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.

Yet another concep­tion from the region of metaphor must be mentioned. It is one which will commend itself to every mind which has been steeped in thoughts of warfare for five years. We are all soldiers now; we think in terms of military affairs. In the case of our hair-streams there are in many regions two forces directly opposed to one another, others in which no struggle has yet occurred, as, in the Great War, Italy was not at one period at open war with Germany.

Between the opposing forces in our small battle-field of the hairy coat there have been waged battles to which those of Mukden, Verdun, the Somme and Arras, are not to be compared in point of time. They are but as one day to a thousand years. On one side of the conflict in our present chosen field the ancient primitive type of the lemur has remained entrenched for some millions of years, until there arose new forces in its descendants on the other side and this changed the war of positions into one of movement. It was indeed “a contemptible little army” which came forward to oppose the ancient barbarian forces of the lemur, long prepared and organised, and these new armies fought under the banner, Habit. In the slowly-formed patterns in many types of mammals we have records of the treaties made after these long struggles and the rectifications of frontier which became necessary. The critic may call these “battles of kites and crows,” and ask What war correspondents were allowed to describe them; but a battle, whether great or small, long or short, is important to the parties concerned, and it is open to us to “reconstruct” the facts of the battle as do the historians on their part, for example, Sir James Ramsay the battle of Agincourt—with tolerable verisimilitude. But in science, especially geological science, the process of reconstruc­tion is much more ambitious and bold than any that is here attempted. Who has not been fascinated, if he has read Sir E. Ray Lankester’s work on Extinct Animals, by the skill and daring with which he conveys to us a vivid idea of the form and mode of life, with scanty data, of the extinct Moa of New Zealand, the great Pterodactyle, Pteranodon, or the Diprotodon of Owen—“the probable appearance in life” of these uncanny but very real inhabitants of the earth in days long past. How skilfully did Owen from a piece of bone seven inches long, sent to him by a gentleman in New Zealand sixty years ago, pronounce it to be a part of the thigh-bone of a bird like an ostrich, and then after a few years had passed, confirmed it by more bones of the skeleton, till the large Moa, extinguished 600 or 700 years ago by the Maoris, lived again before us—an historical personage; or how by the examina­tion of the skull and most of its skeleton the giant marsupial from Australia, Diprotodon, was resuscitated and admired; or again, how from the bones of the arms, shoulder-girdle and fingers was built up the strange body of Pteranodon, the great flying dragon. All of which is the legitimate and approved business of biologists and palæontologists, and this digression is made here to show that my line of treatment of a little subject agrees with that in a greater one; nay, it even proceeds in its explanations of events on the ever valuable principle of Lyell in a still greater one without which to-day geology would be a thing of naught, that is, the principle of explaining changes in the surface of the earth by reference to causes now in action. The objection that one subject is very great and the other very small is not valid; for one as much as the other there are millions of years to be had for the asking. Who in these days hesitates to talk and try to think in millions?—tens of millions of men, millions of soldiers, millions upon millions of money, millions of bacteria in vaccines and millions of money belonging to other people disposed of by the new spendthrift Minister?