Origin of Species Variorum

every naturalist, of species keeping true, or not varying at all, although living under the most opposite climates. Such considerations as these incline me not to lay much weight on the direct and definite action of the conditions of life; but I fully admit that strong arguments of a general nature may be advanced on the other side. ↑

In one sense the conditions of life may be said, not only to cause variability, but likewise to include natural selection; for ... the conditions determine whether this or that variety shall survive. But when man is the selecting agent, we clearly see that the two elements of change are .. distinct; the conditions cause the variability; the will of man, acting either consciously or unconsciously, accumulates the variations in certain .. directions, and this answers to the survival of the fittest under nature.

Effects of Use and Disuse, as controlled by Natural Selection .

From the facts alluded to in the first chapter, I think there can be no doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited. Under free nature, we .. have no standard of comparison, by which to judge of the effects of long-continued use or disuse, for we know not the parent-forms; but many animals have structures which can be explained by the effects of disuse. As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state. The logger-headed duck of South America can only flap along the surface of the water, and has its wings in nearly the same condition as the domestic Aylesbury duck. As the larger ground-feeding birds seldom take flight except to escape danger, I believe that the nearly wingless condition of several birds, which now inhabit