which have long been kept together in the Forest of
Dean, in High Meadow Woods, and in the New Forest, have never been known to
mingle: the dark-coloured deer, it may be added, are believed to have been
first brought by James I. from Norway, on account of their greater
hardiness. I imported from the island of Porto Santo two of the feral
rabbits, which differ, as described in the fourth chapter, from common
rabbits; both proved to be males, and, though they lived during some years
in the Zoological Gardens, the superintendent, Mr. Bartlett, in vain
endeavoured to make them breed with various tame kinds; but whether this
refusal to breed was due to any change in instinct, or simply to their
extreme wildness; or whether confinement had rendered them sterile, as
often occurs, cannot be told.

Whilst matching for the sake of experiment many of the most distinct breeds
of pigeons, it frequently appeared to me that the birds, though faithful to
their marriage vow, retained some desire after their own kind. Accordingly
I asked Mr. Wicking, who has kept a larger stock of various breeds together
than any man in England, whether he thought that they would prefer pairing
with their own kind, supposing that there were males and females enough of
each; and he without hesitation answered that he was convinced that this
was the case. It has often been noticed that the dovecot pigeon seems to
have an actual aversion towards the several fancy breeds;[221] yet all have
{104} certainly sprung from a common progenitor. The Rev. W. D. Fox informs
me that his flocks of white and common Chinese geese kept distinct.

These facts and statements, though some of them are incapable of proof,
resting only on the opinion of experienced observers, show that some
domestic races are led by different habits of life to keep to a certain
extent separate, and that others prefer coupling with their own kind, in
the same manner as species in a state of nature, though in a much less
degree.

With respect to sterility from the crossing of domestic races, I know
of no well-ascertained case with animals. This fact, seeing the great
difference in structure between some breeds of pigeons, fowls, pigs,
dogs, &c., is extraordinary, in contrast with the sterility of many
closely allied natural species when crossed; but we shall hereafter
attempt to show that it is not so extraordinary as it at first appears.
And it may be well here to rec