into feeble exercise, while even its muscular
system is only irregularly brought into action.

Now when a variety of such an animal occurs, having increased power or
capacity in any organ or sense, such increase is totally useless, is
never called into action, and may even exist without the animal ever
becoming aware of it. In the wild animal, on the contrary, all its
faculties and powers being brought into full action for the necessities
of existence, any increase becomes immediately available, is
strengthened by exercise, and must even slightly modify the food, the
habits, and the whole economy of the race. It creates as it were a new
animal, one of superior powers, and which will necessarily increase in
numbers and outlive those which are inferior to it.

Again, in the domesticated animal all variations have an equal chance of
continuance; and those which would decidedly render a wild animal unable
to compete with its fellows and continue its existence are no
disadvantage whatever in a state of domesticity. Our quickly fattening
pigs, short-legged sheep pouter pigeons, and poodle dogs could never
have come into existence in a state of nature, because the very first
step towards such inferior forms would have led to the rapid extinction
of the race; still less could they now exist in competition with their
wild allies. The great speed but slight endurance of the race horse, the
unwieldy strength of the ploughman's team, would both be useless in a
state of nature. If turned wild on the pampas, such animals would
probably soon become extinct, or under favourable circumstances might
each gradually lose those extreme qualities which would never be called
into action, and in a few generations revert to a common type, which
must be that in which the various powers and faculties are so
proportioned to each other as to be best adapted to procure food and
secure safety,--that in which by the full exercise of every part of its
organisation the animal can alone continue to live. Domestic varieties,
when turned wild, _must_ return to something near the type of the
original wild stock, _or become altogether extinct_.[F]

+--------------------------------------------------------------+
| [F] That is, they will vary, and the variations which tend |
| to adapt them to the wild state, and therefore approximate |
| them to wild animals, will be preserved. Those individuals |
| which do not vary sufficiently will peris