Chap. XV.] EECAPITULATION-. 279 



weapons, or means of defence, or charms ; and a slight 

 advantage will lead to victory. 

 VKs geology plainly proclaims that each land has 

 undergone great physical changes, we might have ex- 

 pected to find that organic beings have varied under 

 nature, in the same way as they have varied under 

 domestication. And if there has been any variability 

 under nature, it would be an unaccountable fact if natural 

 selection had not come into playj It has often been 

 asserted, but the assertion is incapable of proof, that the 

 amount of variation under nature is a strictly limited 

 quantity. Man, though acting on external characters 

 alone and often capriciously, can produce within a short 

 period a great result by adding up mere individual 

 differences in his domestic productions ; and every one 

 admits that species present individual differences. But, 

 besides such differences, all naturalists admit that natural 

 varieties exist, which are considered sufficiently distinct 

 to be worthy of record in systematic works. No one 

 has drawn any clear distinction between individual 

 differences and slight varieties ; or between more plainly 

 marked varieties and sub-species, and species. On 

 separate continents, and on different parts of the same 

 continent when divided by barriers of any kind, and on 

 outlying islands, what a multitude of forms exist, which 

 some experienced naturalists rank as varieties, others as 

 geographical races or sub-species, and others as distinct, 

 tliQugh closely allied species ! 



If then, animals and plants do vary, let it be ever so 

 snglitly or slowly, why should not variations or indi- 

 vidual differences, which are in any way beneficial, be 

 preserved and accumulated through natural selection, or 

 the siu'vival of the fittest ? If man can by patience 



