4 Heredity and Eugenics 



If rigid selection is necessary in presenting the recent 

 work, it must be still more rigid in sketching the historical 

 background, with its enormous literature, stretching through 

 many years. Probably no two biologists would put the 

 same details into the background, but probably all of them 

 would give the background the same general aspect; for 

 it is more of an atmosphere than detail that is needed. It 

 will be an aid to understanding and to memory if this 

 sketch is broken up into distinct topics, if it be understood 

 clearly that there are no such natural lines of cleavage in 

 the subject. 



I. THE CONCEPTION OF EVOLUTION 



Those who know of the theory of evolution only in a 

 superficial way, as a thing heard of rather than understood, 

 almost invariably associate it with some man who stands 

 to them as its author. In my own experience, I have 

 encountered a widespread conviction that Darwin is respon- 

 sible for the theory of organic evolution. The fact is that 

 the conception of evolution, both inorganic and organic, is 

 as old as our record of man's thought, and therefore no one 

 is responsible for it. It is the common property of the 

 human race. 



Howe\'er, a sharp distinction must be made between the 

 speculative stage of evolution and the observational stage. 

 The former is imaginative or philosophical, and could not 

 establish evolution as a fact; the latter is scientific, and has 

 Cttablished evolution as a fact. In a real sense, therefore, 

 organic evolution as a definite w^orking principle is compara- 

 tivel}' modern, being but little more than one hundred 

 vears old. 



