CHAPTER II. 



RACE. 



THE term "species" is unsatisfactory, es- 

 pecially in discussing the problems of 

 evolution. 



" Species" is a purely artificial distinction, 

 and has no definite significance. It has 

 been said by some authorities that species 

 is determined by practical experience and 

 common-sense. 



While, therefore, species may serve for pur- 

 poses of classification, its meaning in discuss- 

 ing the origin of species is too indefinite. 



According to Quatrefages, a species in- 

 cludes all more or less similar individuals 

 which descend, or can be supposed to de- 

 scend, from a single ancestral pair in un- 

 broken succession. But many species include 

 varieties that permanently differ from each 

 other, but not, in the opinion of naturalists, 

 sufficiently to constitute a distinct species. 

 The difference necessary to constitute a 



