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-Project Gutenberg's The Methods and Scope of Genetics, by W. Bateson
-
-This eBook is for the use of anyone anywhere at no cost and with
-almost no restrictions whatsoever. You may copy it, give it away or
-re-use it under the terms of the Project Gutenberg License included
-with this eBook or online at www.gutenberg.org/license
-
-
-Title: The Methods and Scope of Genetics
- An inaugural lecture delivered 23 October 1908
-
-Author: W. Bateson
-
-Release Date: June 12, 2016 [EBook #52312]
-
-Language: English
-
-Character set encoding: ISO-8859-1
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-*** START OF THIS PROJECT GUTENBERG EBOOK THE METHODS AND SCOPE OF GENETICS ***
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-
-THE METHODS AND SCOPE OF GENETICS
-
-
-CAMBRIDGE UNIVERSITY PRESS
-London: FETTER LANE, E.C.
-C. F. CLAY, MANAGER
-
-[Illustration: Logo]
-
-Edinburgh: 100, PRINCES STREET
-Berlin: A. ASHER AND CO.
-Leipzig: F. A. BROCKHAUS
-New York: G. P. PUTNAM'S SONS
-Bombay and Calcutta: MACMILLAN AND CO., LTD.
-
-_All rights reserved_
-
-
-
-
-THE METHODS AND SCOPE OF GENETICS
-
-_AN INAUGURAL LECTURE DELIVERED 23 OCTOBER 1908_
-
-by
-W. BATESON, M.A., F.R.S.
-
-PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE
-
-Cambridge:
-at the University Press
-1912
-
-
-_First Edition 1908_
-_Reprinted 1912_
-
-
-
-
-PREFATORY NOTE
-
-
-The Professorship of Biology was founded in 1908 for a period of five
-years partly by the generosity of an anonymous benefactor, and partly by
-the University of Cambridge. The object of the endowment was the
-promotion of inquiries into the physiology of Heredity and Variation, a
-study now spoken of as Genetics.
-
-It is now recognized that the progress of such inquiries will chiefly be
-accomplished by the application of experimental methods, especially
-those which Mendel's discovery has suggested. The purpose of this
-inaugural lecture is to describe the outlook over this field of research
-in a manner intelligible to students of other parts of knowledge.
-
-W. B.
-
-_28 October, 1908_
-
-
-
-
-THE METHODS AND SCOPE OF GENETICS
-
-
-The opportunity of addressing fellow-students pursuing lines of inquiry
-other than his own falls seldom to a scientific man. One of these rare
-opportunities is offered by the constitution of the Professorship to
-which I have had the honour to be called. That Professorship, though
-bearing the comprehensive title "of Biology," is founded with the
-understanding that the holder shall apply himself to a particular class
-of physiological problems, the study of which is denoted by the term
-Genetics. The term is new; and though the problems are among the oldest
-which have vexed the human mind, the modes by which they may be
-successfully attacked are also of modern invention. There is therefore
-a certain fitness in the employment of this occasion for the deliverance
-of a discourse explaining something of the aims of Genetics and of the
-methods by which we trust they may be reached.
-
-You will be aware that the claims put forward in the name of Genetics
-are high, but I trust to be able to show you that they are not high
-without reason. It is the ambition of every one who in youth devotes
-himself to the search for natural truth, that his work may be found
-somewhere in the main stream of progress. So long only as he keeps
-something of the limitless hope with which his voyage of discovery
-began, will his courage and his spirit last. The moment we most dread is
-one in which it may appear that, after all, our effort has been spent in
-exploring some petty tributary, or worse, a backwater of the great
-current. It is because Genetic research is still pushing forward in the
-central undifferentiated trunk of biological science that we confess no
-guilt of presumption in declaring boldly that whatever difficulty may be
-in store for those who cast in their lot with us, they need fear no
-disillusionment or misgiving that their labour has been wasted on a
-paltry quest.
-
-In research, as in all business of exploration, the stirring times come
-when a fresh region is suddenly unlocked by the discovery of a new key.
-Then conquest is easy and there are prizes for all. We are happy in that
-during our own time not a few such territories have been revealed to the
-vision of mankind. I do not dare to suggest that in magnitude or
-splendour the field of Genetics may be compared with that now being
-disclosed to the physicist or the astronomer; for the glory of the
-celestial is one and the glory of the terrestrial is another. But I
-will say that for once to the man of ordinary power who cannot venture
-into those heights beyond, Mendel's clue has shown the way into a realm
-of nature which for surprising novelty and adventure is hardly to be
-excelled.
-
-It is no hyperbolical figure that I use when I speak of Mendelian
-discovery leading us into a new world, the very existence of which was
-unsuspected before.
-
-The road thither is simple and easy to follow. We start from a common
-fact, familiar to everyone, that all the ordinary animals and plants
-began their individual life by the union of two cells, the one male, the
-other female. Those cells are known as germ-cells or _gametes_, that is
-to say, "marrying" cells.
-
-Now obviously the diversity of form which is characteristic of the
-animal and plant world must be somehow represented in the gametes, since
-it is they which bring into each organism all that it contains. I am
-aware that there is interplay between the organism and the circumstances
-in which it grows up, and that opportunity given may bring out a
-potentiality which without that opportunity must have lain dormant. But
-while noting parenthetically that this question of opportunity has an
-importance, which some day it may be convenient to estimate, the one
-certain fact is that all the powers, physical and mental that a living
-creature possesses were contributed by one or by both of the two
-germ-cells which united in fertilisation to give it existence. The fact
-that _two_ cells are concerned in the production of all the ordinary
-forms of life was discovered a long while ago, and has been part of the
-common stock of elementary knowledge of all educated persons for about
-half a century. The full consequences of this double nature seem
-nevertheless to have struck nobody before Mendel. Simple though the
-fact is, I have noticed that to many it is difficult to assimilate as a
-working idea. We are accustomed to think of a man, a butterfly, or an
-apple tree as each _one_ thing. In order to understand the significance
-of Mendelism we must get thoroughly familiar with the fact that they are
-each _two_ things, double throughout every part of their composition.
-There is perhaps no better exercise as a preparation for genetic
-research than to examine the people one meets in daily life and to try
-in a rough way to analyse them into the two assemblages of characters
-which are united in them. That we are assemblages or medleys of our
-parental characteristics is obvious. We all know that a man may have his
-father's hair, his mother's colour, his father's voice, his mother's
-insensibility to music, and so on, but that is not enough.
-
-Such an analysis is true, inasmuch as the various characters _are_
-transmitted independently, but it misses the essential point. For in
-each of these respects the individual is double; and so to get a true
-picture of the composition of the individual we have to think how _each_
-of the two original gametes was provided in the matter of height, hair,
-colour, mathematical ability, nail-shape, and the other features that go
-to make the man we know. The contribution of each gamete in each respect
-has thus to be separately brought to account. If we could make a list of
-all the ingredients that go to form a man and could set out how he is
-constituted in respect of each of them, it would not suffice to give one
-column of values for these ingredients, but we must rule two columns,
-one for the ovum and one for the spermatozoon, which united in
-fertilisation to form that man, and in each column we must represent how
-that gamete was supplied in respect of each of the ingredients in our
-list. When the problem of heredity is thus represented we can hardly
-avoid discovering, by mere inspection, one of the chief conclusions to
-which genetic research has led. For it is obvious that the contributions
-of the male and female gametes may in respect of any of the ingredients
-be either the same, or different. In any case in which the contribution
-made by the two cells is the same, the resulting organism--in our
-example the man--is, as we call it, _pure-bred_ for that ingredient, and
-in all respects in which the contribution from the two sides of the
-parentage is dissimilar the resulting organism is _cross-bred_.
-
-To give an intelligible account of the next step in the analysis without
-having recourse to precise and technical language is not very easy.
-
-We have got to the point of view from which we see the individual made
-up of a large number of distinct ingredients, contributed from two
-sources, and in respect of any of them he may have received two similar
-portions or two dissimilar portions. We shall not go far wrong if we
-extend and elaborate our illustration thus. Let us imagine the contents
-of a gamete as a fluid made by taking a drop from each of a definite
-number of bottles in a chest, containing tinctures of the several
-ingredients. There is one such chest from which the male gamete is to be
-made up, and a similar chest containing a corresponding set of bottles
-out of which the components of the female gamete are to be taken. But in
-either chest one or more of the bottles may be empty; then nothing goes
-in to represent that ingredient from that chest, and if corresponding
-bottles are empty in both chests, then the individual made on
-fertilisation by mixing the two collections of drops together does not
-contain the missing ingredient at all. It follows therefore that an
-individual may thus be "pure-bred," namely alike on both sides of his
-composition as regards each ingredient in one of two ways, either by
-having received the ingredient from the male chest and from the female,
-or in having received it from neither. Conversely in respect of any
-ingredient he may be "cross-bred," receiving the presence of it from one
-gamete and the absence of it from the other.
-
-The second conception with which we have now to become thoroughly
-familiar is that of the individual as composed of what we call presences
-and absences of all the possible ingredients. It is the basis of all
-progress in genetic analysis. Let me give you two illustrations. A blue
-eye is due to the absence of a factor which forms pigment on the front
-of the iris. Two blue-eyed parents therefore, as Hurst has proved, do
-not have dark-eyed children. The dark eye is due to either a single or
-double dose of the factor missing from the blue eye. So dark-eyed
-persons may have families all dark-eyed, or families composed of a
-mixture of dark and light-eyed children in certain proportions which on
-the average are definite.
