commonly linked together by graduated steps? Why should not Nature take a
sudden leap from structure to structure? On the theory of natural
selection, we can clearly understand why she should not; for natural
selection acts only by taking advantage of slight successive variations;
she can never take a great and sudden leap, but must advance by the short
and sure, though slow steps.

ORGANS OF LITTLE APPARENT IMPORTANCE, AS AFFECTED BY NATURAL SELECTION.

As natural selection acts by life and death, by the survival of the
fittest, and by the destruction of the less well-fitted individuals, I have
sometimes felt great difficulty in understanding the origin or formation of
parts of little importance; almost as great, though of a very different
kind, as in the case of the most perfect and complex organs.

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 very
trifling characters, such as the down on fruit and the colour of its flesh,
the colour of the skin and hair of quadrupeds, which, from being correlated
with constitutional differences, or from determining the attacks of
insects, 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 fitted, for so
trifling an object as to drive 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 depend 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