Darzmn's Selection Theory. 29 



on the foundations laid by Darwin. This is especially 

 true of the theory of selection, which now has served its 

 time as an argument for the theory of Descent; happily 

 this theory no longer stands in need of such support. 

 We are now concerned to bring the origin of species into 

 the field of experimental investigation. The position 

 of the theory of Descent as a comparative science is com- 

 pletely assured by the results Darwin obtained ; but as 

 an experimental science it has made feeble progress.^ 



The cause of this lies in my opinion not so much in 

 the difficulties of the investigation as in the lack of 

 definiteness of this part of the theory. In the systematic 

 sphere the discoveries could have been predicted ; this 

 was far from being the case on the physiological side. 



Darwin was never quite clear about the physiolog- 

 ical part of the theory of Selection. It seems to me 

 that he always inclined first in one direction and then 

 in another, never fully deciding between the two views. 

 In his earlier works especially, he treated spontaneous 

 variations (single variations) as the material afforded 

 for natural selection whilst in his later works, in con- 

 sequence of the objections of his critics he gave greater 

 prominence to the part played by individual variation in 

 the production of new species. But he never sharply dis- 

 criminated between these two processes. Moreover, such 

 a discrimination was not in the interests of his main ob- 

 ject. It would have led him to many difficult points whose 

 solution was not necessary to the theory of descent, and 

 would have diverted attention too much from the main 

 point at issue. 



As we have seen in the foregoing section, the 



* See also Bateson^ Materials for the Study of Variation, pp. 7 

 and II. 



