character, the body being relieved from the need of structural change
through some new activity of the mind. In man this was undoubtedly the
case in great, probably in very great, measure. There may have been an
increase in size and strength, some variations in color, in the
breathing organs, in power of resistance of the cuticle to cold, etc.,
but the principal physical change was in a growth of the brain and
expansion of the cranium, giving rise to a less bestial physiognomy and
an advanced mental power.

One physical change that would seem necessary to enable an animal to
endure severe cold, the development of a thick protective covering of
fur or hair, did not take place in man. The change was more likely in
the other direction, since the hairy cover which is possessed by many of
the forest folk has disappeared. This loss of hair by man has been
referred by Darwin to sexual selection, that powerful influence to
which animals seem to owe so many physical structures of no apparent
use, and some of them seemingly disadvantageous. In the case of man in
the circumstances now under consideration, exposed without natural
covering to the growing chill of the advancing ice sheet, the influence
of sexual selection would certainly have found a strong counteracting
force in natural selection, had not some other means of escaping the
influence of the cold been found.

As it was, the difficulty was undoubtedly overcame in great measure by
the adoption of artificial clothing. The mind came to the aid of the
body. The man who could chip a stone into the shape of an axe or spear
head, was sufficiently advanced mentally to conceive the idea of
covering his body with leaves fastened together in some way, with other
vegetable fabrics, or with the skins of slain animals. Protection from
the cold was also sought in caverns and rock shelters, and for a very
long period man remained a cave-dweller. There is hardly a cavern in
western Europe in which he has not left some trace of his residence.
Where caves were not available, rude artificial shelters were probably
built. Even the orang builds a shelter of this kind, and we can readily
conceive of man at a very early period making himself a shelter of
leaves and boughs, from which, as the cold increased, he might easily
evolve a hut composed of a wooden framework covered with skins such as
he used for clothing.

When and where the most important of discoveries, that of fire, was
made, i