See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1859
1861
1866
1869
1872

we 1859 1860 1861 1866
no instance is 1869 1872

no fact countenancing the belief that the child ever reverts to some one ancestor, 1859 1860 1861 1866
crossed descendants reverting to an ancestor of foreign blood, 1869 1872

with some distinct breed, 1859 1860 1861 1866
OMIT 1869 1872

with a distinct breed, 1859 1860 1861 1866
OMIT 1869 1872

are 1859 1860 1861 1866
of reversion are 1869 1872

in treatises 1859 1860
by those who have written 1861 1866
together by those who have written 1869 1872

it is difficult, perhaps impossible, to bring forward one case of the hybrid offspring of two animals clearly distinct being themselves 1859 1860 1861 1866 1869
hardly any cases have been ascertained with certainty of hybrids from two quite distinct species of animals being 1872

from 1859 1860 1861 1866 1869
in species. From 1872

I think there is some probability in this hypothesis, 1859 1860 1861
and of some other domestic animals, there is great probability in this hypothesis, 1866 1869
and of some other domestic animals, this conclusion is probably quite correct, 1872

together, though it is unsupported by a single experiment. 1859 1860 1861
to each other, though it is unsupported by a single experiment. 1866 1869
to each other. 1872

seems to me 1859 1860 1861 1866 1869
would be 1872

that each breed, even the purest, has within a
dozen,
dozen
or
or,
at
most
most,
within a
score,
score
of generations, been crossed by the
rock-pigeon;
rock-pigeon:
I say within a dozen or twenty generations, for we
known
know
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
once,
once
with some distinct breed, the tendency to
revert
reversion
to any character derived from such
a cross
cross
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
cross,
cross
with a distinct breed, and there is a tendency in
the breed
both parents
to revert to a
character
character,
which
was
has been
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
quite distinct
distinct
cases are often confounded in treatises on inheritance.
Lastly, the hybrids or mongrels from between all the
domestic
domestic
breeds of
the pigeon
pigeons
are perfectly
fertile,
fertile.
as I
I
can state
this
this
from my own observations, purposely
made
made,
on the most distinct breeds. Now, it is difficult, perhaps impossible, to bring forward one case of the hybrid offspring of two animals clearly distinct being themselves perfectly fertile. Some authors believe that long-continued domestication eliminates this strong tendency to
sterility
sterility:
from the history of the
dog,
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
it
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
fertile,
inter se , seems to me rash in the extreme.
From these several reasons, namely,
— the
the
improbability of man having formerly
made
got
seven or eight supposed