18 EVOLUTIONS OF ORGANIZATION. 
factor in extinction of species, but it was left for 
Darwin to originate the idea that it could do what 
Owen recognized as due to innate causes, viz., that 
it could produce variety and advance by the con- 
tinual survival in the contest of the “fittest,” z. e. 
of those which by accidental variations of structure 
had in the struggle an advantage over their neigh- 
bours. The struggle exists, beyond all question ; 
and few can read Darwin’s works without being 
impressed with the likelihood of its resulting during 
long periods in an indefinite amount of. variety. 
Yet, even as to this, it may be remarked that there 
is a tacit assumption in the theory, that individuals 
surviving by slight variations of different kinds 
would be separated one from the other, so as not 
to mix the different peculiarities to which they 
severally owed their survival; and it may be ob- 
jected that such separation would be unlikely so 
long as the variations were yet exceedingly slight ; 
while it may be judged probable from Mr. Darwin’s 
own researches that individuals with slight consan- 
guinity and differing minutely one from the other, 
but not too greatly, would be exactly those which 
would be most prolific and so give rise to a mixing 
of incipiently diverging characters. 
The more important criticism can in no way be 
eluded that the doctrine of natural selection has 
