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).
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