-
-Two plants of _Oenothera_ which I exhibit illustrate the same thing. One
-of them is the ordinary _Lamarckiana_. I bend its stem. It will not
-break, or only breaks with difficulty on account of the tough fibres it
-contains. The stem of the other, one of de Vries' famous mutations,
-snaps at once like short pastry, because it does not contain the factor
-for the formation of the fibres. Such plants may be sister-plants
-produced by the self-fertilisation of one parent, but they are distinct
-in their composition and properties--and this distinction turns on the
-presence or absence of elements which are treated as definite entities
-when the germ-cells are formed. When we speak of such qualities as the
-formation of pigment in an eye, or the development of fibres in a stem,
-as due to transmitted elements or factors, you will perhaps ask if we
-have formed any notion as to the actual nature of those factors. For my
-own part as regards that ulterior question I confess to a disposition to
-hold my fancy on a tight rein. It cannot be very long before we shall
-_know_ what some of the factors are, and we may leave guessing till
-then. Meanwhile however there is no harm in admitting that several of
-them behave much as if they were ferments, and others as if they
-constructed the substances on which the ferments act. But we must not
-suppose for a moment that it is the ferment, or the objective substance,
-which is transmitted. The thing transmitted can only be the power or
-faculty to produce the ferment or the objective substance.
-
-So far we have been considering the synthesis of the individual from
-ingredients brought into him by the two gametes. In the next step of our
-consideration we reverse the process, and examine how the ingredients of
-which he was originally compounded are distributed among the gametes
-that are eventually budded off from him.
-
-Take first the case of the components in respect of which he is
-pure-bred. Expectation would naturally suggest that all the germ-cells
-formed from him would be alike in respect of those ingredients, and
-observation shows, except in the rare cases of originating variations,
-the causation of which is still obscure, that this expectation is
-correct.
-
-Hitherto though without experimental evidence no one could have been
-certain that the facts were as I have described them, yet there is
-nothing altogether contrary to common expectation. But when we proceed
-to ask how the germ-cells will be constituted in the case of an
-individual who is cross-bred in some respect, containing that is to say,
-an ingredient from the one side of his parentage and not from the other,
-the answer is entirely contrary to all the preconceptions which either
-science or common sense had formed about heredity. For we find definite
-experimental proof in nearly all the cases which have been examined,
-that the germ-cells formed by such individuals do either contain or not
-contain a representation of the ingredient, just as the original gametes
-did or did not contain it.
-
-If _both_ parent-gametes brought a certain quality in, then all the
-daughter gametes have it; if neither brought it in, then none of the
-daughter gametes have it. If it came in from one side and not from the
-other, then on an average in half the resulting gametes it will be
-present and from half it will be absent. This last phenomenon, which is
-called segregation, constitutes the essence of Mendel's discovery.
-
-So recurring to the simile of the man as made by the mixing of
-tinctures, the process of redistribution of his characters among the
-germ-cells may be represented as a sorting back of the tinctures again
-into a double row of bottles, a pair corresponding to each ingredient;
-and each of the germ-cells as then made of a drop from one or other
-bottle of each pair: and in our model we may represent the phenomenon of
-segregation in a crude way by supposing that the bottles having no
-tincture in them, instead of being empty contained an inoperative fluid,
-say water, with which the tincture would not mix. When the new
-germ-cells are formed, the two fluids instead of diluting each other
-simply separate again. It is this fact which entitles us to speak of the
-purity of germ-cells. They are pure in the possession of an ingredient,
-or in not possessing it; and the ingredients, or factors, as we
-generally call them, are units because they are so treated in the
-process of formation of the new gametes and because they come out of the
-process of segregation in the same condition as they went in at
-fertilisation.
-
-As a consequence of these facts it follows that however complex may be
-the origin of two given parents the composition of the offspring they
-can produce is limited. There is only a limited number of types to be
-made by the possible recombinations of the parental ingredients, and the
-relative numbers in which each type will be represented are often
-predicable by very simple arithmetical rules.
-
-For example, if neither parent possesses a certain factor at all, then
-none of the offspring will have it. If either parent has two doses of
-the factor then all the children will have it; and if either parent has
-one dose of the factor and the other has none, then on an average half
-the family will have it, and half be without it.
-
-To know whether the parent possesses the factor or not may be difficult
-for reasons which will presently appear, but often it is quite easy and
-can be told at once, for there are many factors which cannot be present
-in the individual without manifesting their presence. I may illustrate
-the descent of such a factor by the case of a family possessing a
-peculiar form of night-blindness. The affected individuals marrying with
-those unaffected have a mixture of affected and unaffected children, but
-their unaffected children not having the responsible ingredient cannot
-pass it on[1].
-
-In such an observation two things are strikingly exemplified, (1) the
-fact of the permanence of the unit, and (2) the fact that a _mixture_ of
-types in the family means that one or other parent is cross-bred in some
-respect, and is giving off gametes of more than one type.
-
-The problem of heredity is thus a problem primarily analytical. We have
-to detect and enumerate the factors out of which the bodies of animals
-and plants are built up, and the laws of their distribution among the
-germ-cells. All the processes of which I have spoken are accomplished by
-means of cell-divisions, and in the one cell-union which occurs in
-fertilisation. If we could watch the factors segregating from each
-other in cell-division, or even if by microscopic examination we could
-recognize this multitudinous diversity of composition that must
-certainly exist among the germ-cells of all ordinary individuals, the
-work of genetics would be much simpler than it is.
-
-But so far no such direct method of observation has been discovered. In
-default we are obliged to examine the constitution of the germ-cells by
-experimental breeding, so contrived that each mating shall test the
-composition of an individual in one or more chosen respects, and, so to
-speak, sample its germ-cells by counting the number of each kind of
-offspring which it can produce. But cumbersome as this method must
-necessarily be, it enables us to put questions to Nature which never
-have been put before. She, it has been said, is an unwilling witness.
-Our questions must be shaped in such a way that the only possible
-answer is a direct "Yes" or a direct "No." By putting such questions we
-have received some astonishing answers which go far below the surface.
-Amazing though they be, they are nevertheless true; for though our
-witness may prevaricate, she cannot lie. Piecing these answers together,
-getting one hint from this experiment, and another from that, we begin
-little by little to reconstruct what is going on in that hidden world of
-gametes. As we proceed, like our brethren in other sciences, we
-sometimes receive answers which seem inconsistent or even contradictory.
-But by degrees a sufficient body of evidence can be attained to show
-what is the rule and what the exception. My purpose today must be to
-speak rather of the regular than of the irregular.
-
-One clear exception I may mention. Castle finds that in a cross between
-the long-eared lop-rabbit and a short-eared breed, ears of intermediate
-length are produced: and that these intermediates breed approximately
-true.
-
-Exceptions in general must be discussed elsewhere. Nevertheless if I may
-throw out a word of counsel to beginners, it is: Treasure your
-exceptions! When there are none, the work gets so dull that no one cares
-to carry it further. Keep them always uncovered and in sight. Exceptions
-are like the rough brickwork of a growing building which tells that
-there is more to come and shows where the next construction is to be.
-
-You will readily understand that the presentation here given of the
-phenomena is only the barest possible outline. Some of the details we
-may now fill in. For example, I have spoken of the characters of the
-organism, its colour, shape, and the like, as if they were due each to
-one ingredient or factor. Some of them are no doubt correctly so
-represented; but already we know numerous bodily features which need the
-concurrence of several factors to produce them. Nevertheless though the
-character only appears when all the complementary ingredients are
-together present, each of these severally and independently follows, as
-regards its transmission, the simple rules I have described.
-
-This complementary action may be illustrated by some curious results
-that Mr Punnett and I have encountered when experimenting with the
-height of Sweet Peas. There are two dwarf varieties, one the prostrate
-"Cupid," the other the half-dwarf or "Bush" Sweet Peas. Crossed together
-they give a cross-bred of full height. There is thus some element in the
-Cupid which when it meets the complementary element from the Bush,
-produces the characteristic length of the ordinary Sweet Pea. We may
-note in passing that such a fact demonstrates at once the nature of
-Variation and Reversion. The Reversion occurs because the two factors
-that made the _height_ of the old Sweet Pea again come together after
-being parted: and the Variations by which each of the dwarfs came into
-existence must have taken place by the dropping out of one of these
-elements or of the other.
-
-Conversely there are factors which by their presence can prevent or
-inhibit the development and appearance of others present and
-unperceived.
-
-For example, all the factors for pigmentation may be present in a plant
-or an animal; but in addition there may be another factor present which
-keeps the individual white, or nearly so.
-
-There are cases in which the action of the factors is superposed one on
-top of the other, and not until each factor is removed in turn can the
-effects of the underlying factors be perceived. So in the mouse if no
-other colour-factor is present, the fur is chocolate. If the next factor
-in the series be there, it is black. If still another factor be added,
-it has the brownish grey of the common wild mouse. Conversely, by the
-variation which dropped out the top factor, a black mouse came into
-existence. By the loss of the black factor, the chocolate mouse was
-created, and for aught we can tell there may be still more possibilities
-hidden beneath.
-
-In the disentanglement of the properties and interactions of these
-elementary factors, the science we must call to our aid is Physiological
-Chemistry. The relations of Genetics with the other branches of biology
-are close. Such work can only be conducted by those who have the good
-fortune to be able to count upon continual help and advice from
-specialists in the various branches of Zoology, Physiology, and Botany.
