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282 of direct evidence, for how otherwise could the breeding be accomplished? Then what a most extraordinary thing it would be if she were excited in precisely the same degree—not one jot or tittle more or less—by any one male as by any other! Whatever the nature of that sexual appeal may be which every cock makes to every hen, and by virtue of which she feels that he is a cock, and not a hen like herself, why should we suppose that any two individuals should be more exactly alike in it than they are in anything else? But if there is not this absolute unity, then there is difference, and such difference in the degree of the sexual charm flung out by each male, must produce preference and choice in the female. The whole theory of evolution is based upon the undisputed and indisputable fact of individual variability; nor is there any one thing or quality, bodily or mental—amongst the higher animals at least—that does not vary largely in the different individuals possessing it. As it appears to me, therefore, choice in the one sex with regard to the other is what might have been, on a priori considerations, expected; though I can well understand that, as amongst ourselves, it would often be held in abeyance, or nullified, by the operation of higher—that is to say, more inexorable—laws, and also that its manifestations would often be too subtle and hidden for us to follow them. But we first, in deference to our human prejudices, assume something which is improbable in itself, and then obstinately resist a mass of the