SPECIES AND RACE. 33 



cacy proved an important, but not a decisive mark of distinc- 

 tion between species and race, and could only be considered as 

 a probable sequence. 



Finally, reversion and its allied phenomena appeared insuffi- 

 cient to furnish an undoubted criterion of species and race. 

 And as it became apparent that such a criterion could not be 

 established, we hoped that the defect would be supplied by the 

 conclusions of analogy furnished by the comparison of various 

 species. This expectation was also doomed to disappointment, 

 as the limits of variation in different types seem to be of a greatly 

 diversified extent. The result, therefore, of our investigation 

 (which is scarcely surprising in an entirely empirical subject), 

 is this : that the general question as regards a decided mark of 

 distinction between race and species can only be answered by 

 the particular study of the extent of variation in individual 

 types ; that is to say, that in every question of unity or differ- 

 ence of species we are referred entirely to the study of the 

 individual phenomena themselves. 



The investigation of the unity of mankind as a species can 

 only be finally completed, when the results of long continued in- 

 fluences of all possible external conditions in which man is able 

 to live, are as fully and clearly ascertained, as the results of 

 all possible crossings of various human types after a long series 

 of generations. But as our experience in this respect is very 

 far from being perfect, we are compelled to stop at some more 

 or less probable propositions, which must proceed from the 

 solution of the question, whether a gradual alteration of types 

 belonging to the same stock can be proved, and whether it be 

 sufficiently extensive in order to show that the greatest differ- 

 ences prevailing among mankind are merely variations. Next to 

 that the question will be, whether the cross-breeds of the various 

 types" by limited prolificacy, or by constant reversion to the 

 parent type, resemble more the hybrids or mongrels of different 

 races. 