-Often we have questions with which only a cytologist can deal, and
-often it is the experience of a systematist we must invoke. The school
-of Genetics in Cambridge starts under happy auspices in that we are
-surrounded by colleagues qualified, and as we have often found, willing
-to give us such aid unstinted. But with chemical physiology, we stand in
-an even closer relation; and from the little I have dared to say
-respecting the action and interaction of factors, it is evident that for
-their disentanglement there must one day be an intimate and enduring
-partnership arranged with the physiological chemists.
-
-Now, as the whole of the elaborate process by which the various elements
-are apportioned among the gametes must be got through in a few
-cell-divisions at most, and perhaps in one division only, it is not
-surprising that there is sometimes an interaction between factors that
-have quite distinct rôles to perform. These interactions are probably
-of several kinds. One, which I shall illustrate presently, is probably
-to be represented as a repulsion between two factors. As a consequence
-of its operations when the various factors are sorted out into the
-gametes, if the individual be cross-bred in respect of the _two_
-repelling factors, having received so to speak only a single dose of
-each, then the gametes are made up in such a way that each takes one or
-other of the two repelling factors, not both.
-
-Mutual repulsions of this kind probably play a significant part in the
-phenomena of heredity. A single concrete case which Mr Punnett and I
-have been investigating for some years will illustrate several of these
-principles. We crossed together a pure white Sweet Pea having an erect
-standard, with another pure white Sweet Pea having a hooded standard.
-The result is, as you see, a purple flower with an erect standard. The
-colour comes from the concurrence of complementary elements. A dose of a
-certain ingredient from one parent meets a dose of another ingredient
-from the other parent and the two make pigment in the flower. From other
-experiments we know that the _purple_ colour of the pigment is due to a
-dose of a third ingredient brought in from the hooded parent; and that
-in the absence of that blue factor, as we may call it, the flower would
-be red. The standard is erect because it contains a dose of the
-erectness-factor from the erect parent, and the hooded parent can
-readily be proved to owe its peculiar shape to the absence of that
-element.
-
-Our purple plant is thus cross-bred for four factors, containing only
-one dose of each.
-
-We let it fertilise itself, and its offspring show all the possible
-combinations of the four different factors and their absences which the
-genetic constitution of the plant can make.
-
-Note that one of the combinations we expect to find is missing. There
-are white erect and white hooded--white because they are lacking one or
-other of the complementary ingredients necessary to the production of
-pigment. There are purple erect and purple hooded, of which the purple
-erect must perforce contain all the four factors, and the purple hooded
-must similarly contain all of them except that for erectness. But when
-we turn to the red class we are surprised to find that they are all
-erect, none hooded. One of the possible combinations is missing. If you
-examine this series of facts you will find there is only one possible
-interpretation: namely that the ingredient which turns the flower
-purple--alkalinity, perhaps we may call it--never goes into the same
-germ-cell as the ingredient which makes the standard erect. There are
-plenty of ways of testing the truth of this interpretation. For example,
-it follows that the purple erects from such a family will in perpetuity
-have offspring 1 purple hooded: 2 purple erect: 1 red erect; also that
-all the white hooded crossed with pure reds will give purples, and so
-on. These experiments have been made and the result has in each case
-been conformable to expectation.
-
-Between these two factors, the purpleness and the erectness of standard,
-some antagonism or repulsion must exist. In some way therefore the
-chemical and the geometrical phenomena of heredity must be
-inter-related.
-
-Some one will say perhaps this is all very well as a scientific
-curiosity, but it has nothing to do with real life. The right answer to
-such criticism is of course the lofty one that science and its
-applications are distinct: that the investigator fixes his gaze solely
-on the search for truth and that his attention must not be distracted by
-trivialities of application. But while we make this answer and at least
-try to work in the spirit it proclaims, we know in our hearts that it is
-a counsel of perfection. I suspect that even the astronomer who at his
-spectroscope is analysing the composition of Vega or Capella has still
-an eye sometimes free for the affairs of this planet, and at least the
-fact that his discoveries may throw light on our destinies does not
-diminish his zeal in their pursuit. And surely to the study of Heredity,
-preeminently among all the sciences, we are looking for light on human
-destiny. To pretend otherwise would be mere hypocrisy. So while
-reserving the higher line of defence I will reply that again and again
-in our experimental work we come very near indeed to human affairs.
-Sometimes this is obvious enough. No practical dog-breeder or seeds-man
-can see the results of Mendelian recombination without perceiving that
-here is a bit of knowledge he can immediately apply. No sociologist can
-examine the pedigrees illustrating the simple descent of a deformity or
-a congenital disease, and not see that the new knowledge gives a solid
-basis for practical action by which the composition of a race could be
-modified if society so chose. More than this: we know for certain in one
-case, from the work of Professor Biffen, that the power to resist a
-disease caused by the invasion of a pathogenic organism, wheat-rust, is
-due to the absence of one of the simple factors or ingredients of which
-I have spoken, and what we know to be true in that one case we are
-beginning to suspect to be true of resistance to certain other diseases.
-No pathologist can see such an experiment as this of Professor Biffen's
-without realizing that here is a contribution of the first importance
-to the physiology of disease.
-
-There is no lack of utility and direct application in the study of
-Genetics. I have alluded to some strictly practical results. If we want
-to raise mangels that will not run to seed, or to breed a cow that will
-give more milk in less time, or milk with more butter and less water, we
-can turn to Genetics with every hope that something can be done in these
-laudable directions. But here I would plead what I cannot but regard as
-a higher usefulness in our work. Genetic inquiry aims at providing
-knowledge that may bring, and I think will bring, certainty into a
-region of human affairs and concepts which might have been supposed
-reserved for ages to be the domain of the visionary. We have long known
-that it was believed by some that our powers and conduct were dependent
-on our physical composition, and that other schools have maintained
-that nurture not nature, to use Galton's antithesis, has a
-preponderating influence on our careers; but so soon as it becomes
-common knowledge--not a philosophical speculation, but a certainty--that
-liability to a disease, or the power of resisting its attack, addiction
-to a particular vice, or to superstition, is due to the presence or
-absence of a specific ingredient; and finally that these characteristics
-are transmitted to the offspring according to definite, predicable
-rules, then man's views of his own nature, his conceptions of justice,
-in short his whole outlook on the world, must be profoundly changed. Yet
-as regards the more tangible of these physical and mental
-characteristics there can be little doubt that before many years have
-passed the laws of their transmission will be expressible in simple
-formulae.
-
-The blundering cruelty we call criminal justice will stand forth
-divested of natural sanction, a relic of the ferocious inventions of
-the savage. Well may such justice be portrayed as blind. Who shall say
-whether it is crime or punishment which has wrought the greater
-suffering in the world? We may live to know that to the keen satirical
-vision of Sam Butler on the pleasant mountains of Erewhon there was
-revealed a dispensation, not kinder only, but wiser than the terrific
-code which Moses delivered from the flames of Sinai.
-
-If there are societies which refuse to apply the new knowledge, the
-fault will not lie with Genetics. I think it needs but little
-observation of the newer civilisations to foresee that _they_ will apply
-every scrap of scientific knowledge which can help them, or seems to
-help them in the struggle, and I am good enough Selectionist to know
-that in that day the fate of the recalcitrant communities is sealed.
-
-The thrill of discovery is not dulled by a suspicion that the discovery
-can be applied. No harm is done to the investigator if he can resist the
-temptation to deviate from his aim. With rarest exceptions the
-discoveries which have formed the basis of physical progress have been
-made without any thought but for the gratification of curiosity. Of this
-there can be few examples more conspicuous than that which Mendel's work
-presents. Untroubled by any itch to make potatoes larger or bread
-cheaper, he set himself in the quiet of a cloister garden to find out
-the laws of hybridity, and so struck a mine of truth, inexhaustible in
-brilliancy and profit.
-
-I will now suggest to you that it is by no means unlikely that even in
-an inquiry so remote as that which I just described in the case of the
-Sweet Pea, we may have the clue to a mystery which concerns us all in
-the closest possible way. I mean the problem of the physiological nature
-of Sex. In speaking of the interpretation of sexual difference
-suggested by our experimental work as of some practical moment, I do not
-imply that as in the other instances I have given, the knowledge is
-likely to be of immediate use to our species; but only that if true it
-makes a contribution to the stock of human ideas which no one can regard
-as insignificant.
-
-In the light of Mendelian knowledge, when a family consists of more than
-one type the fact means that the germ-cells of one or other parent must
-certainly be of more than one kind. In the case of sex the members of
-the family are thus of two kinds, and the presumption is overwhelming
-that this distinction is due to a difference among the germ-cells. Next,
-since for all practical purposes the numbers of the two sexes produced
-are approximately equal, sex exhibits the special case in which a family
-consists of two types represented in equal numbers, half being male,
-half female. But I called your attention to the fact that equality of
-types results when _one_ parent was cross-bred in the character
-concerned, having received one dose only of the factor on which it
-depends. So we may feel fairly sure that the distinction between the
-sexes depends on the presence in one or other of them of an unpaired
-factor. This conclusion appears to me to follow so immediately on all
-that we have learnt of genetic physiology that with every confidence we
-may accept it as representing the actual fact.
-
-The question which of the two sexes contains the unpaired factor is less
-easy to answer, but there are several converging lines of evidence which
-point to the deduction that in Vertebrates at least, and in some other
-types, it is the female, and I feel little doubt that we shall succeed
-in proving that in them femaleness is a definite Mendelian factor
-absent from the male and following the ordinary Mendelian rules.
