1em;">Shetland Islands, variety of + ghost-moth in, <a href='#Page_270'>270</a></span><br /> + <br /> + <span style="margin-left: 1em;">Shrews and field-mice, internal + variations of, <a href='#Page_69'>69</a></span><br /> + <br /> + <span style="margin-left: 1em;">Shrikes, recognition marks of, + <a href='#Page_222'>222</a></span><br /> + <br /> + <span style="margin-left: 1em;">Similarity of forms of life not + due to similarity of conditions, <a href= + '#Page_339'>339</a></span><br /> + <br /> + <span style="margin-left: 1em;">Singing of male birds, use of, + <a href='#Page_284'>284</a></span><br /> + <br /> + <span style="margin-left: 1em;">Skull of wolf, diagram of + variations of, <a href='#Page_70'>70</a></span><br /> + <span style="margin-left: 2em;">of Ursus labiatus, diagram of + variations of, <a href='#Page_72'>72</a></span><br /> + <span style="margin-left: 2em;">of Sus cristatus, diagram of + variations of, <a href='#Page_73'>73</a></span><br /> + <br /> + <span style="margin-left: 1em;">Skunk an illustration of warning + colour, <a href='#Page_233'>233</a></span><br /> + <br /> + <span style="margin-left: 1em;">Slack, Baron von, on protective + markings of sloths, <a href='#Page_201'>201</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sloth, protective colour and + marking of, <a href='#Page_201'>201</a></span><br /> + <br /> + <span style="margin-left: 1em;">Snakes, mimicry of poisonous, + <a href='#Page_261'>261</a></span><br /> + <br /> + <span style="margin-left: 1em;">Snipe, tails of two species + (figs.), <a href='#Page_225'>225</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sounds and odours peculiar to + male,</span><br /> + <span style="margin-left: 2em;">how useful, <a href= + '#Page_284'>284</a></span><br /> + <span style="margin-left: 2em;">produced by peculiar feathers, + <a href='#Page_284'>284</a></span><br /> + <br /> + <span style="margin-left: 1em;">South America, fossil and recent + mammals of, <a href='#Page_393'>393</a></span><br /> + <br /> + <span style="margin-left: 1em;">Species, definition of, <a href= + '#Page_1'>1</a>, <a href='#Page_2'>2</a></span><br /> + <span style="margin-left: 2em;">origin of, <a href= + '#Page_2'>2</a>, <a href='#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">Lyell on, <a href= + '#Page_4'>4</a></span><br /> + <span style="margin-left: 2em;">Agassiz on, <a href= + '#Page_5'>5</a></span><br /> + <span style="margin-left: 2em;">transmutation of, <a href= + '#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">Geoffroy St. Hilaire on, <a href= + '#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">Dean Herbert on, <a href= + '#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">Professor Grant on, <a href= + '#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">Von Buch on, <a href= + '#Page_6'>6</a></span><br /> + <span style="margin-left: 2em;">allied, found in distinct areas, + <a href='#Page_36'>36</a></span><br /> + <br /> + <span style="margin-left: 1em;">Species, which vary little, + <a href='#Page_80'>80</a></span><br /> + <a name="Page_492" id="Page_492"></a> <span style= + "margin-left: 2em;">closely allied inhabit distinct areas, + <a href='#Page_111'>111</a></span><br /> + <span style="margin-left: 2em;">vigour and fertility of, how kept + up, <a href='#Page_327'>327</a></span><br /> + <br /> + <span style="margin-left: 1em;">Spencer, Mr. Herbert, on factors + of organic evolution, <a href='#Page_411'>411</a></span><br /> + <span style="margin-left: 2em;">on effects of disuse, <a href= + '#Page_413'>413</a></span><br /> + <span style="margin-left: 2em;">on difficulty as to co-adaptation + of parts, <a href='#Page_417'>417</a></span><br /> + <span style="margin-left: 2em;">on direct action of environment, + <a href='#Page_418'>418</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sphingidae, protective attitudes + of larvae, <a href='#Page_210'>210</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sphinx ligustri, general + resemblance of larva to food plant, <a href= + '#Page_202'>202</a></span><br /> + <br /> + <span style="margin-left: 1em;">Spider, alluring coloration of, + <a href='#Page_211'>211</a></span><br /> + <br /> + <span style="margin-left: 1em;">Spines, on origin of, <a href= + '#Page_431'>431</a></span><br /> + <span style="margin-left: 2em;">rarity of, in oceanic islands, + <a href='#Page_432'>432</a></span><br /> + <br /> + <span style="margin-left: 1em;">Spiny plants abundant in South + Africa and Chile, <a href='#Page_433'>433</a></span><br /> + <br /> + <span style="margin-left: 1em;">Spots a primitive ornamentation + of animals, <a href='#Page_289'>289</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sprengel on flowers and insects, + <a href='#Page_309'>309</a></span><br /> + <br /> + <span style="margin-left: 1em;">Staphylinidae, protective habit + of, <a href='#Page_210'>210</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sterility of mongrels, <a href= + '#Page_165'>165</a></span><br /> + <span style="margin-left: 2em;">correlated with colour, etc., + <a href='#Page_168'>168</a></span><br /> + <span style="margin-left: 2em;">and natural selection, <a href= + '#Page_173'>173</a></span><br /> + <span style="margin-left: 2em;">of hybrids produced by natural + selection, <a href='#Page_179'>179</a></span><br /> + <br /> + <span style="margin-left: 1em;">Struggle for existence, <a href= + '#Page_14'>14</a></span><br /> + <span style="margin-left: 2em;">among plants, <a href= + '#Page_15'>15</a></span><br /> + <span style="margin-left: 2em;">for life, illustrations of, + <a href='#Page_18'>18</a></span><br /> + <span style="margin-left: 2em;">for existence on the pampas, + <a href='#Page_22'>22</a></span><br /> + <span style="margin-left: 2em;">for life between closely allied + forms most severe, <a href='#Page_33'>33</a></span><br /> + <span style="margin-left: 2em;">for existence, ethics of, + <a href='#Page_36'>36</a></span><br /> + <span style="margin-left: 2em;">how it acts among flowers, + <a href='#Page_328'>328</a></span><br /> + <br /> + <span style="margin-left: 1em;">Summary of facts of colouring for + protection and recognition, <a href= + '#Page_227'>227</a></span><br /> + <br /> + <span style="margin-left: 1em;">Survival of the fittest, <a href= + '#Page_11'>11</a>, <a href='#Page_122'>122</a>, <a href= + '#Page_123'>123</a></span><br /> + <br /> + <span style="margin-left: 1em;">Swainson, definition of species, + <a href='#Page_2'>2</a></span><br /> + <br /> + <span style="margin-left: 1em;">Swamping effects of + intercrossing, <a href='#Page_142'>142</a></span><br /> + <br /> + <span style="margin-left: 1em;">Sweden, destruction of grass by + larvae of moths in, <a href='#Page_17'>17</a></span><br /> + <br /> + <span style="margin-left: 1em;">Swinhoe, Mr., on protective + colouring of a bat, <a href='#Page_201'>201</a></span><br /> + <br /> + <span style="margin-left: 1em;">Symmetry, bilateral in colours of + animals needful for recognition, <a href= + '#Page_217'>217</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>T</b></span><br /> + <br /> + <span style="margin-left: 1em;">Tails used as respirators, + <a href='#Page_136'>136</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tapirs, distribution of, <a href= + '#Page_352'>352</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tegetmeier, Mr., on feeding + habits of pigeons and fowls, <a href= + '#Page_75'>75</a></span><br /> + <span style="margin-left: 2em;">on sparrows and crocuses, + <a href='#Page_75'>75</a></span><br /> + <span style="margin-left: 2em;">on curious correlations in + pigeons, <a href='#Page_140'>140</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tegumentary appendages and + colour, <a href='#Page_291'>291</a></span><br /> + <br /> + <span style="margin-left: 1em;">Thousand-fathom line divides + oceanic from continental islands, <a href= + '#Page_347'>347</a></span><br /> + <span style="margin-left: 2em;">the teachings of, <a href= + '#Page_348'>348</a></span><br /> + <span style="margin-left: 2em;">map showing, <a href= + '#Page_349'>349</a></span><br /> + <br /> + <span style="margin-left: 1em;">Thwaites, Mr., on spread of + Lantana mixta in Ceylon, <a href='#Page_30'>30</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tiger, use of stripes of, + <a href='#Page_199'>199</a></span><br /> + <br /> + <span style="margin-left: 1em;">Titmice as illustrating + divergence, <a href='#Page_107'>107</a></span><br /> + <br /> + <span style="margin-left: 1em;">Transformation of species of + crustacea, <a href='#Page_427'>427</a></span><br /> + <br /> + <span style="margin-left: 1em;">Transmutationists, the early, + <a href='#Page_3'>3</a></span><br /> + <br /> + <span style="margin-left: 1em;">Travers, Mr. W.L., on effects of + introduced plants in New Zealand, <a href= + '#Page_29'>29</a></span><br /> + <br /> + <span style="margin-left: 1em;">Trees, great variety of, in many + forests, <a href='#Page_36'>36</a></span><br /> + <br /> + <span style="margin-left: 1em;">Trimen, Mr., on butterfly + deceived by its mimic, <a href='#Page_245'>245</a></span><br /> + <span style="margin-left: 2em;">on mimicry, <a href= + '#Page_247'>247</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tropical animals, why brilliantly + coloured, <a href='#Page_299'>299</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tropics, no proof of lower + temperature of, <a href='#Page_369'>369</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tropidorhynchi mimicked by + orioles, <a href='#Page_263'>263</a></span><br /> + <br /> + <span style="margin-left: 1em;">Trumpeter, <a href= + '#Page_93'>93</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tumblers, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Turbits and owls, <a href= + '#Page_91'>91</a></span><br /> + <br /> + <span style="margin-left: 1em;">Tylor, Mr. A., on <i>Coloration + in Animals and Plants</i>, <a href= + '#Page_285'>285</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>U</b></span><br /> + <br /> + <span style="margin-left: 1em;">Ungulates, origin of feet of, + <a href='#Page_423'>423</a></span><br /> + <br /> + <span style="margin-left: 1em;">Use and disuse, effects of, + overpowered by natural selection, <a href= + '#Page_435'>435</a></span><br /> + <br /> + <span style="margin-left: 1em;">Useless characters, <a href= + '#Page_131'>131</a></span><br /> + <span style="margin-left: 2em;">not specific, <a href= + '#Page_132'>132</a></span><br /> + <br /> + <span style="margin-left: 1em;">Useless specific characters, no + proof of existence of, <a href='#Page_141'>141</a></span><br /> + <a name="Page_493" id="Page_493"></a><br /> + <span style="margin-left: 1em;">Utriculariae inhabiting + bromelias, <a href='#Page_118'>118</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>V</b></span><br /> + <br /> + <span style="margin-left: 1em;">Vanessa callirhoe, small variety + in Porto Santo, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Variability of the lower animals, + <a href='#Page_42'>42</a></span><br /> + <span style="margin-left: 2em;">of the Foraminifera, <a href= + '#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">of sea-anemones, <a href= + '#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">of land mollusca, <a href= + '#Page_43'>43</a></span><br /> + <span style="margin-left: 2em;">of insects, <a href= + '#Page_44'>44</a></span><br /> + <span style="margin-left: 2em;">of lizards, <a href= + '#Page_46'>46</a></span><br /> + <span style="margin-left: 2em;">of birds, <a href= + '#Page_49'>49</a></span><br /> + <span style="margin-left: 2em;">of primary wing-feathers, + <a href='#Page_51'>51</a></span><br /> + <span style="margin-left: 2em;">of wings and tail, <a href= + '#Page_53'>53</a></span><br /> + <span style="margin-left: 2em;">of Dolichonyx oryzivorus, + <a href='#Page_55'>55</a></span><br /> + <span style="margin-left: 2em;">of Agelaeus phoeniceus, <a href= + '#Page_56'>56</a></span><br /> + <span style="margin-left: 2em;">of Cardinalis virginianus, + <a href='#Page_58'>58</a></span><br /> + <span style="margin-left: 2em;">of tarsus and toes, <a href= + '#Page_60'>60</a></span><br /> + <span style="margin-left: 2em;">of birds in Leyden Museum, + <a href='#Page_61'>61</a></span><br /> + <span style="margin-left: 2em;">of Sciurus carolinensis, <a href= + '#Page_67'>67</a></span><br /> + <span style="margin-left: 2em;">of skulls of wolf, <a href= + '#Page_70'>70</a></span><br /> + <span style="margin-left: 2em;">of skulls of a bear, <a href= + '#Page_72'>72</a></span><br /> + <span style="margin-left: 2em;">of skulls of Sus cristatus, + <a href='#Page_73'>73</a></span><br /> + <span style="margin-left: 2em;">of plants, <a href= + '#Page_76'>76</a></span><br /> + <span style="margin-left: 2em;">of oaks, <a