Natural selection, it should never be
forgotten, can act on each part of each being, solely through and for
its advantage.
Rudimentary parts, it has been stated by some authors, and I believe
with truth, are apt to be highly variable. We shall have to recur to
the general subject of rudimentary and aborted organs; and I will here
only add that their variability seems to be owing to their
uselessness, and therefore to natural selection having no power to
check deviations in their structure. Thus rudimentary parts are left
to the free play of the various laws of growth, to the effects of
long-continued disuse, and to the tendency to reversion.
A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER,
IN COMPARISON WITH THE SAME PART IN ALLIED SPECIES, TENDS TO BE HIGHLY
VARIABLE.
Several years ago I was much struck with a remark, nearly to the above
effect, published by Mr. Waterhouse. I infer also from an observation
made by Professor Owen, with respect to the length of the arms of the
ourang-outang, that he has come to a nearly similar conclusion. It is
hopeless to attempt to convince any one of the truth of this
proposition without giving the long array of facts which I have
collected, and which cannot possibly be here introduced. I can only
state my conviction that it is a rule of high generality. I am aware
of several causes of error, but I hope that I have made due allowance
for them.
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