-
-Before showing you how the Sweet Pea phenomenon aids in this inquiry I
-must tell you of some other experimental results. The first concerns the
-common currant moth, _Abraxas grossulariata_. It has a definite pale
-variety called _lacticolor_. With these two forms Doncaster has made a
-remarkable series of experiments. When he began, _lacticolor_ was only
-known as a female form. This was crossed with the _grossulariata_ male
-and gave _grossulariata_ only, showing that the male was pure to type.
-The hybrids bred together gave _grossulariata_ males and females and
-_lacticolor_ females only. But the hybrid males bred to _lacticolor_
-females produced all four combinations, _grossulariata_ males and
-females, and _lacticolor_ males and females. When the _lacticolor_ males
-were bred to _grossulariata_ females, whether hybrid, or wild from a
-district where _lacticolor_ does not exist, the result was that all the
-males were _grossulariata_ and all the females _lacticolor_! It is
-difficult to follow the course of such an experiment on once hearing and
-all I ask you to remember is first that there is a series of matings
-giving very curious distributions of the characters of type and variety
-among the two sexes. And then, what is perhaps the most singular fact of
-all, that the wild typical _grossulariata_ female can when crossed with
-the _lacticolor_ male produce all females _lacticolor_. This last fact
-can, we know, mean only one thing, namely that these wild females are in
-reality hybrids of _lacticolor_; though since the males are pure
-_grossulariata_, that fact would in the natural course of things never
-be revealed.
-
-When we encounter such a series of phenomena as this, our business is to
-find a means of symbolical expression which will represent all the
-factors involved, and show how each behaves in descent. Such a system or
-scheme we have at length discovered, and I incline to think that it must
-be the true one. If you study this case you will find that there are
-nine distinct kinds of matings that can be made between the variety, the
-type and the hybrid, and the scheme fits the whole group of results. It
-is based on two suppositions:
-
-1. That the female is cross-bred, or as we call it heterozygous for
-femaleness-factor, the male being without that factor. The eggs are thus
-each destined from the first to become either males or females, but as
-regards sex the spermatozoa are alike in being non-female.
-
-2. That there is a repulsion between the femaleness-factor and the
-_grossulariata_ factor.
-
-Such a repulsion between two factors we are justified in regarding as
-possible because we have had proof of the occurrence of a similar
-repulsion in the case of the two factors in the Sweet Pea.
-
-If the case of this moth stood alone it would be interesting, but its
-importance is greatly increased by the fact that we know two cases in
-birds which are closely comparable. The simpler case to which alone I
-shall refer has been observed in the Canary. Like the Currant moth it
-has a kind of albino, called Cinnamon, and males of this variety when
-mated with ordinary dark green hen canaries produce dark males and
-Cinnamons which are always hens; while the green male and the Cinnamon
-hen produce nothing but greens of both sexes. This case, which has been
-experimentally studied by Miss Durham, offers a certain complication,
-but in its main outlines it is exactly like that of the moth, and the
-same interpretation is applicable to both.
-
-The particular interpretation may be imperfect and even partially
-wrong; but that we are at last able to form a working idea of the course
-of such phenomena at all is a most encouraging fact. If we are right, as
-I am strongly inclined to believe, we get a glimpse of the significance
-of the popular idea that in certain respects daughters are apt to
-resemble their fathers and sons their mothers; a phenomenon which is
-certainly sometimes to be observed.
-
-There are several collateral indications that we are on the right track
-in our theory of the nature of sex. One of these, derived from the
-peculiar inheritance of colour-blindness, is especially interesting.
-That affection is common in men, rare in women. Men who are colour-blind
-can transmit the affection but men who have normal vision cannot. Women
-however who are ostensibly normal may have colour-blind sons; and women
-who are colour-blind have, so far as we know, no sons who are not
-colour-blind[2].
-
-Mendelian analysis of these facts shows that colour-blindness is due,
-not, as might have been supposed, to the absence of something from the
-composition of the body, but to the presence of something which affects
-the sight. Just as nicotine-poisoning can paralyse the colour sense, so
-may we conceive the development of a secretion in the body which has a
-similar action. The comparative exemption of the woman must therefore
-mean that there is in her a positive factor which counteracts the
-colour-blindness factor, and it is not improbable that the counteracting
-element is no other than the femaleness-factor itself[3].
-
-I think I have said enough to prove that after all, those curiosities
-collected from observation of Sweet Peas and Canaries have no remote
-bearing on some very fascinating problems of human life.
-
-Lastly I suppose it is self-evident that they have a bearing on the
-problem of Evolution. The facts of heredity and variation are the
-materials out of which all theories of Evolution are constructed. At
-last by genetic methods we are beginning to obtain such facts of
-unimpeachable quality, and free from the flaws that were inevitable in
-older collections. From a survey of these materials we see something of
-the changes which will have to be made in the orthodox edifice to admit
-of their incorporation, but he must be rash indeed who would now attempt
-a comprehensive reconstruction. The results of genetic research are so
-bewilderingly novel that we need time and an exhaustive study of their
-inter-relations before we can hope to see them in proper value and
-perspective. In all the discussions of the stability and fitness of
-species who ever contemplated the possibility of a wild species having
-one of its sexes permanently hybrid? When I spoke of adventures to be
-encountered in genetic research I was thinking of such astonishing
-discoveries as that.
-
-There are others no less disconcerting. Who would have supposed it
-possible that the pollen-cells of a plant could be all of one type, and
-its egg-cells of two types? Yet Miss Saunders' experiments have provided
-definite proof that this is the condition of certain Stocks, of which
-the pollen grains all bear doubleness, while the egg-cells are some
-singles and some doubles. We cannot think yet of interpreting these
-complex phenomena in terms of a common plan. All that we know is that
-there is now open for our scrutiny a world of varied, orderly and
-specific physiological wonders into which we have as yet only peeped. To
-lay down positive propositions as to the origin and inter-relation of
-species in general, now, would be a task as fruitless as that of a
-chemist must have been who had tried to state the relationship of the
-elements before their properties had been investigated.
-
-For the first time _Variation_ and _Reversion_ have a concrete, palpable
-meaning. Hitherto they have stood by in all evolutionary debates,
-convenient genii, ready to perform as little or as much as might be
-desired by the conjuror. That vaporous stage of their existence is over;
-and we see Variation shaping itself as a definite, physiological event,
-the addition or omission of one or more definite elements; and Reversion
-as that particular addition or subtraction which brings the total of the
-elements back to something it had been before in the history of the
-race.
-
-The time for discussion of Evolution as a problem at large is closed. We
-face that problem now as one soluble by minute, critical analysis. Lord
-Acton in his inaugural lecture said that in the study of history we are
-at the beginning of the documentary age. No one will charge me with
-disrespect to the great name we commemorate this year, if I apply those
-words to the history of Evolution: Darwin, it was, who first showed us
-that the species have a history that can be read at all. If in the new
-reading of that history, there be found departures from the text laid
-down in his first recension, it is not to his fearless spirit that they
-will bring dismay.
-
-
-FOOTNOTES:
-
-[1] The investigation of this remarkable family was made originally by
-Cunier. The facts have been reexamined and the pedigree much extended by
-Nettleship. The numerical results are somewhat irregular, but it is
-especially interesting as being the largest pedigree of human disease or
-defect yet made. It contains 2121 persons, extending over ten
-generations. Of these persons, 135 are known to have been night-blind.
-In no single case was the peculiarity transmitted through an unaffected
-member. It should be mentioned that for night-blindness such a system of
-descent is peculiar. More usually it follows the scheme described for
-colour-blindness. It is not known wherein the peculiarity of this family
-consists.
-
-[2] We have knowledge now of seven colour-blind women, having, in all,
-17 sons who are all colour-blind. Most of these cases have been
-collected by Mr Nettleship.
-
-[3] An alternative and perhaps more satisfactory interpretation of the
-same facts has been proposed by Doncaster (_Jour. Genetics_ I, Pt 4, p.
-377). Until more progress has been made with the analysis of sexual
-differentiation it is not possible to decide which of the two
-interpretations is correct. The numerical results predicted on both
-systems are the same; but by introducing a more complicated though quite
-reasonable formula for the representation of the sex-differences
-Doncaster's method shows that colour-blindness may be a _recessive_ due
-to the absence of a factor which produces normal colour-vision.
-
-
-Cambridge:
-PRINTED BY JOHN CLAY, M.A.
-AT THE UNIVERSITY PRESS.
