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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/2354-h.zip b/2354-h.zip Binary files differnew file mode 100644 index 0000000..5d977b7 --- /dev/null +++ b/2354-h.zip diff --git a/2354-h/2354-h.htm b/2354-h/2354-h.htm new file mode 100644 index 0000000..f9db666 --- /dev/null +++ b/2354-h/2354-h.htm @@ -0,0 +1,958 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<HTML> +<HEAD> + +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + +<TITLE> +The Project Gutenberg E-text of Note on the Development of the Brain, +by Thomas Henry Huxley +</TITLE> + +<STYLE TYPE="text/css"> +BODY { color: Black; + background: White; + margin-right: 10%; + margin-left: 10%; + font-family: "Times New Roman", serif; + text-align: justify } + +P {text-indent: 4% } + +P.noindent {text-indent: 0% } + +P.poem {text-indent: 0%; + margin-left: 10%; + font-size: small } + +P.letter {text-indent: 0%; + font-size: small ; + margin-left: 10% ; + margin-right: 10% } + +P.intro {text-indent: 0%; + font-size: small ; + margin-left: 10% ; + margin-right: 10% } + +P.finis { text-align: center ; + text-indent: 0% ; + margin-left: 0% ; + margin-right: 0% } + +</STYLE> + +</HEAD> + +<BODY> + + +<pre> + +The Project Gutenberg EBook of Note on the Resemblances and Differences in +the Structure and the Development of Brain in Man and the Apes, by Thomas Henry Huxley + +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 + + +Title: Note on the Resemblances and Differences in the Structure and the Development of Brain in Man and the Apes + +Author: Thomas Henry Huxley + +Posting Date: November 5, 2008 [EBook #2354] +Release Date: October, 2000 + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK RESEMBLANCES-DIFFERENCES OF BRAIN *** + + + + +Produced by Sue Asscher. HTML version by Al Haines. + + + + + +</pre> + + +<BR><BR> + +<H3 ALIGN="center"> +NOTE ON THE RESEMBLANCES AND DIFFERENCES IN THE STRUCTURE<BR> +AND THE DEVELOPMENT OF THE BRAIN IN MAN AND APES<BR> +</H3> + +<BR> + +<H3 ALIGN="center"> +BY +</H3> + +<H3 ALIGN="center"> +PROFESSOR T. H. HUXLEY, F.R.S. +</H3> + +<BR><BR> + +<P CLASS="intro"> +[This essay is taken from 'The Descent of Man and Selection in relation +to Sex' by Charles Darwin where it appears at the end of Chapter VII +which is also the end of Part I. Footnotes are numbered as they appear +in 'The Descent of Man.'] +</P> + +<BR><BR> + +<P> +The controversy respecting the nature and the extent of the differences +in the structure of the brain in man and the apes, which arose some +fifteen years ago, has not yet come to an end, though the subject +matter of the dispute is, at present, totally different from what it +was formerly. It was originally asserted and re-asserted, with +singular pertinacity, that the brain of all the apes, even the highest, +differs from that of man, in the absence of such conspicuous structures +as the posterior lobes of the cerebral hemispheres, with the posterior +cornu of the lateral ventricle and the hippocampus minor, contained in +those lobes, which are so obvious in man. +</P> + +<P> +But the truth that the three structures in question are as well +developed in apes' as in human brains, or even better; and that it is +characteristic of all the Primates (if we exclude the Lemurs) to have +these parts well developed, stands at present on as secure a basis as +any proposition in comparative anatomy. Moreover, it is admitted by +every one of the long series of anatomists who, of late years, have +paid special attention to the arrangement of the complicated sulci and +gyri which appear upon the surface of the cerebral hemispheres in man +and the higher apes, that they are disposed after the very same pattern +in him, as in them. Every principal gyrus and sulcus of a chimpanzee's +brain is clearly represented in that of a man, so that the terminology +which applies to the one answers for the other. On this point there is +no difference of opinion. Some years since, Professor Bischoff +published a memoir (70. 'Die Grosshirn-Windungen des Menschen;' +'Abhandlungen der K. Bayerischen Akademie,' B. x. 1868.) on the +cerebral convolutions of man and apes; and as the purpose of my learned +colleague was certainly not to diminish the value of the differences +between apes and men in this respect, I am glad to make a citation from +him. +</P> + +<P> +"That the apes, and especially the orang, chimpanzee and gorilla, come +very close to man in their organisation, much nearer than to any other +animal, is a well known fact, disputed by nobody. Looking at the matter +from the point of view of organisation alone, no one probably would +ever have disputed the view of Linnaeus, that man should be placed, +merely as a peculiar species, at the head of the mammalia and of those +apes. Both shew, in all their organs, so close an affinity, that the +most exact anatomical investigation is needed in order to demonstrate +those differences which really exist. So it is with the brains. The +brains of man, the orang, the chimpanzee, the gorilla, in spite of all +the important differences which they present, come very close to one +another" (loc. cit. p. 101). +</P> + +<P> +There remains, then, no dispute as to the resemblance in fundamental +characters, between the ape's brain and man's: nor any as to the +wonderfully close similarity between the chimpanzee, orang and man, in +even the details of the arrangement of the gyri and sulci of the +cerebral hemispheres. Nor, turning to the differences between the +brains of the highest apes and that of man, is there any serious +question as to the nature and extent of these differences. It is +admitted that the man's cerebral hemispheres are absolutely and +relatively larger than those of the orang and chimpanzee; that his +frontal lobes are less excavated by the upward protrusion of the roof +of the orbits; that his gyri and sulci are, as a rule, less +symmetrically disposed, and present a greater number of secondary +plications. And it is admitted that, as a rule, in man, the +temporo-occipital or "external perpendicular" fissure, which is usually +so strongly marked a feature of the ape's brain is but faintly marked. +But it is also clear, that none of these differences constitutes a +sharp demarcation between the man's and the ape's brain. In respect to +the external perpendicular fissure of Gratiolet, in the human brain for +instance, Professor Turner remarks: (71. 'Convolutions of the Human +Cerebrum Topographically Considered,' 1866, p. 12.) +</P> + +<P> +"In some brains it appears simply as an indentation of the margin of +the hemisphere, but, in others, it extends for some distance more or +less transversely outwards. I saw it in the right hemisphere of a +female brain pass more than two inches outwards; and on another +specimen, also the right hemisphere, it proceeded for four-tenths of an +inch outwards, and then extended downwards, as far as the lower margin +of the outer surface of the hemisphere. The imperfect definition of +this fissure in the majority of human brains, as compared with its +remarkable distinctness in the brain of most Quadrumana, is owing to +the presence, in the former, of certain superficial, well marked, +secondary convolutions which bridge it over and connect the parietal +with the occipital lobe. The closer the first of these bridging gyri +lies to the longitudinal fissure, the shorter is the external +parieto-occipital fissure" (loc. cit. p. 12). +</P> + +<P> +The obliteration of the external perpendicular fissure of Gratiolet, +therefore, is not a constant character of the human brain. On the +other hand, its full development is not a constant character of the +higher ape's brain. For, in the chimpanzee, the more or less extensive +obliteration of the external perpendicular sulcus by "bridging +convolutions," on one side or the other, has been noted over and over +again by Prof. Rolleston, Mr. Marshall, M. Broca and Professor Turner. +At the conclusion of a special paper on this subject the latter writes: +(72. Notes more especially on the bridging convolutions in the Brain +of the Chimpanzee, 'Proceedings of the Royal Society of Edinburgh,' +1865-6.) +</P> + +<P> +"The three specimens of the brain of a chimpanzee, just described, +prove, that the generalisation which Gratiolet has attempted to draw of +the complete absence of the first connecting convolution and the +concealment of the second, as essentially characteristic features in +the brain of this animal, is by no means universally applicable. In +only one specimen did the brain, in these particulars, follow the law +which Gratiolet has expressed. As regards the presence of the superior +bridging convolution, I am inclined to think that it has existed in one +hemisphere, at least, in a majority of the brains of this animal which +have, up to this time, been figured or described. The superficial +position of the second bridging convolution is evidently less frequent, +and has as yet, I believe, only been seen in the brain (A) recorded in +this communication. The asymmetrical arrangement in the convolutions +of the two hemispheres, which previous observers have referred to in +their descriptions, is also well illustrated in these specimens" (pp. +8, 9). +</P> + +<P> +Even were the presence of the temporo-occipital, or external +perpendicular, sulcus, a mark of distinction between the higher apes +and man, the value of such a distinctive character would be rendered +very doubtful by the structure of the brain in the