Chapter VI · DARWIN’S THEORY OF SEXUAL SELECTION (continued 2)

3. If the female fails to select only the more ornamental males, no result will follow. It has not been shown that she is capable of making such a choice, and in the lower forms particularly, it does not seem probable that this is done. The argument that Darwin often employs, namely, that unless she does select, the display of the males before her is meaningless, is not to the point. So far as we can detect the “cause” of the display of the male, it appears to be due to his own excitement; and even if we go so far as to admit that the “purpose” is to attract the other sex, it still does not in the least follow that the most ornamental male is selected, and unless this occurs the display has no bearing on the hypothesis of sexual selection.

4. The two forms of sexual selection, namely, competition of the males with one another (really one form of natural selection), and the selection of the most ornamental or gifted individuals, are both used by Darwin to explain secondary sexual characters, the one for organs of offence and defence, and the other for ornamental characters. If we fully appreciate the difficulties that any theory of selection meets with, we shall realize how extraordinarily complex the action must be, when two such processes are carried out at the same time, or even during alternating periods.

5. It has been objected to Darwin’s theory of sexual selection, that he suddenly reverses its mode of action to explain those cases in which the female is the stronger and more ornamented sex; but if, as Darwin shows, the instincts of the male have also changed, and have become more like those of the female, I can see no inherent difficulty in this way of applying the theory. A much more serious objection, it seems to me, is that the male is supposed to select the female for one set of characteristics, and the female to select the 216male for another set. It sounds a little strange to suppose that women have caused the beard of man to develop by selecting the best-bearded individuals, and the compliment has been returned by the males selecting the females that have the least amount of beard. It is also assumed that the results of the selection are transmitted to one sex only. Unless, in fact, the character in question were from the beginning peculiar to only one sex as to its inheritance, the two sexes might go on forever selecting at cross-purposes, and the result would be nothing.

6. The development, or the presence, of the æsthetic feeling in the selecting sex is not accounted for on the theory. There is just as much need to explain why the females are gifted with an appreciation of the beautiful, as that the beautiful colors develop in the males. Shall we assume that still another process of selection is going on, as a result of which those females are selected by the males that appreciate their unusual beauty, or that those females whose taste has soared a little higher than that of the average (a variation of this sort having appeared) select males to correspond, and thus the two continue heaping up the ornaments on one side and the appreciation of these ornaments on the other? No doubt an interesting fiction could be built up along these lines, but would any one believe it, and, if he did, could he prove it?

Darwin assumes that the appreciation on the part of the female is always present, and he thus simplifies, in appearance, the problem, but he leaves half of it unexplained.

7. It has been pointed out, that it is important to distinguish between the possible excitement of the female by the display or antics of the male, and the selection of the more beautiful or agile performer. Darwin himself records a few cases, which plainly show that the more beautiful is not always the more successful. It has also been suggested that the battles of the males are sometimes sham performances, and even when they are real, if the less vigorous do not remain 217to be destroyed but run away, they live to find mates of their own. In fact, the conduct of the males at the breeding season appears to be much more the outcome of their own excitement than an attempt to attract the females.

8. There is another side to the question, the importance of which is so great, that it is surprising that Darwin has not taken any notice of it. If, in order to bring about, or even maintain, the results of sexual selection, such a tremendous elimination of individuals must take place, it is surprising that natural selection would not counteract this by destroying those species in which a process, so useless for the welfare of the species, is going on. It is curious that this has not been realized by those who believe in both of these two hypotheses.

9. What has just been said applies also with almost equal force to the development of such structures as the horns of deer, bison, antelopes, and the brilliant colors of many insects and birds. If in nature, competition between species takes place on the scale that the Darwinian theory of natural selection postulates, such forms, if they are much exposed, would be needlessly reduced in numbers in the process of acquiring these structures. So many individuals would have been at such a disadvantage in breeding, that if competition is as severe as the theory of natural selection postulates, these species could hardly be expected to compete successfully with other species in which sexual selection was not taking place.

10. Darwin admits that, in certain cases, external conditions may have acted directly to produce the colors in certain forms, and if these were not injurious he thinks they might have become constant. Such cases are left unexplained in the sense that they are not supposed to be adaptations to anything in particular. That colors produced in this way might afterward be found useful, irrespective of how they arose, is admitted as one of the ways in which sexual differences may have arisen.

21811. It is baffling to find Darwin resorting to the Lamarckian explanation in those cases in which the improbability of the hypothesis of sexual selection is manifest. If either principle is true, we should expect it to apply to all phenomena of the same sort; yet Darwin makes use of the Lamarckian principle, in the hypothesis of sexual selection, only when difficulties arise.

