Chap. XV.J RECAPITULATION. 279 



eial weapons, or means of defence, or charges; and a 

 flight advantage will lead to victory. \ 



As 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 varie,d under do- 

 mestication. And if there has been arty variability 

 under nature, it would be an unaccountable fact if natu- 

 ral selection had not come into play. It has often been 

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

 amount of variation under nature is a si^rictly limited 

 quantity. Man, though acting on exteriial characters 

 alone and often capriciously, can produce within a short 

 period a great result by adding up mere individual dif- 

 ferences in his domestic productions; and 1 every one ad- 

 mits that species present individual differences. But, 

 besides such differences, all naturalists admit that natu- 

 ral varieties exist, which are considered sufficiently disr 

 tinct to be worthy of record in systematic v^^orks. 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 sepa- 

 rate continents, and on different parts of the same conti- 

 nent when divided by barriers of any kind, and on out- 

 lying 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, 

 though closely allied species! 



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

 slightly 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 survival of the fittest? If man can by patience 