Platyrrhine apes. +In fact, while the temporo-occipital is one of the most constant of +sulci in the Catarrhine, or Old World, apes, it is never very strongly +developed in the New World apes; it is absent in the smaller +Platyrrhini; rudimentary in Pithecia (73. Flower, 'On the Anatomy of +Pithecia Monachus,' 'Proceedings of the Zoological Society,' 1862.); +and more or less obliterated by bridging convolutions in Ateles. +</P> + +<P> +A character which is thus variable within the limits of a single group +can have no great taxonomic value. +</P> + +<P> +It is further established, that the degree of asymmetry of the +convolution of the two sides in the human brain is subject to much +individual variation; and that, in those individuals of the Bushman +race who have been examined, the gyri and sulci of the two hemispheres +are considerably less complicated and more symmetrical than in the +European brain, while, in some individuals of the chimpanzee, their +complexity and asymmetry become notable. This is particularly the case +in the brain of a young male chimpanzee figured by M. Broca. ('L'ordre +des Primates,' p. 165, fig. 11.) +</P> + +<P> +Again, as respects the question of absolute size, it is established +that the difference between the largest and the smallest healthy human +brain is greater than the difference between the smallest healthy human +brain and the largest chimpanzee's or orang's brain. +</P> + +<P> +Moreover, there is one circumstance in which the orang's and +chimpanzee's brains resemble man's, but in which they differ from the +lower apes, and that is the presence of two corpora candicantia—the +Cynomorpha having but one. +</P> + +<P> +In view of these facts I do not hesitate in this year 1874, to repeat +and insist upon the proposition which I enunciated in 1863: (74. +'Man's Place in Nature,' p. 102.) +</P> + +<P> +"So far as cerebral structure goes, therefore, it is clear that man +differs less from the chimpanzee or the orang, than these do even from +the monkeys, and that the difference between the brain of the +chimpanzee and of man is almost insignificant when compared with that +between the chimpanzee brain and that of a Lemur." +</P> + +<P> +In the paper to which I have referred, Professor Bischoff does not deny +the second part of this statement, but he first makes the irrelevant +remark that it is not wonderful if the brains of an orang and a Lemur +are very different; and secondly, goes on to assert that, "If we +successively compare the brain of a man with that of an orang; the +brain of this with that of a chimpanzee; of this with that of a +gorilla, and so on of a Hylobates, Semnopithecus, Cynocephalus, +Cercopithecus, Macacus, Cebus, Callithrix, Lemur, Stenops, Hapale, we +shall not meet with a greater, or even as great a, break in the degree +of development of the convolutions, as we find between the brain of a +man and that of an orang or chimpanzee." +</P> + +<P> +To which I reply, firstly, that whether this assertion be true or +false, it has nothing whatever to do with the proposition enunciated in +'Man's Place in Nature,' which refers not to the development of the +convolutions alone, but to the structure of the whole brain. If +Professor Bischoff had taken the trouble to refer to p. 96 of the work +he criticises, in fact, he would have found the following passage: +"And it is a remarkable circumstance that though, so far as our present +knowledge extends, there IS one true structural break in the series of +forms of Simian brains, this hiatus does not lie between man and the +manlike apes, but between the lower and the lowest Simians, or in other +words, between the Old and New World apes and monkeys and the Lemurs. +Every Lemur which has yet been examined, in fact, has its cerebellum +partially visible from above; and its posterior lobe, with the +contained posterior cornu and hippocampus minor, more or less +rudimentary. Every marmoset, American monkey, Old World monkey, baboon +or manlike ape, on the contrary, has its cerebellum entirely hidden, +posteriorly, by the cerebral lobes, and possesses a large posterior +cornu with a well-developed hippocampus minor." +</P> + +<P> +This statement was a strictly accurate account of what was known when +it was made; and it does not appear to me to be more than apparently +weakened by the subsequent discovery of the relatively small +development of the posterior lobes in the Siamang and in the Howling +monkey. Notwithstanding the exceptional brevity of the posterior lobes +in these two species, no one will pretend that their brains, in the +slightest degree, approach those of the Lemurs. And if, instead of +putting Hapale out of its natural place, as Professor Bischoff most +unaccountably does, we write the series of animals he has chosen to +mention as follows: Homo, Pithecus, Troglodytes, Hylobates, +Semnopithecus, Cynocephalus, Cercopithecus, Macacus, Cebus, Callithrix, +Hapale, Lemur, Stenops, I venture to reaffirm that the great break in +this series lies between Hapale and Lemur, and that this break is +considerably greater than that between any other two terms of that +series. Professor Bischoff ignores the fact that long before he wrote, +Gratiolet had suggested the separation of the Lemurs from the other +Primates on the very ground of the difference in their cerebral +characters; and that Professor Flower had made the following +observations in the course of his description of the brain of the Javan +Loris: (75. 'Transactions of the Zoological Society,' vol. v. 1862.) +</P> + +<P> +"And it is especially remarkable that, in the development of the +posterior lobes, there is no approximation to the Lemurine, short +hemisphered brain, in those monkeys which are commonly supposed to +approach this family in other respects, viz. the lower members of the +Platyrrhine group." +</P> + +<P> +So far as the structure of the adult brain is concerned, then, the very +considerable additions to our knowledge, which have been made by the +researches of so many investigators, during the past ten years, fully +justify the statement which I made in 1863. But it has been said, +that, admitting the similarity between the adult brains of man and +apes, they are nevertheless, in reality, widely different, because they +exhibit fundamental differences in the mode of their development. No +one would be more ready than I to admit the force of this argument, if +such fundamental differences of development really exist. But I deny +that they do exist. On the contrary, there is a fundamental agreement +in the development of the brain in men and apes. +</P> + +<P> +Gratiolet originated the statement that there is a fundamental +difference in the development of the brains of apes and that of +man—consisting in this; that, in the apes, the sulci which first make +their appearance are situated on the posterior region of the cerebral +hemispheres, while, in the human foetus, the sulci first become visible +on the frontal lobes. (76. "Chez tous les singes, les plis posterieurs +se developpent les premiers; les plis anterieurs se developpent plus +tard, aussi la vertebre occipitale et la parietale sont-elles +relativement tres-grandes chez le foetus. L'Homme presente une +exception remarquable quant a l'epoque de l'apparition des plis +frontaux, qui sont les premiers indiques; mais le developpement general +du lobe frontal, envisage seulement par rapport a son volume, suit les +memes lois que dans les singes:" Gratiolet, 'Memoire sur les plis +cerebres de l'Homme et des Primateaux,' p. 39, Tab. iv, fig. 3.) +</P> + +<P> +This general statement is based upon two observations, the one of a +Gibbon almost ready to be born, in which the posterior gyri were "well +developed," while those of the frontal lobes were "hardly indicated" +(77. Gratiolet's words are (loc. cit. p. 39): "Dans le foetus dont il +s'agit les plis cerebraux posterieurs sont bien developpes, tandis que +les plis du lobe frontal sont a peine indiques." The figure, however +(Pl. iv, fig. 3), shews the fissure of Rolando, and one of the frontal +sulci plainly enough. Nevertheless, M. Alix, in his 'Notice sur les +travaux anthropologiques de Gratiolet' ('Mem. de la Societe +d'Anthropologie de Paris,' 1868, page 32), writes thus: "Gratiolet a eu +entre les mains le cerveau d'un foetus de Gibbon, singe eminemment +superieur, et tellement rapproche de l'orang, que des naturalistes +tres-competents l'ont range parmi les anthropoides. M. Huxley, par +exemple, n'hesite pas sur ce point. Eh bien, c'est sur le cerveau d'un +foetus de Gibbon que Gratiolet a vu LES CIRCONVOLUTIONS DU LOBE +TEMPORO-SPHENOIDAL DEJA DEVELOPPEES LORSQU'IL N'EXISTENT PAS ENCORE DE +PLIS SUR LE LOBE FRONTAL. Il etait donc bien autorise a dire que, chez +l'homme les circonvolutions apparaissent d'a en w, tandis que chez les +singes elles se developpent d'w en a."), and the other of a human +foetus at the 22nd or 23rd week of uterogestation, in which Gratiolet +notes that the insula was uncovered, but that nevertheless "des +incisures sement de lobe anterieur, une scissure peu profonde indique +la separation du lobe occipital, tres-reduit, d'ailleurs des cette +epoque. Le reste de la surface cerebrale est encore absolument lisse." +</P> + +<P> +Three views of this brain are given in Plate II, figs. 1, 2, 3, of the +work cited, shewing the upper, lateral and inferior views of the +hemispheres, but not the inner view. It is worthy of note that the +figure by no means bears out Gratiolet's description, inasmuch as the +fissure (antero-temporal) on the posterior half of the face of the +hemisphere is more marked than any of those vaguely indicated in the +anterior half. If the figure is correct, it in no way justifies +Gratiolet's conclusion: "Il y a donc entre ces cerveaux [those of a +Callithrix and of a Gibbon] et celui du foetus humain une difference +fondamental. Chez celui-ci, longtemps avant que les plis temporaux +apparaissent, les plis frontaux, ESSAYENT d'exister." +</P> + +<P> +Since Gratiolet's time, however, the development of the gyri and sulci +of the brain has been made the subject of renewed investigation by +Schmidt, Bischoff, Pansch (78. 