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Updated: May 25, 2025
Yet interbreeding has doubtless been an important element in the elaboration of the stupendous caste organization. We have abundant illustration of this very process and its results in modern times. Among the Dravidians, especially, there are many castes which trace their origin to miscegenation.
In like manner, if animals breed freely inter se before our eyes, as for example the horse and ass, the fact was to be noted, but no animals were to be classed as capable of interbreeding until they had asserted their right to such classification by breeding with tolerable certainty.
Horticulturists raise large beds of the same hybrids, and such alone are fairly treated, for by insect agency the several individuals of the same hybrid variety are allowed to freely cross with each other, and the injurious influence of close interbreeding is thus prevented.
I do not doubt that this is usually the case, and that the fertility often suddenly decreases in the first few generations. Nevertheless I believe that in all these experiments the fertility has been diminished by an independent cause, namely, from close interbreeding.
Under such circumstances, the variety can only have been preserved through not interbreeding with the common form, either from a dislike to such unions, or by some amount of sterility when they are formed.
For in such cases, we may believe, that a plant could exist only where the conditions of its life were so favourable that many could exist together, and thus save the species from utter destruction. I should add that the good effects of intercrossing, and the ill effects of close interbreeding, no doubt come into play in many of these cases; but I will not here enlarge on this subject.
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 Parallelism between the effects of changed conditions of life and crossing Fertility of varieties when crossed and of their mongrel offspring not universal Hybrids and mongrels compared independently of their fertility Summary.
I have collected so large a body of facts, showing that close interbreeding lessens fertility, and, on the other hand, that an occasional cross with a distinct individual or variety increases fertility, that I cannot doubt the correctness of this almost universal belief amongst breeders.
I have no theory in regard to the origin of the Ainos, who are most likely the aboriginal inhabitants. They are quite evidently a distinct race from the Japanese proper, although of course there has been some interbreeding between them. The language of Japan naturally suggests some reference to its literature, of which there is no lack, either ancient or modern.
So long as they interbreed together, the possible divergence is kept within narrow limits, but whenever a variety is produced, the individuals of which have a partiality for interbreeding, and some amount of sterility when crossed with the parent form, the tie that bound it to the central stock is loosened, and the foundation is laid for the formation of a new species.
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