THE 



AMERICAN NATURALIST 



Vol. LI. October, 1917 No. 610 



THE MUTATION THEORY AND TllK SPECIES- 

 CONCEPT^ 



R. R. GATES 



I?r the early days of natural history, when the concep- 

 tions of special creation held sway, it was supposed that 

 any one could determine species who was capable of ob- 

 serving the differences between existing forms. Linnaeus 

 crystallized this sentiment into the dictum that there are 

 as many species as were created in the beginning, imply- 

 ing that any one with sufficient powers of discrimination 

 could determine exactly how many species there were in 

 each group. But with the introduction of the theory of 

 evolution, species came to be viewed more and more as 

 d\Tiamic entities, and questions of origin have entered 

 progro^-^iv.'ly into tlie ^])('('i(^-c()iuv]>t. The latter has 

 grown contiiiunllN- iiiorc coiii] ilrx. nm] yet Darwin's an- 

 ticii)ati(«ii that -\ -icmnti-l- would cca-c' to discuss how 

 many ]\ul)i tliere wern^ in Jiritaiii or liow many Crataegi 

 in Nortli America, has not been realized. 



On the contrary, with tills increase in the complexity of 

 the conception of species, the extreme views as to what 

 constitutes a species have become more and more di- 

 vergent, until the "lumpers" and "splitters" among sys- 

 tematists usually differ radically in their interpretation 

 of the species in a given genus. This diversity of opinion 

 among systematists has been partly a direct result of our 

 increasing knowledge of the coDi])lexity of species, de- 



