RECAPITULATION. 485 



of the females. The most vigorous males, or those which 

 have most successfully struggled with their conditions of 

 life, will generally leave most progeny. But success will 

 often depend on the males having special weapons or means 

 of defense or charms ; and a slight advantage will lead 

 to victory. 



As geology plainly proclaims that each land has under- 

 gone great physical changes, we might have expected 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 play. 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 differ- 

 ences. But, beside such differences, all naturalists admit 

 that natural varieties exist, which are considered 

 sufBciently distin'ct 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 subspecies and species. On 

 separate continents, and on different parts of the same con- 

 tinent, 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 geo- 

 graphical races or subspecies, 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 individual 

 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 select variations useful 

 to him, why, under changing and complex conditions of 

 life, should not variations useful to nature's living products 

 often arise, and be preserved or selected? What limit can 

 be put to this power, acting during long ages and rigidly 

 scrutinizing the whole constitution, structure and habits 

 of each creature, favoring the good and rejecting the bad? 



