ll languages, and knows the pedigrees of our British breeds better than
most Englishmen, but has imported many of our improved animals, and is
himself an experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be
acquired in the case of animals, such as fowls, pigeons, &c., which
propagate quickly, and, from being kept in the same place, are exposed to
the same conditions. Now I have inquired of very many breeders of these
birds, and I have hitherto not met with a single man who was not thoroughly
convinced that an occasional cross with another strain of the same
sub-variety was absolutely necessary. Most breeders of highly-improved or
fancy birds value their own strain, and are most unwilling, at the risk, in
their opinion, of deterioration, to make a cross. The purchase of a
first-rate bird of another strain is expensive, and exchanges are
troublesome; yet all breeders, as far as I can hear, excepting those who
keep large stocks at different places for the sake of crossing, are driven
after a time to take this step.

Another general consideration which has had great influence on my mind is,
that with all hermaphrodite animals and plants, which it might have been
thought would have perpetually fertilised themselves, and thus have been
subjected for long ages to the closest interbreeding, there is no single
species, as far as I can discover, in which the structure ensures
self-fertilisation. On the contrary, there are in a multitude of cases, as
briefly stated in the fifteenth chapter, manifest adaptations which favour
or inevitably lead to an occasional cross between one hermaphrodite and
another of the same species; and these adaptive structures are utterly
purposeless, as far as we can see, for any other end.

With _Cattle_ there can be no doubt that extremely close interbreeding
may be long carried on, advantageously with respect to external
characters and with no manifestly apparent evil as far as constitution
is concerned. The same remark is applicable to sheep. Whether these
animals have gradually been rendered less susceptible than others to
this evil, in order to permit them to live in herds,--a habit which
leads the old and vigorous males to expel all intruders, and in
consequence often to pair with their own daughters, I will not pretend
to decide. The case of Bakewell's Long-horns, which were closely
interbred for a long period, has