24 THE PROBLEMS OF EVOLUTION 



emphasizing environment and the other heritage 

 in the evolution of species. But since Darwin, in 

 his assumption that characters must be useful or 

 harmful in order to have evolutionary value, recog- 

 nized environmental relationships, and since La- 

 marck, in that he regarded environment as influ- 

 encing the animal through its nervous system, 

 recognized the activity of the heritage, I have 

 never yet been able to find the fundamental disa- 

 greement in their views. However, there are differ- 

 ences, and the work of neither man is above criti- 

 cism, so they may well continue to stand as the 

 exponents of the opposed schools. 



A more promising approach by far seems the 

 inquiry, first of all, into the nature of species and 

 individuals, their association, and the relationship 

 in each of heritage and environment. The possi- 

 bility of change, both in individuals and in species, 

 then engages our attention. Sources of change, 

 methods by which it is brought about, the nature 

 of change in organisms in relation both to organ- 

 ism and to environment, are all pertinent to our 

 problem. When once these things are disposed in 

 an orderly manner we have a sound basis for the 

 consideration of the various theories of evolution 

 already proposed and for inquiry into the nature 

 of evolutionary processes from the point of view 

 adopted in this work. As I have already said, I 

 do not regard it as a final solution, but I feel that 



