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 
