THEORIES OF EVOLUTION 129 



mutants as new species. Others have suggested the 

 availabihty of mutations of large or small degree 

 as materials for selection, leading ultimately to the 

 production of new species. Here we must be sure 

 of our definition of species, but on the basis of 

 definite departure from the condition of a previous 

 heritage we may recognize both possibilities. Ob- 

 served mutations have failed to provide us with 

 new species, but it may be that our knowledge of 

 their origin influences unfavorably our judgment 

 of their rank. 



Lotsy ^° has attempted an explanation of the 

 origin of species on the basis of hybridization. His 

 theory has been given very full expression and we 

 must admit that hybridization provides a means 

 of securing reassortments of characters beyond the 

 results of selection and that it is effective in con- 

 nection with mutations. Lotsy 's species, however, 

 is the pure line of other scientists, and when we 

 extend his idea to include the type of change which 

 evolutionists usually seek to explain we encounter 

 the intricacies of hybridization among natural 

 species — the linneons of Lotsy — which show at 

 once that the process is too limited to be an expla- 

 nation in itself of species formation in the ordinary 

 sense. The idea also encounters difficulty when 

 we inquire into the source of the parent stocks, 

 for unless we base it upon a polyphyletic scheme 



^° Evolution by Means of Hybridization, 1916. 



