stly, in certain breeds, the males and females have
come to differ to a slight degree from each other.

Altogether at least a score of pigeons might be chosen, which if shown
to an ornithologist, and he were told that they were wild birds, would
certainly, I think, be ranked by him as well-defined species. Moreover,
I do not believe that any ornithologist would place the English carrier,
the short-faced tumbler, the runt, the barb, pouter, and fantail in
the same genus; more especially as in each of these breeds several
truly-inherited sub-breeds, or species as he might have called them,
could be shown him.

Great as the differences are between the breeds of pigeons, I am fully
convinced that the common opinion of naturalists is correct, namely,
that all have descended from the rock-pigeon (Columba livia), including
under this term several geographical races or sub-species, which differ
from each other in the most trifling respects. As several of the reasons
which have led me to this belief are in some degree applicable in other
cases, I will here briefly give them. If the several breeds are not
varieties, and have not proceeded from the rock-pigeon, they must have
descended from at least seven or eight aboriginal stocks; for it is
impossible to make the present domestic breeds by the crossing of any
lesser number: how, for instance, could a pouter be produced by crossing
two breeds unless one of the parent-stocks possessed the characteristic
enormous crop? The supposed aboriginal stocks must all have been
rock-pigeons, that is, not breeding or willingly perching on trees. But
besides C. livia, with its geographical sub-species, only two or three
other species of rock-pigeons are known; and these have not any of the
characters of the domestic breeds. Hence the supposed aboriginal stocks
must either still exist in the countries where they were originally
domesticated, and yet be unknown to ornithologists; and this,
considering their size, habits, and remarkable characters, seems very
improbable; or they must have become extinct in the wild state. But
birds breeding on precipices, and good fliers, are unlikely to be
exterminated; and the common rock-pigeon, which has the same habits with
the domestic breeds, has not been exterminated even on several of the
smaller British islets, or on the shores of the Mediterranean. Hence the
supposed extermination of so many species having similar habits with the
rock-pigeon seems to