The energy and vitality of fair people is not, however, it is probable, merely an indirect cause of the greater tendency of fair men to become husbands; that is to say, it is not merely the result of the generally somewhat greater ability of the fair to attain success in temporal affairs. In addition to this, fair men, if not fair women, would appear to show a tendency to a greater activity in their specifically sexual proclivities. This is a point which we shall encounter in a later Study and it is therefore unnecessary to discuss it here.
In dealing with the question of sexual selection in man various writers have been puzzled by the problem presented by that abhorrence of incest which is usually, though not always so clearly marked among the different races of mankind.[[184]] It was once commonly stated, as by Morgan and by Maine, that this abhorrence was the result of experience; the marriages of closely related persons were found to be injurious to offspring and were therefore avoided. This theory, however, is baseless because the marriages of closely related persons are not injurious to the offspring. Consanguineous marriages, so closely as they can be investigated on a large scale,—that is to say, marriages between cousins,—as Huth was the first to show, develop no tendency to the production of offspring of impaired quality provided the parents are sound; they are only injurious in this respect in so far as they may lead to the union of couples who are both defective in the same direction. According to another theory, that of Westermarck, who has very fully and ably discussed the whole question,[[185]] "there is an innate aversion to sexual intercourse between persons living very closely together from early youth, and, as such persons are in most cases related, this feeling displays itself chiefly as a horror of intercourse between near kin." Westermarck points out very truly that the prohibition of incest could not be founded on experience even if (as he is himself inclined to believe) consanguineous marriages are injurious to the offspring; incest is prevented "neither by laws, nor by customs, nor by education, but by an instinct which under normal circumstances makes sexual love between the nearest kin a psychic impossibility." There is, however, a very radical objection to this theory. It assumes the existence of a kind of instinct which can with difficulty be accepted. An instinct is fundamentally a more or less complicated series of reflexes set in action by a definite stimulus. An innate tendency at once so specific and so merely negative, involving at the same time deliberate intellectual processes, can only with a certain force be introduced into the accepted class of instincts. It is as awkward and artificial an instinct as would be, let us say, an instinct to avoid eating the apples that grew in one's own yard.[[186]]
The explanation of the abhorrence to incest is really, however, exceedingly simple. Any reader who has followed the discussion of sexual selection in the present volume and is also familiar with the "Analysis of the Sexual Impulse" set forth in the previous volume of these Studies will quickly perceive that the normal failure of the pairing instinct to manifest itself in the case of brothers and sisters, or of boys and girls brought up together from infancy, is a merely negative phenomenon due to the inevitable absence under those circumstances of the conditions which evoke the pairing impulse. Courtship is the process by which powerful sensory stimuli proceeding from a person of the opposite sex gradually produce the physiological state of tumescence, with its psychic concomitant of love and desire, more or less necessary for mating to be effected. But between those who have been brought up together from childhood all the sensory stimuli of vision, hearing, and touch have been dulled by use, trained to the calm level of affection, and deprived of their potency to arouse the erethistic excitement which produces sexual tumescence.[[187]] Brothers and sisters in relation to each other have at puberty already reached that state to which old married couples by the exhaustion of youthful passion and the slow usage of daily life gradually approximate. Passion between brother and sister is, indeed, by no means so rare as is sometimes supposed, and it may be very strong, but it is usually aroused by the aid of those conditions which are normally required for the appearance of passion, more especially by the unfamiliarity caused by a long separation. In reality, therefore, the usual absence of sexual attraction between brothers and sisters requires no special explanation; it is merely due to the normal absence under these circumstances of the conditions that tend to produce sexual tumescence and the play of those sensory allurements which lead to sexual selection.[[188]] It is a purely negative phenomenon and it is quite unnecessary, even if it were legitimate, to invoke any instinct for its explanation. It is probable that the same tendency also operates among animals to some extent, tending to produce a stronger sexual attraction toward those of their species to whom they have not become habituated.[[189]] In animals, and in man also when living under primitive conditions, sexual attraction is not a constant phenomenon[[190]]; it is an occasional manifestation only called out by the powerful stimulation. It is not its absence which we need to explain; it is its presence which needs explanation, and such an explanation we find in the analysis of the phenomena of courtship.
