eliminates this strong tendency to sterility: from the history of the
dog I think there is some probability in this hypothesis, if applied
to species closely related together, though it is unsupported by a
single experiment. But to extend the hypothesis so far as to suppose
that species, aboriginally as distinct as carriers, tumblers, pouters,
and fantails now are, should yield offspring perfectly fertile, inter
se, seems to me rash in the extreme.

From these several reasons, namely, the improbability of man having
formerly got seven or eight supposed species of pigeons to breed
freely under domestication; these supposed species being quite unknown
in a wild state, and their becoming nowhere feral; these species
having very abnormal characters in certain respects, as compared with
all other Columbidae, though so like in most other respects to the
rock-pigeon; the blue colour and various marks occasionally appearing
in all the breeds, both when kept pure and when crossed; the mongrel
offspring being perfectly fertile;--from these several reasons, taken
together, I can feel no doubt that all our domestic breeds have
descended from the Columba livia with its geographical sub-species.

In favour of this view, I may add, firstly, that C. livia, or the
rock-pigeon, has been found capable of domestication in Europe and in
India; and that it agrees in habits and in a great number of points of
structure with all the domestic breeds. Secondly, although an English
carrier or short-faced tumbler differs immensely in certain characters
from the rock-pigeon, yet by comparing the several sub-breeds of these
breeds, more especially those brought from distant countries, we can
make an almost perfect series between the extremes of structure.
Thirdly, those characters which are mainly distinctive of each breed,
for instance the wattle and length of beak of the carrier, the