30 ORIGIN OF SPECIES 



liarities go together, of which many remarkable cases could 

 be given amongst animals and plants. From facts collected 

 by Heusinger, it appears that white sheep and pigs are in- 

 jured by certain plants, whilst dark-coloured individuals es- 

 cape : Professor Wyman has recently communicated to me 

 a good illustration of this fact; on asking some farmers in 

 Virginia how it was that all their pigs were black, they in- 

 formed him that the pigs ate the paint-root (Lachnanthes), 

 which colored their bones pink, and which caused the hoofs 

 of all but the black varieties to drop off; and one of the 

 "crackers" (i.e. Virginia squatters) added, "we select the 

 black members of a litter for raising, as they alone have a 

 good chance of living.'' Hairless dogs have imperfect teeth ; 

 long-haired and coarse-haired animals are apt to have, as is 

 asserted, long or many horns ; pigeons with feathered feet 

 have skin between their outer toes ; pigeons with short beaks 

 have small feet, and those with long beaks large feet. Hence 

 if man goes on selecting, and thus augmenting, any pecu- 

 liarity, he will almost certainly modify unintentionally other 

 parts of the structure, owing to the mysterious laws of cor- 

 relation. 



The results of the various, unknown, or but dimly under- 

 stood laws of variation are infinitely complex and diversified. 

 It is well worth whde carefully to study the several treatises 

 on some of our old cultivated plants, as on the hyacinth, 

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

 note the endless points of structure and constitution in which 

 the varieties and sub-varieties differ slightly from each 

 other. The whole organisation seems to have become 

 plastic, and departs in a slight 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, are 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; that like produces like is his fundamental be- 

 lief: doubts have been thrown on this principle only by theo- 

 retical writers. When any deviation of structure often 



