s to {466} doubt their weight.
But it deserves especial notice that the more important objections relate
to questions on which we are confessedly ignorant; nor do we know how
ignorant we are. We do not know all the possible transitional gradations
between the simplest and the most perfect organs; it cannot be pretended
that we know all the varied means of Distribution during the long lapse of
years, or that we know how imperfect the Geological Record is. Grave as
these several difficulties are, in my judgment they do not overthrow the
theory of descent from a few created forms with subsequent modification.

Now let us turn to the other side of the argument. Under domestication we
see much variability. This seems to be mainly due to the reproductive
system being eminently susceptible to changes in the conditions of life; so
that this system, when not rendered impotent, fails to reproduce offspring
exactly like the parent-form. Variability is governed by many complex
laws,--by correlation of growth, by use and disuse, and by the direct
action of the physical conditions of life. There is much difficulty in
ascertaining how much modification our domestic productions have undergone;
but we may safely infer that the amount has been large, and that
modifications can be inherited for long periods. As long as the conditions
of life remain the same, we have reason to believe that a modification,
which has already been inherited for many generations, may continue to be
inherited for an almost infinite number of generations. On the other hand
we have evidence that variability, when it has once come into play, does
not wholly cease; for new varieties are still occasionally produced by our
most anciently domesticated productions. {467}

Man does not actually produce variability; he only unintentionally exposes
organic beings to new conditions of life, and then nature acts on the
organisation, and causes variability. But man can and does select the
variations given to him by nature, and thus accumulate them in any desired
manner. He thus adapts animals and plants for his own benefit or pleasure.
He may do this methodically, or he may do it unconsciously by preserving
the individuals most useful to him at the time, without any thought of
altering the breed. It is certain that he can largely influence the
character of a breed by selecting, in each successive generation,
individual differences so slight as to be quite inappreciable by