|
tail and red spot on the forehead, and which notoriously breeds very true; the mongrels were dusky and mottled. I then crossed one of the mongrel barb-fantails with a mongrel barb-spot, and they produced a bird of as beautiful a blue colour, with the white
double black wing-bar, and barred and white-edged tail-feathers, as any wild rock-pigeon! We can understand these facts, on the well-known principle of reversion to ancestral
→if
all the domestic breeds
descended from the rock-pigeon. But if we deny this, we must make one of the two following highly improbable suppositions. Either,
that all the several imagined aboriginal stocks were coloured and marked like the rock-pigeon, although no other existing species is thus coloured and marked, so that in each separate breed there might be a tendency to revert to the very same colours and markings. Or, secondly, that each breed, even the purest, has within a
at
within a
of generations, been crossed by the
I say within a dozen or twenty generations, for
→no instance is
of
→crossed descendants reverting to an ancestor of foreign blood,
removed by a greater number of generations. In a breed which has been crossed only
→OMIT
the tendency to
to any character derived from such
will naturally become less and less, as in each succeeding generation there will be less of the foreign blood; but when there has been no
→OMIT
and there is a tendency in
to revert to a
which
lost during some former generation, this tendency, for all that we can see to the contrary, may be transmitted undiminished for an indefinite number of generations. These two
cases
→of reversion are
often confounded
→together by those who have written
on inheritance. |
| Lastly, the hybrids or mongrels from between all the
breeds of
are perfectly
can state
from my own observations, purposely
on the most distinct breeds. Now,
→hardly any cases have been ascertained with certainty of hybrids from two quite distinct species of animals being
perfectly fertile. Some authors believe that long-continued domestication eliminates this strong tendency to
→in species. From
the history of the
→and of some other domestic animals, this conclusion is probably quite correct,
if applied to species closely related
→to each other. But to extend
so far as to suppose that species, aboriginally as distinct as carriers, tumblers, pouters, and fantails now are, should yield offspring perfectly
inter
se
, →would be
rash in the extreme. |