'Ueber die typische Anordnung der +Furchen und Windungen auf den Grosshirn-Hemispharen des Menschen und +der Affen,' 'Archiv fur Anthropologie,' iii. 1868.), and more +particularly by Ecker (79. 'Zur Entwicklungs Geschichte der Furchen und +Windungen der Grosshirn-Hemispharen im Foetus des Menschen.' 'Archiv +fur Anthropologie,' iii. 1868.), whose work is not only the latest, but +by far the most complete, memoir on the subject. +</P> + +<P> +The final results of their inquiries may be summed up as follows:— +</P> + +<P> +1. In the human foetus, the sylvian fissure is formed in the course of +the third month of uterogestation. In this, and in the fourth month, +the cerebral hemispheres are smooth and rounded (with the exception of +the sylvian depression), and they project backwards far beyond the +cerebellum. +</P> + +<P> +2. The sulci, properly so called, begin to appear in the interval +between the end of the fourth and the beginning of the sixth month of +foetal life, but Ecker is careful to point out that, not only the time, +but the order, of their appearance is subject to considerable +individual variation. In no case, however, are either the frontal or +the temporal sulci the earliest. +</P> + +<P> +The first which appears, in fact, lies on the inner face of the +hemisphere (whence doubtless Gratiolet, who does not seem to have +examined that face in his foetus, overlooked it), and is either the +internal perpendicular (occipito-parietal), or the calcarine sulcus, +these two being close together and eventually running into one another. +As a rule the occipito-parietal is the earlier of the two. +</P> + +<P> +3. At the latter part of this period, another sulcus, the +"posterio-parietal," or "Fissure of Rolando" is developed, and it is +followed, in the course of the sixth month, by the other principal +sulci of the frontal, parietal, temporal and occipital lobes. There +is, however, no clear evidence that one of these constantly appears +before the other; and it is remarkable that, in the brain at the period +described and figured by Ecker (loc. cit. pp. 212-213, Taf. II, figs. +1, 2, 3, 4), the antero-temporal sulcus (scissure parallele) so +characteristic of the ape's brain, is as well, if not better developed +than the fissure of Rolando, and is much more marked than the proper +frontal sulci. +</P> + +<P> +Taking the facts as they now stand, it appears to me that the order of +the appearance of the sulci and gyri in the foetal human brain is in +perfect harmony with the general doctrine of evolution, and with the +view that man has been evolved from some ape-like form; though there +can be no doubt that form was, in many respects, different from any +member of the Primates now living. +</P> + +<P> +Von Baer taught us, half a century ago, that, in the course of their +development, allied animals put on at first, the characters of the +greater groups to which they belong, and, by degrees, assume those +which restrict them within the limits of their family, genus, and +species; and he proved, at the same time, that no developmental stage +of a higher animal is precisely similar to the adult condition of any +lower animal. It is quite correct to say that a frog passes through +the condition of a fish, inasmuch as at one period of its life the +tadpole has all the characters of a fish, and if it went no further, +would have to be grouped among fishes. But it is equally true that a +tadpole is very different from any known fish. +</P> + +<P> +In like manner, the brain of a human foetus, at the fifth month, may +correctly be said to be, not only the brain of an ape, but that of an +Arctopithecine or marmoset-like ape; for its hemispheres, with their +great posterior lobster, and with no sulci but the sylvian and the +calcarine, present the characteristics found only in the group of the +Arctopithecine Primates. But it is equally true, as Gratiolet remarks, +that, in its widely open sylvian fissure, it differs from the brain of +any actual marmoset. No doubt it would be much more similar to the +brain of an advanced foetus of a marmoset. But we know nothing +whatever of the development of the brain in the marmosets. In the +Platyrrhini proper, the only observation with which I am acquainted is +due to Pansch, who found in the brain of a foetal Cebus Apella, in +addition to the sylvian fissure and the deep calcarine fissure, only a +very shallow antero-temporal fissure (scissure parallele of Gratiolet). +</P> + +<P> +Now this fact, taken together with the circumstance that the +antero-temporal sulcus is present in such Platyrrhini as the Saimiri, +which present mere traces of sulci on the anterior half of the exterior +of the cerebral hemispheres, or none at all, undoubtedly, so far as it +goes, affords fair evidence in favour of Gratiolet's hypothesis, that +the posterior sulci appear before the anterior, in the brains of the +Platyrrhini. But, it by no means follows, that the rule which may hold +good for the Platyrrhini extends to the Catarrhini. We have no +information whatever respecting the development of the brain in the +Cynomorpha; and, as regards the Anthropomorpha, nothing but the account +of the brain of the Gibbon, near birth, already referred to. At the +present moment there is not a shadow of evidence to shew that the sulci +of a chimpanzee's, or orang's, brain do not appear in the same order as +a man's. +</P> + +<P> +Gratiolet opens his preface with the aphorism: "Il est dangereux dans +les sciences de conclure trop vite." I fear he must have forgotten +this sound maxim by the time he had reached the discussion of the +differences between men and apes, in the body of his work. No doubt, +the excellent author of one of the most remarkable contributions to the +just understanding of the mammalian brain which has ever been made, +would have been the first to admit the insufficiency of his data had he +lived to profit by the advance of inquiry. The misfortune is that his +conclusions have been employed by persons incompetent to appreciate +their foundation, as arguments in favour of obscurantism. (80. For +example, M. l'Abbe Lecomte in his terrible pamphlet, 'Le Darwinisme et +l'origine de l'Homme,' 1873.) +</P> + +<P> +But it is important to remark that, whether Gratiolet was right or +wrong in his hypothesis respecting the relative order of appearance of +the temporal and frontal sulci, the fact remains; that before either +temporal or frontal sulci, appear, the foetal brain of man presents +characters which are found only in the lowest group of the Primates +(leaving out the Lemurs); and that this is exactly what we should +expect to be the case, if man has resulted from the gradual +modification of the same form as that from which the other Primates +have sprung. +</P> + +<BR><BR><BR><BR> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Note on the Resemblances and +Differences in the Structure and the Development of Brain in Man and the Apes, by Thomas Henry Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK RESEMBLANCES-DIFFERENCES OF BRAIN *** + +***** This file should be named 2354-h.htm or 2354-h.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/2/3/5/2354/ + +Produced by Sue Asscher. 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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 + + +Title: Note on the Resemblances and Differences in the Structure and the Development of Brain in Man and the Apes + +Author: Thomas Henry Huxley + +Posting Date: November 5, 2008 [EBook #2354] +Release Date: October, 2000 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK RESEMBLANCES-DIFFERENCES OF BRAIN *** + + + + +Produced by Sue Asscher. HTML version by Al Haines. + + + + + + + + + + + NOTE ON THE RESEMBLANCES AND DIFFERENCES IN THE STRUCTURE + AND THE DEVELOPMENT OF THE BRAIN IN MAN AND APES + + +BY + +PROFESSOR T. H. HUXLEY, F.R.S. + + +[This essay is taken from 'The Descent of Man and Selection in relation +to Sex' by Charles Darwin where it appears at the end of Chapter VII +which is also the end of Part I. Footnotes are numbered as they appear +in 'The Descent of Man.'] + + + +The controversy respecting the nature and the extent of the differences +in the structure of the brain in man and the apes, which arose some +fifteen years ago, has not yet come to an end, though the subject +matter of the dispute is, at present, totally different from what it +was formerly. It was originally asserted and re-asserted, with +singular pertinacity, that the brain of all the apes, even the highest, +differs from that of man, in the absence of such conspicuous structures +as the posterior lobes of the cerebral hemispheres, with the posterior +cornu of the lateral ventricle and the hippocampus minor, contained in +those lobes, which are so obvious in man. + +But the truth that the three structures in question are as well +developed in apes' as in human brains, or even better; and that it is +characteristic of all the Primates (if we exclude the Lemurs) to have +these parts well developed, stands at present on as secure a basis as +any proposition in comparative anatomy. Moreover, it is admitted by +every one of the long series of anatomists who, of late years, have +paid special attention to the arrangement of the complicated sulci and +gyri which appear upon the surface of the cerebral hemispheres in man +and the higher apes, that they are disposed after the very same pattern +in him, as in them. Every principal gyrus and sulcus of a chimpanzee's +brain is clearly represented in that of a man, so that the terminology +which applies to the one answers for the other. On this point there is +no difference of opinion. Some years since, Professor Bischoff +published a memoir (70. 