action of
a humid climate and poor pasture the horse rapidly decreases in size in
the Falkland Islands. From information which I have received, this
seems likewise to be the case to a certain extent with sheep in
Australia.

Climate definitely influences the hairy covering of animals; in the
West Indies a great change is produced in the fleece of sheep, in about
three generations. Dr. Falconer states[686] that the Thibet mastiff and
goat, when brought down from the Himalaya to Kashmir, lose their fine
wool. At Angora not only goats, but shepherd-dogs and cats, have fine
fleecy hair, and Mr. Ainsworth[687] attributes the thickness of the
fleece to the severe winters, and its silky lustre to the hot summers.
Burnes states positively[688] that the Karakool sheep lose their
peculiar black curled fleeces when removed into any other country. Even
within the limits of England, I have been assured that with two breeds
of sheep the wool was slightly changed by the flocks being pastured in
different localities.[689] It has been asserted on good authority[690]
that horses kept during several years in the deep coal-mines of Belgium
become covered with velvety hair, almost like that on the mole. These
cases probably stand in close relation to the natural change of coat in
winter and summer. Naked varieties of several domestic animals have
occasionally appeared; but there is no reason to {279} believe that
this is in any way related to the nature of the climate to which they
have been exposed.[691]

It appears at first sight probable that the increased size, the
tendency to fatten, the early maturity and altered forms of our
improved cattle, sheep, and pigs, have directly resulted from their
abundant supply of food. This is the opinion of many competent judges,
and probably is to a great extent true. But as far as form is
concerned, we must not overlook the equal or more potent influence of
lessened use on the limbs and lungs. We see, moreover, as far as size
is concerned, that selection is apparently a more powerful agent than a
large supply of food, for we can thus only account for the existence,
as remarked to me by Mr. Blyth, of the largest and smallest breeds of
sheep in the same country, of Cochin-China fowls and Bantams, of small
Tumbler and large Runt pigeons, all kept together and suppl