href= + '#Page_77'>77</a></span><br /> + <br /> + <span style="margin-left: 1em;">Variation, Lyell on, <a href= + '#Page_4'>4</a></span><br /> + <span style="margin-left: 2em;">in internal organs, <a href= + '#Page_66'>66</a></span><br /> + <span style="margin-left: 2em;">the facts of, <a href= + '#Page_83'>83</a></span><br /> + <span style="margin-left: 2em;">proofs of generality of, <a href= + '#Page_85'>85</a></span><br /> + <span style="margin-left: 2em;">of vegetables and fruits, + <a href='#Page_86'>86</a></span><br /> + <span style="margin-left: 2em;">of apples and melons, <a href= + '#Page_87'>87</a></span><br /> + <span style="margin-left: 2em;">under domestication accords with + that under nature, <a href='#Page_100'>100</a></span><br /> + <span style="margin-left: 2em;">coincident not necessary, + <a href='#Page_127'>127</a></span><br /> + <span style="margin-left: 2em;">and heredity, problems of, + <a href='#Page_410'>410</a></span><br /> + <span style="margin-left: 2em;">Professor Geddes's theory of, + <a href='#Page_428'>428</a></span><br /> + <span style="margin-left: 2em;">the cause of, <a href= + '#Page_439'>439</a></span><br /> + <br /> + <span style="margin-left: 1em;">Variations of flowers, <a href= + '#Page_88'>88</a></span><br /> + <span style="margin-left: 2em;">of domestic animals, <a href= + '#Page_88'>88</a></span><br /> + <span style="margin-left: 2em;">of domestic pigeons, <a href= + '#Page_89'>89</a></span><br /> + <span style="margin-left: 2em;">conditions favourable to + production of, <a href='#Page_98'>98</a></span><br /> + <span style="margin-left: 2em;">beneficial, <a href= + '#Page_143'>143</a></span><br /> + <br /> + <span style="margin-left: 1em;">Varieties, importance of, + <a href='#Page_41'>41</a></span><br /> + <span style="margin-left: 2em;">of same species adapted to self + or to insect-fertilisation, <a href= + '#Page_330'>330</a></span><br /> + <br /> + <span style="margin-left: 1em;">Vegetables, variation of, + <a href='#Page_86'>86</a></span><br /> + <br /> + <span style="margin-left: 1em;">Vegetation and reproduction, + antagonism of, <a href='#Page_428'>428</a></span><br /> + <br /> + <span style="margin-left: 1em;">Vertebrata, mimicry among, + <a href='#Page_261'>261</a></span><br /> + <span style="margin-left: 2em;">geological succession of, + <a href='#Page_405'>405</a></span><br /> + <br /> + <span style="margin-left: 1em;"><i>Vestiges of Creation</i>, + <a href='#Page_3'>3</a></span><br /> + <br /> + <span style="margin-left: 1em;">Viola odorata, <a href= + '#Page_2'>2</a></span><br /> + <span style="margin-left: 2em;">canina, <a href= + '#Page_2'>2</a></span><br /> + <br /> + <span style="margin-left: 1em;">Violets, as illustrating species, + <a href='#Page_2'>2</a></span><br /> + <br /> + <span style="margin-left: 1em;">Von Buch on species, <a href= + '#Page_6'>6</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>W</b></span><br /> + <br /> + <span style="margin-left: 1em;">Wallace, Dr. Alexander, on + absence of choice by female moths, <a href= + '#Page_275'>275</a></span><br /> + <br /> + <span style="margin-left: 1em;">Ward, Mr. Lester F., on + progressive development of plants, <a href= + '#Page_398'>398</a></span><br /> + <br /> + <span style="margin-left: 1em;">Warning coloration, <a href= + '#Page_232'>232</a></span><br /> + <br /> + <span style="margin-left: 1em;">Warning colours of marine + animals, <a href='#Page_265'>265</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wasps and bees, mimicry of, + <a href='#Page_258'>258</a></span><br /> + <span style="margin-left: 2em;">poisonous with warning colours, + <a href='#Page_287'>287</a></span><br /> + <br /> + <span style="margin-left: 1em;">Water-cress, chokes rivers in New + Zealand, <a href='#Page_24'>24</a></span><br /> + <span style="margin-left: 2em;">driven out by willows, <a href= + '#Page_24'>24</a></span><br /> + <br /> + <span style="margin-left: 1em;">Water-ouzels, probable origin of, + <a href='#Page_116'>116</a></span><br /> + <br /> + <span style="margin-left: 1em;">Weale, Mr. Mansel, on protective + colours of butterflies, <a href='#Page_206'>206</a></span><br /> + <br /> + <span style="margin-left: 1em;">Weeds of United States, <a href= + '#Page_15'>15</a></span><br /> + <br /> + <span