508 ORIGIN OF SPECIES 



ing any season, over those with which they come into com- 

 petition, or better adaptation in however slight a degree to 

 the surrounding physical conditions, will, in the long run, 

 turn the balance. 



With animals having separated sexes, there will be in most 

 cases a struggle between the males for the possession of the 

 females. The most vigorous males, or those which have most 

 successfully struggled with their conditions of life, will gen- 

 erally leave most progeny. But success will often depend on 

 the males having special weapons, or means of defence, or 

 charms; and a slight advantage will lead to victory. 



As geology plainly proclaims that each land has undergone 

 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 quan- 

 tity. 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 domes- 

 tic productions; and every one admits that species present 

 individual differences. But, besides such differences, all nat- 

 uralists admit that natural varieties exist, which are consid- 

 ered sufficiently distinct to be worthy of record in systematic 

 works. No one has drawn any clear distinction between in- 

 dividual 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 con- 

 tinent when divided by barriers of any kind, and on outlying 

 islands, what a multitude of forms exist, which some experi- 

 enced 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 individual differences, 

 which are in any way beneficial, be preserved and accumu- 

 lated through natural selection, or the survival of the fittest? 

 If man can by patience select variations useful to him, why. 



