The evolution of man.

Abstract

The present paper is an attempt to consider some of the modem conceptions of biology in relation to the human species. With regard to species in general the Darwinian theory assumed that the differences between species were differences of adaptation, that specific characters were useful, that species were adapted to different modes of life. It has, on the other hand, been maintained by later zoologists that in the vast majority of specific characters there is no evidence of such utility, or of correlation with useful characters, and the pure Darwinian doctrine is now held by a few pious disciples of Darwin as an article of faith rather than as a scientific conclusion. The most eminent systematists distinguish now, as those of pre-Darwinian days did, between diagnostic characters, which are of chief systematic value, and adaptive characters, which for purposes of classification are often rather misleading than significant. The more useless a character is the more valuable it is as an indication of affinity. One modern school of evolutionists, recognising the uselessness of diagnostic characters, holds that they have not been evolved by selection but have arisen spontaneously as mutations; and, with the usual tendency to carry a doctrine to extremes, they maintain that all characters are independent of utility, that all arose as mutations. The American investigator, Dr. T.H. Morgan, has published a book specially devoted to this doctrine, in which he endeavours to show that adaptations to not really exist, that mutations have occurred which could only survive under special conditions of life, which in some cases the modified creatures have found, so that habits have been determined by structure, not structure by habits. Thus, in the short period of half a century, we have had the swing of the pendulum of biological opinion from one extreme to another, from the belief that all characters were adaptive or useful to the belief that none were adaptive. In the meantime the common-sense view has persisted, that some characters are useful and some are not, and that the former are easily modified by conditions of life, the latter unaffected by such conditions. It must, at any rate, be admitted that usually in studying any group of animals we can certainly distinguish between characters which have no visible relation to the maintenance of life, and others which are necessary or advantageous to that purpose, and it is therefore possible to consider the origin of these two kinds of characters separately. The human species, in spite of the attention devoted to anthropology, and although it is to us the most familiar species, has, perhaps, been less studied from the zoological point of view than any other. It is also from this point of view the most difficult, partly because it is our own species, and we cannot get far enough away from it to see it in true perspective; partly because it has had such an exceptional history, having spread over the whole earth and become largely independent of physical conditions, that is to say it has attained to a great extent the power of making artificially uniform conditions which render it independent of differences of climate, geographical features, and differences of fauna and flora in different habitats. The first question to consider is whether man is a single species or several, and what is his relation to other species. This question, as well as most of the others which I propose to consider in this paper, has been discussed with his usual thoroughness and judgement by Darwin in his Descent of Man, so that I am really only trying to see whether we know any more about these problems than Darwin taught us. The chief peculiarities of man, as compared with his nearest allies, the anthropoid apes, are all adaptive and useful characters, namely the erect position, the structure of the hand and foot, and the faculty of articulate speech. Associated with the possession of language are the size and differentiation of the brain, especially of the cerebral hemispheres, and the correlated size and shape of the cranium. …