No. 602] THE SELECTION PROBLEM 



to which the whole of this paper has been leading, and 

 which one may hope will be heartily concurred in by both 

 sides in the selection controversy, that the great outstand- 

 ing need in research on the problem of evolution in gen- 

 eral, and of selection in particular, is more, and more 

 searching, investigations as to the causes of genetic {fac- 

 torial) variation. That both sides realize this need, and 

 are all the time bending more and more energies to its 

 selection, is indeed cause for congratulation and augurs 

 well for the future of that branch of biological science in 

 which America has taken a leading place. 



