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diff --git a/old/huxbr10.txt b/old/huxbr10.txt new file mode 100644 index 0000000..36d63fe --- /dev/null +++ b/old/huxbr10.txt @@ -0,0 +1,746 @@ +T.H. Huxley's On the Brain [from Descent of Man by Charles Darwin] + +The complete title is: +Note on the Resemblances and Differences in the Structure and the +Development of the Brain in Man and Apes + +#3 in our series by T.H. Huxley + +#8 in our series by Charles Darwin + +Our Darwin editor says this should be list under both names. + + +Copyright laws are changing all over the world, be sure to check +the copyright laws for your country before posting these files!! + +Please take a look at the important information in this header. +We encourage you to keep this file on your own disk, keeping an +electronic path open for the next readers. Do not remove this. + + +**Welcome To The World of Free Plain Vanilla Electronic Texts** + +**Etexts Readable By Both Humans and By Computers, Since 1971** + +*These Etexts Prepared By Hundreds of Volunteers and Donations* + +Information on contacting Project Gutenberg to get Etexts, and +further information is included below. We need your donations. + + +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. + +From The Descent of Man by Charles Darwin + +October, 2000 [Etext #2354] + + +T.H. 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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 |