124 DARWINISM 



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 