'Die Grosshirn-Windungen des Menschen;' +'Abhandlungen der K. Bayerischen Akademie,' B. x. 1868.) on the +cerebral convolutions of man and apes; and as the purpose of my learned +colleague was certainly not to diminish the value of the differences +between apes and men in this respect, I am glad to make a citation from +him. + +"That the apes, and especially the orang, chimpanzee and gorilla, come +very close to man in their organisation, much nearer than to any other +animal, is a well known fact, disputed by nobody. Looking at the matter +from the point of view of organisation alone, no one probably would +ever have disputed the view of Linnaeus, that man should be placed, +merely as a peculiar species, at the head of the mammalia and of those +apes. Both shew, in all their organs, so close an affinity, that the +most exact anatomical investigation is needed in order to demonstrate +those differences which really exist. So it is with the brains. The +brains of man, the orang, the chimpanzee, the gorilla, in spite of all +the important differences which they present, come very close to one +another" (loc. cit. p. 101). + +There remains, then, no dispute as to the resemblance in fundamental +characters, between the ape's brain and man's: nor any as to the +wonderfully close similarity between the chimpanzee, orang and man, in +even the details of the arrangement of the gyri and sulci of the +cerebral hemispheres. Nor, turning to the differences between the +brains of the highest apes and that of man, is there any serious +question as to the nature and extent of these differences. It is +admitted that the man's cerebral hemispheres are absolutely and +relatively larger than those of the orang and chimpanzee; that his +frontal lobes are less excavated by the upward protrusion of the roof +of the orbits; that his gyri and sulci are, as a rule, less +symmetrically disposed, and present a greater number of secondary +plications. And it is admitted that, as a rule, in man, the +temporo-occipital or "external perpendicular" fissure, which is usually +so strongly marked a feature of the ape's brain is but faintly marked. +But it is also clear, that none of these differences constitutes a +sharp demarcation between the man's and the ape's brain. In respect to +the external perpendicular fissure of Gratiolet, in the human brain for +instance, Professor Turner remarks: (71. 'Convolutions of the Human +Cerebrum Topographically Considered,' 1866, p. 12.) + +"In some brains it appears simply as an indentation of the margin of +the hemisphere, but, in others, it extends for some distance more or +less transversely outwards. I saw it in the right hemisphere of a +female brain pass more than two inches outwards; and on another +specimen, also the right hemisphere, it proceeded for four-tenths of an +inch outwards, and then extended downwards, as far as the lower margin +of the outer surface of the hemisphere. The imperfect definition of +this fissure in the majority of human brains, as compared with its +remarkable distinctness in the brain of most Quadrumana, is owing to +the presence, in the former, of certain superficial, well marked, +secondary convolutions which bridge it over and connect the parietal +with the occipital lobe. The closer the first of these bridging gyri +lies to the longitudinal fissure, the shorter is the external +parieto-occipital fissure" (loc. cit. p. 12). + +The obliteration of the external perpendicular fissure of Gratiolet, +therefore, is not a constant character of the human brain. On the +other hand, its full development is not a constant character of the +higher ape's brain. For, in the chimpanzee, the more or less extensive +obliteration of the external perpendicular sulcus by "bridging +convolutions," on one side or the other, has been noted over and over +again by Prof. Rolleston, Mr. Marshall, M. Broca and Professor Turner. +At the conclusion of a special paper on this subject the latter writes: +(72. Notes more especially on the bridging convolutions in the Brain +of the Chimpanzee, 'Proceedings of the Royal Society of Edinburgh,' +1865-6.) + +"The three specimens of the brain of a chimpanzee, just described, +prove, that the generalisation which Gratiolet has attempted to draw of +the complete absence of the first connecting convolution and the +concealment of the second, as essentially characteristic features in +the brain of this animal, is by no means universally applicable. In +only one specimen did the brain, in these particulars, follow the law +which Gratiolet has expressed. As regards the presence of the superior +bridging convolution, I am inclined to think that it has existed in one +hemisphere, at least, in a majority of the brains of this animal which +have, up to this time, been figured or described. The superficial +position of the second bridging convolution is evidently less frequent, +and has as yet, I believe, only been seen in the brain (A) recorded in +this communication. The asymmetrical arrangement in the convolutions +of the two hemispheres, which previous observers have referred to in +their descriptions, is also well illustrated in these specimens" (pp. +8, 9). + +Even were the presence of the temporo-occipital, or external +perpendicular, sulcus, a mark of distinction between the higher apes +and man, the value of such a distinctive character would be rendered +very doubtful by the structure of the brain in the Platyrrhine apes. +In fact, while the temporo-occipital is one of the most constant of +sulci in the Catarrhine, or Old World, apes, it is never very strongly +developed in the New World apes; it is absent in the smaller +Platyrrhini; rudimentary in Pithecia (73. Flower, 'On the Anatomy of +Pithecia Monachus,' 'Proceedings of the Zoological Society,' 1862.); +and more or less obliterated by bridging convolutions in Ateles. + +A character which is thus variable within the limits of a single group +can have no great taxonomic value. + +It is further established, that the degree of asymmetry of the +convolution of the two sides in the human brain is subject to much +individual variation; and that, in those individuals of the Bushman +race who have been examined, the gyri and sulci of the two hemispheres +are considerably less complicated and more symmetrical than in the +European brain, while, in some individuals of the chimpanzee, their +complexity and asymmetry become notable. This is particularly the case +in the brain of a young male chimpanzee figured by M. Broca. ('L'ordre +des Primates,' p. 165, fig. 11.) + +Again, as respects the question of absolute size, it is established +that the difference between the largest and the smallest healthy human +brain is greater than the difference between the smallest healthy human +brain and the largest chimpanzee's or orang's brain. + +Moreover, there is one circumstance in which the orang's and +chimpanzee's brains resemble man's, but in which they differ from the +lower apes, and that is the presence of two corpora candicantia--the +Cynomorpha having but one. + +In view of these facts I do not hesitate in this year 1874, to repeat +and insist upon the proposition which I enunciated in 1863: (74. +'Man's Place in Nature,' p. 102.) + +"So far as cerebral structure goes, therefore, it is clear that man +differs less from the chimpanzee or the orang, than these do even from +the monkeys, and that the difference between the brain of the +chimpanzee and of man is almost insignificant when compared with that +between the chimpanzee brain and that of a Lemur." + +In the paper to which I have referred, Professor Bischoff does not deny +the second part of this statement, but he first makes the irrelevant +remark that it is not wonderful if the brains of an orang and a Lemur +are very different; and secondly, goes on to assert that, "If we +successively compare the brain of a man with that of an orang; the +brain of this with that of a chimpanzee; of this with that of a +gorilla, and so on of a Hylobates, Semnopithecus, Cynocephalus, +Cercopithecus, Macacus, Cebus, Callithrix, Lemur, Stenops, Hapale, we +shall not meet with a greater, or even as great a, break in the degree +of development of the convolutions, as we find between the brain of a +man and that of an orang or chimpanzee." + +To which I reply, firstly, that whether this assertion be true or +false, it has nothing whatever to do with the proposition enunciated in +'Man's Place in Nature,' which refers not to the development of the +convolutions alone, but to the structure of the whole brain. If +Professor Bischoff had taken the trouble to refer to p. 96 of the work +he criticises, in fact, he would have found the following