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Distinction between the sterility of first crosses and of hybrids. Sterility various in degree, not universal, affected by close interbreeding, removed by domestication. Laws governing the sterility of hybrids. Sterility not a special endowment, but incidental on other differences. Causes of the sterility of first crosses and of hybrids.
This constant interbreeding of individuals will tend to prevent the formation of many modifications in the machine which become started by variations. Now plainly if some such individuals, with a peculiar variation, should migrate into a new territory or become isolated from their relatives which do not have similar variations, these individuals will be obliged to breed with each other.
It was the call of his breed, growing in him slowly but insistently. He was still a wanderer pupamootao, the Indians call it. It is this "wander spirit" that inspires for a time nearly every creature of the wild as soon as it is able to care for itself nature's scheme, perhaps, for doing away with too close family relations and possibly dangerous interbreeding.
The general fact of variability, and the general tendency of the variety to propagate its like the patent facts that all species vary more or less; that domesticated plants and animals, being in conditions favorable to the production and preservation of varieties, are apt to vary widely; and that, by interbreeding, any variety may be fixed into a race, that is, into a variety which comes true from seed.
It does very greatly help in this question to bear in mind the conflict of our origins. Every age is an age of transition, of minglings, of the breaking up of old, narrow cultures, and the breaking down of barriers, of spiritual and often of actual interbreeding. Not only is the physical but the moral and intellectual ancestry of everyone more mixed than ever it was before.
And thus, the strange fact of the increase of fertility in the successive generations of artificially fertilised hybrids may, I believe, be accounted for by close interbreeding having been avoided. Now let us turn to the results arrived at by the third most experienced hybridiser, namely, the Hon. and Rev. W. Herbert.
'He wants me, and I would dearly love to bear his child..... If we could only mix our blood with theirs, through interbreeding, maybe we could end the tragedy of sure death in adolescence. 'But they will only mate in the North, she continued, stepping back and clearing her eyes with the back of her wrist. 'How..... How can I reach him? She could only repeat herself, an echo of tragedy.
In attempting to rescue us from the ape as our ancestor, they have shown that we are descendants of the whole monkey family and every species of ape and of many of their more disreputable relatives also. Great is evolution! It certainly would be impossible for one single pair to have become the ancestors of the human race, without mixing and interbreeding with their kindred primates.
Horticulturists raise large beds of the same hybrid, and such alone are fairly treated, for by insect agency the several individuals are allowed to cross freely with each other, and the injurious influence of close interbreeding is thus prevented.
The Standard Dictionary says that the term is used for "a classificatory group of animals or plants subordinate to a genus, and having members that differ among themselves only in minor details of proportion and color, and are capable of fertile interbreeding indefinitely."
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