-
-
-
-
-
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-Title: The Methods and Scope of Genetics
- An inaugural lecture delivered 23 October 1908
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-<div class="center"><a name="cover.jpg" id="cover.jpg"></a><img src="images/cover.jpg" alt="cover" /></div>
-
-<hr />
-
-<p class="bold2">THE METHODS AND SCOPE<br />OF<br />GENETICS</p>
-
-<hr />
-
-<p class="bold">CAMBRIDGE UNIVERSITY PRESS<br />
-London: FETTER LANE, E.C.<br />
-<span class="smcap">C. F. CLAY, Manager</span></p>
-
-<div class="center"><img src="images/logo.jpg" alt="logo" /></div>
-
-<p class="bold">Edinburgh: 100, PRINCES STREET<br />
-Berlin: A. ASHER AND CO.<br />
-Leipzig: F. A. BROCKHAUS<br />
-New York: G. P. PUTNAM'S SONS<br />
-Bombay and Calcutta: <span class="smcap">MACMILLAN AND CO., Ltd.</span></p>
-
-<p class="bold space-above"><i>All rights reserved</i></p>
-
-<hr />
-
-<h1>THE METHODS AND SCOPE<br />OF<br />GENETICS</h1>
-
-<p class="bold space-above"><i>AN INAUGURAL LECTURE DELIVERED<br />
-23 OCTOBER 1908</i></p>
-
-<p class="bold space-above">by<br />W. BATESON, M.A., F.R.S.<br />PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE</p>
-
-<p class="bold space-above">Cambridge:<br />at the University Press<br />1912</p>
-
-<hr />
-
-<p class="center"><i>First Edition 1908</i><br /><i>Reprinted 1912</i></p>
-
-<hr />
-
-<h2>PREFATORY NOTE</h2>
-
-<p>The Professorship of Biology was founded in 1908 for a period of five
-years partly by the generosity of an anonymous benefactor, and partly by
-the University of Cambridge. The object of the endowment was the
-promotion of inquiries into the physiology of Heredity and Variation, a
-study now spoken of as Genetics.</p>
-
-<p>It is now recognized that the progress of such inquiries will chiefly be
-accomplished by the application of experimental methods, especially
-those which Mendel's discovery has suggested. The purpose of this
-inaugural lecture is to describe the outlook over this field of research
-in a manner intelligible to students of other parts of knowledge.</p>
-
-<p class="right">W. B.</p>
-
-<p><i>28 October, 1908</i></p>
-
-
-<hr />
-
-<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
-
-<h2>THE METHODS AND SCOPE OF<br />GENETICS</h2>
-
-<p>The opportunity of addressing fellow-students pursuing lines of inquiry
-other than his own falls seldom to a scientific man. One of these rare
-opportunities is offered by the constitution of the Professorship to
-which I have had the honour to be called. That Professorship, though
-bearing the comprehensive title "of Biology," is founded with the
-understanding that the holder shall apply himself to a particular class
-of physiological problems, the study of which is denoted by the term
-Genetics. The term is new; and though the problems are among the oldest
-which have vexed the human mind, the modes by which they may be
-successfully attacked<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span> are also of modern invention. There is therefore
-a certain fitness in the employment of this occasion for the deliverance
-of a discourse explaining something of the aims of Genetics and of the
-methods by which we trust they may be reached.</p>
-
-<p>You will be aware that the claims put forward in the name of Genetics
-are high, but I trust to be able to show you that they are not high
-without reason. It is the ambition of every one who in youth devotes
-himself to the search for natural truth, that his work may be found
-somewhere in the main stream of progress. So long only as he keeps
-something of the limitless hope with which his voyage of discovery
-began, will his courage and his spirit last. The moment we most dread is
-one in which it may appear that, after all, our effort has been spent in
-exploring some petty tributary, or worse, a backwater of the great
-current. It is because<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span> Genetic research is still pushing forward in the
-central undifferentiated trunk of biological science that we confess no
-guilt of presumption in declaring boldly that whatever difficulty may be
-in store for those who cast in their lot with us, they need fear no
-disillusionment or misgiving that their labour has been wasted on a
-paltry quest.</p>
-
-<p>In research, as in all business of exploration, the stirring times come
-when a fresh region is suddenly unlocked by the discovery of a new key.
-Then conquest is easy and there are prizes for all. We are happy in that
-during our own time not a few such territories have been revealed to the
-vision of mankind. I do not dare to suggest that in magnitude or
-splendour the field of Genetics may be compared with that now being
-disclosed to the physicist or the astronomer; for the glory of the
-celestial is one and the glory of the terrestrial is another. But I
-will<span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span> say that for once to the man of ordinary power who cannot venture
-into those heights beyond, Mendel's clue has shown the way into a realm
-of nature which for surprising novelty and adventure is hardly to be
-excelled.</p>
-
-<p>It is no hyperbolical figure that I use when I speak of Mendelian
-discovery leading us into a new world, the very existence of which was
-unsuspected before.</p>
-
-<p>The road thither is simple and easy to follow. We start from a common
-fact, familiar to everyone, that all the ordinary animals and plants
-began their individual life by the union of two cells, the one male, the
-other female. Those cells are known as germ-cells or <i>gametes</i>, that is
-to say, "marrying" cells.</p>
-
-<p>Now obviously the diversity of form which is characteristic of the
-animal and plant world must be somehow represented in the gametes, since
-it is they which bring into each organism<span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span> all that it contains. I am
-aware that there is interplay between the organism and the circumstances
-in which it grows up, and that opportunity given may bring out a
-potentiality which without that opportunity must have lain dormant. But
-while noting parenthetically that this question of opportunity has an
-importance, which some day it may be convenient to estimate, the one
-certain fact is that all the powers, physical and mental that a living
-creature possesses were contributed by one or by both of the two
-germ-cells which united in fertilisation to give it existence. The fact
-that <i>two</i> cells are concerned in the production of all the ordinary
-forms of life was discovered a long while ago, and has been part of the
-common stock of elementary knowledge of all educated persons for about
-half a century. The full consequences of this double nature seem
-nevertheless to have struck nobody before Mendel. Simple though<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> the
-fact is, I have noticed that to many it is difficult to assimilate as a
-working idea. We are accustomed to think of a man, a butterfly, or an
-apple tree as each <i>one</i> thing. In order to understand the significance
-of Mendelism we must get thoroughly familiar with the fact that they are
-each <i>two</i> things, double throughout every part of their composition.
-There is perhaps no better exercise as a preparation for genetic
-research than to examine the people one meets in daily life and to try
-in a rough way to analyse them into the two assemblages of characters
-which are united in them. That we are assemblages or medleys of our
-parental characteristics is obvious. We all know that a man may have his
-father's hair, his mother's colour, his father's voice, his mother's
-insensibility to music, and so on, but that is not enough.</p>
-
-<p>Such an analysis is true, inasmuch as the various characters <i>are</i>
-transmitted<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span> independently, but it misses the essential point. For in
-each of these respects the individual is double; and so to get a true
-picture of the composition of the individual we have to think how <i>each</i>
-of the two original gametes was provided in the matter of height, hair,
-colour, mathematical ability, nail-shape, and the other features that go
-to make the man we know. The contribution of each gamete in each respect
-has thus to be separately brought to account. If we could make a list of
-all the ingredients that go to form a man and could set out how he is
-constituted in respect of each of them, it would not suffice to give one
-column of values for these ingredients, but we must rule two columns,
-one for the ovum and one for the spermatozoon, which united in
-fertilisation to form that man, and in each column we must represent how
-that gamete was supplied in respect of each of the ingredients in our
-list. When the problem of<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> heredity is thus represented we can hardly
-avoid discovering, by mere inspection, one of the chief conclusions to
-which genetic research has led. For it is obvious that the contributions
-of the male and female gametes may in respect of any of the ingredients
-be either the same, or different. In any case in which the contribution
-made by the two cells is the same, the resulting organism&mdash;in our
-example the man&mdash;is, as we call it, <i>pure-bred</i> for that ingredient, and
-in all respects in which the contribution from the two sides of the
-parentage is dissimilar the resulting organism is <i>cross-bred</i>.</p>
-
-<p>To give an intelligible account of the next step in the analysis without
-having recourse to precise and technical language is not very easy.</p>
-
-<p>We have got to the point of view from which we see the individual made
-up of a large number of distinct ingredients,<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span> contributed from two
-sources, and in respect of any of them he may have received two similar
-portions or two dissimilar portions. We shall not go far wrong if we
-extend and elaborate our illustration thus. Let us imagine the contents
-of a gamete as a fluid made by taking a drop from each of a definite
-number of bottles in a chest, containing tinctures of the several
-ingredients. There is one such chest from which the male gamete is to be
-made up, and a similar chest containing a corresponding set of bottles
-out of which the components of the female gamete are to be taken. But in
-either chest one or more of the bottles may be empty; then nothing goes
-in to represent that ingredient from that chest, and if corresponding
-bottles are empty in both chests, then the individual made on
-fertilisation by mixing the two collections of drops together does not
-contain the missing ingredient at all. It follows<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> therefore that an
-individual may thus be "pure-bred," namely alike on both sides of his
-composition as regards each ingredient in one of two ways, either by
-having received the ingredient from the male chest and from the female,
-or in having received it from neither. Conversely in respect of any
-ingredient he may be "cross-bred," receiving the presence of it from one
-gamete and the absence of it from the other.</p>
-
-<p>The second conception with which we have now to become thoroughly
-familiar is that of the individual as composed of what we call presences
-and absences of all the possible ingredients. It is the basis of all
-progress in genetic analysis. Let me give you two illustrations. A blue
-eye is due to the absence of a factor which forms pigment on the front
-of the iris. Two blue-eyed parents therefore, as Hurst has proved, do
-not have dark-eyed children. The dark eye<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> is due to either a single or
-double dose of the factor missing from the blue eye. So dark-eyed
-persons may have families all dark-eyed, or families composed of a
-mixture of dark and light-eyed children in certain proportions which on
-the average are definite.</p>
-
-<p>Two plants of <i>Oenothera</i> which I exhibit illustrate the same thing. One
-of them is the ordinary <i>Lamarckiana</i>. I bend its stem. It will not
-break, or only breaks with difficulty on account of the tough fibres it
-contains. The stem of the other, one of de Vries' famous mutations,
-snaps at once like short pastry, because it does not contain the factor
-for the formation of the fibres. Such plants may be sister-plants
