274 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
(2) “Separation does not necessarily imply any external barriers, or 
even the occupation of separate districts.” 
(3) Diversity of natural selection is not necessary to diversity of 
evolution. 
(4) Difference of external conditions is not necessary to diversity of 
evolution. 
(5) “Separation and variation,” that is, variation not overwhelmed 
by crossing, “is all that is necessary to secure a divergence of types in 
the descendants of one stock,” though external conditions remain the 
same, and though the separation is other than geological. 
(6) The separation of which I speak is anything, in the species or in 
the environment, that divides the species into two or more sections 
that do not freely inter-cross, whether the different sections remain in 
the original home or enter new and dissimilar environments. 
Though these propositions were very briefly and imperfectly pre- 
sented, I am not aware that any better statement of the facts of segre- 
gation had been previously published. 
The present paper is the result of a long-continued endeavor to un- 
derstand the relations in which this factor stands to natural selection 
and the other causes that co-operate in producing divergent evolution ; 
and though my work has been done under the great disadvantage of 
entire separation from libraries and from other workers in similar lines, 
I trust it may contribute something towards the elucidation of the sub- 
ject. In expanding my theory I have been unable to make any use of 
the positions taken in Moritz Wagner’s paper, as they seem to me very 
extreme and far removed from the facts of nature. The two theories 
correspond chiefly in that they discuss the relation of separation to the 
transformation of species, while the explanations given of the nature, 
causes, and effects of separation widely differ. I am informed that my 
paper on ‘“ Diversity of evolution under one set of external conditions ” 
was translated and circulated in Germany; but whether it had any 
effect in modifying Wagner’s theory I have not the means of knowing. 
I have recently discovered that the principle of segregate breeding, 
which I have found to be of such importance in the evolution of species, 
is allied to the law of segregation propounded by Spencer in his “ First 
Principles.” By direct consideration of the conditions that have been 
found necessary for the development of divergent races of domestic 
plants and animals I have discovered segregate breeding as a neces- 
sary condition for divergent evolution, and by direct observation on the 
propagation of plants and animals under natural conditions I have dis- 
covered cumulative segregation as a constant result from certain forms 
of activity in the organism when dealing with a complex environment. 
It is therefore with special pleasure that I observe thata law of very simi- 
lar import may be derived by a wholly different method from the general 
laws of action and reaction in the physical world. It should, however, 
be noticed that in the brief references made to the subject in Spencer’s 
