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418 become fixed. Finally, this principle extends into the field of psychology and throws light even upon the origin of our ethical aspirations. In short, in lieu of final causes we would have in organic nature a most complex but blindly acting mechanism; and the cosmic problem would be reduced to the two enigmas: "What are matter and force?" and, "How can these think?"

The objections to this doctrine of natural selection are essentially three in number:

The first group of its opponents simply question the facts on which the theory is based, namely, the tendency to variation, the transmissibility of varieties, the fecundity of hybrids, the mutability of species; above all, Darwin's very ingenious explanation of the dying out of intermediate forms. These opponents, however, urge but little beyond the arguments on which the doctrine of the old systematic school rested, and which have been shown by Darwin to be untenable. Still, there is one objection which possesses undoubted weight. I myself early called attention to it in my lectures, in which I believe I was the first public expositor of the new doctrine in Germany. The objection was not printed till much later, so far as I know, and then by Prof. A. W. Volkmann. It is this, that the minute variations in which new species are supposed to have their rise can not be of any material advantage to the individual in which they appear. Still, in my opinion, this objection applies only in certain cases, and perhaps only provisionally. In the case of electrical organs, for instance, it still seems to be unanswerable, for we can not assign any possible use for the so-called pseudo-electrical organs. But, as concerns wings, we see in the example of the flying opossum, the flying lemur, and of the flying frog, discovered by Wallace, how difficult it is to say of a rudimentary organ whether it is or is not of advantage to an animal. In short, the question is not whether this or that definite structure, but whether any adapted structure whatever, can be explained in the way pointed out by Mr. Darwin. In many cases of adaptation by mimicry, and of sexual selection, this is admitted by the great majority of naturalists; and this, as we shall see, is for the present enough.

The second group of opponents do not question the general correctness of the principle or the validity of natural selection in certain cases. But they object that the principle does not explain all structures. To suppose that it must, implies a misapprehension. It never was pretended that natural selection could, by itself alone, account for the fashioning of organic nature; laws of organic structure have always been supposed to act simultaneously with it. Mr. Darwin himself has dwelt on this aspect of the problem, but, as was natural, it has no paramount place in his treatise, despite its importance. If I mistake not, in the innumerable essays which have been written on the Darwinian theory, sufficient stress has not been laid on the fact that the laws of organic structure must account for whatever in organisms is either not