[20 CJO YERGENCE OF CHARACTER. 



as we may believe, presented the simplest structure, how, 

 it has been asked, could the first step in the advancement 

 or differentiation of parts have arisen? Mr. Herbert 

 Spencer would probably answer that, as soon as simple 

 unicellular organism came by growth or division to be 

 compounded of several cells, or became attached to any 

 supporting surface, his law '^that homologous units of 

 any order become differentiated in proportion as their rela- 

 "tions to incident forces become different'' would come 

 into action. But as we have no facts to guide us, specula- 

 tion on the subject is almost useless. It is, however, an 

 error to suppose that there would be no struggle for exist- 

 ence, and, consequently, no natural selection, until many 

 forms had been produced: variations in a single species 

 inhabiting an isolated station might be beneficial, and 

 thus the whole mass of individuals might be modified, or 

 two distinct forms might arise. But, as I remarked toward 

 the close of the introduction, no one ought to feel surprise 

 at much remaining as yet unexplained on the origin of 

 species, if we make due allowance for our profound ignor- 

 ance on the mutual relations of the inhabitants of the 

 world at the present time, and still more so during past 

 ages. 



COl!?'VBRGE]!q'CE OF CHARACTER. 



Mr. H. C. Watson thinks that I have overrated the im- 

 portance 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 at- 

 tribute to convergence a close and general similarity of struct- 

 ure 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 de- 

 pends on an infinitude of complex relations, namely on the 



