Chap. VII. THE KACES OF MAN. 231 



would be extremely rash in most cases to attribute to 

 convergence close similarity in many points of struc- 

 ture in beings which had once been widely different. 

 The form 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, and this depends on the surrounding physical 

 conditions, and in a still higher degree on the sur- 

 rounding organisms with which each 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 appears utterly incredible 

 that two organisms, if differing in a marked manner, 

 should ever afterwards converge so closely as to lead 

 to a near approach to identity throughout their whole 

 organisation. In the case of the convergent races of pigs 

 above referred to, evidence of their descent from two pri- 

 mitive stocks is still plainly retained, according to Von 

 Nathusius, in certain bones of their skulls. If the races 

 of man were descended, as supposed by some naturalists, 

 from two or more distinct species, which had differed as 

 much, or nearly as much, from each other, as the orang 

 differs from the gorilla, it can hardly be doubted that 

 marked differences in the structure of certain bones would 

 still have been discoverable in man as he now exists. 



Although the existing races of man differ in many 

 respects, as in colour, hair, shape of skull, proportions 

 of the body, &c, yet if their whole organisation be taken 



