Inconsistencies of Utilitarianism. 135 
(p. 174); but his reasoning does not seem to me conclusive. 
Even if we grant that the increase of this character occurs by 
the steps which he describes, it is not a process of accumula- 
tion by natural selection. In order to be a means of cumula- 
tive modification of varieties, races, or species, selection, whether 
artificial or adaptational, must preserve certain forms of ail 
intergenerating stock, to the exclusion of other forms of the 
same stock. Progressive change in the size of the occupants 
of a poultry -yard may be secured by raising only bantams the 
first, only common fowls the second, and only Shanghai fowls 
the third year : but this is not the form of selection that has 
produced the different races of fowls. So in nature rats may 
drive out and supplant mice ; but this kind of selection 
modifies neither rats nor mice. On the other hand, if certain 
variations of mice prevail over others through their superior 
success in escaping their pursuers, then modification begins. 
Now, turning to p. 175, we find that in the illustrative case 
introduced by Mr. Wallace the commencement of infertility 
between the incipient species is in relations to each other of 
two portions of a species that are locally segregated from the 
rest of the species, and partially segregated from each other 
by different modes of life. These two local varieties, by the 
terms of his supposition, being better adapted to the environ- 
ment than the freely interbreeding forms in other parts of the 
general area, increase till they supplant these original forms. 
Then, in some limited portion of the general area, there arise 
two still more divergent forms, with greater mutual infertility 
and with increased adaptation to the environment, enabling 
them to prevail throughout the whole area. The process here 
described, if it takes place, is not modification by natural 
selection. The natural selection of which he speaks does not 
arise till, with each advancing step, a new and complicated 
adjustment (which introduces the two new forms, each with 
unabated fertility with its own kind, but with diminished 
fertility with the other kind) has been attained by some other 
process. That other process is the one described in the passage 
I have already quoted from pp. 184-185, where, according to 
my apprehension, the cause of divergence is more correctly 
stated than it is in the passage now under consideration. In 
the latter part of my paper on u Divergent Evolution through 
Cumulative Segregation ” I have shown that the different 
kinds of incompatibility, preventing complete fertility between 
incipient species (and there called forms of Negative Segre- 
gation), cannot arise except as accompaniments of Positive 
Segregation in some form ; but that, having once arisen in 
connexion with partial Positive Segregation, they increase 