12. In attempting to explain the development of the musical sense in man, it is clear that the hypothesis of sexual selection fails to give a satisfactory explanation. To suppose that the genius of a Beethoven or of a Mozart could have been the result of a process of sexual selection is too absurd to discuss. Neither the power of appreciation nor of expression in music could possibly have been the outcome of such a process, and it does not materially help the problem to refer it back to a troop of monkeys making the woods hideous with their cries.

We come now to some of the special cases to which Darwin’s hypothesis has been applied.

13. In one case at least, it is stated that a bird living on the ground might have acquired the color of the upper surface of the body through natural selection, while the under surface of the males of the same species might have become ornamented through the action of sexual selection. Thus in one and the same individual the two processes are supposed to have been at work, and it does not lessen the difficulty very much by supposing the two processes to have been carried out at different times, because it is evident that what had been gained at one time by one process might become lost while the color of certain parts was being acquired through the other process.

14. Darwin points out that “the plumage of certain birds goes on increasing in beauty during many years after they are fully mature,” as in the peacock, and in some of the birds of paradise, and with the plumes and crests of some herons. 219This is explained as possibly merely the result of “continued growth.” The improbability of selection is manifest in these cases, but if “continued growth” can accomplish this much, why may not the whole process be also the outcome of such growth? At any rate, whatever the explanation is, it is important to find a case of a secondary sexual character that the hypothesis obviously is insufficient to explain.

15. It is admitted in a number of cases, as in the stag for instance, that, although the larynx of the male is enlarged, this is not, in all probability, the outcome of sexual selection, but in other forms this same enlargement is ascribed to the selection process.

16. It is admitted that in none of the highly colored British moths is there much difference according to sex, although when a difference of color is found in butterflies this is put down to the action of sexual selection. If such wonderful colors as those of moths can arise without the action of selection, why make a special explanation for those cases in which this difference is associated with sex?

17. It is well known that birds sing at other times of the year than at the breeding season, and an attempt is made to account for this in that birds take pleasure in practising those instincts that they make use of at other times, as the cat plays with the captive mouse. Does not this suggest that, if they had certain instincts, they would be more likely to employ them at the times when their vitality or excitement is at its highest without regard to the way in which they have come by them?

18. The color of the iris of the eyes of many species of hornbills is said to be an intense crimson in the males, and white in the females. In the male condor the eye is yellowish brown, and in the female a bright red. Darwin admits that it is doubtful if this difference is the result of sexual selection, since in the latter case the lining of the mouth is black in the males, and flesh-colored in the females, which does not 220affect the external beauty. Yet if these colors were more extensive and on the exterior, there can be little doubt that they would have been explained as due to sexual selection.

19. When the females in certain species of birds differ more from each other than they do from their respective males, the case is compared to “those inexplicable ones, which occur independently of man’s selection in certain sub-breeds of the game-fowl, in which the females are very different, whilst the males can hardly be distinguished.” Here then is a case of difference in color associated with sex, but not the outcome of sexual selection.

20. The long hairs on the throat of the stag are said possibly to be of use to him when hunted, since the dogs generally seize him by the throat, “but it is not probable that the hairs were specially developed for this purpose; otherwise the young and the females would have been equally protected.” Here also is a sexual difference that can scarcely be ascribed to selection.

Some cases of differences in color between the sexes “may be the result of variations confined to one sex, and transmitted to the same sex without any good being gained, and, therefore, without the aid of selection. We have instances of this with our domesticated animals, as in the males of certain cats being rusty-red while the females are tortoise-shell colored. Analogous cases occur in nature: Mr. Bartlett has seen many black varieties of the jaguar, leopard, vulpine phalanger, and wombat; and he is certain that all or nearly all of these animals were males.” If changes of this sort occur, associated with one sex, why is there any need of a special explanation in other cases of difference?

In the light of the many difficulties that the theory of sexual selection meets with, I think we shall be justified in rejecting it as an explanation of the secondary sexual differences 221amongst animals. Other attempts to explain these differences have been equally unsuccessful. Thus Wallace accounts for them as due to the excessive vigor of the male, but Darwin’s reply to Wallace appears to show that this is not the cause of the difference. He points out that, while the hypothesis might appear plausible in the case of color, it is not so evident in the case of other secondary sexual characters, such, for instance, as the musical apparatus of the males of certain insects, and the difference in the size of the larynx of certain birds and mammals.

Darwin’s theory served to draw attention to a large number of most interesting differences between the sexes, and, even if it prove to be a fiction, it has done much good in bringing before us an array of important facts in regard to differences in secondary sexual characters. More than this I do not believe it has done. The theory meets with fatal objections at every turn.

In a later chapter the question will be more fully discussed as to the sense in which these secondary sexual differences may be looked upon as adaptations.

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