| [148] | Reisen in Lykien, etc., Vienna, 1889. |
| [149] | Vide History of the Negro Race in America. G. W. Williams. |
| [150] | Science, Feb. 13, 1891. A. F. Chamberlain. |
| [151] | See p. 290. |
VIII
RELATIVE RACIAL BRAIN-WEIGHT AND SIZE
Consistently with the recognition of the brain as the organ of intellectual activity, it seems not unnatural to assume for man, as the rational animal, a very distinctive cerebral development. One of the most distinguished of living naturalists, Professor Owen, has even made this organ the basis of a system of classification, by means of which he separates man into a sub-class, distinct from all other mammalia. But while a comparison between man and the anthropoid apes, as the animals most nearly approximating to him in physical structure, lends confirmation to the idea not only that a well-developed brain is essential to natural activity, but that there is a close relation between the development of the brain and the manifestation of intellectual power; the distinctive features in the human brain, as compared with those of the anthropomorpha, prove to be greatly less than had been assumed under imperfect knowledge. The substantial difference is in volume. “No one, I presume,” says Darwin, “doubts that the large size of the brain in man, relatively to his body, in comparison to that of the gorilla or orang, is closely connected with his higher mental powers”;[[152]] and it might not unfairly be reasoned from analogy, that the same test distinguishes the intellectual man from the stolid, and the civilised man from the savage. A careful study of the subject, however, shows some remarkable deviations from such a scale of progression. Attention is indeed directed to greatly more ample proofs of inequality between the organic source of power and the manifestations of mental energy; as, for example, in the ant, with its cerebral ganglia not so large as the quarter of a small pin’s head, displaying instincts and apparent affections of wonderful intensity and compass. Viewed in this aspect, “the brain of an ant is one of the most marvellous atoms of matter in the world, perhaps more marvellous than the brain of man.” Here, however, we look on elements of contrast rather than analogy; and seek in vain in this direction for any appreciable test of the soundness of the popular belief in the size of the brain as a measure of intellectual power. It is otherwise when we turn to the anthropomorpha. There, alike in the scientific and in the popular creed, very special and exceptional affinities to man are admitted; and a careful study of their anatomical structure tends to increase the recognised points of analogy.
Mr. Lockhart Clarke, in a contribution to Dr. Maudsley’s work on the Physiology and Pathology of Mind, gives a minute description of the concentric layers of nervous substance which combine to form the convolutions of the human brain; and of the forms and disposition of the various nerve-cells of which its vesicular structure consists. Comparing the human brain with those of other animals, he says: “Between the cells of the convolutions in man and those of the ape tribe I could not perceive any difference whatever; but they certainly differ in some respects from those of the larger mammalia: from those, for instance, of the ox, sheep, or cat.”[[153]] Apart from the difference in volume (55 to 115 cubic inches), the only distinctive features, according to Professor Huxley, between the brain of the anthropomorpha and that of man, are “the filling up of the occipito-temporal fissure; the greater complexity and less symmetry of the other sulci and gyri; the less excavation of the orbital face of the frontal lobe; and the larger size of the cerebral hemispheres, as compared with the cerebellum and the cerebral nerves.”
The brain of the orang is the one which seems most nearly to approximate to that of man. In volume it is about 26 or 27 cubic inches; or about half the minimum size of a normal human brain. The frontal height is greater than in that of other anthropomorpha; the frontal lobe is in all respects larger as compared with the occipital lobe; and certain folds of brain-substance, styled “bridging convulsions,” which in the human brain are interposed between the parietal and occipital lobes, also occur, though greatly reduced, in the brain of the orang; while they appear to be wholly wanting in the chimpanzee, the gibbon, and other apes which superficially present a greater resemblance to man. Referring to the convolutions of the central cerebral lobe, Huschke says: “With their formation in the ape, the brain enters the last stage of development until it arrives at its perfection in man”; and the higher class of brains may be arranged between the extremes of poorly and richly convoluted examples.
But it must not be overlooked that, apart from structural differences, relative, and not absolute mass and weight of brain has to be considered, otherwise the elephant and the whale would take the foremost place. “The brain of the porpoise,” Professor Huxley remarks,[[154]] “is quite wonderful for its mass, and for the development of the cerebral convolutions”; but it is the centre of a nervous system of corresponding capacity, while as compared with the size of the animal, the brain is not relatively large. Vogt states the weight of the human body to be to the brain, on an average, as 36 to 1; whereas in the most intelligent animals the difference is rarely less than 100 to 1.