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, I think they
must be 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, looking to all the ascertained facts on the intercrossing of
plants and animals, it may be concluded that some degree of sterility,
both in first crosses and in hybrids, is an extremely general result;
but that it cannot, under our present state of knowledge, be
considered as absolutely universal.
LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF HYBRIDS.
We will now consider a little more in detail the circumstances and
rules governing the sterility of first crosses and of hybrids. Our
chief object will be to see whether or not the rules indicate that
species have specially been endowed with this quality, in order to
prevent their crossing and blending together in utter confusion. The
following rules and conclusions are chiefly drawn up from Gartner's
admirable work on the hybridisation of plants. I have taken much pains
to ascertain how far the rules apply to animals, and considering how
scanty our knowledge is in regard to hybrid animals, I have been
surprised to find how generally the same rules apply to both kingdoms.
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