and you cannot say, 'I can, by selective modification, produce these
same results.' Now, it is admitted on all hands that, at present, so
far as experiments have gone, it has not been found possible to produce
this complete physiological divergence by selective breeding. I stated
this very clearly before, and I now refer to the point, because, if it
could be proved, not only that this 'has' not been done, but that it
'cannot' be done; if it could be demonstrated that it is impossible to
breed selectively, from any stock, a form which shall not breed with
another, produced from the same stock; and if we were shown that this
must be the necessary and inevitable results of all experiments, I hold
that Mr. Darwin's hypothesis would be utterly shattered.

But has this been done? or what is really the state of the case? It is
simply that, so far as we have gone yet with our breeding, we have not
produced from a common stock two breeds which are not more or less
fertile with one another.

I do not know that there is a single fact which would justify any one in
saying that any degree of sterility has been observed between breeds
absolutely known to have been produced by selective breeding from a
common stock. On the other hand, I do not know that there is a single
fact which can justify any one in asserting that such sterility cannot
be produced by proper experimentation. For my own part, I see every
reason to believe that it may, and will be so produced. For, as Mr.
Darwin has very properly urged, when we consider the phenomena of
sterility, we find they are most capricious; we do not know what it is
that the sterility depends on. There are some animals which will not
breed in captivity; whether it arises from the simple fact of their
being shut up and deprived of their liberty, or not, we do not know,
but they certainly will not breed. What an astounding thing this is, to