| Let us now briefly consider the steps by which domestic races have been produced, either from one or from several allied species. Some
effect
be attributed to the direct
→and definite action
of the external conditions of life, and some
to habit; but he would be a bold man who would account by such agencies for the differences
a dray and race horse, a greyhound and
a carrier and tumbler pigeon. One of the most remarkable features in our domesticated races is that we see in them adaptation, not indeed to the animal's or plant's own good, but to
use or fancy. Some variations useful to him have probably arisen suddenly, or by one step; many botanists, for instance, believe that the
with its hooks, which cannot be rivalled by any mechanical contrivance, is only a variety of the wild Dipsacus; and this amount of change may have suddenly arisen in a seedling. So it has probably been with the turnspit dog; and this is known to have been the case with the ancon sheep. But when we compare the dray-horse and race-horse, the dromedary and camel, the various breeds of sheep fitted either for cultivated land or mountain pasture, with the wool of one breed good for one purpose, and that of another breed for another purpose; when we compare the many breeds of dogs, each good for man in
different ways; when we compare the game-cock, so pertinacious in battle, with other breeds so little
with "everlasting layers" which never desire to sit, and with the bantam so small and elegant; when we compare the host of agricultural, culinary, orchard, and flower-garden races of plants, most useful to man at different seasons and for different purposes, or so beautiful in his eyes, we must, I think, look further than to mere variability. We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we now see them; indeed, in
cases, we know that this has not been their history. The key is
power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to
for himself useful breeds. |
