Page - 508 - in The Origin of Species

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.