100 



THE GENESIS OF SPECIES, 



[CHAP. 



But cases of simultaneous and similar modifications 



THE GREAT SHIELDED GRASSHOPPER. 



abound on all sides. Even as regards the human species, 

 there is a very general!} 7 admitted opinion that a new 



Those that did not so turn would much more easily become the prey of 

 others (if they were vegetarians), or (if they were carnivorous animals) 

 their prey would more readily perceive and avoid them. Here, then, it 

 seems at first that we have the obvious action of natural selection. Yet, 

 in fact, this faculty now appears to be rather the result of some obscure 

 internal tendency, intensified, no doubt, by natural selection, but by no 

 means due to the action of the latter on mere accidental minute varia- 

 tions. For in Siberia it is not only timid or predacious animals that 

 tend to become light-coloured in winter, since Pallas tells us that such a 

 phenomenon is observable in domestic cattle and in horses. In such 

 animals, of course, this character cannot be due to natural selection, and 

 therefore, as we must admit it in this case to be due to some spontaneous 

 internal tendency, it immediately becomes probable that a similar ten- 

 dency also exists in the other cases, and the onus probandi lies with him 

 who denies that such is the case." Novce Species Quadrupedum e Glirium 

 ordine, 1778, p. 7, quoted by Mr. Darwin in "Descent of Man:" see 

 vol. i. p. 282. 



