Origin of Species Variorum

his work. But when many men, without intending to alter the breed, have a nearly common standard of perfection, and all try to procure and breed from the best animals, much improvement .. surely but slowly follows from this unconscious process of selection, notwithstanding a large amount of crossing with inferior animals. Thus it will be in nature; for within a confined area, with some place in its polity not .. perfectly occupied, natural selection will always tend to preserve all the individuals varying in the right direction, though in different degrees, so as better to fill up the unoccupied place. But if the area be very large, its several districts will almost certainly present different conditions of life; and then, ↑ if the same species undergoes modification in different parts, the newly-formed varieties will intercross on the confines of each district. But we shall see in the seventh chapter that intermediate varieties, inhabiting an intermediate district, whether the result of the crossing of other varieties, or originally formed with an intermediate character, will in the long run generally be supplanted by one of the varieties on either hand. .. Intercrossing will affect those animals most which unite for each birth and wander much, and which do not breed at a very quick rate. Hence with animals of this nature, for instance .. birds, varieties will generally be confined to separated countries; and this I find to be the case. With hermaphrodite organisms which cross only occasionally, and likewise with animals which unite for each birth, but which wander little and .. can increase at a very rapid rate, a new and improved variety might be quickly formed on any one spot, and might there maintain itself in a body and afterwards spread, so that the crossing would be chiefly between the individuals of the new variety living together in the same place. On this principle, nurserymen