CHAPTER XII.

STERILITY OF HYBRIDS.

An objection, which has ever obtained, to Darwin's theory, is the fact of the sterility of species, when crossed, or the sterility of the hybrids from a cross between two species. This has ever precluded the idea of the evolution of one species into another.

Since varieties cross readily, and their offspring are fertile, this feature, of the sterility of hybrids, clearly appears to be a fundamental distinction between varieties and species.

Darwin admits the fact, of the sterility of species when crossed, or of their hybrids, and recognizes the antagonism it bears to his hypothesis.

He says (p. 293, Origin of Species):

"Hybrids * * have their reproductive organs functionally impotent, as may be clearly seen in the state of the male element in both plants and animals; though their formative organs themselves are perfect in structure, as far as the microscope reveals."

Again, on p. 299, Origin of Species, he says:

"I doubt whether any case of a perfectly fertile hybrid can be considered as thoroughly well authenti

cated."

On p. 27, Origin of Species, he says:

"It is difficult, perhaps impossible, to bring forward

one case of the hybrid offspring of two animals, clearly distinct, being themselves perfectly fertile."

On page 327, Origin of Species, he says:

"The perfect fertility of the many domestic varieties differing widely from each other in appearance, for instance those of the Pigeon or (those) of the cabbage, is a remarkable fact; more especially when we reflect, how many species there are which though resembling each other most closely, are utterly sterile, when crossed."

On page 126, Vol. ii, Animals and Plants, &c., he

says:

* *

"The domestic races of both animals and plants, when crossed, are with extremely few exceptions, quite fertile. The offspring, also, raised from such crosses, are likewise generally more vigorous and fertile than their parents. On the other hand, species when crossed, and their hybrid offspring are almost invariably, in some degree sterile; and here there seems to exist a broad and insuperable distinction (sic) between races and species."

On page 213, Vol. ii, Animals and Plants, &c., he says that, where species are crossed, "though size is often gained, fertility is lost."

On page 490 of same volume, he says:

"There is, however, one important constitutional difference (!) between domestic races and species. I refer to the sterility which almost invariably follows, • in a greater or less degree, when species are crossed, and the perfect fertility of the most distinct domestic races, with the exception of very few plants, when similarly crossed. It certainly appears à remarkable fact, that many closely allied species, which in appearance differ extremely little, should yield, when united,

only a few more or less sterile offspring, or none at all; whilst domestic races, which differ conspicuously from each other, are when united, remarkably fertile, and yield perfectly fertile offspring."

He finds it impossible to reconcile this sterility, with his theory. But, he has endeavored to show, that the objection may not be so conclusive against his theory, as it appears to be. He essays this, in two ways, each of which betrays about as cool a device as may be conceived.

He argues, (1) that the objection should not be deemed conclusive, because there is an infinite number of degrees of fertility, and of sterility, among even individuals of the same species, all of which phenomena, he says, are inexplicable; and argues that, therefore, our ignorance of such phenomena, deprives us of a full assurance, that the obvious and conceded import of the sterility of hybrids, is the true one!

He argues further, (2) "that the invariable sterility of first crosses between species, and of their hybrids, is not a special endowment, but is incidental on modifications slowly impressed, by unknown means, on the reproductive systems of the parent forms."

I. It is on page 327 of his Origin of Species, that he advances the first argument (?). He there exclaims, "how ignorant we are on the precise causes of sterility;" and asserts, that, in presence of all the cases of lessened fertility, and of sterility, among individuals of the same species, "we must feel how ignorant we are, and how little likely it is, that we should understand, why certain forms are fertile and other forms are sterile when crossed."

It is in pursuance of this design, to show "how ignorant we are," and thus to weaken the force of the principal objection to his theory; that he, in his different. works, devotes such an amount of space, to the many instances of crossing and of close-interbreeding, of which "we are so ignorant."

It is with this same design, that he says (p. 462, Vol. ii, Animals and Plants, &c.):

"With respect to the sterility of hybrids, produced from the union of two distinct species, it was shown in the xixth chapter, that this depends exclusively on the reproductive organs being specially affected; but, why these organs should be thus affected, we do not know any more (sic) than why unnatural conditions of life, though compatible with health, should cause sterility, or why continued close-interbreeding, or the illegitimate union of dimorphic or trimorphic plants should induce the same result."

The idea he wishes to convey, is, that the whole subject of sterility and of fertility, forms such an inextricable maze, that it is presumption, in any one, to say, that any aspect of the question, either rebuts, or confirms, any theory. In other words: instead of explaining anything to his readers, he demands of them to give up, for his gratification, the little positive knowledge they have upon the subject, merely because there is quite a number of similar orders of facts which seem inexplicable! It is a curious feature, discernible throughout all of Darwin's works purporting to prove the evolution of the species, that his hypothesis absolutely demands, that an embargo should be laid on the acquisition of any knowledge of the cause of any class

of facts he has in hand. His theory requires, that all of the phenomena of Variation, of Reversion, of Correlation, of Crossing, of Close-Interbreeding, of Generation, &c., be deemed inscrutable, ultimate in their character, and absolutely inexplicable. True it is, that his theory demands this, not without reason; for, as the reader sees, knowledge of the causes of these phenomena, explodes his theory.

The answer, to be made to his argument of an appeal to every person's ignorance of the causes of the evil effects of close-interbreeding, and of the good resulting from crossing individuals of the same species, is,—that there is no such ignorance!—all of the phenomena, to which he appeals, as being inexplicable, are susceptible, as has been fully shown in previous chapters of this book, of a full qualitative and quantitative explanation. Evil effects flow from the interbreeding of individuals of the same species, because such individuals have characters of their species, reduced or suppressed. Those differences in the quantity of effects, which make Darwin so confident, that the subject is hopelessly confused, are simply due to corresponding degrees of defective development, in the individuals so interbred. The good resulting from the crossing of varieties, is, as has been shown, due to the fact, that one variety contributes, to the offspring, a character or characters which the other variety lacks; and the physiological gain, evidenced in the fertility resulting, is because, by such contribution of characters, the mongrel offspring has removed the nearer to the perfect type of the species. Those dif