124 
DARWINISM 
CHAP. 
characters of a species—and so few even among naturalists 
have ever compared, accurately, considerable numbers of 
individuals, that the conception of variability as a general 
characteristic of all dominant and widespread species, large in 
its amount and affecting, not a few, but considerable masses of 
the individuals which make up the species, will be to many 
entirely new. Equally important is the fact that the vari¬ 
ability extends to every organ and every structure, external 
and internal; while perhaps most important of all is the 
independent variability of these several parts, each one vary¬ 
ing without any constant or even usual dependence on, or 
correlation with, other parts. No doubt there is some such 
correlation in the differences that exist between species and 
species—more developed wings usually accompanying smaller 
feet and vice versa —but this is, generally, a useful adaptation 
which has been brought about by natural selection, and does 
not apply to the individual variability which occurs within 
the species. 
It is because these facts of variation are so important and 
so little understood, that they have been discussed in what 
will seem to some readers wearisome and unnecessary detail. 
Many naturalists, however, will hold that even more evidence 
is required; and more, to almost any amount, could easily 
have been given. The character and variety of that already 
adduced will, however, I trust, convince most readers that 
the facts are as stated ; while they have been drawn from 
a sufficiently wide area to indicate a general principle through¬ 
out nature. 
If, now, we fully realise these facts of variation, along with 
those of rapid multiplication and the struggle for existence, 
most of the difficulties in the way of comprehending how species 
have originated through natural selection will disappear. For 
whenever, through changes of climate, or of altitude, or of 
the nature of the soil, or of the area of the country, any 
species are exposed to new dangers, and have to maintain 
themselves and provide for the safety of their offspring under 
new and more arduous conditions, then, in the variability of 
all parts, organs, and structures, no less than of habits and 
intelligence, we have the means of producing modifications 
which will certainly bring the species into harmony with its 
