|
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
→we
of
→no fact countenancing the belief that the child ever reverts to some one ancestor,
removed by a greater number of generations. In a breed which has been crossed only
→with some distinct breed,
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
→with a distinct breed,
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
→are
often confounded
→by those who have written
on inheritance. |
