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Show 272 HYBRIDISM. CHAP. VIII. fertility of varieties can be proved to be of uni versa! occurrence or to form a fundamental distinction between varieties :nd species. The general fertility of varie~ies does not seem to me sufficient to overthrow the VIew which I have taken with respect to the very general, but not invariable, sterility of first crosses and ofh!b~id~, namely, that it is not a special en~owment, but IS ~nmdental on slowly acquired modifications, more es~emally in the reproductive systems of the forms whiCh are crossed. Hybrids and Mongrels compared, independently of their fertility.-Independently of the question of fertility, the offspring of species when crossed and of varieties when crossed may be compared in several other respects. Gartner, whose strong wish was to draw a marked line of distinction between species and varieties, could find very few and, as it seems to me, quite unimportant differences between the so-called hybrid offspring of species, and the so-called mongrel offspring of varieties. And, on the other hand, they agree most closely in very many important respects. . I shall here discuss this subject with extreme brevity. The most important distinction is, that in the first generation mongrels are more variable than hybri~s ; but Gartner admits that hybrids from species whiCh have long been cultivated are often variable in the first generation; and I have myself seen striking instances of this fact. Gartner further admits that hybrids between very closely allied species are more .variable than those from very distinct species ; and tlns shows that the difference in the degree of variability graduates away. When mongrels and the more f~rtile hybrids are propagated for several generations an e~treme amount of variability in their offspring is notori- CHAP. YIII. HYBRIDS AND MONGRELS. 273 otis ; but .s~me few cases both of hybrids and mongrels long ret~In~~g uniformity .of character could be given. The variability, however, In the successive generations of mongrels is, perhaps, greater than in hybrids. This greater variability of mongrels than of hybrids does not seem to me at all surprising. For the parents of mongrels are varieties, and mostly domestic varieties (very few experiments having been tried on natural varieties), and this implies in most cases that there has been recent variability; and therefore we might expect that such variability would often continue and be superadded. to that arising from the rnere act of crossing. The slight degree of variability in hybrids from the first cross or in the first generation, in contrast with their ext:eme variability in the succeeding generations, is a curwus fact and deserves attention. For it bears on and corroborates the view which I have taken on the cause of ordinary variability; namely, that it is due to the reproductive system being eminently sensitive to any change in the conditions of life, being thus oft~n rendered either impotent or at least incapable o~ Its proper function of producing offspring identical Wit~ the parent-form. Now hybrids in the first generatiOn are descended from species (excluding those long. cultivated) which have not had their reproductive. systems in any way affected, and they are not ~ariable ; but hybrids themselves have their reproductive systems seriously affected, and their descendants are highly variable. B~t to return to our comparison of mongrels and hybnds: ?artner states that mongrels are more liable than hybrids to revert to either parent-form · but ~·I s, H I.t be true, is certainly only a differenc' e in degr~e. Gartner further insists that when any two species, although most closely allied to each other, are N 3 |