182 THE ORIGIN OF SPECIES 



allowance for our profound ignorance on the mutual 

 relations of the inhabitants of the world at the present 

 time, and still more so during past ages. 



Convergence of Character 



Mr. n. C. Watson thinks that I have overrated the 

 importance of divergence of character (in which, however, 

 he apparently believes), and that convergence, as it may 

 be called, has likewise played a part. If two species, 

 belonging to two distinct though allied genera, had both 

 produced a large number of new and divergent forms, it 

 is conceivable that these might approach each other so 

 closely that they would have all to be classed under the 

 same genus; and thus the descendants of two distinct 

 genera would converge into one. But it would in most 

 cases be extremely rash to attribute to convergence a 

 close and general similarity of structure in the modified 

 descendants of widely distinct forms. The shape of a 

 crystal is determined solely by the molecular forces, and 

 it is not surprising that dissimilar substances should 

 sometimes assume the same form; but with organic 

 beings we should bear in mind that the form of each 

 depends on an infinitude of complex relations, namely 

 on the variations which have arisen, these being due to 

 causes far too intricate to be followed out — on the nature 

 of the variations which have been preserved or selected, 

 and this depends on the surrounding physical conditions, 

 and in a still higher degree on the surrounding organisms 

 with which each being has come into competition — and 

 lastly, on inheritance (in itself a fluctuating element) 

 from innumerable progenitors, all of which have had 

 their forms determined through equally complex rela- 



