'40 INDIVIDUAL DIFFERENCES. 



It may be doubted whether sudden and considerable 

 deviations of structure, such as we occasionally see in our 

 domestic productions, more especially with plants, are ever 

 permanently 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 complex machine should have been invented by 

 man in a perfect state. Under domestication monstrosi- 

 ties sometimes occur which resemble normal structures in 

 widely diiferent animals. Thus pigs have occasionally been 

 born with a sort of proboscis, and if any wild species of the 

 same genus had naturally 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 resembling 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 reproduction (which is not 

 always the case), as they occur rarely and singly, their 

 preservation would depend on unusually favorable circum- 

 stances. 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 preserva- 

 tion and perpetuation of single or occasional variations. 



INDIVIDUAL DIFFERENCES. 



The many slight differences which appear in the offspring 

 from the same jiarents, 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 differences. No one supposes that all 

 the individuals of the same species are cast in the same 

 actual mold. These individual differences are of the 

 highest importance for us, for they are often inherited, as 

 must be familiar to every one; and they thus afford mate- 

 rials for natural selection to act on and accumulate, in the 

 same manner as man accumulates in any given direction 

 individual differences in his domesticated productions. 

 These individual differences generally affect what naturalists 



