Page - 59 - in The Origin of Species

INDIVIDUAL DIFFERENCES SB ations of structure such as we occasionally see in our domes- tic productions, more especially with plants, are ever perma- nently propagated in a state of nature. Almost every part of every organic being is so beautifully related to its complex conditions of life that it seems as improbable that any part should have been suddenly produced perfect, as that a com- plex machine should have been invented by man in a perfect state. Under domestication monstrosities sometimes occur which resemble normal structures in widely different animals. Thus pigs have occasionally been born with a sort of pro- boscis, and if any wild species of the same genus had nat- urally possessed a proboscis, it might have been argued that this had appeared as a monstrosity ; but I have as yet failed to find, after diligent search, cases of monstrosities resem- bling normal structures in nearly allied forms, and these alone bear on the question. If monstrous forms of this kind ever do appear in a state of nature and are capable of reproduc- tion (which is not always the case), as they occur rarely and singly, their preservation would depend on unusually favour- able circumstances. They would, also, during the first and succeeding generations cross with the ordinary form, and thus their abnormal character would almost inevitably be lost. But I shall have to return in a future chapter to the pres- ervation and perpetuation of single or occasional variations. INDIVIDUAL DIFFERENCES The many slight differences which appear in the oft'spring from the same parents, or which it may be presumed have thus arisen, from being observed in the individuals of the same species inhabiting the same confined locality, may be called individual dift'erences. No one supposes that all the individuals of the same species are cast in the same actual mould. These individual differences are of the highest im- portance for us, for they are often inherited, as must be familiar to every one ; and they thus aft'ord materials for natural selection to act on and accumulate, in the same man- ner as man accumulates in any given direction individual dif- ferences in his domesticated productions. These individual differences generally aft'ect what naturalists consider unim-