These statements, of course, prove nothing, but they may perhaps derive some value from the fact that they are made by so many different observers. The statistical investigation of Professor Alphonse de Candolle, bearing upon the same question, rests on firmer ground. He has found, from facts collected in Switzerland, North Germany, and Belgium, that marriages are most commonly contracted between persons with different colours of the eye, except in the case of brown-eyed women, who are generally considered more attractive than others.[2061] He has noted, further, that the number of children is considerably smaller in families where the parents have the same colour of the eye than where the reverse is the case.[2062] But Professor Wittrock could not, in Sweden, find any such difference in fecundity between the two categories of marriages;[2063] and Mr. Galton observes, “Whatever may be the sexual preferences for similarity or for contrast, I find little indication in the average results obtained from a fairly large number of cases, of any single measurable personal peculiarity, whether it be stature, temper, eye-colour or artistic tastes, influencing marriage selection to a notable degree.”[2064] If contrasts instinctively seek each other, this may partly account for the readiness with which love awakens love. Every one knows some unhappy lover who has never been able to win the heart of the person he adores; but in most cases, I should say, love is mutual. And this, perhaps, is owing not only to the contagiousness of the passion, but also to the attractive power of contrasts, which acts equally upon both parties. Thus we might explain, to some extent, the extreme variation of tastes, and the fact that, besides the general standard of beauty common to the whole race, there exists a more detailed ideal special to each individual. CHAPTER XVI SEXUAL SELECTION AS INFLUENCED BY AFFECTION AND SYMPATHY, AND BY CALCULATION Sexual love is the passion which unites the sexes. The stimulating impressions produced by health, youth, and beauty, and ornaments and other artificial means of attraction, are all elements of this feeling. The antipathy to sexual intercourse with individuals of another species, and the horror of incest, belong to the same phenomenon. But the psychology of love is by no means exhausted by this. “Simple et primitif comme toutes les forces colossales,” says Professor Mantegazza, “l’amour paraît pourtant formé des éléments de toutes les passions humaines.”[2065] Around the sexual appetite as the leading element there are aggregated many different feelings, such as admiration, pleasure of possession, love of freedom, self-esteem, and love of approbation.[2066] A complete analysis of love would fill a volume. Here I shall discuss only one of the most important elements of this highly compound feeling, the sentiment of affection.