style="margin-left: 1em;">Weir, Mr. Jenner, on deceptive + resemblance of a caterpillar to</span><br /> + <span style="margin-left: 1em;">a twig, <a href= + '#Page_204'>204</a></span><br /> + <span style="margin-left: 2em;">on inedibility of conspicuous + caterpillars, <a href='#Page_236'>236</a></span><br /> + <span style="margin-left: 2em;">on birds disregarding inedible + larvae, <a href='#Page_254'>254</a></span><br /> + <br /> + <span style="margin-left: 1em;">Weismann on progressive + adaptation of colours of larva, <a href= + '#Page_206'>206</a></span><br /> + <span style="margin-left: 2em;">on non-heredity of acquired + characters, <a href='#Page_440'>440</a></span><br /> + <span style="margin-left: 2em;">and Galton's theories of heredity + almost identical, 443 (note)</span><br /> + <span style="margin-left: 2em;">on origin of the mathematical + faculty, (<a href="#Footnote_236_236">note</a>)</span><br /> + <br /> + <span style="margin-left: 1em;">Weismann's theory of heredity, + <a href='#Page_437'>437</a></span><br /> + <br /> + <span style="margin-left: 1em;">Westwood, Professor, on variation + of insects, <a href='#Page_44'>44</a></span><br /> + <span style="margin-left: 2em;">deceived by a mimicking cricket, + <a href='#Page_259'>259</a></span><br /> + <br /> + <span style="margin-left: 1em;">White coloration of insular birds + and butterflies, <a href='#Page_230'>230</a></span><br /> + <br /> + <span style="margin-left: 1em;">Whymper, Mr., his sensations when + falling on the Matterhorn, <a href='#Page_38'>38</a></span><br /> + <br /> + <span style="margin-left: 1em;">Willows, species and varieties of + British, <a href='#Page_77'>77</a></span><br /> + <a name="Page_494" id="Page_494"></a><br /> + <span style="margin-left: 1em;">Wilson, Alexander, his account of + the passenger-pigeon in North</span><br /> + <span style="margin-left: 2em;">America, <a href= + '#Page_31'>31</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wind-carriage of seeds explains + many facts of plant distribution, <a href= + '#Page_371'>371</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wind-dispersal of seeds, + objections to, <a href='#Page_365'>365</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wind-fertilised degraded from + insect-fertilised flowers, <a href= + '#Page_324'>324</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wings of stone-curlews (figure), + <a href='#Page_223'>223</a></span><br /> + <span style="margin-left: 2em;">why small but useless are + retained, <a href='#Page_416'>416</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wit and humour, origin of + faculties of, <a href='#Page_472'>472</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wollaston, Mr. T.W., on variation + of beetles, <a href='#Page_44'>44</a></span><br /> + <span style="margin-left: 1em;">on small butterfly in Porto + Santo, <a href='#Page_106'>106</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wolves, varieties of in Catskill + Mountains, <a href='#Page_105'>105</a></span><br /> + <br /> + <span style="margin-left: 1em;">Wood, Mr. J., on muscular + variations, <a href='#Page_447'>447</a></span><br /> + <br /> + <span style="margin-left: 1em;">Mr. T.W., on variable colouring + of pupae of cabbage butterflies,</span><br /> + <span style="margin-left: 2em;"><a href= + '#Page_197'>197</a></span><br /> + <br /> + <span style="margin-left: 1em;">Woodward, Dr. S.P., on variation + of mollusca, <a href='#Page_43'>43</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>Y</b></span><br /> + <br /> + <span style="margin-left: 1em;">Youatt, on breeds of sheep, + <a href='#Page_97'>97</a></span><br /> + <br /> + <span style="margin-left: 1em;">Young animals often spotted, + <a href='#Page_289'>289</a></span><br /> + <br /> + <br /> + <span style="margin-left: 1em;"><b>Z</b></span><br /> + <br /> + <span style="margin-left: 1em;">Zebra, markings for recognition + and protection, (<a href= + "#Footnote_85_85">note</a>)</span><br /></p> + + <h3>THE END</h3> + +<div>*** END OF THE PROJECT GUTENBERG EBOOK 14558 ***</div> +</body> +</html> diff --git a/14558-h/images/fig01.jpg b/14558-h/images/fig01.jpg Binary files differnew file mode 100644 index 0000000..1841f2b --- 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