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160 THE ORIGIN OF SPECIES 



ture 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 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 individ- 

 uals, 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 modi- 

 fications 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 color of its flesh, the color of the skin and hair of 

 quadrupeds, which, from being correlated with constitutional dif- 

 ferences, or from determining the attacks of insects might as- 

 suredly 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 



