|
apt suddenly to acquire these
→To give one instance out of several which I have observed: —
I crossed
↑
fantails, which breed very true, with some black barbs — and it so happens that blue varieties of barbs are so rare that I never heard of an instance in England; and the mongrels were black, brown, and mottled. I also crossed a barb with a spot, which is a white bird with a red 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
→(confined, as far as I have seen, to colour alone), 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
|
