128 Evolution and Adaptation 
“Mere chance, as we may call it, might cause one variety 
to differ in some character from its parents, and the off- 
spring of this variety again to differ from its parent in the 
very same character and in a greater degree; but this alone 
would never account for so habitual and large a degree of 
difference as that between the species of the same genus. 
As has always been my practice, I have sought light on this 
head from our domestic productions.” 
Then, after pointing out that under domestication two 
different races, the race-horse and the dray-horse, for in- 
stance, might arise by selecting different sorts of variations, 
Darwin inquires : — : 
“But how, it may be asked, can any analogous principle 
apply in nature? I believe it can and does apply most 
efficiently (though it was a long time before I saw how), from 
the simple circumstance that the more diversified the descen- 
dants from any one species become in structure, constitution, 
and habits, by so much will they be better enabled to seize 
on many and widely diversified places in the polity of nature, 
and so be enabled to increase in numbers.” 
Here we touch on one of the fundamental principles of the 
doctrine of evolution. It is intimated that the new form of 
animal or plant first appears (without regard to any kind of 
selection), and then finds that place in nature where it can 
remain in existence and propagate its kind. Darwin refers 
here, of course, only to the less extensive variations, the in- 
dividual or fluctuating kind; but as we shall discuss at greater 
length in another place, this same process, if extended to 
other kinds of variation, may give us an explanation of evolu- 
tion without competition, or selection, or destruction of the 
individuals of the same kind taking place at all. 
