THEORY OF EVOLUTION 85 



are unnatural instruments used to torture Na- 

 ture's secrets from her. I venture to think that 

 the real antithesis is not between unnatural 

 and natural treatment of Nature, but rather 

 between controlled or verifiable data on the one 

 hand, and unrestrained generalization on the 

 other. 



If a systematist were asked whether these 

 new races of Drosophila are comparable to 

 wild species, he would not hesitate for a mo- 

 ment. He would call them all one species. If 

 he were asked why, he would say, I think, 

 "These races differ only in one or two striking 

 points, while in a hundred other respects they 

 are identical even to the minutest details." He 

 would add, that as large a group of wild spe- 

 cies of flies would show on the whole the reverse 

 relations, viz., they would differ in nearly every 

 detail and be identical in only a few points. 

 In all this I entirely agree with the systematist, 

 for I do not think such a group of types dif- 

 fering by one character each, is comparable to 

 most wild groups of species because the differ- 

 ence between wild species is due to a large num- 

 ber of such single differences. The characters 