passage: +"And it is a remarkable circumstance that though, so far as our present +knowledge extends, there IS one true structural break in the series of +forms of Simian brains, this hiatus does not lie between man and the +manlike apes, but between the lower and the lowest Simians, or in other +words, between the Old and New World apes and monkeys and the Lemurs. +Every Lemur which has yet been examined, in fact, has its cerebellum +partially visible from above; and its posterior lobe, with the +contained posterior cornu and hippocampus minor, more or less +rudimentary. Every marmoset, American monkey, Old World monkey, baboon +or manlike ape, on the contrary, has its cerebellum entirely hidden, +posteriorly, by the cerebral lobes, and possesses a large posterior +cornu with a well-developed hippocampus minor." + +This statement was a strictly accurate account of what was known when +it was made; and it does not appear to me to be more than apparently +weakened by the subsequent discovery of the relatively small +development of the posterior lobes in the Siamang and in the Howling +monkey. Notwithstanding the exceptional brevity of the posterior lobes +in these two species, no one will pretend that their brains, in the +slightest degree, approach those of the Lemurs. And if, instead of +putting Hapale out of its natural place, as Professor Bischoff most +unaccountably does, we write the series of animals he has chosen to +mention as follows: Homo, Pithecus, Troglodytes, Hylobates, +Semnopithecus, Cynocephalus, Cercopithecus, Macacus, Cebus, Callithrix, +Hapale, Lemur, Stenops, I venture to reaffirm that the great break in +this series lies between Hapale and Lemur, and that this break is +considerably greater than that between any other two terms of that +series. Professor Bischoff ignores the fact that long before he wrote, +Gratiolet had suggested the separation of the Lemurs from the other +Primates on the very ground of the difference in their cerebral +characters; and that Professor Flower had made the following +observations in the course of his description of the brain of the Javan +Loris: (75. 'Transactions of the Zoological Society,' vol. v. 1862.) + +"And it is especially remarkable that, in the development of the +posterior lobes, there is no approximation to the Lemurine, short +hemisphered brain, in those monkeys which are commonly supposed to +approach this family in other respects, viz. the lower members of the +Platyrrhine group." + +So far as the structure of the adult brain is concerned, then, the very +considerable additions to our knowledge, which have been made by the +researches of so many investigators, during the past ten years, fully +justify the statement which I made in 1863. But it has been said, +that, admitting the similarity between the adult brains of man and +apes, they are nevertheless, in reality, widely different, because they +exhibit fundamental differences in the mode of their development. No +one would be more ready than I to admit the force of this argument, if +such fundamental differences of development really exist. But I deny +that they do exist. On the contrary, there is a fundamental agreement +in the development of the brain in men and apes. + +Gratiolet originated the statement that there is a fundamental +difference in the development of the brains of apes and that of +man--consisting in this; that, in the apes, the sulci which first make +their appearance are situated on the posterior region of the cerebral +hemispheres, while, in the human foetus, the sulci first become visible +on the frontal lobes. (76. "Chez tous les singes, les plis posterieurs +se developpent les premiers; les plis anterieurs se developpent plus +tard, aussi la vertebre occipitale et la parietale sont-elles +relativement tres-grandes chez le foetus. L'Homme presente une +exception remarquable quant a l'epoque de l'apparition des plis +frontaux, qui sont les premiers indiques; mais le developpement general +du lobe frontal, envisage seulement par rapport a son volume, suit les +memes lois que dans les singes:" Gratiolet, 'Memoire sur les plis +cerebres de l'Homme et des Primateaux,' p. 39, Tab. iv, fig. 3.) + +This general statement is based upon two observations, the one of a +Gibbon almost ready to be born, in which the posterior gyri were "well +developed," while those of the frontal lobes were "hardly indicated" +(77. Gratiolet's words are (loc. cit. p. 39): "Dans le foetus dont il +s'agit les plis cerebraux posterieurs sont bien developpes, tandis que +les plis du lobe frontal sont a peine indiques." The figure, however +(Pl. iv, fig. 3), shews the fissure of Rolando, and one of the frontal +sulci plainly enough. Nevertheless, M. Alix, in his 'Notice sur les +travaux anthropologiques de Gratiolet' ('Mem. de la Societe +d'Anthropologie de Paris,' 1868, page 32), writes thus: "Gratiolet a eu +entre les mains le cerveau d'un foetus de Gibbon, singe eminemment +superieur, et tellement rapproche de l'orang, que des naturalistes +tres-competents l'ont range parmi les anthropoides. M. Huxley, par +exemple, n'hesite pas sur ce point. Eh bien, c'est sur le cerveau d'un +foetus de Gibbon que Gratiolet a vu LES CIRCONVOLUTIONS DU LOBE +TEMPORO-SPHENOIDAL DEJA DEVELOPPEES LORSQU'IL N'EXISTENT PAS ENCORE DE +PLIS SUR LE LOBE FRONTAL. Il etait donc bien autorise a dire que, chez +l'homme les circonvolutions apparaissent d'a en w, tandis que chez les +singes elles se developpent d'w en a."), and the other of a human +foetus at the 22nd or 23rd week of uterogestation, in which Gratiolet +notes that the insula was uncovered, but that nevertheless "des +incisures sement de lobe anterieur, une scissure peu profonde indique +la separation du lobe occipital, tres-reduit, d'ailleurs des cette +epoque. Le reste de la surface cerebrale est encore absolument lisse." + +Three views of this brain are given in Plate II, figs. 1, 2, 3, of the +work cited, shewing the upper, lateral and inferior views of the +hemispheres, but not the inner view. It is worthy of note that the +figure by no means bears out Gratiolet's description, inasmuch as the +fissure (antero-temporal) on the posterior half of the face of the +hemisphere is more marked than any of those vaguely indicated in the +anterior half. If the figure is correct, it in no way justifies +Gratiolet's conclusion: "Il y a donc entre ces cerveaux [those of a +Callithrix and of a Gibbon] et celui du foetus humain une difference +fondamental. Chez celui-ci, longtemps avant que les plis temporaux +apparaissent, les plis frontaux, ESSAYENT d'exister." + +Since Gratiolet's time, however, the development of the gyri and sulci +of the brain has been made the subject of renewed investigation by +Schmidt, Bischoff, Pansch (78. 'Ueber die typische Anordnung der +Furchen und Windungen auf den Grosshirn-Hemispharen des Menschen und +der Affen,' 'Archiv fur Anthropologie,' iii. 1868.), and more +particularly by Ecker (79. 'Zur Entwicklungs Geschichte der Furchen und +Windungen der Grosshirn-Hemispharen im Foetus des Menschen.' 'Archiv +fur Anthropologie,' iii. 1868.), whose work is not only the latest, but +by far the most complete, memoir on the subject. + +The final results of their inquiries may be summed up as follows:-- + +1. In the human foetus, the sylvian fissure is formed in the course of +the third month of uterogestation. In this, and in the fourth month, +the cerebral hemispheres are smooth and rounded (with the exception of +the sylvian depression), and they project backwards far beyond the +cerebellum. + +2. The sulci, properly so called, begin to appear in the interval +between the end of the fourth and the beginning of the sixth month of +foetal life, but Ecker is careful to point out that, not only the time, +but the order, of their appearance is subject to considerable +individual variation. In no case, however, are either the frontal or +the temporal sulci the earliest. + +The first which appears, in fact, lies on the inner face of the +hemisphere (whence doubtless Gratiolet, who does not seem to have +examined that face in his foetus, overlooked it), and is either the +internal perpendicular (occipito-parietal), or the calcarine sulcus, +these two being close together and eventually running into one another. +As a rule the occipito-parietal is the earlier of the two. + +3. At the latter part of this period, another sulcus, the +"posterio-parietal," or "Fissure of Rolando" is developed, and it is +followed, in the course of the sixth month, by the other principal +sulci of the frontal, parietal, temporal and occipital lobes. There +is, however, no clear evidence that one of these constantly appears +before the other; and it is remarkable that, in the brain at the period +described and figured by Ecker (loc. cit. pp. 212-213, Taf. II, figs. +1, 2, 3, 4), the antero-temporal sulcus (scissure parallele) so +characteristic of the ape's brain, is as well, if not better developed +than the fissure of Rolando, and is much more marked than the proper +frontal sulci. + +Taking the facts as they now stand, it appears to me that the order of +the appearance of the sulci and gyri in the foetal human brain is in +perfect harmony with the general doctrine of evolution, and with the +view that man has been evolved from some ape-like form; though there +can be no doubt that form was, in many respects, different from any +member of the Primates now living. + +Von Baer taught us, half a century ago, that, in the course of their +development, allied animals put on