tly in size, shape, colour, and
habits, as well as in the form and proportions of all the different
parts of the body, that it seems impossible that they could have
descended from any of the known wild dogs, wolves, or allied animals,
none of which differ nearly so much in size, form, and proportions. We
have here a remarkable proof that variation is not confined to
superficial characters--to the colour, hair, or external appendages,
when we see how the entire skeletons of such forms as the greyhound and
the bulldog have been gradually changed in opposite directions till they
are both completely unlike that of any known wild animal, recent or
extinct. These changes have been the result of some thousands of years
of domestication and selection, different breeds being used and
preserved for different purposes; but some of the best breeds are known
to have been improved and perfected in modern times. About the middle of
the last century a new and improved kind of foxhound was produced; the
greyhound was also greatly improved at the end of the last century,
while the true bulldog was brought to perfection about the same period.
The Newfoundland dog has been so much changed since it was first
imported that it is now quite unlike any existing native dog in that
island.[33]

_Domestic Pigeons._

The most remarkable and instructive example of variation produced by
human selection is afforded by the various races and breeds of domestic
pigeons, not only because the variations produced are often most
extraordinary in amount and diverse in character, but because in this
case there is no doubt whatever that all have been derived from one wild
species, the common rock-pigeon (Columba livia). As this is a very
important point it is well to state the evidence on which the belief is
founded. The wild rock-pigeon is of a slaty-blue colour, the tail has a
dark band across the end, the wings have two black bands, and the outer
tail-feathers are edged with white at the base. No other wild pigeon in
the world has this combination of characters. Now in every one of the
domestic varieties, even the most extreme, all the above marks, even to
the white edging of the outer tail-feathers, are sometimes found
perfectly developed. When birds belonging to two distinct breeds are
crossed one or more times, neither of the parents being blue, or having
any of the above-named marks, the mongrel offspring are very apt to
acquire some of these charact