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favour of monogenism. To confirm this conclusion, however, we must turn our attention to other facts which correspond to the idea of filiation, and consider the teachings of physiology concerning the phenomena of generation.
CROSSING OF RACES AND SPECIES IN THE ANIMAL AND
VEGETABLE KINGDOMS.-MONGRELS AND HYBRIDS.
I SEXUAL unions in plants, as in animals, can take place between individuals of the same species and the same race ; further, between different races of the same species, and, finally, between different species. In the two latter cases we have what is called a cross. This crossing itself is differently named according to whether it takes place between different races or different species. In the first case it produces a mongrel, in the second a hybrid. When the cross unions are fertile the product of the union of mongrels is called a mongrel, the product of the union of hybrids & hybrid.
If the difference of the relations existing between the race and the species has been properly understood, we ought to be inclined to admit that mongrels and hybrids would not present the same phenomena; experience and observation confirm this presentiment.
We have, therefore, in this crossing a means of judging whether the human groups are only races of a single species, or rather distinct species. For this purpose it will be sufficient to study the phenomena which, in other organised avd living beings, accompany the production of mongrels and hybrids, and then to compare with both the phenomena which characterise the crosses effected between human groups. If, in the latter case, the phenomena are those which characterise hybridism, we must conclude that the groups are specifically distinct, and admit the multiplicity of human species. If, however, crosses between human groups, morphologically different, are accompanied by phenomena peculiar to the production of mongrels, we shall only be justified in considering these groups as races of one species; we must take our stand upon the doctrine of the Specific Unity of all mankind.
The question before us becomes then entirely a physiological one, and depends simply upon observation and experiment. For its solution we must again turn our attention to plants as well as to animals. It is in the phenomena of reproduction that the two kingdoms show the greatest resemblance. This is not a case of mere analogy, but almost of identity, and it is not the superior which lowers itself but the inferior which is raised. We might say that, ennobled by the importance of the function, the plant, as far as its reproductive system is concerned, becomes, for the time, animal.
II. In these kingdoms the unions between races of the same species, that is to say, the production of mongrels, may be accomplished without any intervention on the part of man, or it may take place under his direction. It is consequently either natural or artificial.
Mongrels among plants could only be recognised after the discovery of the distinction of the sexes in 1744. The honour of this great discovery belongs to Linnæus. He at once comprehended the importance of the subject, and even exaggerated it, as we shall presently see. Linnæus admitted that cross-unions, which had been observed for centuries between animals, might be repeated between plants. And he thus explained the appearance of variegated tulips in the midst of borders originally formed of uniformly coloured flowers. Observation and experiment have confirmed the views of the founder of the natural sciences again and again. Moreover, it has been observed that the crossing may become apparent in all parts of the plant by a mixture of characters similar to that exhibited by the colouring of the tulips. M. Naudin, among others, who, during one year, watched the development of more than 1200 gourds, saw the seeds of a single fruit reproduce all the races contained in the garden
in which his observations were made. Superfetation bad taken place. It is a fact of great importance, as it demonstrates the equality of action enjoyed by the pollen of all these races, which, morphologically, differ so widely from each other. No better example could be given of the faculty of crossing between races.
The natural and spontaneous production of mongrels among animals presents the same characters. Facilitated by locomotion it is accomplished every day in our houses, our poultry-yards, and our farms. The difficulty does not consist in the accomplishment of the cross but in its prevention, and in the preservation of the purity of the race. The careful observations made by Isidore Geoffroy at the Paris Museum, have shown that with sheep, dogs, pigs, and fowls, mongrels between the most different races were invariably fertile. Here again the phenomena of superfetation was often proved. Bitches produced, by males of several races successively, young which showed three or four distinct sources. Here the case was the same as with the gourds of M. Naudin.
We see that man has found no difficulty in breeding mongrels, and that, when he has wished to do so for any purpose whatever, he has been able to regulate it by merely choosing the animal or plant. This kind of union has, indeed, been long in daily practice for the amelioration, modification, and diversification of the living beings upon which human industry is exercised. It is useless to insist upon facts which are known to all gardeners and breeders, and I shall confine myself to one remark, the importance of which will be understood later.
We have already seen that in the endeavour to perfect a vegetable or animal race, the physiological equilibrium has sometimes been destroyed at the expense of the reproductive power. In such cases, crossing with another race which is less modified, generally revives the extinguished fertility. For example, the English pigs imported into the middle of France by M. de Ginestous became sterile after several generations. Upon crossing them with a leaner and less perfect local race, their fertility returned.
All these facts, and their inevitable consequences, have been admitted by every naturalist who has studied the question. Even Darwin has recognised the truth of them in his valuable work upon the Variation of Animals and Plants. At that time he confined himself to the conclusion that the crosses between some races of plants are less fertile than between others, a proposition which no one would think of denying. He has gone further in the latest editions of his work upon the Origin of Species. Without bringing forward clear facts, the meaning of which would go further than the wise conclusions he bad previously admitted, he invokes our relative ignorance of what takes place among wild varieties, and concludes that we must admit that the crosses between varieties must always be perfectly fertile. This is one of those appeals to the unknown, one of those arguments where even our ignorance is invoked as a proof, which we too often meet with in Darwin, who is often carried away by his convictions. I shall have to return to this point, but I here make the statement as an established fact, on the authority even of Darwin, that all known facts attest the perfect fertility of mongrels.
Finally, the formation of crosses between races, or the production of mongrels, is spontaneous, and may be promoted by man without the least difficulty ; the results are as certain as those with the union of individuals of the same race ; in certain cases, indeed, fertility is increased or revived under the influence of this crossing.
Crosses between species, or hybrids, will exhibit facts of an entirely contrary nature.
III. The formation of hybrids, as of mongrels, may be either natural or artificial.
The former is so rare that eminent naturalists have doubted its reality. There are, however, according to M. Decaisne, a score of well proved examples among plants. What is this number compared with the thousands of