Halfbreed

“ Again, with respect to the fertility in successive generations of the more fertile hybrid animals, I hardly know of an instance in which two families of the same hybrid have been raised at the same time from different parents, so as to avoid the ill effects of close interbreeding. On the contrary, brothers and sisters have usually been crossed in each successive generation, in opposition to the constantly repeated admonition of every breeder. And in this case, it is not at all surprising that the inherent sterility in the hybrids should have gone on increasing. ”

“ The black form of the female was regarded for a long while as a distinct species, until by the test of breeding it was ascertained that some eggs laid by yellow females produced black females, and that, conversely, eggs laid by black females often produced yellow females. ”

“ But neither in the case of a breed which has been contaminated by a single cross, nor when, in the attempt to form an intermediate breed, half-bred animals have been matched together during many generations, can any rule be laid down how soon the tendency to reversion will be obliterated. It depends on the difference in the strength or prepotency of transmission in the two parent-forms, on their actual amount of difference, and on the nature of the conditions of life to which the crossed offspring are exposed. ”

“ If you cross two such species with each other, then,—although you may get offspring in the case of the first cross, yet, if you attempt to breed from the products of that crossing, which are what are called HYBRIDS—that is, if you couple a male and a female hybrid—then the result is that in ninety-nine cases out of a hundred you will get no offspring at all ”

“ Nevertheless I believe that in all these experiments the fertility has been diminished by an independent cause, namely, from close interbreeding. 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. Hybrids are seldom raised by experimentalists in great numbers ”

“ Yet it is to one of this class,Dzierzon, pastor of Carlsmarkt, in Silesia, that science ultimately owes the discovery of the true physiological relations which rule the generation of the race. The main facts are these :—the Queen bee, or perfect female, before impregnation lays eggs which produce Males only. After impregnation, which takes place but once in the course of her life time, the eggs pro duce male or female larvae according to the sort of cells in which they are laid. ”

“ It would be a matter of vast interest to determine what is the difference in the structure of the sperm-cells of a fertile and of an infertile male hybrid. At present, so far as I know, this has not been done.
So far what I have written applies to hybridization—the inter-breeding of distinct species. A similar but by no means identical subject is that of the inter-breeding of distinct races or varieties of one species, and the production of "mongrels." "Mongrels" are to races what "hybrids" are to species. ”

“ T. H. Morgan [Footnote: A Critique of the Theory of Evolution.] has observed a number of cases of sex-linked inheritance in the mutations which occurred in his cultures of Drosophila. The eye of the wild original fly is red, one of the mutants has a white eye, i.e. the red colour and its factor are absent. When a white-eyed male is mated to a red-eyed female all the offspring have red eyes. ”

“ First crosses between forms known to be varieties, or sufficiently alike to be considered as varieties, and their mongrel offspring, are very generally, but not quite universally, fertile. Nor is this nearly general and perfect fertility surprising, when we remember how liable we are to argue in a circle with respect to varieties in a state of Nature; and when we remember that the greater number of varieties have been produced under domestication by the selection of mere external differences, and not of differences in the reproductive system. ”

“ From the standpoint of heredity, however, the important consideration is to determine if these experimentally induced changes have been reflected on to the germ-cells so that they reappear in the offspring of the modified individuals.
It has been found that in some cases where male and female are of different color, the color of the female can be changed to that of the male by altering the conditions of temperature. In certain cases types can be changed by cold so that they resemble varieties of the same species found farther north, and by heat, varieties found farther south. ”

“ When these are mated, no matter which color is the father or the mother, the next or hybrid generation are always a queer mixture of black and white called by fanciers blue. When these blues are interbred, one-quarter of their offspring will be white, which will prove to breed true ever afterwards, one-quarter will be black that will breed true, and fifty per cent. will be blue which will break up in the next generation in the very same way as before. In this case neither white nor black character is dominant, and accordingly we have a blending of both in the first hybrid generation. ”

“ Consanguinity.—Before concluding this chapter we must study the question of hybrids. It is important to know to what point fecundity and descent are influenced by the degree of relationship between the two procreators. Conjugation probably arises from the general necessity of organisms to reënforce their race by variety. Consanguinity perpetuated is harmful to the species, in the same way as parthenogenesis, or indefinite reproduction by fission or budding. It produces enfeeblement and degeneration of the race, and leads to extinction by causing sterility. ”

“ The Seed is for the most part indifferent as to the two Sexes, and if it happens to meet with a Ball or Egg in the Horns of the Womb that is full of Spirits, and includes a hot, dry, and close Matter, it will impregnate so as to produce a Boy; but if the Seed meets with a Ball or Egg, not hot nor dry or fill'd with Spirits, tho' it will animate it, yet 'tis with less strength, so as a Girl will be produc'd. ”

“ The edge of the crest also is then tipped with bright red or violet. The female is usually of a yellowish-brown colour with scattered brown dots, and the lower surface is often quite plain. [44] The young are obscurely tinted. The ova are fertilised during the act of deposition, and are not subsequently tended by either parent. We may therefore conclude that the males have acquired their strongly-marked colours and ornamental appendages through sexual selection; these being transmitted either to the male offspring alone, or to both sexes. ”

