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
able to range into new pastures and thus gain a great advantage. It is
not that the larger quadrupeds are actually destroyed (except in some
rare cases) by flies, but they are incessantly harassed and their
strength reduced, so that they are more subject to disease, or not so
well enabled in a coming dearth to search for food, or to escape from
beasts of prey.

Organs now of trifling importance have probably in some cases been of
high importance to an early progenitor, and, after having been slowly
perfected at a former period, have been transmitted to existing species
in nearly the same state, although now of very slight use; but any
actually injurious deviations in their structure would of course have
been checked by natural selection. Seeing how important an organ of
locomotion the tail is in most aquatic animals, its general presence and
use for many purposes in so many land animals, which in their lungs or
modified swim-bladders betray their aquatic origin, may perhaps be thus
accounted for. A well-developed ta