METHODS AND RESULTS OF ETHNOLOGY. 243 



before they will admit the infertility of crosses 

 between two allied kinds of plants. They will 

 then, I think, be satisfied that the doctrine in ques- 

 tion rests upon a very unsafe foundation; that 

 the facts adduced in its support are capable of 

 many other interpretations; and, indeed, that from 

 the very nature of the case, demonstrative evidence 

 one way or the other is almost unattainable. 

 A priori, I should be disposed to expect a certain 

 amount of infertility between some of the extreme 

 modifications of mankind; and still more between 

 the offsprings of their intermixture. A posteriori, 

 I cannot discover any satisfactory proof that such 

 infertility exists. 



From the facts of ethnology I now turn to the 

 theories and speculations of ethnologists, which 

 have been devised to explain these facts, and to 

 furnish satisfactory answers to the inquiry — what 

 conditions have determined the existence of the 

 persistent modifications of mankind, and have 

 caused their distribution to be what it is? 



These speculations may be grouped under three 

 heads: firstly, the Monogenist hypotheses; second- 

 ly, those of the Polygenists; and thirdly, that which 

 would result from a simple application of Darwin- 

 ian principles to mankind. 



According to the Monogenists, all mankind 

 have sprung from a single pair, whose multitudi- 

 nous progeny spread themselves over the world, 

 such as it now is, and became modified into the 



