GENERAL SUMMARS. 603 



about the causes of such occasional modifications, especially 

 through the study of monstrosities: hence the labors of experi- 

 mentalists, such as those of M. Camille Dareste, are full ot 

 pi-omise for the future. In general we can only say that the 

 cause of each slight variation and of each monstrosity lies much 

 more in the constitution of the organism, than in the nature of 

 the surrounding conditions; though new and changed conditions 

 certainly play an important part in exciting organic changes of 

 many 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 diverged 

 into distinct races, or as they may be more fitly called, sub- 

 species. Some of these, such as the Negro and European, are 

 so distinct that, if specimens had been brought to a naturalist 

 without any further information, they would undoubtedly 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 by inheritance from a common progenitor; and a pro- 

 genitor thus characterized would probably deserve to rank as man. 



It must not be supposed that the divergence of each race from 

 the other races, and of all 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 better fitted for their conditions of life, though 

 in different degrees, would have survived in greater numbers 

 than the less well-fitted. The process would have been like that 

 followed by man, when he does not intentionally select particular 

 individuals, but breeds from all the superior individuals, and 

 neglects the inferior. He thus slowly but surely modifies his 

 stock, and unconsciously forms a new strain. So with respect 

 to modifications acquired independently of selection, and due 

 to variations arising from the nature of the organism and the 

 action of the surrounding conditions, or from changed habits ot: 

 life, no single pair will have been modified much more than the 

 other pairs inhabiting the same country, for all will have been 

 continually blended through free intercrossing. 



By considering the embryological structure of man, — the homo- 

 logies which he presents with the lower animals, — the rudi- 

 ments which he retains, — and the reversions to which he is liable, 

 we can partly recall in imagination the former condition of our 

 early progenitors; and can approximately place them in their 

 proper place in the zoological series. We thus learn that man ia 

 descended from a hairy, tailed quadruped, probably arboreal In 

 its habits, and an inhabitant of the Old World. This creature, 

 if its whole structure had been examined by a naturalist, would 



