Now we know that it is similarly useless
in all tribes of men, and must therefore come from a pre-human ancestor.
It is also vestigial in the higher apes, and it is only when we descend
to the lower monkeys and femurs that we see it approaching its primitive
useful form. One may almost say that it is a reminiscence of the far-off
period when, probably in the early Tertiary, the ancestors of the
Primates took to the trees. The animals living on the plain needed
acute senses to detect the approach of their prey or their enemies;
the tree-dweller found less demand on his sense of hearing, the
"speaking-trumpet" was discarded, and the development of the internal
ear proceeded on the higher line of the perception of musical sounds.

We might take a very large number of parts of the actual human body, and
discover that they are similar historical or archaeological monuments
surviving in a modern system, but we have space only for a few of the
more conspicuous.

The hair on the body is a vestigial organ, of actual use to no race of
men, an evident relic of the thick warm coat of an earlier ancestor. It
in turn recalls the dwellers in the primeval forest. In most cases--not
all, because the wearing of clothes for ages has modified this
feature--it will be found that the hairs on the arm tend upward from the
wrist to the elbow, and downward from the shoulder to the elbow. This
very peculiar feature becomes intelligible when we find that some of the
apes also have it, and that it has a certain use in their case. They put
their hands over their heads as they sit in the trees during ram, and in
that position the sloping hair acts somewhat like the thatched roof of a
cottage.

Again, it will be found that in the natural position of standing we are
not perfectly flat-footed, but tend to press much more on the outer than
on the inner edge of the foot. This tendency, surviving after ages
of living on the level ground, is a lingering effect of the far-off
arboreal days.

A more curious reminiscence is seen in the fact that the very young
infant, flabby and powerless as it is in most of its muscles, is so
strong in the muscles of the hand and arm that it can hang on to a stick
by its hands, and sustain the whole weight of its body, for several
minutes. Finally, our vestigial tail--for we have a tail comparable to
that of the higher apes--must be mentioned. In embryonic development
the tail is much longer than the legs, and some chil