— 



34 Individual Differences. Chap. ii. 



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 m 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 favourable 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 1 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 in- 

 habiting 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 individual 

 differences in his domesticated productions. These individual 

 differences generally affect what naturalists consider unimportant 

 parts ; but I could show by a long catalogue of facts, that parts 

 which must be called important, whether viewed under a physio- 

 logical or classificatory point of view, sometimes vary in the 

 individuals of the same species. 1 am convinced that the most 

 experienced naturalist would be surprised at the number of the 

 cases of variability, even in important parts of structure, which he 

 could collect on good authority, as I have collected, during a course 

 of years. It should be remembered that systematise are far from 

 being pleased at finding variability in important characters, and 

 that there are not many men who will laboriously examine internal 

 and important organs, and compare them in many specimens of 



