o the warmest-clad
individuals having been favoured and preserved during many generations,
and how much to the direct action of the severe climate? for it would
appear that climate has some direct action on the hair of our domestic
quadrupeds.

Instances could be given of the same variety being produced under
conditions of life as different as can well be conceived; and, on the
other hand, of different varieties being produced from the same species
under the same conditions. Such facts show how indirectly the conditions
of life must act. Again, innumerable instances are known to every
naturalist of species keeping true, or not varying at all, although
living under the most opposite climates. Such considerations as these
incline me to lay very little weight on the direct action of the
conditions of life. Indirectly, as already remarked, they seem to play
an important part in affecting the reproductive system, and in thus
inducing variability; and natural selection will then accumulate
all profitable variations, however slight, until they become plainly
developed and appreciable by us.

EFFECTS OF USE AND DISUSE.

From the facts alluded to in the first chapter, I think there can be
little 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 can 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 or have lately inhabited several oceanic islands, tenanted by
no beast of prey, has been caused by disuse. The ostrich indeed inhabits
continents and is exposed to danger from which it cannot escape by
flight, but by kicking it can defend itself from enemies, as well as any
of the smaller quadrupeds. We may imagine that the early progenitor
of the ostrich had habits like those of a bustard, and that