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1859
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fertile. 1859 1860 1861
or perfectly fertile. 1866 1869 1872

2 blocks not present in 1859 1860 1861 1866; present in 1869 1872
The various races of each kind of domesticated animal are quite fertile when crossed together; yet in many cases they are descended from two or more wild species. From this fact we must conclude either that the aboriginal parent-species produced at first perfectly fertile hybrids, or that the hybrids subsequently reared under domestication became quite fertile.

seems to me 1859 1860
seems 1861 1866
which was first propounded by Pallas, seems 1869
which was first propounded by Pallas, seems by far 1872

I am inclined to believe in its truth, although it rests on no direct evidence. 1859 1860 1861
I have hardly any doubt of its truth, although it rests on no direct evidence. 1866
can, indeed, hardly be doubted. 1869 1872

that 1859 1860 1861
almost certain that 1866 1869 1872

there is reason to believe that our European and the humped Indian 1859 1860 1861
I have lately acquired decisive evidence that the crossed offspring from the Indian humped and common 1866 1869 1872

quite fertile together; but from facts communicated to me 1859 1860 1861
inter se perfectly fertile; and from the observations by Rütimeyer on their important osteological differences, as well as from those 1866 1869
inter se perfectly fertile; and from the observations by Rütimeyer on their important osteological differences, as well as from those 1872

I think they 1859 1860 1861
on their differences in habits, voice, constitution, &c., these two forms 1866 1869 1872

distinct species. 1859 1860 1861
good and distinct species—as good as any in the world. 1866
good and distinct species as any in the world. 1869
good and distinct species. 1872

1 blocks not present in 1859 1860 1861 1866 1869; present in 1872
The same remarks may be extended to the two chief races of the pig.

On this view 1859 1860 1861 1866
According to this view 1869
We must, therefore, either give up the belief 1872

origin of many of our domestic animals, 1859 1860 1861 1866
origin of many domestic animals, 1869
universal sterility of species when crossed; or 1872

either give up the belief of the almost universal sterility of distinct species of animals when crossed; or we must 1859 1860 1861 1866 1869
OMIT 1872

sterility, 1859 1860 1861 1866 1869
this sterility in animals, 1872

Mr. Blyth and Capt. Hutton, that whole flocks of these crossed geese are kept in various parts of the country; and as they are kept for profit, where neither pure parent-species exists, they must certainly be highly fertile.
A doctrine which originated with
Pallas
Pallas,
has been largely accepted by modern naturalists; namely, that most of our domestic animals have descended from two or more
aboriginal
wild
species, since commingled by intercrossing. On this view, the aboriginal species must either at first have produced quite fertile hybrids, or the hybrids must have become in subsequent
generation
generations
quite fertile under domestication. This latter
alternative,
alternative
seems to me the most probable, and I am inclined to believe in its truth, although it rests on no direct evidence.
It is,
I believe,
for instance, that our dogs
are
have
descended from several wild stocks; yet, with perhaps the exception of certain indigenous domestic dogs of South America, all are quite fertile together;
but
and
analogy makes me greatly doubt, whether the several aboriginal species would at first have freely bred together and have produced quite fertile hybrids. So again there is reason to believe that our European and the humped Indian cattle are quite fertile together; but from facts communicated to me by Mr.
Blyth
Blyth,
I think they must be
regarded
considered
as distinct species. On this view of the origin of many of our domestic animals, we must either give up the belief of the almost universal sterility of distinct species of animals when crossed; or we must look at sterility, not as an indelible characteristic, but as one capable of being removed by domestication.
Finally,
considering
looking to
all the ascertained facts on the intercrossing of plants and animals, it may be
con- cluded
concluded
that some degree of sterility, both in first crosses