Hair of the Back of Man.

When the hair on the back of man is examined a remarkable change from the patterns of any of his known or supposed ancestors is found. It is by no means easy to trace the course of the hairs on the human back. A young, hairy and dark-haired person gives much the best field, and a lens may be necessary. In older subjects the hair is often so much worn away by friction that the direction can no longer be followed. Suffice it to say that the examina­tion, though somewhat difficult, can well be carried out if the proper conditions are observed; and that it bears out the results which have come from the corresponding examina­tion of infants. The arrangement is congenital.

Fig. 41.—Arrangement of hair on the back of lemur—chimpanzee—man.

From the neck the hair passes on each side nearly downwards, and in the middle directly downwards in a narrow stream between the two muscular borders of the vertebral furrows, and continues in this normal direction to the end of the spinal region. It will be seen that below the two upper arrows there are three levels of arrows, the first with one, the second with two, and the third with one, on each side of the surface of the back. At the level of the shoulder-joints the side-streams curve upwards towards the spine and join the central stream; at the second the direction is rather more upwards before it curves inwards and downwards to the vertebral furrow; at the third the streams curve slightly upwards and towards the middle-line and coalesce with the other streams. The contrast between the straight, simple slope of the hair on the lemur’s and ape’s back, and that of man is very great. In the latter the side-streams make an angle of 45° or less with the axis of the spine and this arrangement is unique among mammals. It will be, therefore, necessary to inquire into its history and causation, for it goes far towards reversing the well-established and accredited pattern of apes, monkeys and lemurs. If the reader will carry his mind back to the arrangement of hair on man’s forearm he will see that it exhibits some features analogous to those on the back of man. In the forearm there is that curious little stream on the extensor surface which may be looked upon as a relic from the ape-stock, but in the rest of that limb-segment man has boldly gone back, beyond the ape, to an arrangement found in the lemur; and in the case of the back of man there is the small primitive area down the vertebral furrow and an entirely novel arrangement on each side such as might startle the leaders of animal fashions in hair.

The question at once arises: “How has this change come to pass?” In the case of the strange arrangement on man’s forearms I have shown that the Pan-Selectionist thought he detected there one of his particular kinds of vestige. He cannot find any such here. I can conceive a biologist making play with Heredity, Variation and Selection in the case of an ape, monkey, or lemur whose hairs are long and thick and functionally very active. There he might make use of the well-known “argument from ignorance,” and maintain that we cannot be sure that such and such factors might not have survival-value, but I defy the most hardy among the Pan-Selectionist High Command to put in that plea in connec­tion with the fine short hairs of man which even require a lens for their detection; they have little value as a protec­tion of the skin from friction; their arrangement has none. And if some leader did attempt this task I doubt if the most docile Prussian would not rebel against the statement that the withdrawal in question was “according to plan.” My purpose, however, in this book being to build up and not to pull down, I must perforce show a reasonable and better explana­tion of a remarkable little fact.