292 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
a degree that the species falls into two or more sections, between which 
crossing is interrupted, without its being interrupted within the bounds 
of each section. And all that is necessary to produce segregation is 
that to separation should be added some cause that secures difference 
of character in the different sections. And as separation long contin- 
ued inevitably ends in segregation through the development of differ- 
ence of character in the different sections, we need not in our classifi- 
sation set them wholly apart, though for the sake of clearly recogniz- 
ing the difference it will be well to note in each class of causes whether 
the primary effect is separation or segregation. 
CUMULATIVE SEGREGATION AND THE CLASSIFICATION OF ITS DIF- 
FERENT FORMS. 
The fundamental law to which I would call attention may be expressed 
in the following formula: Cumulative segregation produces accumulated 
divergence and accumulated divergence produces permanent segrega- 
tion, and the segregate subdivision of those permanently segregated 
produces the divisions and subdivisions of organic phyla. If then we 
san discover the causes of segregation, we Shall understand the causes 
of a wide range of phenomena, for this is the fundamental principle in 
the formation of varieties, species, genera, families, orders, and all 
ereater divergences that have been produced in the descendants of 
common ancestry. 
In treating of the causes of segregation I have found it convenient 
to make two distinct classifications. In the one the fundamental dis- 
tinction is between segregation produced by the purpose of man, which 
I call rational segregation in its two forms, artificial segregation, insti- 
tutional segregation, and that produced by nature outside of man, 
which I eall responsive segregation; while any of these forms of segre- 
gation may be intensified by independent transformation through the 
principles of diversity of selection, diversity of use, or diversity of 
direct effects of the environment; and the combined action of segrega- 
tion with these and other principles of transformation I call intensive 
segregation. 
In the other classification the fundamental distinction is between 
segregation arising from the relations in which the organism stands to 
the environment, which I call environal segregation, and segregation 
arising from the relations in which the members of the same species 
stand to each other, which I call reflexive segregation; while any form 
of segregation belonging to either of these classes may be enhanced by 
one or more of the forms of intension, and thus present what I call in- 
sive segregation. 
THE EFFECTS OF SEGREGATION. 
The effects of segregation can be studied to advantage in the vast 
experience that has been accumulated in the domestication of plants 
and animals. ; 
