tendency must make itself felt; for though the doctrine of chances or
averages can never be trusted to on a limited scale, yet, if applied to
high numbers, the results come nearer to what theory demands, and, as we
approach to an infinity of examples, become strictly accurate. Now the
scale on which nature works is so vast--the numbers of individuals and
periods of time with which she deals approach so near to infinity, that
any cause, however slight, and however liable to be veiled and
counteracted by accidental circumstances, must in the end produce its
full legitimate results.

Let us now turn to domesticated animals, and inquire how varieties
produced among them are affected by the principles here enunciated. The
essential difference in the condition of wild and domestic animals is
this,--that among the former, their well-being and very existence depend
upon the full exercise and healthy condition of all their senses and
physical powers, whereas, among the latter, these are only partially
exercised, and in some cases are absolutely unused. A wild animal has to
search, and often to labour, for every mouthful of food--to exercise
sight, hearing, and smell in seeking it, and in avoiding dangers, in
procuring shelter from the inclemency of the seasons, and in providing
for the subsistence and safety of its offspring. There is no muscle of
its body that is not called into daily and hourly activity; there is no
sense or faculty that is not strengthened by continual exercise. The
domestic animal, on the other hand, has food provided for it, is
sheltered, and often confined, to guard it against the vicissitudes of
the seasons, is carefully secured from the attacks of its natural
enemies, and seldom even rears its young without human assistance. Half
of its senses and faculties are quite useless; and the other half are
but occasionally called into feeble exercise, while even its muscular
system is only irregularly called 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 wh