l8o THE GENESIS OF SPECIES. 



Since all variations are potentially useful, but only those 

 are preserved which suit the surrounding* conditions 

 among which they are exhibited, the calculation of 

 chances will itself plead for the probability that a 

 variety of variations will be preserved, rather than the 

 same many times over. Other species competing with 

 the giraffe for food would be little likely to gain an 

 advantage over it by a slight increase in length of neck, 

 though by other variations they might achieve a decided 

 superiority. It is obvious, also, that the advantage 

 assigned to the elongated neck would belong to many 

 other possible variations, such as a lengthened proboscis, 

 far-reaching arms, the climbing powers of the snake or 

 the monkey, the flight of the bird or the insect ; all of 

 which may be due to Natural Selection and the sub- 

 sidiary principles which the theory of Development 

 embraces. 



The calling in of subsidiary principles may be thought 

 to spoil the boasted simplicity of the theory. But such 

 an opinion is hypercritical. One might truthfully say 

 of a great patriot that all he did was in obedience 

 to the simple law of duty, without implying that he 

 was exempt from the law of association of ideas, or 

 independent of the mechanical, chemical, and vital laws 

 which regulate many of the functions of all human 

 beings alike. 



