100 CONVERGENCE OF CHARACTER. [Chap. IV. 



development. In some few cases there has br.en what we must call 

 retrogression of organisation. But the main cause lies in the fact 

 that under very simple conditions of life a high organisation would 

 he of no service, — possibly would be of actual disservice, as being 

 of a mere delicate nature, and more liable to be put out of order 

 and injured. 



Looking to the first dawn of life, when all organic beings, as we 

 may believe, presented the simplest structure, how, it has been 

 asked, could the first steps 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 relations to inci- 

 dent forces become different" would corne into action. But as we 

 have no facts to guide us, speculation on the subject is almost useless. 

 It is, however, an error to suppose that there would be no struggle 

 for existence, and, consequently, no natural selection, until ma^r 

 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 igno- 

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

 present time, and still more so during past ages. 



Convergence of Character. 



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 diver- 

 gent 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 con- 

 verge into one. But it would in most cases be extremely rash to attri- 

 bute 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 



