NATURAL HISTORY OF MAN. 4S3 



we must limit ourselves to the reasons which best explain and 

 vindicate the conclusions obtained. 



The question naturally first occurs and it is a question 

 which becomes an argument in itself If Man be not a 

 single species, how many species of the human being must 

 we count on the earth? The Negro is the most striking 

 contrast to the European ; but the beardless yellow Mon- 

 golian also has characteristics so strongly marked, that we 

 cannot concede the difference of species in the one case 

 without admitting it in the other. How, or where, are we 

 to stop in these admissions, when we find diversities similar 

 in kind, and different only in degree, existing everywhere 

 around us ; and marking those divisions into races, of which 

 many have retained the same distinctive characters from 

 the earliest periods of history? This question is further 

 perplexed by the intermixture of races and varieties ; 

 rendering it difficult, if not impossible, to define any 

 such primitive separation of origin as the phrase of different 

 species implies. Multiplicity then in this case becomes 

 itself an argument for unity. No lines of demarcation are 

 found sufficiently strong to render the plurality of species 

 natural or probable. Every such line is crossed by others 

 which, while effacing its distinctness, do all point to a 

 certain common origin expressing in this what we believe 

 to be the unity of the species over the earth. 



This manner of putting the argument however, though 

 strong, is obviously not conclusive. It is rendered much 

 more forcible by a regard in detail to those conditions which 

 may fitly be considered as showing the identity or diversity 

 of species; and further, by analogies derived from the 

 variations of species in other parts of the animal creation. 

 From these two sources, concurring in their evidence, we 

 derive conclusions as certain as can be had in those parts of 

 natural science where the proof is presumptive only. 



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