at first, the characters of the +greater groups to which they belong, and, by degrees, assume those +which restrict them within the limits of their family, genus, and +species; and he proved, at the same time, that no developmental stage +of a higher animal is precisely similar to the adult condition of any +lower animal. It is quite correct to say that a frog passes through +the condition of a fish, inasmuch as at one period of its life the +tadpole has all the characters of a fish, and if it went no further, +would have to be grouped among fishes. But it is equally true that a +tadpole is very different from any known fish. + +In like manner, the brain of a human foetus, at the fifth month, may +correctly be said to be, not only the brain of an ape, but that of an +Arctopithecine or marmoset-like ape; for its hemispheres, with their +great posterior lobster, and with no sulci but the sylvian and the +calcarine, present the characteristics found only in the group of the +Arctopithecine Primates. But it is equally true, as Gratiolet remarks, +that, in its widely open sylvian fissure, it differs from the brain of +any actual marmoset. No doubt it would be much more similar to the +brain of an advanced foetus of a marmoset. But we know nothing +whatever of the development of the brain in the marmosets. In the +Platyrrhini proper, the only observation with which I am acquainted is +due to Pansch, who found in the brain of a foetal Cebus Apella, in +addition to the sylvian fissure and the deep calcarine fissure, only a +very shallow antero-temporal fissure (scissure parallele of Gratiolet). + +Now this fact, taken together with the circumstance that the +antero-temporal sulcus is present in such Platyrrhini as the Saimiri, +which present mere traces of sulci on the anterior half of the exterior +of the cerebral hemispheres, or none at all, undoubtedly, so far as it +goes, affords fair evidence in favour of Gratiolet's hypothesis, that +the posterior sulci appear before the anterior, in the brains of the +Platyrrhini. But, it by no means follows, that the rule which may hold +good for the Platyrrhini extends to the Catarrhini. We have no +information whatever respecting the development of the brain in the +Cynomorpha; and, as regards the Anthropomorpha, nothing but the account +of the brain of the Gibbon, near birth, already referred to. At the +present moment there is not a shadow of evidence to shew that the sulci +of a chimpanzee's, or orang's, brain do not appear in the same order as +a man's. + +Gratiolet opens his preface with the aphorism: "Il est dangereux dans +les sciences de conclure trop vite." I fear he must have forgotten +this sound maxim by the time he had reached the discussion of the +differences between men and apes, in the body of his work. No doubt, +the excellent author of one of the most remarkable contributions to the +just understanding of the mammalian brain which has ever been made, +would have been the first to admit the insufficiency of his data had he +lived to profit by the advance of inquiry. The misfortune is that his +conclusions have been employed by persons incompetent to appreciate +their foundation, as arguments in favour of obscurantism. (80. For +example, M. l'Abbe Lecomte in his terrible pamphlet, 'Le Darwinisme et +l'origine de l'Homme,' 1873.) + +But it is important to remark that, whether Gratiolet was right or +wrong in his hypothesis respecting the relative order of appearance of +the temporal and frontal sulci, the fact remains; that before either +temporal or frontal sulci, appear, the foetal brain of man presents +characters which are found only in the lowest group of the Primates +(leaving out the Lemurs); and that this is exactly what we should +expect to be the case, if man has resulted from the gradual +modification of the same form as that from which the other Primates +have sprung. + + + + + + + + + + +End of the Project Gutenberg EBook of Note on the Resemblances and +Differences in the Structure and the Development of Brain in Man and the Apes, by Thomas Henry Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK RESEMBLANCES-DIFFERENCES OF BRAIN *** + +***** This file should be named 2354.txt or 2354.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/2/3/5/2354/ + +Produced by Sue Asscher. 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HUXLEY, F.R.S. + + +[This essay is taken from 'The Descent of Man and Selection in +relation to Sex' by Charles Darwin where it appears at the end of +Chapter VII which is also the end of Part I. Footnotes are +numbered as they appear in 'The Descent of Man.'] + + +The controversy respecting the nature and the extent of the +differences in the structure of the brain in man and the apes, +which arose some fifteen years ago, has not yet come to an end, +though the subject matter of the dispute is, at present, totally +different from what it was formerly. It was originally asserted +and re-asserted, with singular pertinacity, that the brain of all +the apes, even the highest, differs from that of man, in the +absence of such conspicuous structures as the posterior lobes of +the cerebral hemispheres, with the posterior cornu of the lateral +ventricle and the hippocampus minor, contained in those lobes, +which are so obvious in man. + +But the truth that the three structures in question are as well +developed in apes' as in human brains, or even better; and that +it is characteristic of all the Primates (if we exclude the +Lemurs) to have these parts well developed, stands at present on +as secure a basis as any proposition in comparative anatomy. +Moreover, it is admitted by every one of the long series of +anatomists who, of late years, have paid special attention to the +arrangement of the complicated sulci and gyri which appear upon +the surface of the cerebral hemispheres in man and the higher +apes, that they are disposed after the very same pattern in him, +as in them. Every principal gyrus and sulcus of a chimpanzee's +brain is clearly represented in that of a man, so that the +terminology which applies to the one answers for the other. On +this point there is no difference of opinion. Some years since, +Professor Bischoff published a memoir (70. 'Die Grosshirn- +Windungen des Menschen;' 'Abhandlungen der K. Bayerischen +Akademie,' B. x. 1868.) on the cerebral convolutions of man and +apes; and as the purpose of my learned colleague was certainly +not to diminish the value of the differences between apes and men +in this respect, I am glad to make a citation from him. + +"That the apes, and especially the orang, chimpanzee and gorilla, +come very close to man in their organisation, much nearer than to +any other animal, is a well known fact, disputed by nobody. +Looking at the matter from the point of view of organisation +alone, no one probably would ever have disputed the view of +Linnaeus, that man should be placed, merely as a peculiar +species, at the head of the mammalia and of those apes. Both +shew, in all their organs, so close an affinity, that the most +exact anatomical investigation is needed in order to demonstrate +those differences which really exist. So it is with the brains. +The brains of man, the orang, the chimpanzee, the gorilla, in +spite of all the important differences which they present, come +very close to one another" (loc. cit. p. 101). + +There remains, then, no dispute as to the resemblance in +fundamental characters, between the ape's brain and man's: nor +any as to the wonderfully close similarity between the +chimpanzee, orang and man, in even the details of the arrangement +of the gyri and sulci of the cerebral hemispheres. Nor, turning +to the differences between the brains of the highest apes and +that of man, is there any serious question as to the nature and +extent of these differences. It is admitted that the man's +cerebral hemispheres are absolutely and relatively larger than +those of the orang and chimpanzee; that his frontal lobes are +less excavated by the upward protrusion of the roof of the +orbits; that his gyri and sulci are, as a rule, less +symmetrically disposed, and present a greater number of secondary +plications. And it is admitted that, as a rule, in man, the +temporo-occipital or "external perpendicular" fissure, which is +usually so strongly marked a feature of the ape's brain is but +faintly marked. But it is also clear, that none of these +differences constitutes a sharp demarcation between the man's and +the ape's brain. In respect to the external perpendicular +fissure of Gratiolet, in the human brain for instance, Professor +Turner remarks: (71. 