Chap. II. INDIVIDUAL DIFFERENCES. 53 



tions, more especially with plants, are ever permanently prop- 

 agated in a state of nature. Almost every part of every 

 organic being is so beautifully related in 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 invente4 by man in a perfect state. Under 

 domestication monstrosities often occur which resemble noi 

 mal structures in widely-different animals. Thus pigs have 

 often been born with a sort of proboscis like that of tlie tapir 

 or elephant. Now, if any wild species of the pig-genus had 

 naturally possessed a proboscis, it might have been argued that 

 tliis in like manner had suddenly 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 would bear on the question. If mon- 

 strous forms of this kind ever do appear in a state of nature 

 and are capable of propagation (which is not always the case), 

 as they occur rarely and singly, their preservation would de- 

 pend on unusually favorable circumstances. They would, also, 

 during the first and succeeding generations cross with the or- 

 dinary form, and thus they would almost inevitably lose their 

 abnormal character. But I shall have to retvu^n in a future 

 cliapter to the preservation and perpetuation of occasional va- 

 riations. 



Individual Differences. 



Tlie many slight differences Avhich frequently appear in the 

 offspring from the same parents, or which may be presumed to 

 have thus arisen, from being frequently observed in the indi- 

 viduals of the same species inhabiting the same confined local- 

 ity, may be called indiA-idual differences. No one supposes 

 that all the indi\'iduals 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 fa- 

 miliar 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 production.s. 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 physiolo- 

 gical or classificatory point of view, sometimes vary in the indi- 

 viduals of the same species. I am convinced that the most ex- 