“ A hybrid embryo which partakes of the constitution of its father and mother is exposed to unnatural conditions, as long as it is nourished within the womb, or egg, or seed of the mother-form; and as we know that unnatural conditions often induce sterility, the reproductive organs of the hybrid might at this early age be permanently affected. ”

“ The fact of infertility of this peculiar nature being one of the results of long-continued interbreeding, shows that interbreeding does not act merely by combining and augmenting various morbid tendencies common to both parents; for animals with such tendencies, if not at the time actually ill, can generally propagate their kind. Although offspring descended from the nearest blood-relations are not necessarily deteriorated in structure, yet some authors [78] believe that they are eminently liable to malformations ”

“ Thus, when a black bean e. c. is crossed with a white bean, all the offspring in the first generation will be black but hybrids. When two of these hybrids are then crossed, the dominant color black will be represented by 75 per cent. of the offspring and the recessive color white by 25 per cent., i. e., the offspring in the second generation, although both parents are black, will be three-fourths black and one-fourth white. For the gamete of two hybrid parents is always pure. The zygote of two hybrid parents is either pure or hybrid. ”

“ It is obvious that if half the germ-cells of the hybrid form are of the type B then half the progeny will be of the BW type, which is blue, and the other half will be of the WW type, which is white. In the same way if we mate a hybrid and a black fowl, half of the progeny will be black and half will be blue, that is, there could only be WB and BB types. ”

“ The mixing of hereditary units and blending of heritages is shown in the color of the skin, as where a mulatto child is born to a negress by a white father; mutually exclusive heritages are well illustrated in the color of the eyes, as where a child has either the blue eyes of one parent or the black of the other, but never any blending of the colors; this may also be illustrated where the white game bird and black one are crossed, the young being either white or black, but never blended. ”

“ By heredity he understands the production from a fertilized ovum of an individual, with all the general characteristics of structure and function of body and brain of the species to which it belongs. It means that the offspring, however much they may vary in general characters, will always be of the same species as the parents. The offspring of dogs will be dogs; of wolves, wolves; of negroes, negroes, and of white men, white men. Anything less is not heredity in its full sense. ”

“ To sum up, judging by the three species that form the subject of my investigations, the Halicti have two generations a year: one in the spring, issuing from the mothers who have lived through the winter after being fecundated in the autumn; the other in the summer, the fruit of parthenogenesis, that is to say, of reproduction by the powers of the mother alone. Of the union of the two sexes, females alone are born; parthenogenesis gives birth at the same time to females and males. ”

“ In pre-Mendelian times all that was known was that some forms could freely interbreed without diminution of fertility in the product, while others could not. But now we find that, by virtue of segregation, from one and the same pair of parents, or even, in the case of hermaphrodites, from one and the same individual, offspring commonly arises showing among themselves exactly such differences as distinguish species—and very good species too. ”

“ He also informs me that pure white beasts of either sex are so well known by experienced breeders to be comparatively infertile together, that they are never used for breeding purposes, so that "in some parts of the country, where a tendency to sterility had become so confirmed in the white race that they utterly died out," only the coloured breeds are now to be found. ”

“ We thus see hermaphrodite ants with one half of the body male and the other half female—black on one side and red on the other, a large eye on one side and a small eye on the other, thirteen joints in one antenna and twelve in the other, and so on. In this case the mental faculties are sometimes female, sometimes male, according as the ecphoria of the brain is influenced by the hereditary mneme of the male or female part of the hermaphrodite sexual organs, which results in a male or female brain. ”

“ But the sterility which must be obtained by the selective breeder in order to convert his morphological species into physiological species—such as we have in nature—must be quite irrespective of breeding in and in. ”

“ Individual varieties are constantly being formed and again funded back into the common stock by cross-breeding. If the varieties thus formed be decided, the cross-breeding will strengthen the stock, and especially will preserve and increase its plasticity or tendency to variation. Finally, among the widely divergent varieties there is one affecting the reproductive248 organs of several individuals in such wise that they are infertile, or imperfectly fertile, with the parent stock, though perfectly fertile among themselves. These form a new species, which continue to increase indefinitely. ”

“ We need not feel surprise at sterility incidentally resulting from crosses between distinct species,—the modified descendants of a common progenitor,—when we bear in mind how easily the reproductive system is affected by various causes—often by extremely slight changes in the conditions of life, by too close interbreeding, and by other agencies. ”

“ When black and white, or black and red birds, are crossed, it would appear that a slight tendency exists in both parents to produce blue offspring, and that this, when combined, overpowers the separate tendency in either parent to produce black, or white, or red offspring. ”

“ When we remember the large number of distinct characters which are presented by the very numerous varieties of any of our cultivated plants, we arrive at an understanding of the possibilities of improvement which the field of hybridization affords, yet I doubt if many of us have even then an adequate conception of the possibilities. Possibly I may make this more clear by an illustration from my timothy breeding experiments. ”

“ With this peculiar transition generation, which has arisen in the lower stages asexually, and in the following higher stages by the union of a male and a female cell, and which hence is hermaphrodite, there are generally associated later two other single generations—viz., a generation preceding and one following the hermaphrodite, the former as a sex-producing generation, the other as a sex-produced generation. ”