Chap. IV.] CONVEEGENCE OF CHAEACTEE. 157 



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 surround- 

 ing 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 through- 

 out their whole organisation. If this had occurred, we 

 should meet with the same form, independently of 

 genetic connection, recurring in widely separated geo- 

 logical 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 mere inorganic conditions are con- 

 cerned, it seems probable that a sufficient number of 

 species would soon become adapted to all considerable 

 diversities of heat, moisture, &c. ; but I fully admit that 

 the mutual relations of organic beings are more im- 

 portant ; and as the number of species in any country 

 goes on increasing, the organic conditions of life must 

 become more and nore complex. Consequently there 



