Origin of Species, p. 169. 
3 26 
of the herd prevents that survival of the swiftest only, 
which the theory requires. 
But we will assume that from some cause or other one 
or more groups of variants have arisen in connection with 
a given species. It does not follow that Natural Selection 
will necessarily interfere. For it is quite conceivable that 
variant groups may arise which do not differ in any vital 
point from the parent species. One may have as good 
a chance of living as the other, and Natural Selection 
would then not come upon the scene. On the other hand, 
unfavourable variations, even in their incipient stages, 
would be suppressed by Natural Selection, if it were a law 
of nature, so that the co-existence of variants with 
parental forms cannot be accounted for by the action of 
Natural Selection. 
Again, it is quite possible, when there is sufficient room, 
that variants might segregate themselves, or adopt different 
habits, or migrate to a distance, so as not to compete 
with the parent form. Mr. Darwin admits that, “ If both 
have become fitted for slightly different habits of life or 
conditions, they might live togetherA good illustration 
of this point is to be found in the Uria lacrymans :— 
“ In various parts of the Northern seas a remarkable variety of the 
common Guillemot (Uria troile) is found ; and in Faroe one out of every 
five birds, according to Graba’s estimation, presents this variation. 
It is characterised by a pure white ring round the eye, with a curved 
narrow white line, an inch and a half in length, extending back from 
the ring. This conspicuous character has caused the bird to be 
ranked by several ornithologists as a distinct species under the name 
of U. lacrymans, but it is now known to be merely a variety. . . . 
We thus see that two distinct forms of the same species may co-exist 
in the same district.”—(Descent of Man. p. 424I) 
But, for the sake of argument, we will assume that there 
is a struggle for existence between a group of variants and