220 bey. j. t. gulick on divebgext eyolution 
find that the different branches are liable to be again subjected 
to segregative influences, by which each branch is subdivided, 
and in time differentiated into divergent forms that are not liable 
to intercross in a state of nature. 
Xow, as we have just pointed out, we know, from the funda- 
mental laws of the organic world, that Cumulative Segregation 
of this kind must produce Cumulative Divergence of Types. 
The Segregation that results from the natural causes enume- 
rated in this paper is cumulative in two respects. In the first 
place, every new form of segregation that now appears depends 
on, and is superimposed upon, forms of Segregation that have 
been previously induced ; for when Xegative Segregation arises, 
and the varieties of a species become less and less fertile with 
each other, the complete infertility that has existed between them 
and some other species does not disappear, nor does the Positive 
Segregation (that is, the prevention of the consortiug of the 
species characterized by this mutual incapacity) cease. The 
means by which the males and females of one species find each 
other are not abrogated when the species falls into segregated 
varieties. In the second place, whenever Segregation is directly 
produced by some quality of the organism, variations that possess 
the endowment in a superior degree will have a larger share in 
producing the segregated forms of the next generation, and 
accordingly the Segregative endowment of the next generation 
will be greater than that of the present generation : and so with 
each successive generation the segregation will become in- 
creasingly complete. 
The principle of Cumulative Segregation, first in its inde- 
pendent action, and still further when combined with the differ- 
ent principles by which the divergence of the segregated branches 
is intensified, gives a formal explanation of the ever-expanding 
diversities of the organic world. It shows how varieties arise 
and pass into species,' how species pass into genera, genera into 
families, families into orders, and orders into classes and the 
higher divisions, as far as evolution by descent extends. It 
briugs to light the dependence of this whole process on the 
influences that produce segregation : and shows how these 
influences, added to Variation, Heredity, and the other acknow- 
ledged powers residing in organisms, must piroduce the phe- 
nomena of divergent evolution. 
