the pasture is burnt up; at such times common
cattle and horses perish by the thousand, but many survive by browsing on
twigs, reeds, &c.; this the Niata cattle cannot so well effect from their
upturned jaws and the shape of their lips; consequently, if not attended
to, they perish before the other cattle. In Colombia, according to Roulin,
there is a breed of nearly hairless cattle, called Pelones; these succeed
in their native hot district, but are found too tender for the Cordillera;
in this case, 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 peculiarities 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 ascertained that these
animals feed on the roots of the _Lachnanthes tinctoria_, 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 _Hypericum crispum_ abounds there; and this
plant does not injure black sheep, but kills the white ones in about a
fortnight's time.[540]

Complexion, and liability to certain diseases, are believed to run together
in man and the lower animals. Thus