immediately comes into play, and by its action these
organs gradually become adapted to their new requirements. But man,
under similar circumstances, does not require longer nails or teeth,
greater bodily strength or swiftness. He makes sharper spears, or a
better bow, or he constructs a cunning pitfall, or combines in a hunting
party to circumvent his new prey. The capacities which enable him to do
this are what he requires to be strengthened, and these will, therefore,
be gradually modified by "natural selection," while the form and
structure of his body will remain unchanged. So, when a glacial epoch
comes on, some animals must acquire warmer fur, or a covering of fat, or
else die of cold. Those best clothed by nature are, therefore, preserved
by natural selection. Man, under the same circumstances, will make
himself warmer clothing, and build better houses; and the necessity of
doing this will react upon his mental organization and social
condition--will advance them while his natural body remains naked as
before.

When the accustomed food of some animal becomes scarce or totally fails,
it can only exist by becoming adapted to a new kind of food, a food
perhaps less nourishing and less digestible. "Natural selection" will
now act upon the stomach and intestines, and all their individual
variations will be taken advantage of, to modify the race into harmony
with its new food. In many cases, however, it is probable that this
cannot be done. The internal organs may not vary quick enough, and then
the animal will decrease in numbers, and finally become extinct. But
man guards himself from such accidents by superintending and guiding the
operations of nature. He plants the seed of his most agreeable food, and
thus procures a supply, independent of the accidents of varying seasons
or natural extinction. He domesticates animals, which serve him either
to capture food or for food itself, and thus, changes of any great
extent in his teeth or digestive organs are rendered unnecessary. Man,
too, has everywhere the use of fire, and by its means can render
palatable a variety of animal and vegetable substances, which he could
hardly otherwise make use of; and thus obtains for himself a supply of
food far more varied and abundant than that which any animal can
command.

Thus man, by the mere capacity of clothing himself, and making weapons
and tools, has taken away from nature that power of slowly but
permanently changing the e