Initiative in Evolution

by Walter Kidd

Fig 1.—Arrangement of Hair on the Forearm.

In the ape the hairs of the forearm are much longer and thicker than those of man, and both on the front and back all point from the wrist to the elbow.

In the lemur all the hairs point from the elbow to the wrist.

In the products of Nature there are no freaks, or impish tricks performed, and it is not for nothing she does her work. Every one of them asks for and should receive an explana­tion consistent with fact and reason, and here comes in the need for studying, as one may, the broad outlines of man’s ancestry. His ancestor being now sought in an earlier and more generalized stock than that of the four genera of anthropoid apes known to us, the most instructive and safest line to take is to trace him back to the stock lemur, who remains to-day among the most Chinese or unchanging of known mammals. In his illuminating work, Prehistoric Man and History, Professor Scott Elliott adopts an excellent term, “lemur-monkey-man,” to sum up, without missing links, the long ancestry of man. I take the liberty of adapting this term more closely to the present inquiry and use that of lemur-ape-man instead, for whatever may be the relation of man to present apes some ape-like ancestors enter into his genealogical tree.[45] For my purpose the monkey is less useful because his hair-slope differs so little from that of lemurs, whereas apes have made for themselves a very remarkable position as regards the hair of their forearms. Our series of animals for study is then well represented by the lemur-ape-man—hypothetical, necessary and serviceable. Through all the immense stretch of time occupied in this process of descent there has been ample opportunity for the lemur to change his fashion to that of the ape, and the latter to change to the present fashion of man.

This simple arrangement of the lemur’s hair is common to that of all the more primitive long-bodied mammals, of which an otter is a good example, and I venture, greatly daring, to call this the normal slope of hair. Somewhere and somehow in the human tree there has appeared a total reversal of the lemur-type; the stock of apes acquired a new fashion, and gradually discarded altogether their ancient inheritance, beginning their innova­tion perhaps, with Dryopithecus fontani in the Miocene Age.

The Dynamics of Hair-Pattern.

There are a few well-known facts which it is necessary to bear in mind if one is endeavouring to understand the mode of origin and order of the events before us. The hairy coat of a mammal is composed of individual hairs of varying length, colour and thickness, each being rooted in a tiny pit in the skin and growing from a papilla at its base. As the hair grows, its free end is pushed away from the papilla at the rate of one inch in two months. This is the rate in man’s hair, and it is probably greater in the case of lower mammals on account of the greater importance and physiological activity of their hairy coat than in man’s. But one inch in two months is a close enough calcula­tion. Here, then, is a structure which grows throughout the whole life of the animal, and has to dispose itself somehow on the surface of the skin. It does this in the line of least resistance, and to trace this line is the Alpha and Omega of the present inquiry.

There is a concep­tion of much value in understanding the dynamics of the distribu­tion of hair, and that is to view the hair of mammals as composed of certain streams. As in every illustra­tion, this concep­tion may be challenged because of some difference the critic may find between these streams and a stream of fluid. It certainly does not leave its bed as do the component parts of a river, a glacier or molten lava, for the base of the hair is fixed. But it will serve, and is at least not more open to objection than certain useful metaphors in biology as when the genealogy of man and animals is pictured as a tree, or the living things of the earth as a “web of life.” It is, then, as streams moving at the rate of one inch in two months in the lines of least resistance that I propose to discuss the animal hair and its diverse patterns and offer no further apology for doing so. Just as in the cases of a stream of water with varying banks and rocks in its course, or a glacier with its mountain-sides and sinuous valleys, or a stream of lava with small projecting surfaces of a mountain, our stream of hair flows on, hindered only by adequate obstructions.