VIEWS OF CHARLES DARWIN 387 



changed conditions as they were originally. It has been shown 

 in a former part of this work, that such changes of external 

 conditions would, from their acting on the reproductive system, 

 probably cause the organization of those beings which were 

 most affected to become, as under domestication, plastic. Now, 

 can it be doubted, from the struggle each individual has to obtain 

 subsistence, that any minute variation in structure, habits, or 

 instincts, adapting that individual better to the new conditions, 

 would tell upon its vigour and health ? In the struggle it would 

 have a better chance of surviving ; and those of its offspring 

 which inherited the variation, be it ever so slight, would also 

 have a better chance. Yearly more are bred than can survive ; 

 the smallest grain in the balance, in the long run, must tell on 

 which death shall fall, and which shall survive. Let this work 

 of selection on the one hand, and death on the other, go on for 

 a thousand generations, who will pretend to affirm that it would 

 produce no effect, when we remember what, in a few years, 

 Bakewell effected in cattle, and Western in sheep, by this identical 

 principle of selection ? " 



" In nature we have some slight variation occasionally in all 

 parts ; and I think it can be shewn that changed conditions of 

 existence is the main cause of the child not exactly resembling 

 its parents; and in nature geology shews us what changes have 

 taken place, and are taking place. We have almost unlimited 

 time ; " 



" Another principle, which may be called the principle of diver- 

 gence, plays, I believe, an important part in the origin of species. 

 The same spot will support more life if occupied by very diverse 

 forms. We see this in the many generic forms in a square yard 

 of turf, and in the plants or insects on any little uniform islet, 

 belonging almost invariably to as many genera and families 

 as species. . . . Now, every organic being, by propagating so 

 rapidly, may be said to be striving its utmost to increase in 

 numbers. So it will be with the offspring of any species after it 

 has become diversified into varieties, or subspecies, or true 

 species. And it follows, I think, from the foregoing facts, that 

 the varying offspring of each species will try (only few will 

 succeed) to seize on as many and as diverse places in the 

 economy of nature as possible. Each new variety or species, 

 when formed, will generally take the place of, and thus exter- 

 minate its less well-fitted parent. This I believe to be the origin 

 of the classification and affinities of organic beings at all times ; 

 for organic beings always seem to branch and sub-branch like 

 the limbs of a tree from a common trunk, the flourishing and 



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