94 CONVERGENCE OF CHARACTER. [CHAP. IV. 



there would be no struggle for existence, 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 

 towards 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 ignorance 

 on the mutual relations of the inhabitants of the world at the 

 present time, and still more so during past ages. 



Convergence of CJiaracter. 



Mr. H. 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 relation;?, 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 relations. It is incredible that the descendants 

 of two organisms, which had originally differed in a marked 

 manner, should ever afterwards converge so closely as to lead to 

 a near approach to identity throughout their whole organisation. 

 If this had occurred, we should meet with the same form, inde- 

 pendently of genetic connection, recurring in widely separated 

 geological formations ; and the balance of evidence is opposed to 

 any such an admission. 



Mr. Watson has also objected that the continued action of 

 natural selection, together with divergence of character, would 

 tend to make an indefinite number of specific forms. As far as 



