Page:Popular Science Monthly Volume 1.djvu/80

70 different species or to two different races. Well, the results of these marriages obey the following laws, which are:

When this union takes place between two animals belonging to different species—that is, when we attempt hybridization—in the immense majority of cases the marriage is sterile. Thus, for example, it has been tried thousands of times and in all the world, to unite rabbits and hares. It is said that they have succeeded twice. But these two quoted facts are much more doubtful than the results of experiments recently made by a man of true talent, skilled in the art of experimenting, and who believes in the possibility of these unions, who has completely failed. Although he furnished the best conditions for success, he was not more fortunate in his results than Buffon, and the two Geoffroy Saint-Hilaires before him.

So the rabbit and the hare are of such a nature that, although presenting in appearance a great conformity, they cannot reproduce together.

Such is the general result of crossing two different species.

In many cases, the union of two individuals of different species is fertile, but the offspring cannot reproduce. For example, I refer you to the union of the ass and horse. This union produces the mule. All the mules in the world are offspring of the jackass and the mare. Now, these animals are numerous, for in Spain and in tropical America they are much preferred for work to horses, because of their resistance to fatigue. The hinny, less in demand, because less robust than the mule, is the result of an inverse cross; it is the offspring of the horse and the ass. The hinny, like the mule, cannot reproduce its kind. When we wish for either, we must have recourse to the two species.

Finally, in extremely rare exceptions, the fertility persists in the offspring, but it is much diminished. It diminishes still more in the grandchildren, and it is extinguished in the third or fourth generation at the most. This is the case when we unite the canary bird with the goldfinch.

I might here accumulate a mass of analogous facts and details. But over them all would appear a great general fact including them, which is the expression of a law; and here is this fact: notwithstanding observations reaching back for thousands of years, and made on hundreds of species, we do not yet know a single example of intermediate species obtained by the crossing of animals belonging to different species.

This general fact explains how order is maintained in the present living creation. If it had been otherwise, the animal world and the vegetable world would be filled with intermediate groups, passing into each other by insensible shades, and, in the midst of this confusion, it would be impossible for even naturalists to discriminate.

The general conclusion from all this is, that infertility is the law when animals of different species unite.