-produced by the self-fertilisation of one parent, but they are distinct
-in their composition and properties&mdash;and this distinction turns on the
-presence or absence of elements which are treated as definite entities
-when the germ-cells are<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span> formed. When we speak of such qualities as the
-formation of pigment in an eye, or the development of fibres in a stem,
-as due to transmitted elements or factors, you will perhaps ask if we
-have formed any notion as to the actual nature of those factors. For my
-own part as regards that ulterior question I confess to a disposition to
-hold my fancy on a tight rein. It cannot be very long before we shall
-<i>know</i> what some of the factors are, and we may leave guessing till
-then. Meanwhile however there is no harm in admitting that several of
-them behave much as if they were ferments, and others as if they
-constructed the substances on which the ferments act. But we must not
-suppose for a moment that it is the ferment, or the objective substance,
-which is transmitted. The thing transmitted can only be the power or
-faculty to produce the ferment or the objective substance.</p>
-
-<p><span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span></p><p>So far we have been considering the synthesis of the individual from
-ingredients brought into him by the two gametes. In the next step of our
-consideration we reverse the process, and examine how the ingredients of
-which he was originally compounded are distributed among the gametes
-that are eventually budded off from him.</p>
-
-<p>Take first the case of the components in respect of which he is
-pure-bred. Expectation would naturally suggest that all the germ-cells
-formed from him would be alike in respect of those ingredients, and
-observation shows, except in the rare cases of originating variations,
-the causation of which is still obscure, that this expectation is
-correct.</p>
-
-<p>Hitherto though without experimental evidence no one could have been
-certain that the facts were as I have described them, yet there is
-nothing altogether contrary to<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span> common expectation. But when we proceed
-to ask how the germ-cells will be constituted in the case of an
-individual who is cross-bred in some respect, containing that is to say,
-an ingredient from the one side of his parentage and not from the other,
-the answer is entirely contrary to all the preconceptions which either
-science or common sense had formed about heredity. For we find definite
-experimental proof in nearly all the cases which have been examined,
-that the germ-cells formed by such individuals do either contain or not
-contain a representation of the ingredient, just as the original gametes
-did or did not contain it.</p>
-
-<p>If <i>both</i> parent-gametes brought a certain quality in, then all the
-daughter gametes have it; if neither brought it in, then none of the
-daughter gametes have it. If it came in from one side and not from the
-other, then on an average in half the resulting gametes it will be
-present and from half it will be<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span> absent. This last phenomenon, which is
-called segregation, constitutes the essence of Mendel's discovery.</p>
-
-<p>So recurring to the simile of the man as made by the mixing of
-tinctures, the process of redistribution of his characters among the
-germ-cells may be represented as a sorting back of the tinctures again
-into a double row of bottles, a pair corresponding to each ingredient;
-and each of the germ-cells as then made of a drop from one or other
-bottle of each pair: and in our model we may represent the phenomenon of
-segregation in a crude way by supposing that the bottles having no
-tincture in them, instead of being empty contained an inoperative fluid,
-say water, with which the tincture would not mix. When the new
-germ-cells are formed, the two fluids instead of diluting each other
-simply separate again. It is this fact which entitles us to speak of the
-purity of germ-cells. They<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> are pure in the possession of an ingredient,
-or in not possessing it; and the ingredients, or factors, as we
-generally call them, are units because they are so treated in the
-process of formation of the new gametes and because they come out of the
-process of segregation in the same condition as they went in at
-fertilisation.</p>
-
-<p>As a consequence of these facts it follows that however complex may be
-the origin of two given parents the composition of the offspring they
-can produce is limited. There is only a limited number of types to be
-made by the possible recombinations of the parental ingredients, and the
-relative numbers in which each type will be represented are often
-predicable by very simple arithmetical rules.</p>
-
-<p>For example, if neither parent possesses a certain factor at all, then
-none of the offspring will have it. If either parent has two doses of
-the factor then all the children will<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> have it; and if either parent has
-one dose of the factor and the other has none, then on an average half
-the family will have it, and half be without it.</p>
-
-<p>To know whether the parent possesses the factor or not may be difficult
-for reasons which will presently appear, but often it is quite easy and
-can be told at once, for there are many factors which cannot be present
-in the individual without manifesting their presence. I may illustrate
-the descent of such a factor by the case of a family possessing a
-peculiar form of night-blindness. The affected individuals marrying with
-those unaffected have a mixture of affected and unaffected children, but
-their unaffected children not having the responsible ingredient cannot
-pass it on<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a>.</p>
-
-<p><span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span></p><p>In such an observation two things are strikingly exemplified, (1) the
-fact of the permanence of the unit, and (2) the fact that a <i>mixture</i> of
-types in the family means that one or other parent is cross-bred in some
-respect, and is giving off gametes of more than one type.</p>
-
-<p>The problem of heredity is thus a problem primarily analytical. We have
-to detect and enumerate the factors out of which the bodies of animals
-and plants are built up, and the laws of their distribution among the
-germ-cells. All the processes of which I have spoken are accomplished by
-means of cell-divisions, and in the one cell-union which occurs in
-fertilisation. If we could watch<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span> the factors segregating from each
-other in cell-division, or even if by microscopic examination we could
-recognize this multitudinous diversity of composition that must
-certainly exist among the germ-cells of all ordinary individuals, the
-work of genetics would be much simpler than it is.</p>
-
-<p>But so far no such direct method of observation has been discovered. In
-default we are obliged to examine the constitution of the germ-cells by
-experimental breeding, so contrived that each mating shall test the
-composition of an individual in one or more chosen respects, and, so to
-speak, sample its germ-cells by counting the number of each kind of
-offspring which it can produce. But cumbersome as this method must
-necessarily be, it enables us to put questions to Nature which never
-have been put before. She, it has been said, is an unwilling witness.
-Our questions must be shaped in such a way that<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> the only possible
-answer is a direct "Yes" or a direct "No." By putting such questions we
-have received some astonishing answers which go far below the surface.
-Amazing though they be, they are nevertheless true; for though our
-witness may prevaricate, she cannot lie. Piecing these answers together,
-getting one hint from this experiment, and another from that, we begin
-little by little to reconstruct what is going on in that hidden world of
-gametes. As we proceed, like our brethren in other sciences, we
-sometimes receive answers which seem inconsistent or even contradictory.
-But by degrees a sufficient body of evidence can be attained to show
-what is the rule and what the exception. My purpose today must be to
-speak rather of the regular than of the irregular.</p>
-
-<p>One clear exception I may mention. Castle finds that in a cross between
-the long-eared lop-rabbit and a short-eared<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> breed, ears of intermediate
-length are produced: and that these intermediates breed approximately
-true.</p>
-
-<p>Exceptions in general must be discussed elsewhere. Nevertheless if I may
-throw out a word of counsel to beginners, it is: Treasure your
-exceptions! When there are none, the work gets so dull that no one cares
-to carry it further. Keep them always uncovered and in sight. Exceptions
-are like the rough brickwork of a growing building which tells that
-there is more to come and shows where the next construction is to be.</p>
-
-<p>You will readily understand that the presentation here given of the
-phenomena is only the barest possible outline. Some of the details we
-may now fill in. For example, I have spoken of the characters of the
-organism, its colour, shape, and the like, as if they were due each to
-one ingredient or factor. Some of them are no doubt correctly so<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span>
-represented; but already we know numerous bodily features which need the
-concurrence of several factors to produce them. Nevertheless though the
-character only appears when all the complementary ingredients are
-together present, each of these severally and independently follows, as
-regards its transmission, the simple rules I have described.</p>
-
-<p>This complementary action may be illustrated by some curious results
-that Mr Punnett and I have encountered when experimenting with the
-height of Sweet Peas. There are two dwarf varieties, one the prostrate
-"Cupid," the other the half-dwarf or "Bush" Sweet Peas. Crossed together
-they give a cross-bred of full height. There is thus some element in the
-Cupid which when it meets the complementary element from the Bush,
-produces the characteristic length of the ordinary Sweet Pea. We may
-note in passing that such a fact demonstrates<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> at once the nature of
-Variation and Reversion. The Reversion occurs because the two factors
-that made the <i>height</i> of the old Sweet Pea again come together after
-being parted: and the Variations by which each of the dwarfs came into
-existence must have taken place by the dropping out of one of these
-elements or of the other.</p>
-
-<p>Conversely there are factors which by their presence can prevent or
-inhibit the development and appearance of others present and
-unperceived.</p>
-
-<p>For example, all the factors for pigmentation may be present in a plant
-or an animal; but in addition there may be another factor present which
-keeps the individual white, or nearly so.</p>
-
-<p>There are cases in which the action of the factors is superposed one on
-top of the other, and not until each factor is removed in turn can the
-effects of the underlying<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> factors be perceived. So in the mouse if no
-other colour-factor is present, the fur is chocolate. If the next factor
-in the series be there, it is black. If still another factor be added,
-it has the brownish grey of the common wild mouse. Conversely, by the
-variation which dropped out the top factor, a black mouse came into
-existence. By the loss of the black factor, the chocolate mouse was
-created, and for aught we can tell there may be still more possibilities
-hidden beneath.</p>
-
-<p>In the disentanglement of the properties and interactions of these
-elementary factors, the science we must call to our aid is Physiological
-Chemistry. The relations of Genetics with the other branches of biology
-are close. Such work can only be conducted by those who have the good
-fortune to be able to count upon continual help and advice from
-specialists in the various branches of Zoology, Physiology, and Botany.
