388 GENEEAL SUMMARY Part II. 



fications, especially tlirougli the study of monstrosities : 

 hence the labours of experimentalists, such as those of 

 M. Camille Dareste, are full of promise for the future. 

 In the greater number of cases we can only say that the 

 cause of each slight variation and of each monstrosity 

 lies much more in the nature or constitution of the 

 organism, than in the nature of the surrounding con- 

 ditions ; though new and changed conditions ceitainly 

 play an important part in exciting organic changes of 

 all kinds. 



Through the means just specified, aided perhaps by 

 others as yet undiscovered, man has been raised to his 

 present state. But since he attained to the rank of 

 manhood, he has diverge;! into distinct races, or as they 

 may be more appropriately called sub-species. Some 

 of these, for instance the Negro and European, are so 

 distinct that, if specimens had been brought to a natu- 

 ralist without any further information, they w^ould un- 

 doubtedly have been considered by him as good and 

 true species. Nevertheless all the races agree in so 

 many unimportant details of structure and in so many 

 mental peculiarities, that these can be accounted for 

 only through inheritance from a common progenitor ; 

 and a progenitor thus characterised would probably 

 have deserved to rank as man. 



It must not be supposed that the divergence of 

 each race from the other races, and of all the races 

 from a common stock, can be traced back to any one 

 pair of progenitors. On the contrary, at every stage 

 in the process of modification, all the individuals which 

 were in any way best fitted for their conditions of life, 

 though in different degrees, would have survived in 

 greater numbers than the less well fitted. The pro- 

 cess w^ould have been like that followed by man, when 

 he does not intentionally select particular individuals, 



