Chap. XXI. NATURAL SELECTION. 227 



determines only the range of the variety. It is obvious that a 

 host of artificial races could never survive in a state of nature ; 

 — such as Italian greyhounds, — hairless and almost toothless 

 Turkish dogs, — fantail pigeons, which cannot fly well against a 

 strong wind,— barbs with their vision impeded by their eye- 

 wattle, — Polish fowls with their vision impeded by their great 

 topknots, — hornless bulls and rams which consequently cannot 

 cope with other males, and thus have a poor chance of leaving 

 offspring,; — seedless plants, and many other such cases. 



Colour is generally esteemed by the systematic naturalist as 

 unimportant : let us, therefore, see how far it indirectly affects 

 our domestic productions, and how far it would affect them if 

 they were left exposed to the full force of natural selection. In 

 a future chapter I shall have to show that constitutional pecu- 

 liarities of the strangest kind, entailing liability to the action 

 of certain poisons, are correlated with the colour of the skin. 

 I will here give a single case, on the high authority of Professor 

 Wyman ; he informs me that, being surprised at all the pigs in 

 a part of Virginia being black, he made inquiries, and ascer- 

 tained that these animals feed on the roots of the Lachnanthes 

 tindoria, which colours their bones pink, and, excepting in the 

 case of the black varieties, causes the hoofs to drop off. Hence, 

 as one of the squatters remarked, " we select the black members 

 of the litter for raising, as they alone have a good chance of 

 living." So that here we have artificial and natural selection 

 working hand in hand. I may add that in the Tarentino the 

 inhabitants keep black sheep alone, because the Eypericum 

 crisjpum abounds there ; and this plant does not injure black 

 sheep, but kills the white ones in about a fortnight's time. 6 



Complexion, and liability to certain diseases, are believed 

 to run together in man and the lower animals. Thus white 

 terriers suffer more than terriers of any other colour from the 

 fatal Distemper. 7 In North America plum-trees are liable to 

 a disease which Downing* believes is not caused by insects; 

 the kinds bearing purple fruit are most affected, " and we have 

 "never known the green or yellow fruited varieties infected 



« Dr Heusinger, « Wochenschrift filr 8 < The Fruit-trees of America,' 1845, 



die Heilkunde Berlin, 1846, s. 279. p . 27 : for peaches, p. 4G6. 



Youatt on the Dog, p. 232. 



Q 2 



