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Show 148 MR. DARWIN'S WORK AND duce 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 ltas 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 result 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 con1mon 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. vVhat an astounding THE PHENO}.IENA O}l' ORGANIC NATURE. 149 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~* which are more or less infertile with one another. There are other cases which are truly extraordinary ; there is one, for e~ample, which has been carefully examined,-of two lnnds 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 tha~ those conditions will not be better understood by ana by, and we have no ground for supposing that \Ve m~y not be able to experiment so as to obtain that crucml result which I mentioned just now. So that though l\1r. Darwin's hypothesis does not completely extricate us from this difficulty at present, we have not the least rio-ht to sav it will not do so. b " There is a wide gulf between the thing you cannot * And as I conceive with very good reason; but if any objcct~r urrres that we cannot prove that they have been produced by a.rt1~ ficial or natural selection, the objection must be admitted-ultrasceptical as it is. But in science, scepticism is a duty. |