Page - 30 - in The Origin of Species

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