eir
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
find one of the most important of all functions annihilated by mere
imprisonment!

So, again, there are cases known of animals which have been thought
by naturalists to be undoubted species, which have yielded perfectly
fertile hybrids; while there are other species which present what
everybody believes to be varieties [1] which are more or less infertile
with one another. There are other cases which are truly extraordinary;
there is one, for example, which has been carefully examined,--of two
kinds of sea-weed, of which the male element of the one, which we may
call A, fertilizes the female element of the other, B; while the male
element of B will not fertilize the female element of A; so that, while
the former experiment seems to show us that they are 'varieties', the
latter leads to the conviction that they are 'species'.

When we see how capricious and uncertain this sterility is, how unknown
the conditions on which it depends, I say that we have no right to
affirm that those conditions will not be better understood by and
by, and we have no ground for supposing that we may not be able to
experiment so as to obtain that crucial result which I mentioned
just now. So that though Mr. Darwin's hypothesis does not completely
extricate us from this difficulty at present, we have not the least
right to say it will not do so.

There is a wide gulf between the thing you cannot explain and the thing
that upsets you altogether. There is hardly any hypothesis in this
world which has not some fact in connection with it which has not been
explained, but that is a very different affair to a fact that entirely
opposes your hypothesis; in this case all you can say is, that your
hypothesis is in the same position as a good many others.

Now, as to the third test, that there are no other causes competent to
explain the phenomena, I explained to you that one should be able to say
of an hypothesis, that no other known causes than those supposed by it
are competent to give rise to the phenomena. Here, I think, Mr. Darwin's
view is pretty strong. I really believe that the alternative is either
Darwinism or nothing, for I do not know of any rational conception or
theory of the organic universe which has any scientific position at all
beside Mr. Darwin's. I do not know of any proposition that h