12 BIONOMIC LAWS. 



Further observation brings to light many cases in which separated 

 portions of a species have adopted different industrial habits, while 

 exposed to the same set of conditions, the diversity in the forms of 

 selection by which they are molded being due to the different uses 

 they have made of the same resources, and not to any difference in 

 the resources found in the different districts. 



As these facts will be presented in detail when discussing the prin- 

 ciples upon which I believe they depend, I need not dwell upon them 

 here. It is sufficient for our present purpose to show that the prob- 

 lems of divergence are not fully explained by natural and sexual 

 selection. 



5. Comparison of the Conditions to which Natural Species are Exposed 

 with the Conditions producing Domestic Varieties. 



Believing that other principles besides natural and sexual selection 

 must be effective in the production of specific differences, I propose to 

 make systematic search for them in the interactions between the 

 members of the same species and between the species and the environ- 

 ment. Following the example of Darwin and Wallace, I shall seek 

 suggestions for the guidance of my search from the experience of the 

 breeder of artificial races. In the maxims and traditions of those 

 who are engaged in raising highly prized varieties of plants and ani- 

 mals, we have the treasured results of thousands of years of experi- 

 ment in biology. In these results we shall, I think, find principles 

 that have not been fully considered in the problems of evolution. 

 This method of presenting the subject I adopt as best suited for 

 exhibiting the relations in which the different laws stand to each 

 other, but I would not wish to have anyone suppose that it represents 

 the order of the steps by which these laws were first reached and by 

 which their relations to the origin and transformation of species were 

 first recognized. The problems requiring solution were in every case 

 forced upon my attention, not by the study of domestic races, but by 

 observing the conditions under which divergence has arisen between 

 natural varieties and species. Having discovered that in nature 

 many divergencies appear in varieties and closely allied species ex- 

 posed to the same environment, and sometimes in those using the 

 environment in the same way, I concluded that natural selection 

 could not be the essential and fundamental factor in the multiplica- 

 tion of species. I then turned to the production of domestic races, 

 and found, on the one hand, that artificial selection could avail noth- 

 ing in producing divergent forms, unless it was aided by isolation, 

 and, on the other hand, that isolation, if not producing divergence 



