38 INDIVIDUAL DIFFERENCES. 



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 monstrosities some- 

 times occur which resemble normal structures in widely 

 different 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 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 preservation and perpetuation of single 

 or occasional variations. 



INDIVIDUAL DIFFERENCES. 



The many slight differences which appear in the offspring 

 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 differences. 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 

 importance for us, for they are often inherited, as must be 

 familiar to every one ; and they thus afford materials for 

 natural selection to act on and accumulate, in the same 

 manner as man accumulates in any given direction indi- 

 vidual differences in his domesticated productions. These 

 individual differences generally affect what naturalists con- 

 sider unimportant parts ; but I could show, by a long cata- 

 logue of facts, that parts which must be called important, 

 whether viewed under a physiological or classificatory point 

 of view, sometimes vary in the individuals of the same 



