Correlation 



facts collected by Heusinger, it appears that 

 white sheep and pigs are injured by certain 

 plants, whilst dark-coloured individuals escape. 

 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 informed him that 

 the pigs ate the paint-root (Lachnanthes), which 

 coloured 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 peculiarity, he will almost cer- 

 tainly modify unintentionally other parts of the 

 structure, owing to the mysterious laws of the 

 correlation of growth." 



The great importance of the principle of the 

 correlation of organs is, that natural selection 

 may indirectly cause the survival of unfavourable 

 variations, or of variations which are of no 

 utility to the organism, because they happen to 



357 



