This, in fact, is the great bar to the
domestication of animals. Between the sterility thus superinduced and
that of hybrids, there are many points of similarity. In both cases
the sterility is independent of general health, and is often
accompanied by excess of size or great luxuriance. In both cases, the
sterility occurs in various degrees; in both, the male element is the
most liable to be affected; but sometimes the female more than the
male. In both, the tendency goes to a certain extent with systematic
affinity, for whole groups of animals and plants are rendered impotent
by the same unnatural conditions; and whole groups of species tend to
produce sterile hybrids. On the other hand, one species in a group
will sometimes resist great changes of conditions with unimpaired
fertility; and certain species in a group will produce unusually
fertile hybrids. No one can tell, till he tries, whether any
particular animal will breed under confinement or any plant seed
freely under culture; nor can he tell, till he tries, whether any two
species of a genus will produce more or less sterile hybrids. Lastly,
when organic beings are placed during several generations under
conditions not natural to them, they are extremely liable to vary,
which is due, as I believe, to their reproductive systems having been
specially affected, though in a lesser degree than when sterility
ensues. So it is with hybrids, for hybrids in successive generations
are eminently liable to vary, as every experimentalist has observed.
Pages:
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324