[25] I do not understand how any reader of my book can, like Herr Cunow (op. cit. p. 186 sqq.), attribute to me the statement that the group within which intermarriage is prohibited is identical with the group of people who live closely together. If he had read a little more carefully what I have said, he might have saved himself the trouble he has taken to prove my great ignorance of early social organisations.
[26] Cf. Tylor, Early History of Mankind, p. 285 sq.
[27] Nansen, Eskimo Life, p. 230.
The question arises:—How has this instinctive aversion to marriage and sexual intercourse in general between persons living closely together from early youth originated? I have suggested that it may be the result of natural selection. Darwin’s careful studies of the effects of cross- and self-fertilisation in the vegetable kingdom, the consensus of opinion among eminent breeders, and experiments made with rats, rabbits, and other animals, seem to have proved that self-fertilisation of plants and close inter-breeding of animals are more or less injurious to the species; and it is probable that the evil chiefly results from the fact that the uniting sexual elements were not sufficiently differentiated. Now it is impossible to believe that a physiological law which holds good of the rest of the animal kingdom, as also of plants, would not apply to man as well. But it is difficult to adduce direct evidence for the evil effects of consanguineous marriages. We cannot expect very conspicuous results from other alliances than those between the nearest relatives—between brothers and sisters, parents and children,—and the injurious results even of such unions would not necessarily appear at once. The closest kind of intermarriage which we have opportunities of studying is that between first cousins. Unfortunately, the observations hitherto made on the subject are far from decisive. Yet it is noteworthy that of all the writers who have discussed it the majority, and certainly not the least able of them, have expressed their belief in marriages between first cousins being more or less unfavourable to the offspring; and no evidence which can stand the test of scientific investigation has hitherto been adduced against this view. Moreover, we have reason to believe that consanguineous marriages are much more injurious in savage regions, where the struggle for existence is often very severe, than they have proved to be in civilised societies, especially as it is among the well-to-do classes that such marriages occur most frequently.
Taking all these facts into consideration, I am inclined to think that consanguineous marriages are in some way or other detrimental to the species. And here I find a quite sufficient explanation of the horror of incest; not because man at an early stage recognised the injurious influence of close intermarriage, but because the law of natural selection must inevitably have operated. Among the ancestors of man, as among other animals, there was no doubt a time, when blood-relationship was no bar to sexual intercourse. But variations, here as elsewhere, would naturally present themselves—we know how extremely liable to variations the sexual instinct is; and those of our ancestors who avoided in-and-in breeding would survive, while the others would gradually decay and ultimately perish. Thus a sentiment would be developed which would be powerful enough, as a rule, to prevent injurious unions. Of course it would display itself, not as an innate aversion to sexual connections with near relatives as such, but as an aversion on the part of individuals to union with others with whom they lived; but these, as a matter of fact, would be blood-relations, so that the result would be the survival of the fittest. Whether man inherited this sentiment from the predecessors from whom he sprang, or whether it was developed after the evolution of distinctly human qualities, we cannot know. It must have arisen at a stage when family ties became comparatively strong, and children remained with their parents until the age of puberty or even longer. And exogamy, resulting from a natural extension of this sentiment to a larger group, would arise when single families united into hordes.
This attempt to explain the prohibition of marriage between kindred and exogamy has not lacked sympathetic support,[28] but more commonly, I think, it has been rejected. Yet after a careful consideration of the various objections raised against it I find no reason to alter my opinion. Some of my opponents have evidently failed to grasp the argument on which the theory is based. Thus Professor Robertson Smith argued that it begins by presupposing the very custom which it professes to explain, the custom of exogamy; that “it postulates the existence of groups which through many generations (for the survival of the fittest implies this) avoided wiving within the group.”[29] But what my theory postulates is not the existence of exogamous groups, but the spontaneous appearance of individual sentiments of aversion. And if, as Mr. Andrew Lang maintains, my whole argument is a “vicious circle,”[30] then the theory of natural selection itself is a vicious circle, since there never could be a selection of qualities that did not exist before.
[28] A. R. Wallace, in his ‘Introductory Note’ to my History of Human Marriage, p. vi. Giddings, Principles of Sociology, p. 267. Howard, History of Matrimonial Institutions, i. 125 sqq. Sir E. B. Tylor (in Academy, xl. 289) says with regard to my theory that, at any rate, I am “well on the track.” See also Crooke, Tribes and Castes of the North-Western Provinces and Oudh, i. pp. clxxix, clxxx, ccii.
[29] Robertson Smith, in Nature, xliv. 271.
[30] Lang, Social Origins, p. 33.
It has been argued that if close living together calls forth aversion to sexual intercourse, such aversion ought to display itself between husband and wife as well as between near relatives.[31] But these cases are certainly not identical. The feeling of which I have spoken is aversion associated with the idea of sexual intercourse between persons who have lived in a long-continued intimate relationship from a period of life when the action of sexual desire is naturally out of the question.[32] On the other hand, when a man marries a woman his feeling towards her is of a very different kind, and his love impulse may remain, nay increase, during the conjugal union; though even in this case long living together has undoubtedly a tendency to lead to sexual indifference and sometimes to positive aversion. The opinion that the home is kept free from incestuous intercourse only by law, custom, and education,[33] shows lack of discrimination. Law may forbid a son to marry his mother, a brother to marry his sister, but it could not prevent him from desiring such a union. Have the most draconic codes ever been able to suppress, say, homosexual love? As Plato observed, an unwritten law defends as sufficiently as possible parents from incestuous intercourse with their children, brothers from intercourse with their sisters; “nor does the thought of such a thing ever enter at all into the minds of most of them.”[34] Considering the extreme variability to which the sexual impulse is subject, it is not astonishing that cases of what we consider incestuous intercourse sometimes do occur. It seems to me more remarkable that the abhorrence of incest should be so general, and the exceptions to the rule so few.