CHAPTER IX. HYBRIDISM.
7. HYBRIDS AND MONGRELS COMPARED, INDEPENDENTLY OF THEIR FERTILITY.
Independently of the question of fertility, the offspring of species and of
varieties when crossed may be compared in several other respects. Gartner,
whose strong wish it was to draw a distinct line 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 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 hybrids; 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 this shows that the difference in the
degree of variability graduates away. When mongrels and the more fertile
hybrids are propagated for several generations, an extreme amount of
variability in the offspring in both cases is notorious; but some few
instances of both hybrids and mongrels long retaining a uniform character
could be given. The variability, however, in the successive generations of
mongrels is, perhaps, greater than in hybrids.
This greater variability in mongrels than in hybrids does not seem 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 that there has been recent variability; which would often
continue and would augment that arising from the act of crossing. The
slight variability of hybrids in the first generation, in contrast with
that in the succeeding generations, is a curious fact and deserves
attention. For it bears on the view which I have taken of one of the
causes of ordinary variability; namely, that the reproductive system, from
being eminently sensitive to changed conditions of life, fails under these
circumstances to perform its proper function of producing offspring closely
similar in all respects to 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 variable; but hybrids themselves have their reproductive systems
seriously affected, and their descendants are highly variable.