GENERAL SUMMARY AND CONCLUSION. (595 



logical importance, some indeed of considerable importance, 

 have been gained through sexual selection. 



No doubt man, as well as every other animal, presents 

 structures, which seem to our limited knowledge, not to be 

 now of any service to him, nor to have been so formerly, 

 either for the general conditions of life, or in the relations 

 of one sex to the other. Such structures cannot be 

 accounted for by any form of selection, or by the inherited 

 effects of the use and disuse of parts. We know, however, 

 that many strange and strongly marked peculiarities of 

 structure occasionally appear in our domesticated produc- 

 tions, and if their unknown causes were to act more uni- 

 formly, they would probably become common to all the 

 individuals of the species. We may hope hereafter to 

 understand something about the causes of such occasional 

 modifications, especially through the study of monstrosities; 

 hence, the labors of experimentalists, such as those of M. 

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

 general we can only say that the cause of each slight varia- 

 tion and of each monstrosity lies much more in the con- 

 stitution of the organism than in the nature of the sur- 

 rounding 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 lias been raised to his 

 present state. But since he attained to the rank of man- 

 hood, 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 in- 

 formation, they would undoubtedly have been considered 

 by him as good and true species. Nevertheless, all the 

 races agree in so many unimportant Setails of structure and 

 in so many mental peculiarities that these can be ac- 

 counted for only by inheritance from a common progenitor; 

 and a progenitor thus characterized would probably deserve 

 to rank as man. 



It must not be supposed that the divergence of each raco 

 from the other races and of all from a common stock can 

 be traced back to any one pair of progenitors. On the con- 

 trary, at every stage in the process of modification, all the 

 individuals which were in any way better fitted for their 



