Chap. VI. affected by Natural Selection. *57 



great, though of a very different kind, as in the case of the most 

 perfect and complex organs. 



P In the first place, we are much too ignorant in regard to the- 

 whole economy of any one organic being, to say what slight modifi- 

 cations would be of importance or not. In a former chapter I have 

 oiven instances of very trifling characters such as the down on 

 fruit and the colour of its flesh, the colour of the skm 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 swimbladders 

 betray their aquatic origin, may perhaps be thus accounted for. A 

 well-developed tail having been formed in an aquatic animal, it 

 might subsequently come to be worked in for all sorts of purposes,, 

 — as a fly-flapper, an organ of prehension, or as an aid in turning, as 

 in the case of the dog, though the aid in this latter respect must be 

 slight, for the hare, with hardly any tail, can double still more- 

 quickly. 



In the second place, we may easily err in attributing importance 

 to characters, and in believing that they have been developed 



