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Updated: May 10, 2025
If a male and a female, selected from each group, produce offspring, and that offspring is fertile with others produced in the same way, the groups are races and not species. If, on the other hand, no result ensues, or if the offspring are infertile with others produced in the same way, they are true physiological species.
Groups having the morphological character of species distinct and permanent races in fact have been so produced over and over again; but there is no positive evidence, at present, that any group of animals has, by variation and selective breeding, given rise to another group which was, even in the least degree, infertile with the first. Mr.
On the other hand, not only is it not proved that all species give rise to hybrids infertile 'inter se', but there is much reason to believe that, in crossing, species exhibit every gradation from perfect sterility to perfect fertility. Such are the most essential characteristics of species.
Infertile eggs cannot heat because the germ has not been fertilized and can make no growth. That such infertile eggs cannot spoil is, however, a mistaken notion, for they are subjected to all the other factors by which eggs may be spoiled. The sale of eggs tested out of the incubators has been encouraged by the dissemination of the knowledge that infertile eggs are not changed by incubation.
So, again, there are cases known of animals which have been thought by naturalists to be undoubted species, which have yielded perfectly fertile hybrids; while there are other species which present what everybody believes to be varieties which are more or less infertile with one another.
"If Darwin is right, it must be demonstrated that forms may be produced by selection, which, like the present sharply distinguished animal forms, are infertile, when coupled with one another, and this has not been done."
Unions between these stocks, and still more between the half-breeds arising from their mixture, are affirmed to be either infertile, or less fertile than those which take place between males and females of either stock under the same circumstances.
The best way to feed beef-scrap is to keep a supply in the hopper so the chickens may help themselves. In case meat food is given, bone-meal, fed in small quantities, will form a valuable addition to their ration. Infertile eggs from incubators, as well as by-products of the dairy, can be used to help out in the animal-food portion of the ration. Chickens may be given all the milk they will drink.
From these facts; from the great difficulty of ascertaining the infertility of varieties in a state of nature, for a supposed variety if infertile in any degree would generally be ranked as species; from man selecting only external characters in the production of the most distinct domestic varieties, and from not wishing or being able to produce recondite and functional differences in the reproductive system; from these several considerations and facts, I do not think that the very general fertility of varieties can be proved to be of universal occurrence, or to form a fundamental distinction between varieties and species.
From its beginning the earthly study of economics has been infertile and unhelpful, because of the mass of unanalysed and scarcely suspected assumptions upon which it rested.
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