'Convolutions of the Human Cerebrum +Topographically Considered,' 1866, p. 12.) + +"In some brains it appears simply as an indentation of the margin +of the hemisphere, but, in others, it extends for some distance +more or less transversely outwards. I saw it in the right +hemisphere of a female brain pass more than two inches outwards; +and on another specimen, also the right hemisphere, it proceeded +for four-tenths of an inch outwards, and then extended downwards, +as far as the lower margin of the outer surface of the +hemisphere. The imperfect definition of this fissure in the +majority of human brains, as compared with its remarkable +distinctness in the brain of most Quadrumana, is owing to the +presence, in the former, of certain superficial, well marked, +secondary convolutions which bridge it over and connect the +parietal with the occipital lobe. The closer the first of these +bridging gyri lies to the longitudinal fissure, the shorter is +the external parieto-occipital fissure" (loc. cit. p. 12). + +The obliteration of the external perpendicular fissure of +Gratiolet, therefore, is not a constant character of the human +brain. On the other hand, its full development is not a constant +character of the higher ape's brain. For, in the chimpanzee, the +more or less extensive obliteration of the external perpendicular +sulcus by "bridging convolutions," on one side or the other, has +been noted over and over again by Prof. Rolleston, Mr. Marshall, +M. Broca and Professor Turner. At the conclusion of a special +paper on this subject the latter writes: (72. Notes more +especially on the bridging convolutions in the Brain of the +Chimpanzee, 'Proceedings of the Royal Society of Edinburgh,' +1865-6.) + +"The three specimens of the brain of a chimpanzee, just +described, prove, that the generalisation which Gratiolet has +attempted to draw of the complete absence of the first connecting +convolution and the concealment of the second, as essentially +characteristic features in the brain of this animal, is by no +means universally applicable. In only one specimen did the +brain, in these particulars, follow the law which Gratiolet has +expressed. As regards the presence of the superior bridging +convolution, I am inclined to think that it has existed in one +hemisphere, at least, in a majority of the brains of this animal +which have, up to this time, been figured or described. The +superficial position of the second bridging convolution is +evidently less frequent, and has as yet, I believe, only been +seen in the brain (A) recorded in this communication. The +asymmetrical arrangement in the convolutions of the two +hemispheres, which previous observers have referred to in their +descriptions, is also well illustrated in these specimens" (pp. +8, 9). + +Even were the presence of the temporo-occipital, or external +perpendicular, sulcus, a mark of distinction between the higher +apes and man, the value of such a distinctive character would be +rendered very doubtful by the structure of the brain in the +Platyrrhine apes. In fact, while the temporo-occipital is one of +the most constant of sulci in the Catarrhine, or Old World, apes, +it is never very strongly developed in the New World apes; it is +absent in the smaller Platyrrhini; rudimentary in Pithecia (73. +Flower, 'On the Anatomy of Pithecia Monachus,' 'Proceedings of +the Zoological Society,' 1862.); and more or less obliterated by +bridging convolutions in Ateles. + +A character which is thus variable within the limits of a single +group can have no great taxonomic value. + +It is further established, that the degree of asymmetry of the +convolution of the two sides in the human brain is subject to +much individual variation; and that, in those individuals of the +Bushman race who have been examined, the gyri and sulci of the +two hemispheres are considerably less complicated and more +symmetrical than in the European brain, while, in some +individuals of the chimpanzee, their complexity and asymmetry +become notable. This is particularly the case in the brain of a +young male chimpanzee figured by M. Broca. ('L'ordre des +Primates,' p. 165, fig. 11.) + +Again, as respects the question of absolute size, it is +established that the difference between the largest and the +smallest healthy human brain is greater than the difference +between the smallest healthy human brain and the largest +chimpanzee's or orang's brain. + +Moreover, there is one circumstance in which the orang's and +chimpanzee's brains resemble man's, but in which they differ from +the lower apes, and that is the presence of two corpora +candicantia--the Cynomorpha having but one. + +In view of these facts I do not hesitate in this year 1874, to +repeat and insist upon the proposition which I enunciated in +1863: (74. 'Man's Place in Nature,' p. 102.) + +"So far as cerebral structure goes, therefore, it is clear that +man differs less from the chimpanzee or the orang, than these do +even from the monkeys, and that the difference between the brain +of the chimpanzee and of man is almost insignificant when +compared with that between the chimpanzee brain and that of a +Lemur." + +In the paper to which I have referred, Professor Bischoff does +not deny the second part of this statement, but he first makes +the irrelevant remark that it is not wonderful if the brains of +an orang and a Lemur are very different; and secondly, goes on to +assert that, "If we successively compare the brain of a man with +that of an orang; the brain of this with that of a chimpanzee; of +this with that of a gorilla, and so on of a Hylobates, +Semnopithecus, Cynocephalus, Cercopithecus, Macacus, Cebus, +Callithrix, Lemur, Stenops, Hapale, we shall not meet with a +greater, or even as great a, break in the degree of development +of the convolutions, as we find between the brain of a man and +that of an orang or chimpanzee." + +To which I reply, firstly, that whether this assertion be true or +false, it has nothing whatever to do with the proposition +enunciated in 'Man's Place in Nature,' which refers not to the +development of the convolutions alone, but to the structure of +the whole brain. If Professor Bischoff had taken the trouble to +refer to p. 96 of the work he criticises, in fact, he would have +found the following passage: "And it is a remarkable +circumstance that though, so far as our present knowledge +extends, there IS one true structural break in the series of +forms of Simian brains, this hiatus does not lie between man and +the manlike apes, but between the lower and the lowest Simians, +or in other words, between the Old and New World apes and monkeys +and the Lemurs. Every Lemur which has yet been examined, in +fact, has its cerebellum partially visible from above; and its +posterior lobe, with the contained posterior cornu and +hippocampus minor, more or less rudimentary. Every marmoset, +American monkey, Old World monkey, baboon or manlike ape, on the +contrary, has its cerebellum entirely hidden, posteriorly, by the +cerebral lobes, and possesses a large posterior cornu with a +well-developed hippocampus minor." + +This statement was a strictly accurate account of what was known +when it was made; and it does not appear to me to be more than +apparently weakened by the subsequent discovery of the relatively +small development of the posterior lobes in the Siamang and in +the Howling monkey. Notwithstanding the exceptional brevity of +the posterior lobes in these two species, no one will pretend +that their brains, in the slightest degree, approach those of the +Lemurs. And if, instead of putting Hapale out of its natural +place, as Professor Bischoff most unaccountably does, we write +the series of animals he has chosen to mention as follows: Homo, +Pithecus, Troglodytes, Hylobates, Semnopithecus, Cynocephalus, +Cercopithecus, Macacus, Cebus, Callithrix, Hapale, Lemur, +Stenops, I venture to reaffirm that the great break in this +series lies between Hapale and Lemur, and that this break is +considerably greater than that between any other two terms of +that series. Professor Bischoff ignores the fact that long +before he wrote, Gratiolet had suggested the separation of the +Lemurs from the other Primates on the very ground of the +difference in their cerebral characters; and that Professor +Flower had made the following observations in the course of his +description of the brain of the Javan Loris: (75. 'Transactions +of the Zoological Society,' vol. v. 1862.) + +"And it is especially remarkable that, in the development of the +posterior lobes, there is no approximation to the Lemurine, short +hemisphered brain, in those monkeys which are commonly supposed +to approach this family in other respects, viz. the lower members +of the Platyrrhine group." + +So far as the structure of the adult brain is concerned, then, +the very considerable additions to our knowledge, which have been +made by the researches of so many investigators, during the past +ten years, fully justify the statement which I made in 1863. But +it has been said, that, admitting the similarity between the +adult brains of man and apes, they are nevertheless, in reality, +widely different, because they exhibit fundamental differences in +the mode of their development. No one would be more ready than I +to admit the force of this argument, if such fundamental +differences of development really exist. But I deny that they do +exist. On the contrary, there is a fundamental agreement in the +development of the brain in men and apes. + +Gratiolet originated the statement that there is a fundamental +difference in the development of the brains of apes and that of +man--consisting in this; that, in the apes, the sulci which first +make their appearance are situated on the posterior region of the +cerebral hemispheres, while, in the human foetus, the sulci first +become visible on the frontal lobes. (76. "Chez tous les singes, +les plis posterieurs se developpent les premiers; les plis +anterieurs se developpent plus tard, aussi la vertebre occipitale +et la parietale sont-elles relativement tres-grandes chez le +foetus. L'Homme presente une exception remarquable quant a +l'epoque de l'apparition des plis frontaux, qui sont les premiers +indiques; mais le developpement general du lobe frontal, envisage +seulement par rapport a son volume, suit les memes lois que dans +les singes:" Gratiolet, 'Memoire sur les plis cerebres de +l'Homme et des Primateaux,' p. 39, Tab. iv, fig. 3.) + +This general statement is based upon two observations, the one of +a Gibbon almost ready to be born, in which the posterior gyri +were "well developed," while those of the frontal lobes were +"hardly indicated" (77. Gratiolet's words are (loc. cit. p. 39): +"Dans le foetus dont il s'agit les plis cerebraux posterieurs +sont bien developpes, tandis que les plis du lobe frontal sont a +peine indiques." The figure, however (Pl. iv, fig. 3), shews the +fissure of Rolando, and one of the frontal sulci plainly enough. +Nevertheless, M. Alix, in his 'Notice sur les travaux +anthropologiques de Gratiolet' ('Mem. de la Societe +d'Anthropologie de Paris,' 1868, page 32), writes thus: +"Gratiolet a eu entre les mains le cerveau d'un foetus de Gibbon, +singe eminemment superieur, et tellement rapproche de l'orang, +que des naturalistes tres-competents l'ont range parmi les +anthropoides. M. Huxley, par exemple, n'hesite pas sur ce point. +Eh bien, c'est sur le cerveau d'un foetus de Gibbon que Gratiolet +a vu LES CIRCONVOLUTIONS DU LOBE TEMPORO-SPHENOIDAL DEJA +DEVELOPPEES LORSQU'IL N'EXISTENT PAS ENCORE DE PLIS SUR LE LOBE +FRONTAL. Il etait donc bien autorise a dire que, chez l'homme +les circonvolutions apparaissent d'a en w, tandis que chez les +singes elles se developpent d'w en a."), and the other of a human +foetus at the 22nd or 23rd week of uterogestation, in which +Gratiolet notes that the insula was uncovered, but that +nevertheless "des incisures sement de lobe anterieur, une +scissure peu profonde indique la separation du lobe occipital, +tres-reduit, d'ailleurs des cette epoque. Le reste de la surface +cerebrale est encore absolument lisse." + +Three views of this brain are given in Plate II, figs. 1, 2, 3, +of the work cited, shewing the upper, lateral and inferior views +of the hemispheres, but not the inner view. It is worthy of note +that the figure by no means bears out Gratiolet's description, +inasmuch as the fissure (antero-temporal) on the posterior half +of the face of the hemisphere is more marked than any of those +vaguely indicated in the anterior half. If the figure is +correct, it in no way justifies Gratiolet's conclusion: "Il y a +donc entre ces cerveaux [those of a Callithrix and of a Gibbon] +et celui du foetus humain une difference fondamental. Chez +celui-ci, longtemps avant que les plis temporaux apparaissent, +les plis frontaux, ESSAYENT d'exister." + +Since Gratiolet's time, however, the development of the gyri and +sulci of the brain has been made the subject of renewed +investigation by Schmidt, Bischoff, Pansch (78. 'Ueber die +typische Anordnung der Furchen und Windungen auf den Grosshirn- +Hemispharen des Menschen und der Affen,' 'Archiv fur +Anthropologie,' iii. 1868.), and more particularly by Ecker (79. +'Zur Entwicklungs Geschichte der Furchen und Windungen der +Grosshirn-Hemispharen im Foetus des Menschen.' 'Archiv fur +Anthropologie,' iii. 1868.), whose work is not only the latest, +but by far the most complete, memoir on the subject. + +The final results of their inquiries may be summed up as +follows:-- + +1. In the human foetus, the sylvian fissure is formed in the +course of the third month of uterogestation. In this, and in the +fourth month, the cerebral hemispheres are smooth and rounded +(with the exception of the sylvian depression), and they project +backwards far beyond the cerebellum. + +2. The sulci, properly so called, begin to appear in the +interval between the end of the fourth and the beginning of the +sixth month of foetal life, but Ecker is careful to point out +that, not only the time, but the order, of their appearance is +subject to considerable individual variation. In no case, +however, are either the frontal or the temporal sulci the +earliest. + +The first which appears, in fact, lies on the inner face of the +hemisphere (whence doubtless Gratiolet, who does not seem to have +examined that face in his foetus, overlooked it), and is either +the internal perpendicular (occipito-parietal), or the calcarine +sulcus, these two being close together and eventually running +into one another. As a rule the occipito-parietal is the earlier +of the two. + +3. At the latter part of this period, another sulcus, the +"posterio-parietal," or "Fissure of Rolando" is developed, and it +is followed, in the course of the sixth month, by the other +principal sulci of the frontal, parietal, temporal and occipital +lobes. There is, however, no clear evidence that one of these +constantly appears before the other; and it is remarkable that, +in the brain at the period described and figured by Ecker (loc. +cit. pp. 212-213, Taf. II, figs. 1, 2, 3, 4), the antero-temporal +sulcus (scissure parallele) so characteristic of the ape's brain, +is as well, if not better developed than the fissure of Rolando, +and is much more marked than the proper frontal sulci. + +Taking the facts as they now stand, it appears to me that the +order of the appearance of the sulci and gyri in the foetal human +brain is in perfect harmony with the general doctrine of +evolution, and with the view that man has been evolved from some +ape-like form; though there can be no doubt that form was, in +many respects, different from any member of the Primates now +living. + +Von Baer taught us, half a century ago, that, in the course of +their development, allied animals put on at first, the characters +of the greater groups to which they belong, and, by degrees, +assume those which restrict them within the limits of their +family, genus, and species; and he proved, at the same time, that +no developmental stage of a higher animal is precisely similar to +the adult condition of any lower animal. It is quite correct to +say that a frog passes through the condition of a fish, inasmuch +as at one period of its life the tadpole has all the characters +of a fish, and if it went no further, would have to be grouped +among fishes. But it is equally true that a tadpole is very +different from any known fish. + +In like manner, the brain of a human foetus, at the fifth month, +may correctly be said to be, not only the brain of an ape, but +that of an Arctopithecine or marmoset-like ape; for its +hemispheres, with their great posterior lobster, and with no +sulci but the sylvian and the calcarine, present the +characteristics found only in the group of the Arctopithecine +Primates. But it is equally true, as Gratiolet remarks, that, in +its widely open sylvian fissure, it differs from the brain of any +actual marmoset. No doubt it would be much more similar to the +brain of an advanced foetus of a marmoset. But we know nothing +whatever of the development of the brain in the marmosets. In +the Platyrrhini proper, the only observation with which I am +acquainted is due to Pansch, who found in the brain of a foetal +Cebus Apella, in addition to the sylvian fissure and the deep +calcarine fissure, only a very shallow antero-temporal fissure +(scissure parallele of Gratiolet). + +Now this fact, taken together with the circumstance that the +antero-temporal sulcus is present in such Platyrrhini as the +Saimiri, which present mere traces of sulci on the anterior half +of the exterior of the cerebral hemispheres, or none at all, +undoubtedly, so far as it goes, affords fair evidence in favour +of Gratiolet's hypothesis, that the posterior sulci appear before +the anterior, in the brains of the Platyrrhini. But, it by no +means follows, that the rule which may hold good for the +Platyrrhini extends to the Catarrhini. We have no information +whatever respecting the development of the brain in the +Cynomorpha; and, as regards the Anthropomorpha, nothing but the +account of the brain of the Gibbon, near birth, already referred +to. At the present moment there is not a shadow of evidence to +shew that the sulci of a chimpanzee's, or orang's, brain do not +appear in the same order as a man's. + +Gratiolet opens his preface with the aphorism: "Il est dangereux +dans les sciences de conclure trop vite." I fear he must have +forgotten this sound maxim by the time he had reached the +discussion of the differences between men and apes, in the body +of his work. No doubt, the excellent author of one of the most +remarkable contributions to the just understanding of the +mammalian brain which has ever been made, would have been the +first to admit the insufficiency of his data had he lived to +profit by the advance of inquiry. The misfortune is that his +conclusions have been employed by persons incompetent to +appreciate their foundation, as arguments in favour of +obscurantism. (80. For example, M. l'Abbe Lecomte in his +terrible pamphlet, 'Le Darwinisme et l'origine de l'Homme,' +1873.) + +But it is important to remark that, whether Gratiolet was right +or wrong in his hypothesis respecting the relative order of +appearance of the temporal and frontal sulci, the fact remains; +that before either temporal or frontal sulci, appear, the foetal +brain of man presents characters which are found only in the +lowest group of the Primates (leaving out the Lemurs); and that +this is exactly what we should expect to be the case, if man has +resulted from the gradual modification of the same form as that +from which the other Primates have sprung. + + + + + +End of T.H. Huxley's On the Brain [from Descent of Man by Charles Darwin] + diff --git a/old/huxbr10.zip b/old/huxbr10.zip Binary files differnew file mode 100644 index 0000000..8993348 --- /dev/null +++ b/old/huxbr10.zip |