The abhorrence of incest is an interesting and significant phenomenon from our present point of view, because it instructively points out to us the limits to that charm of parity which apparently makes itself felt to some considerable extent in the constitution of the sexual ideal and still more in the actual homogamy which seems to predominate over heterogamy. This homogamy is, it will be observed, a racial homogamy; it relates to anthropological characters which mark stocks. Even in this racial field, it is unnecessary to remark, the homogamy attained is not, and could not be, absolute; nor would it appear that such absolute racial homogamy is even desired. A tall man who seeks a tall woman can seldom wish her to be as tall as himself; a dark man who seeks a dark woman, certainly will not be displeased at the inevitably greater or less degree of pigment which he finds in her eyes as compared to his own.
But when we go outside the racial field this tendency to homogamy disappears at once. A man marries a woman who, with slight, but agreeable, variations, belongs to a like stock to himself. The abhorrence of incest indicates that even the sexual attraction to people of the same stock has its limits, for it is not strong enough to overcome the sexual indifference between persons of near kin. The desire for novelty shown in this sexual indifference to near kin and to those who have been housemates from childhood, together with the notable sexual attractiveness often possessed by a strange youth or maiden who arrives in a small town or village, indicates that slight differences in stock, if not, indeed, a positive advantage from this point of view, are certainly not a disadvantage. When we leave the consideration of racial differences to consider sexual differences, not only do we no longer find any charm of parity, but we find that there is an actual charm of disparity. At this point it is necessary to remember all that has been brought forward in earlier pages[[191]] concerning the emphasis of the secondary sexual characters in the ideal of beauty. All those qualities which the woman desires to see emphasized in the man are the precise opposite of the qualities which the man desires to see emphasized in the woman. The man must be strong, vigorous, energetic, hairy, even rough, to stir the primitive instincts of the woman's nature; the woman who satisfies this man must be smooth, rounded, and gentle. It would be hopeless to seek for any homogamy between the manly man and the virile woman, between the feminine woman and the effeminate man. It is not impossible that this tendency to seek disparity in sexual characters may exert some disturbing influences on the tendency to seek parity in anthropological racial characters, for the sexual difference to some extent makes itself felt in racial characters. A somewhat greater darkness of women is a secondary (or, more precisely, tertiary) sexual character, and on this account alone, it is possible, somewhat attractive to men[[192]]. A difference in size and stature is a very marked secondary sexual character. In the considerable body of data concerning the stature of married couples reproduced by Pearson from Galton's tables, although the tall on the average tend to marry the tall, and the short the short, it is yet noteworthy that, while the men of 5 ft. 4 ins. have more wives at 5 ft. 2 ins. than at any other height, men of 6 ft. show, in an exactly similar manner, more wives at 5 ft. 2 ins. than at any other height, although for many intermediate heights the most numerous groups of wives are taller[[193]].
In matters of carriage, habit, and especially clothing the love of sexual disparity is instinctive, everywhere well marked, and often carried to very great lengths. To some extent such differences are due to the opposing demands of more fundamental differences in custom and occupation. But this cause by no means adequately accounts for them, since it may sometimes happen that what in one land is the practice of the men is in another the practice of the women, and yet the practices of the two sexes are still opposed[[194]]. Men instinctively desire to avoid doing things in women's ways, and women instinctively avoid doing things in men's ways, yet both sexes admire in the other sex those things which in themselves they avoid. In the matter of clothing this charm of disparity reaches its highest point, and it has constantly happened that men have even called in the aid of religion to enforce a distinction which seemed to them so urgent[[195]]. One of the greatest of sex allurements would be lost and the extreme importance of clothes would disappear at once if the two sexes were to dress alike; such identity of dress has, however, never come about among any people.
L. da Vinci, Frammenti, selected by Solmi, pp. 177-180.