Page:The New International Encyclopædia 1st ed. v. 05.djvu/710

* CROSS-FERTILIZATION. 614 CROSS-FERTILIZATION. dcpeiulcut im aiiiiiuU life for the continuance of the species. Adrantages of Inlercrossing. — This brief ac- count of cross-fertilization of flowers shows, as pointed out li}' Darwin and others, that we ])rol)ably owe to the visits of insects and birds the peculiar and varied forms and structures of our most beautiful and attractive flowers, and that as the result of intercrossing the size, height, vigor, and fertility of the race or species is en- hanced. Yet with plants, as we shall see is the case with animals, the mere act of inter- crossing by itself does no good. Tlie good depends on the individuals which are crossed differing slightly in constitution, owing to their progenitors having been subjected during several generations to slightlj' different condi- tions. Cross-Fertilization in Animals and ilan. — In- tercrossing in animals, as among plants, may, within due limits, be beneficial. These limits are confined to the same variety, race, or stock. If individuals of widely different races or breeds intermix, (he result is degeneracy and steril- ity, the outcome of such unions being of the same natuie as hybrids between different though allied species. As Darwin states: "After plants have been propagated by self-fertilization for several generations, a single cross with a fresh stock restores their pristine vigor; and we have a "Strictly analogous result with oir domestic animals." This will apply to man also. When the French aristocracy was, as the result of the Revolution, broken up and forced to intermarry with the hoiirfjeoisie, the resiilt was an increase in the population and additional vigor in the race. An old family in its decline may be re- juvenated and restored by intermarriage with a more vigorous, even if a coarser, stock or strain. The population of our cities is main- tained by the constant influx of fresh blood from the rural districts. The mixture of the European races, now so marked, has been going on from early prehistoric (Neolithic) times. The French population is highly composite. The Anglo-Saxon race is equally or still more so, and the American peo- ple so in a still more marked degree; the inter- mixtiire being the result of emigration from the countries of northern and central Europe. It is not only that the old mixes with new stock, but the latter conies from regions differing in soil, climate, etc. Intermarriages between the stocks or breeds or strains of the white race are happy in their effects, resulting in in- creased vigor and fertility; and so with the stocks of the yellow, brown, or black races. The same law prevails throughout the animal world ; evei'ywhere Nature abhors too close in- breeding. Interracial Marriage. — lliscegenation. or 'mt>- tissage,' is marriage between individuals of widely different races — i.e. a high and a low race or variety. Its effects are bad physically and morally, since the product, like mules or hybrids between species, is inferior to the higher though superior to the lower race; the result is that, when general, the higher race is pulled down, or tends to degeneracy, while the lower is in a de- gree elevated. Hybrids, or half-castes, are no- toriously inferior to either pure race, though so partly from social causes. The results, so ap- jiarent in human history, show that crosses are injurious between races too far removed in physical characters and constitution, or where living under remote climatic conditions. While niarria.ucs between black or other backward races and white races are markedly evil in their ellccts, unions between those nearer allied, such as those between the white race and the •Japanese or the Polynesian or Malayan or North American Indian, also tend to result in sterility; on the other hand crosses between the yellow and brown races, and the brown and black, are apparently fertile, and (lie results not harmful. In-and-in Breeding. — The deleterious ell'ects of self-fertilization, or of marriage between l)lood- relatives, are recognized both l)y Darwin and by Wallace. Darwin found that certain plants which had been naturally cross-fertilized for many or all previous generations suffered to an extreme degree from a single act of self- fertilization. "Nothing of the kind," he adds, "has been obsened in our domestic animals; but then one must remember that the closest possible interbreeding with svich animals — that is, between brothers and sisters — cannot be con- sidered as nearly so close a union as that between the pollen and ovules of the same flower." Consanguineous Marriages. — The bearings of the previous statements on this important sub- ject are obvious. Yet the matter is involved in doubt, authorities differing. The popular notion is that marriages between first cousins result in disease, idiocy, insanity, sterility, etc. That the results are not. however, always deleterious is a matter of frequent observation. Darwin refers to his son's (G. H. Darwin) attempt to discover by a statistical investigation whetlier the mar- riages of first cousins are at all injurious, "al- though this is a degree of relationship which would not be objected to in our domestic ani- mals." It appears from these and other re- searches that "the evidence as to any evil thus caused is conflicting, but on the whole points to its being very small." He concludes "that with mankind the marriages of nearly related persons, some of whose parents or ancestors had lived under veiy different conditions, would be much less injurious than that of persons who had always lived in the same place and followed the same habits of life. Nor can I see reason to doubt that tlie widely different habits of life of men and women in civilized na- tions, especially among the upper classes, would tend to counterbalance any evil from marriages between healthy and somewhat closely related persons." Finally, to simi up the results thus far ob- tained, it appears, as conchided by Wallace, that a slight amount of crossing, attended by slight changes of the conditions of life, is beneficial ; while extreme changes and crosses between indi- viduals too far removed in structure or eonsti tvition are injurious. BiBLioGR.PHY. Hermann Miiller, The Fertiliza- tion of Floaers (Eng. trans. London, 1883) ; Wallace. Darwinism (London, 1880) ; Darwin, ]'nrious Contrivances bg Wliirli Orchids Are Fer- tilized by Insects (2d ed.. London, 1877) ; Effects of Cross and Helf Fertilization in the Vegetable Kingdom (2d ed., London. 18781 : Different Forms of Flou-ers on Plants of the Same Species (2d