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“ It is notorious, and we shall immediately adduce proofs, that
increased use or action strengthens muscles, glands, sense-
organs, &c. ; and that disuse, on the other hand, weakens them.
I have not met with any clear explanation of this fact in works on
physiology.”—(The Variation, vol. ii., p. 2QJ.)
He denies that in some cases the principle of inherited
effect of habit comes into action, and we may note here
three reasons which are given for this view. He contends
that mere habit may have done nothing towards the
acclimatisation of the fruit trees of North America, be
cause a multitude of seedlings are annually raised in that
country, and none of them would succeed unless born
with a fitting constitution.* That, in short, is to say that
the direct effect of climate may have nothing to do with
the acclimatisation, because Natural Selection may secure
the survival of those which happened to be born with
stronger constitutions. But it is not a question of what
may be, but what actually is.
Again, Mr. Darwin argues :—
“ 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.”—(Origin of Species, p. 108.)
But in some cases we do undoubtedly know the parent
forms. We know the year in which man has introduced
certain animals into certain countries ; we know what they
were when he took them there ; we know what they are
now ; and, in some cases, we know how greatly they have
been changed when they have been permitted to run wild.
It is also argued that habits change while structures
remain unmodified. That may take place sometimes, but
it certainly does not take place universally. We have to
account for the fixity of species as well as the transmu
* The Variation, vol. ii., p. 312.