ormer times, almost every district had its own breed
of cattle and sheep; "they were indigenous to the soil, climate, and
pasturage of the locality on which they grazed: they seemed to have been
formed for it and by it."[538] But in this case we are quite unable to
disentangle the effects of the direct action of the conditions of life,--of
use or habit--of natural selection--and of that kind of selection which we
have seen is occasionally and unconsciously followed by man even during the
rudest periods of history.

Let us now look to the action of natural selection on special characters.
Although nature is difficult to resist, yet man often strives against her
power, and sometimes, as we shall see, with {226} success. From the facts
to be given, it will also be seen that natural selection would powerfully
affect many of our domestic productions if left unprotected. This is a
point of much interest, for we thus learn that differences apparently of
very slight importance would certainly determine the survival of a form
when forced to struggle for its own existence. It may have occurred to some
naturalists, as it formerly did to me, that, though selection acting under
natural conditions would determine the structure of all important organs,
yet that it could not affect characters which are esteemed by us of little
importance; but this is an error to which we are eminently liable, from our
ignorance of what characters are of real value to each living creature.

When man attempts to breed an animal with some serious defect in structure,
or in the mutual relation of parts, he will either partially or completely
fail, or encounter much difficulty; and this is in fact a form of natural
selection. We have seen that the attempt was once made in Yorkshire to
breed cattle with enormous buttocks, but the cows perished so often in
bringing forth their calves, that the attempt had to be given up. In
rearing short-faced tumblers, Mr. Eaton says,[539] "I am convinced that
better head and beak birds have perished in the shell than ever were
hatched; the reason being that the amazingly short-faced bird cannot reach
and break the shell with its beak, and so perishes." Here is a more curious
case, in which natural selection comes into play only at long intervals of
time: during ordinary seasons the Niata cattle can graze as well as others,
but occasionally, as from 1827 to 1830, the plains of La Plata suffer from
long-continued droughts and