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closely related, for one part may be wholly suppressed or rendered
monstrous without any other part of the body being affected.”—(The
Variation, vol. ii., p. 31Q.)
This looks like putting the cart before the horse. The
general principle should surely be first announced, and
then the exceptions or apparent exceptions should be
stated. Mr. Darwin also urges the plea of ignorance in
this case :—
“ In cases of true correlated variation, we are sometimes able to see
the nature of the connexion ; but in most cases the bond is hidden
from us, and certainly differs in different cases. We can seldom say
which of two correlated parts first varies and induces a change in the
other, or whether the two are simultaneously produced by some
distinct cause.”—(The Variation, vol. ii., p.320.)
Remarks like these would in some connections require
no comment. They are simply an honest expression of
a present ignorance or of a very partial knowledge, and
they produce the pleasing effect of suggesting the keen
insight and perfect candour of the writer. But we must
beware of giving such statements a different significance.
Either correlated variation is a law of nature or not. If it
is not, let us say so at once, and have no more to do with
it. But if it is a law of nature, it will be as efficient as
all other laws are ; and if we do not find the results which
we anticipate, we may depend upon it that the reason is
either because we are looking for results which we have no
right to expect, or because some other law of nature
is modifying the effect of this. So far as we are ignorant
we are bound to remove that ignorance, if possible; but if
not, we have no right to question the existence of a law
whose action is in other connections manifest to all.
The doubts thrown upon the efficacy of the principle of
correlated variation assume a new significancy when we
find that Mr. Darwin introduces the principle of Natural
Selection into his very definitions of correlated variation ;