Page:Popular Science Monthly Volume 46.djvu/398

384 for the parasite theory, it is among "the classes" who are certainly above suspicion so far as parasites are concerned that the loss of hair on the head is most conspicuously shown, while in the case of Hodge, who can not be regarded in the same manner, loss of hair from the head is decidedly rare. An explanation which pretends to account for what has taken place, and yet fails in application to analogous circumstances at the present day, is not one to be accepted. A true explanation of the loss of hair will explain the present-day loss as well as that of the past; the loss of hair from the head as well as that from the body; the loss of hair by the elephant as compared with the mammoth; the loss of hair on the chests of old monkeys; the loss of hair during disease in animals generally; the loss of hair during pregnancy in domestic and other animals; the loss of feathers by penned-up fowls. An explanation which is wholly physiological, and accounts for loss of hair as a pathematic symptom of individual or racial decline, assumes that such loss of hair is an exemplification of a law of reversion, that as progressive ontogenetic or phylogenetic development is, necessarily, progressive acquirement or elaboration, retrogressive development in similar cases is, accordingly, loss or degeneration of character developed during progression. This explanation, together with the assumption warranted by evidence, that the longer any character or particular feature has been transmitted in the race, the longer it will withstand adverse influences, may be applied to all the instances of hair-loss given above.

In connection with the hair it may be noticed that certain peculiarities in its mode of growth had their origin in the habits of monkeylike ancestors. On a child's head the hair grows from the crown to the forehead; but in animals which move head-first on all fours—a rabbit, for instance—it may be noticed that the hair is always directed from front to back, a character acquired by the fact of motion through air in a given direction having imparted a given lie to the hair. Such may be assumed to have been the case with the hair in the ancestors of monkeys; but when it is found, as in Cebus vellerosus, that the hair grows the contrary way—namely, from back to front—some cause must have induced the change. The flow of rain may be cited the head being hung down, so that the crown is the highest part, and the rain flows off in all directions, giving the hair a lie in accordance. Now, flow of rain in the case of quadrupeds, as well as the tendency of hair to grow according to gravity, unless other causes are more potent, has made the hair on their limbs grow from the body to the extremities. In the case of man, however, and certain monkeys, the hair on the forearm grows in just the contrary direction—namely, toward the