Chap. YI. 
ORGANS OF LITTLE IMPORTANCE. 
195 
understanding the origin of simple parts, of which the 
importance does not seem sufficient to cause the pre¬ 
servation of successively varying individuals. I have 
sometimes felt as much difficulty, though of a very dif¬ 
ferent 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 its flesh, which, from determining the 
attacks of insects or from being correlated with con¬ 
stitutional 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 posi¬ 
tive 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. 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 pro¬ 
genitor, and, after having been slowly perfected at a 
K 2 
