DIVERGENT EVOLUTION THROUGH SEGREGATION. 295 
will tend to distribute the species over the whole area; and if the ayail- 
able resources in the different districts are considerably diverse, the 
overflow of population from the crowded district will be subjected to 
a necessary change of habits; and thus, through competition, there 
will be the disruption of old relations to the environment, and the 
bringing in of conditions that give the highest efficiency and the full- 
est opportunity to all the activities that produce segregation. In the 
vase of animals, no condition can tend more strongly to produce migra- 
tion than searcity of food in the old habitat; and in the case of both 
plants and animals, a great increase in the numbers that are exposed 
to the winds, currents, and other transporting influences of the envi- 
ronment increases the probability that individuals will be carried to 
new districts where circumstances will allow of their multiplying, and 
where they will, at the same time, be prevented from crossing with the 
original stock. In many cases the segregation thus brought about 
will be in districts where the environment is the same, and in other 
cases the pressure for food or other resources will lead portions of the 
species to take up new habits in the effort to appropriate resources not 
previously used; and through these new habits they will often be seg- 
regated from those maintaining the original habits. I shall hereafter 
show that in both these cases there is a tendency to divergent evolu- 
tion. 
I at one time thought of describing this principle as a form of segre- 
gation, calling it dominational segregation; but fuller reflection convinces 
me that the domination of the strong over the weak is not a form of 
segregation, but rather a cause that prepares the way for segregation, 
by forcing portions of the community out of their inherited relations to 
the environment. 
CHAPTER ITI. 
DESCRIPTION AND CLASSIFICATION OF THE CAUSES OF CUMULATIVE 
SEGREGATION.* 
A. ENVIRONAL SEGREGATION. 
Environal segregation is segregation arising from the relations in 
which the organism stands to the environment. 
It includes four classes, which I call industrial, chronal, spatial, and 
artificial segregation.t 
(a) Industrial segregation. 
is segregation arising from the activities by which the organism pro- 
tects itself against adverse intluences in the environment, or by which 
it finds and appropriates special resources in the environment. 
“In the following chapters numerals are attached to what I consider separate 
causes of segregation independent of human purpose. 
t Francis Galton has suggested another class, which might appropriately be called 
fertilizational segregation, 
