| → is due, as I believe, 1859 1860 1861 1866 |
| seems to be partly due 1869 1872 |
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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
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
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
or any
seed freely under culture; nor can he
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
in successive generations are eminently liable to vary, as every experimentalist has observed. |
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| Thus we see that when organic beings are placed under new and unnatural conditions, and when hybrids are produced by the unnatural crossing of two species, the reproductive system, independently of the general state of health, is affected
in a very similar manner. In the one case, the conditions of life have been disturbed, though often in so slight a degree as to
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