12 ON THE ORIGIN OF SPECIES 



cultivated plants, as on the hyacinth, potato, even the 

 dahlia, etc. ; and it is really surprising to note the 

 endless points in structure and constitution in which 

 the varieties and sub-varieties differ slightly from each 

 other. The whole organisation seems to have become 

 plastic, and tends to depart in some small degree from 

 that of the parental type. 



Any variation which is not inherited is unimportant 

 for us. But the number and diversity of inheritable 

 deviations of structure, both those of slight and those of 

 considerable physiological importance, is endless. Dr. 

 Prosper Lucas's treatise, in two large volumes, is the 

 fullest and the best on this subject. No breeder doubts 

 how strong is the tendency to inheritance : like produces 

 like is his fundamental belief: doubts have been thrown 

 on this principle by theoretical writers alone. When 

 any deviation of structure often appears, and we see it 

 in the father and child, we cannot tell whether it may 

 not be due to the same cause having acted on both ; 

 but when amongst individuals, apparently exposed to 

 the same conditions, any very rare deviation, due to 

 some extraordinary combination of circumstances, 

 appears in the parent — say, once amongst several million 

 individuals — and it reappears in the child, the mere 

 doctrine of chances almost compels us to attribute its 

 reappearance to inheritance. Every one must have 

 heard of cases of albinism, prickly skin, hairy bodies, 

 etc. , appearing in several members of the same family. 

 If strange and rare deviations of structure are truly 

 inherited, less strange and commoner deviations may 

 be freely admitted to be inheritable. Perhaps the 

 correct way of viewing the whole subject, would be, to 

 look at the inheritance of every character whatever as 

 the rule, and non-inheritance as the anomaly. 



The laws governing inheritance are quite unknown ; 

 no one can say why a peculiarity in different individuals 

 of the same species, or in individuals of different 

 species, is sometimes inherited and sometimes not so ; 

 why the child often reverts in certain characters to 

 its grandfather or grandmother or other more remote 



