to become, as under domestication, plastic.
Now, can it be doubted, from the struggle each individual has to obtain
subsistence, that any minute variation in structure, habits, or
instincts, adapting that individual better to the new conditions, would
tell upon its vigour and health? In the struggle it would have a better
_chance_ of surviving; and those of its offspring which inherited the
variation, be it ever so slight, would also have a better _chance_.
Yearly more are bred than can survive; the smallest grain in the
balance, in the long run, must tell on which death shall fall, and which
shall survive. Let this work of selection on the one hand, and death on
the other, go on for a thousand generations, who will pretend to affirm
that it would produce no effect, when we remember what, in a few years,
Bakewell effected in cattle, and Western in sheep, by this identical
principle of selection?

To give an imaginary example from changes in progress on an island:--let
the organization of a canine animal which preyed chiefly on rabbits, but
sometimes on hares, become slightly plastic; let these same changes
cause the number of rabbits very slowly to decrease, and the number of
hares to increase; the effect of this would be that the fox or dog would
be driven to try to catch more hares: his organization, however, being
slightly plastic, those individuals with the lightest forms, longest
limbs, and best eyesight, let the difference be ever so small, would be
slightly favoured, and would tend to live longer, and to survive during
that time of the year when food was scarcest; they would also rear more
young, which would tend to inherit these slight peculiarities. The less
fleet ones would be rigidly destroyed. I can see no more reason to doubt
that these causes in a thousand generations would produce a marked
effect, and adapt the form of the fox or dog to the catching of hares
instead of rabbits, than that greyhounds can be improved by selection
and careful breeding. So would it be with plants under similar
circumstances. If the number of individuals of a species with plumed
seeds could be increased by greater powers of dissemination within its
own area (that is, if the check to increase fell chiefly on the seeds),
those seeds which were provided with ever so little more down, would in
the long run be most disseminated; hence a greater number of seeds thus
formed would germinate, and would tend to produce plants inheriting t