DIVERGENT EVOLUTION THROUGH SEGREGATION. mA AF 
The first of these differences, though of considerable importance, is 
I think due to the method of presentation rather than to any funda- 
mental discrepancy in the theories. The positive forms of segregation 
are I judge assumed to be present, though their co-operation is not 
distinctly recognized as a necessary condition for the breeding of forms 
that are mutually sterile. 
I must, however, confess that Ido not see how to reconcile his state- 
ment that “ Physiological selection can never have had anything at all 
to do with the formation of families, orders, or classes” with what I 
believe to be the facts concerning Segregate Fecundity; and if physio- 
logical selection is to be understood as ineluding Seasonal and perhaps 
other forms of Segregation, this passage seems to be still more opposed 
to the principles of divergent evolution as I understand them. He cer- 
tainly could not have intended to say that mutual fertility between 
allied genera not otherwise segregated would not have stood in the 
way of their becoming different families, and that, therefore, mutual 
sterility has had nothing to do with their continued divergence; still 
he seems to have failed to perceive the important influence this prin- 
ciple must have had on the divergent evolution of the higher groups of 
organisms. 
The correspondences in the two papers are, notwithstanding, more 
remarkable than the ditferences. Of these, the most conspicuous is the 
use of the word segregation to express the principle under considera- 
tion.* As I have already pointed out, [ used this word for the same 
purpose in an article in the Chrysanthemum, published in January, 
1883; and again in the Chinese Recorder tor July, 1855, where I spoke 
of the “law of segregation rising out of the very nature of organic 
activities, bringing together those similarly endowed,” and causing ‘the 
division of the survivors of one stock, occupying one country, into forms 
differing more and more widely from each other.” 
I trust that my discussion of the various forms of segregation, both 
negative and positive, though presented in so condensed a form, will 
throw light on the subject of the mutual sterility of species; and that 
in other ways my presentation of the subject will contribute something, 
not only to the theory of physiological segregation but to other branches 
of the general theory of evolution. 
I should here acknowledge (what will, 1 think, be manifest on every 
page of my paper) that my obligations to Darwin and Wallace are far 
greater than are indicated by quotations and references. 
I very much regret that [have failed of obtaining a copy of “ Evolu- 
tion without Natural Selection,” by Charles Dixon; but, from his letter 
in Nature, vol. Xxx, p. 100, I see that he maintains “ That isolation 
can preserve a non-beneficial variation as effectually as natural selection 
can preserve a beneficial variation.” He does not there refer to the fact, 
*See paper on “ Physiolgical Selection,” Linn. Soc. Journ. Zodlogy, vol. XIX, pp. 
354, 356, 391, 395. 
