Africa. The
disappearance of the hair in man has been traced to no well established
cause. Darwin's view that it may have been a result of sexual selection
seems the most probable explanation. Certainly this is the case with the
beard, whose absence in women shows it to be of no utility, and whose
presence in man is in accord with the many structures in male animals
apparently due to this form of selection.

Darwin has pointed out and explained a very curious peculiarity of the
hair in man, which is absolutely inexplicable except on the theory of
descent. This is the fact that the hairs on man's arms are directed
toward the elbow from above and below, thus growing in opposite
directions on the upper and lower arms. The same peculiarity exists in
the larger anthropoid apes and in some of the gibbons, but is not found
in the lower mammals. In the apes it is believed to be due to the habit
of protecting the head from rain by covering it with the hands, the
hairs turning so that the rain can run downward freely in both
directions toward the bent elbow. This is so useless in man that it can
be explained only as a survival.

There are some other survivals in man of ancient structures to which a
passing allusion must suffice. In man's eye is a minute membrane, the
semilunar fold, which is absolutely useless in his economy. There is
every reason to believe that this is the rudiment of a membrane which is
fully developed in many animals, and is especially useful to birds, the
nictitating membrane, or third eyelid. Again, the muscles which move the
skin in many animals, especially in horses, have left inactive remnants
in many parts of the human body. These are normally active only in the
forehead, where they serve to lift the eyebrows, but they occasionally
become active elsewhere. Thus there are some persons who can move the
skin of the scalp. Darwin cites some who could throw heavy books from
the head in this manner. The same may be said of the rudimentary muscles
of the ear. There are persons who can move their ears in the same way as
is done by the lower animals. Again, the whole external ear may be
looked upon as a rudimentary structure, since it does not appear to aid
the hearing in man. As regards the pointed ear of man's probable
ancestor, Darwin calls attention to what seems a trace in man of the
lost tip.

Carrying this consideration farther, it may be asked, Of what use are
the five toes to man? Would not a solid f