The foregoing remarks lead me to say a few words on the protest lately
made by some naturalists, against the utilitarian doctrine that every
detail of structure has been produced for the good of its possessor.
They believe that very many structures have been created for beauty in
the eyes of man, or for mere variety. This doctrine, if true, would be
absolutely fatal to my theory. Yet I fully admit that many structures
are of no direct use to their possessors. Physical conditions probably
have had some little effect on structure, quite independently of any
good thus gained. Correlation of growth has no doubt played a most
important part, and a useful modification of one part will often have
entailed on other parts diversified changes of no direct use. So again
characters which formerly were useful, or which formerly had arisen
from correlation of growth, or from other unknown cause, may reappear
from the law of reversion, though now of no direct use. The effects of
sexual selection, when displayed in beauty to charm the females, can
be called useful only in rather a forced sense. But by far the most
important consideration is that the chief part of the organisation of
every being is simply due to inheritance; and consequently, though
each being assuredly is well fitted for its place in nature, many
structures now have no direct relation to the habits of life of each
species. Thus, we can hardly believe that the webbed feet of the
upland goose or of the frigate-bird are of special use to these birds;
we cannot believe that the same bones in the arm of the monkey, in the
fore leg of the horse, in the wing of the bat, and in the flipper of
the seal, are of special use to these animals.
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