ORGANS OF LITTLE APPARENT IMPORTANCE.
As natural selection acts by life and death,--by the preservation of
individuals with any favourable variation, and by the destruction of
those with any unfavourable deviation of structure,--I have sometimes
felt much difficulty in understanding the origin of simple parts, of
which the importance does not seem sufficient to cause the
preservation of successively varying individuals. I have sometimes
felt as much difficulty, though of a very different kind, on this
head, as in the case of an organ as perfect and complex as the eye.
In the first place, we are much too ignorant in regard to the whole
economy of any one organic being, to say what slight modifications
would be of importance or not. In a former chapter I have given
instances of most trifling characters, such as the down on fruit and
the colour of the flesh, which, from determining the attacks of
insects or from being correlated with constitutional differences,
might assuredly be acted on by natural selection. The tail of the
giraffe looks like an artificially constructed fly-flapper; and it
seems at first incredible that this could have been adapted for its
present purpose by successive slight modifications, each better and
better, for so trifling an object as driving away flies; yet we should
pause before being too positive even in this case, for we know that
the distribution and existence of cattle and other animals in South
America absolutely depends on their power of resisting the attacks of
insects: so that individuals which could by any means defend
themselves from these small enemies, would be able to range into new
pastures and thus gain a great advantage.
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