XVII.-A New View of Human Descent.

By JOHN H. LYELL, M.D.

(Read 13th December, 1906).

(Abstract).

The question of human descent is one which has a perennial fascination for all who are interested in the deeper and more speculative problems of Biology. The advent of the theory of evolution has entirely altered our point of view towards such subjects of enquiry. Indeed it is only since the time of Darwin and Huxley that the origin of man has come to be seriously looked upon as a problem of Biology at all. When Darwin published his epoch-making "Origin of Species" he hardly dared to include mankind in his speculations. But not many years elapsed before it was seen that there was no other way for it, and we have now reached the stage when it is no longer a matter of controversy that man is an integral part of the animal kingdom, and like every other living creature has been slowly evolved from more primitive ancestors which peopled the globe in remote geological eras.

It must be admitted, however, that while we are compelled to accept the general truth of man's evolution from the lower animals, much obscurity still rests upon the various stages passed through in the process, and more especially upon what were the immediate progenitors of man in the evolutionary series. The popular mind has for long associated what is known as Darwinism or the Darwinian Theory with the very unflattering notion that our race is descended from those gorillas, chimpanzees, and other larger apes, with whose uncouth forms we are made acquainted in museums and zoological gardens. It cannot, however, be too often pointed out that Darwin never said any such thing. In no case does he go further than to state his conviction that "man is an offshoot of the Old World simian stem," that he is a descendant of "some tailed quadruped, probably arboreal in its habits, which, if its whole. structure had been examined by a naturalist, would have been classed amongst the quadrumana (or anthropoid apes), as surely as the still more ancient progenitor of the Old and New World monkeys." The derivation of man from some primitive, but now extinct, member of the ape family is therefore the true Darwinian doctrine. Presentday ape and man are divergent branches from a common ancestral form, which already possessed the distinctive simian characters clearly differentiated.

The great majority of naturalists have for many years accepted this theory as the only explanation of the extraordinary anatomical and physiological resemblances between man and the anthropoid apes. It is an interesting fact, however, that of late various considerations have been brought forward, chiefly by American and German investigators, which would lead us to believe that this doctrine is subject to several very important modifications. A more profound study of various peculiarities in human anatomy seems, in short, to point to a much more remote origin for our race than directly from the simian or ape stem. There would now appear to be good ground for the opinion that man is after all one of the great primary branches of the fundamental mammalian stock, the apes being merely a parallel race, whose only affinity with man is in virtue of the close origin of both types from the primary root out of which all the different branches of the great class of the Mammalia have sprung. The most recent conception of the descent of man is thus that he forms a root-branch of the great mammalian tree, growing up for a time very close to the ape stem, but afterwards diverging from it on totally independent lines, and finally overtopping the whole growth.

The chief argument advanced in favour of the new view is that although man has far outstripped all other animals in the development of his brain, he still retains in various parts of his bodily structure the undoubted evidences of an extremely primitive origin. One of man's most distinctive characters, for example, is the formation of his hands, in respect of which he really stands quite unique in the animal kingdom. The human hand is undoubtedly the most perfect mechanical device in nature. Its varied uses have helped to raise man above every other living creature, and hence there is no part of the body which strikes us more forcibly as being one of the highest triumphs of evolution. We are thus very naturally led to the supposition that it must be one of the last acquirements of the race, or at least of our more immediate progenitors. This, however, is quite a false conclusion. The hand is really one of the most primitive structures in the whole class of the Mammalia, and to find its earliest prototype we must retrace our steps to the very lowest representatives of that great group, and to their remote ancestors in far-distant geological time. Away back, towards the end of the Primary, or commencement of the Secondary Period, there existed certain large forms of land vertebrates with grasping extremities, which must have closely resembled those of present-day men or apes. The well-known Chirotherium footprints of Permian or Trias age might almost have been made by the large muscular hands of a modern working navvy. The thick cushion of the ball of the thumb, and even the very creases between the joints of the fingers, are