-Often we have<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span> questions with which only a cytologist can deal, and
-often it is the experience of a systematist we must invoke. The school
-of Genetics in Cambridge starts under happy auspices in that we are
-surrounded by colleagues qualified, and as we have often found, willing
-to give us such aid unstinted. But with chemical physiology, we stand in
-an even closer relation; and from the little I have dared to say
-respecting the action and interaction of factors, it is evident that for
-their disentanglement there must one day be an intimate and enduring
-partnership arranged with the physiological chemists.</p>
-
-<p>Now, as the whole of the elaborate process by which the various elements
-are apportioned among the gametes must be got through in a few
-cell-divisions at most, and perhaps in one division only, it is not
-surprising that there is sometimes an interaction between factors that
-have quite distinct r&ocirc;les<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> to perform. These interactions are probably
-of several kinds. One, which I shall illustrate presently, is probably
-to be represented as a repulsion between two factors. As a consequence
-of its operations when the various factors are sorted out into the
-gametes, if the individual be cross-bred in respect of the <i>two</i>
-repelling factors, having received so to speak only a single dose of
-each, then the gametes are made up in such a way that each takes one or
-other of the two repelling factors, not both.</p>
-
-<p>Mutual repulsions of this kind probably play a significant part in the
-phenomena of heredity. A single concrete case which Mr Punnett and I
-have been investigating for some years will illustrate several of these
-principles. We crossed together a pure white Sweet Pea having an erect
-standard, with another pure white Sweet Pea having a hooded standard.
-The result is, as you see,<span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span> a purple flower with an erect standard. The
-colour comes from the concurrence of complementary elements. A dose of a
-certain ingredient from one parent meets a dose of another ingredient
-from the other parent and the two make pigment in the flower. From other
-experiments we know that the <i>purple</i> colour of the pigment is due to a
-dose of a third ingredient brought in from the hooded parent; and that
-in the absence of that blue factor, as we may call it, the flower would
-be red. The standard is erect because it contains a dose of the
-erectness-factor from the erect parent, and the hooded parent can
-readily be proved to owe its peculiar shape to the absence of that
-element.</p>
-
-<p>Our purple plant is thus cross-bred for four factors, containing only
-one dose of each.</p>
-
-<p>We let it fertilise itself, and its offspring<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> show all the possible
-combinations of the four different factors and their absences which the
-genetic constitution of the plant can make.</p>
-
-<p>Note that one of the combinations we expect to find is missing. There
-are white erect and white hooded&mdash;white because they are lacking one or
-other of the complementary ingredients necessary to the production of
-pigment. There are purple erect and purple hooded, of which the purple
-erect must perforce contain all the four factors, and the purple hooded
-must similarly contain all of them except that for erectness. But when
-we turn to the red class we are surprised to find that they are all
-erect, none hooded. One of the possible combinations is missing. If you
-examine this series of facts you will find there is only one possible
-interpretation: namely that the ingredient which turns the flower
-purple&mdash;alkalinity,<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> perhaps we may call it&mdash;never goes into the same
-germ-cell as the ingredient which makes the standard erect. There are
-plenty of ways of testing the truth of this interpretation. For example,
-it follows that the purple erects from such a family will in perpetuity
-have offspring 1 purple hooded: 2 purple erect: 1 red erect; also that
-all the white hooded crossed with pure reds will give purples, and so
-on. These experiments have been made and the result has in each case
-been conformable to expectation.</p>
-
-<p>Between these two factors, the purpleness and the erectness of standard,
-some antagonism or repulsion must exist. In some way therefore the
-chemical and the geometrical phenomena of heredity must be
-inter-related.</p>
-
-<p>Some one will say perhaps this is all very well as a scientific
-curiosity, but it has nothing to do with real life. The right answer to
-such criticism is of course the lofty one that science<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> and its
-applications are distinct: that the investigator fixes his gaze solely
-on the search for truth and that his attention must not be distracted by
-trivialities of application. But while we make this answer and at least
-try to work in the spirit it proclaims, we know in our hearts that it is
-a counsel of perfection. I suspect that even the astronomer who at his
-spectroscope is analysing the composition of Vega or Capella has still
-an eye sometimes free for the affairs of this planet, and at least the
-fact that his discoveries may throw light on our destinies does not
-diminish his zeal in their pursuit. And surely to the study of Heredity,
-preeminently among all the sciences, we are looking for light on human
-destiny. To pretend otherwise would be mere hypocrisy. So while
-reserving the higher line of defence I will reply that again and again
-in our experimental work we come very near indeed to human affairs.
-Sometimes this is obvious<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> enough. No practical dog-breeder or seeds-man
-can see the results of Mendelian recombination without perceiving that
-here is a bit of knowledge he can immediately apply. No sociologist can
-examine the pedigrees illustrating the simple descent of a deformity or
-a congenital disease, and not see that the new knowledge gives a solid
-basis for practical action by which the composition of a race could be
-modified if society so chose. More than this: we know for certain in one
-case, from the work of Professor Biffen, that the power to resist a
-disease caused by the invasion of a pathogenic organism, wheat-rust, is
-due to the absence of one of the simple factors or ingredients of which
-I have spoken, and what we know to be true in that one case we are
-beginning to suspect to be true of resistance to certain other diseases.
-No pathologist can see such an experiment as this of Professor Biffen's
-without realizing<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> that here is a contribution of the first importance
-to the physiology of disease.</p>
-
-<p>There is no lack of utility and direct application in the study of
-Genetics. I have alluded to some strictly practical results. If we want
-to raise mangels that will not run to seed, or to breed a cow that will
-give more milk in less time, or milk with more butter and less water, we
-can turn to Genetics with every hope that something can be done in these
-laudable directions. But here I would plead what I cannot but regard as
-a higher usefulness in our work. Genetic inquiry aims at providing
-knowledge that may bring, and I think will bring, certainty into a
-region of human affairs and concepts which might have been supposed
-reserved for ages to be the domain of the visionary. We have long known
-that it was believed by some that our powers and conduct were dependent
-on our physical composition, and that other schools<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span> have maintained
-that nurture not nature, to use Galton's antithesis, has a
-preponderating influence on our careers; but so soon as it becomes
-common knowledge&mdash;not a philosophical speculation, but a certainty&mdash;that
-liability to a disease, or the power of resisting its attack, addiction
-to a particular vice, or to superstition, is due to the presence or
-absence of a specific ingredient; and finally that these characteristics
-are transmitted to the offspring according to definite, predicable
-rules, then man's views of his own nature, his conceptions of justice,
-in short his whole outlook on the world, must be profoundly changed. Yet
-as regards the more tangible of these physical and mental
-characteristics there can be little doubt that before many years have
-passed the laws of their transmission will be expressible in simple
-formulae.</p>
-
-<p>The blundering cruelty we call criminal justice will stand forth
-divested of natural<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> sanction, a relic of the ferocious inventions of
-the savage. Well may such justice be portrayed as blind. Who shall say
-whether it is crime or punishment which has wrought the greater
-suffering in the world? We may live to know that to the keen satirical
-vision of Sam Butler on the pleasant mountains of Erewhon there was
-revealed a dispensation, not kinder only, but wiser than the terrific
-code which Moses delivered from the flames of Sinai.</p>
-
-<p>If there are societies which refuse to apply the new knowledge, the
-fault will not lie with Genetics. I think it needs but little
-observation of the newer civilisations to foresee that <i>they</i> will apply
-every scrap of scientific knowledge which can help them, or seems to
-help them in the struggle, and I am good enough Selectionist to know
-that in that day the fate of the recalcitrant communities is sealed.</p>
-
-<p>The thrill of discovery is not dulled<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> by a suspicion that the discovery
-can be applied. No harm is done to the investigator if he can resist the
-temptation to deviate from his aim. With rarest exceptions the
-discoveries which have formed the basis of physical progress have been
-made without any thought but for the gratification of curiosity. Of this
-there can be few examples more conspicuous than that which Mendel's work
-presents. Untroubled by any itch to make potatoes larger or bread
-cheaper, he set himself in the quiet of a cloister garden to find out
-the laws of hybridity, and so struck a mine of truth, inexhaustible in
-brilliancy and profit.</p>
-
-<p>I will now suggest to you that it is by no means unlikely that even in
-an inquiry so remote as that which I just described in the case of the
-Sweet Pea, we may have the clue to a mystery which concerns us all in
-the closest possible way. I mean the problem of the physiological nature
-of Sex. In speaking<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> of the interpretation of sexual difference
-suggested by our experimental work as of some practical moment, I do not
-imply that as in the other instances I have given, the knowledge is
-likely to be of immediate use to our species; but only that if true it
-makes a contribution to the stock of human ideas which no one can regard
-as insignificant.</p>
-
-<p>In the light of Mendelian knowledge, when a family consists of more than
-one type the fact means that the germ-cells of one or other parent must
-certainly be of more than one kind. In the case of sex the members of
-the family are thus of two kinds, and the presumption is overwhelming
-that this distinction is due to a difference among the germ-cells. Next,
-since for all practical purposes the numbers of the two sexes produced
-are approximately equal, sex exhibits the special case in which a family
-consists of two types represented in equal numbers, half being<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> male,
-half female. But I called your attention to the fact that equality of
-types results when <i>one</i> parent was cross-bred in the character
-concerned, having received one dose only of the factor on which it
-depends. So we may feel fairly sure that the distinction between the
-sexes depends on the presence in one or other of them of an unpaired
-factor. This conclusion appears to me to follow so immediately on all
-that we have learnt of genetic physiology that with every confidence we
-may accept it as representing the actual fact.</p>
-
-<p>The question which of the two sexes contains the unpaired factor is less
-easy to answer, but there are several converging lines of evidence which
-point to the deduction that in Vertebrates at least, and in some other
-types, it is the female, and I feel little doubt that we shall succeed
-in proving that in them femaleness is a definite Mendelian factor<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span>
-absent from the male and following the ordinary Mendelian rules.</p>
-
-<p>Before showing you how the Sweet Pea phenomenon aids in this inquiry I
-must tell you of some other experimental results. The first concerns the
-common currant moth, <i>Abraxas grossulariata</i>. It has a definite pale
-variety called <i>lacticolor</i>. With these two forms Doncaster has made a
-remarkable series of experiments. When he began, <i>lacticolor</i> was only
-known as a female form. This was crossed with the <i>grossulariata</i> male
-and gave <i>grossulariata</i> only, showing that the male was pure to type.
