the same species. Pigeons can be mated for life, and this is a
great convenience to the fancier, for thus many races may be kept true,
though mingled in the same aviary; and this circumstance must have
largely favoured the improvement and formation of new breeds. Pigeons,
I may add, can be propagated in great numbers and at a very quick rate,
and inferior birds may be freely rejected, as when killed they serve
for food. On the other hand, cats, from their nocturnal rambling habits,
cannot be matched, and, although so much valued by women and children,
we hardly ever see a distinct breed kept up; such breeds as we do
sometimes see are almost always imported from some other country, often
from islands. Although I do not doubt that some domestic animals vary
less than others, yet the rarity or absence of distinct breeds of the
cat, the donkey, peacock, goose, etc., may be attributed in main part
to selection not having been brought into play: in cats, from the
difficulty in pairing them; in donkeys, from only a few being kept by
poor people, and little attention paid to their breeding; in peacocks,
from not being very easily reared and a large stock not kept; in geese,
from being valuable only for two purposes, food and feathers, and more
especially from no pleasure having been felt in the display of distinct
breeds.

To sum up on the origin of our Domestic Races of animals and plants.
I believe that the conditions of life, from their action on the
reproductive system, are so far of the highest importance as causing
variability. I do not believe that variability is an inherent and
necessary contingency, under all circumstances, with all organic beings,
as some authors have thought. The effects of variability are modified by
various degrees of inheritance and of reversion. Variability is governed
by many unknown laws, more especially by that of correlation of growth.
Something may be attributed to the direct action of the conditions of
life. Something must be attributed to use and disuse. The final result
is thus rendered infinitely complex. In some cases, I do not doubt
that the intercrossing of species, aboriginally distinct, has played an
important part in the origin of our domestic productions. When in
any country several domestic breeds have once been established, their
occasional intercrossing, with the aid of selection, has, no doubt,
largely aided in the formation of new sub-breeds; but the importance of
the crossi