-The hybrids bred together gave <i>grossulariata</i> males and females and
-<i>lacticolor</i> females only. But the hybrid males bred to <i>lacticolor</i>
-females produced all four combinations, <i>grossulariata</i> males and
-females, and <i>lacticolor</i> males and females. When the <i>lacticolor</i> males
-were bred to <i>grossulariata</i> females, whether hybrid, or wild<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> from a
-district where <i>lacticolor</i> does not exist, the result was that all the
-males were <i>grossulariata</i> and all the females <i>lacticolor</i>! It is
-difficult to follow the course of such an experiment on once hearing and
-all I ask you to remember is first that there is a series of matings
-giving very curious distributions of the characters of type and variety
-among the two sexes. And then, what is perhaps the most singular fact of
-all, that the wild typical <i>grossulariata</i> female can when crossed with
-the <i>lacticolor</i> male produce all females <i>lacticolor</i>. This last fact
-can, we know, mean only one thing, namely that these wild females are in
-reality hybrids of <i>lacticolor</i>; though since the males are pure
-<i>grossulariata</i>, that fact would in the natural course of things never
-be revealed.</p>
-
-<p>When we encounter such a series of phenomena as this, our business is to
-find a means of symbolical expression which will<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> represent all the
-factors involved, and show how each behaves in descent. Such a system or
-scheme we have at length discovered, and I incline to think that it must
-be the true one. If you study this case you will find that there are
-nine distinct kinds of matings that can be made between the variety, the
-type and the hybrid, and the scheme fits the whole group of results. It
-is based on two suppositions:</p>
-
-<p>1. That the female is cross-bred, or as we call it heterozygous for
-femaleness-factor, the male being without that factor. The eggs are thus
-each destined from the first to become either males or females, but as
-regards sex the spermatozoa are alike in being non-female.</p>
-
-<p>2. That there is a repulsion between the femaleness-factor and the
-<i>grossulariata</i> factor.</p>
-
-<p>Such a repulsion between two factors we are justified in regarding as
-possible because<span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span> we have had proof of the occurrence of a similar
-repulsion in the case of the two factors in the Sweet Pea.</p>
-
-<p>If the case of this moth stood alone it would be interesting, but its
-importance is greatly increased by the fact that we know two cases in
-birds which are closely comparable. The simpler case to which alone I
-shall refer has been observed in the Canary. Like the Currant moth it
-has a kind of albino, called Cinnamon, and males of this variety when
-mated with ordinary dark green hen canaries produce dark males and
-Cinnamons which are always hens; while the green male and the Cinnamon
-hen produce nothing but greens of both sexes. This case, which has been
-experimentally studied by Miss Durham, offers a certain complication,
-but in its main outlines it is exactly like that of the moth, and the
-same interpretation is applicable to both.</p>
-
-<p><span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span></p><p>The particular interpretation may be imperfect and even partially
-wrong; but that we are at last able to form a working idea of the course
-of such phenomena at all is a most encouraging fact. If we are right, as
-I am strongly inclined to believe, we get a glimpse of the significance
-of the popular idea that in certain respects daughters are apt to
-resemble their fathers and sons their mothers; a phenomenon which is
-certainly sometimes to be observed.</p>
-
-<p>There are several collateral indications that we are on the right track
-in our theory of the nature of sex. One of these, derived from the
-peculiar inheritance of colour-blindness, is especially interesting.
-That affection is common in men, rare in women. Men who are colour-blind
-can transmit the affection but men who have normal vision cannot. Women
-however who are ostensibly normal may have colour-blind sons; and<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> women
-who are colour-blind have, so far as we know, no sons who are not
-colour-blind<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a>.</p>
-
-<p>Mendelian analysis of these facts shows that colour-blindness is due,
-not, as might have been supposed, to the absence of something from the
-composition of the body, but to the presence of something which affects
-the sight. Just as nicotine-poisoning can paralyse the colour sense, so
-may we conceive the development of a secretion in the body which has a
-similar action. The comparative exemption of the woman must therefore
-mean that there is in her a positive factor which counteracts the
-colour-blindness factor, and it is not improbable that the counteracting
-element is no other than the femaleness-factor itself<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a>.</p>
-
-<p><span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span></p><p>I think I have said enough to prove that after all, those curiosities
-collected from observation of Sweet Peas and Canaries have no remote
-bearing on some very fascinating problems of human life.</p>
-
-<p>Lastly I suppose it is self-evident that they have a bearing on the
-problem of Evolution. The facts of heredity and variation are the
-materials out of which all theories of Evolution are constructed. At
-last by genetic methods we are beginning to obtain such facts of
-unimpeachable quality, and free from the flaws that were inevitable in
-older collections. From a survey of these materials we see something of
-the changes which will have to be made in the orthodox edifice to<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> admit
-of their incorporation, but he must be rash indeed who would now attempt
-a comprehensive reconstruction. The results of genetic research are so
-bewilderingly novel that we need time and an exhaustive study of their
-inter-relations before we can hope to see them in proper value and
-perspective. In all the discussions of the stability and fitness of
-species who ever contemplated the possibility of a wild species having
-one of its sexes permanently hybrid? When I spoke of adventures to be
-encountered in genetic research I was thinking of such astonishing
-discoveries as that.</p>
-
-<p>There are others no less disconcerting. Who would have supposed it
-possible that the pollen-cells of a plant could be all of one type, and
-its egg-cells of two types? Yet Miss Saunders' experiments have provided
-definite proof that this is the condition of certain Stocks, of which
-the pollen grains<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span> all bear doubleness, while the egg-cells are some
-singles and some doubles. We cannot think yet of interpreting these
-complex phenomena in terms of a common plan. All that we know is that
-there is now open for our scrutiny a world of varied, orderly and
-specific physiological wonders into which we have as yet only peeped. To
-lay down positive propositions as to the origin and inter-relation of
-species in general, now, would be a task as fruitless as that of a
-chemist must have been who had tried to state the relationship of the
-elements before their properties had been investigated.</p>
-
-<p>For the first time <i>Variation</i> and <i>Reversion</i> have a concrete, palpable
-meaning. Hitherto they have stood by in all evolutionary debates,
-convenient genii, ready to perform as little or as much as might be
-desired by the conjuror. That vaporous stage of their existence is over;
-and we see Variation shaping itself as<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> a definite, physiological event,
-the addition or omission of one or more definite elements; and Reversion
-as that particular addition or subtraction which brings the total of the
-elements back to something it had been before in the history of the
-race.</p>
-
-<p>The time for discussion of Evolution as a problem at large is closed. We
-face that problem now as one soluble by minute, critical analysis. Lord
-Acton in his inaugural lecture said that in the study of history we are
-at the beginning of the documentary age. No one will charge me with
-disrespect to the great name we commemorate this year, if I apply those
-words to the history of Evolution: Darwin, it was, who first showed us
-that the species have a history that can be read at all. If in the new
-reading of that history, there be found departures from the text laid
-down in his first recension, it is not to his fearless spirit that they
-will bring dismay.</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> The investigation of this remarkable family was made
-originally by Cunier. The facts have been reexamined and the pedigree
-much extended by Nettleship. The numerical results are somewhat
-irregular, but it is especially interesting as being the largest
-pedigree of human disease or defect yet made. It contains 2121 persons,
-extending over ten generations. Of these persons, 135 are known to have
-been night-blind. In no single case was the peculiarity transmitted
-through an unaffected member. It should be mentioned that for
-night-blindness such a system of descent is peculiar. More usually it
-follows the scheme described for colour-blindness. It is not known
-wherein the peculiarity of this family consists.</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> We have knowledge now of seven colour-blind women, having,
-in all, 17 sons who are all colour-blind. Most of these cases have been
-collected by Mr Nettleship.</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> An alternative and perhaps more satisfactory interpretation
-of the same facts has been proposed by Doncaster (<i>Jour. Genetics</i> I, Pt
-4, p. 377). Until more progress has been made with the analysis of
-sexual differentiation it is not possible to decide which of the two
-interpretations is correct. The numerical results predicted on both
-systems are the same; but by introducing a more complicated though quite
-reasonable formula for the representation of the sex-differences
-Doncaster's method shows that colour-blindness may be a <i>recessive</i> due
-to the absence of a factor which produces normal colour-vision.</p></div></div>
-
-<p><span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span></p>
-
-<p class="center space-above">Cambridge:<br />PRINTED BY JOHN CLAY, M.A.<br />AT THE UNIVERSITY PRESS.</p>
-
-
-
-
-
-
-
-
-<pre>
-
-
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