It is impossible here to do more than indicate the character of the evidence by which Westermarck powerfully supports his conclusion. Among the Greenlanders, for instance, "it would be reckoned uncouth and blamable, if a lad and a girl, who had served and been educated in one family, desired to be married to one another." It is even "preferred that the contracting parties should belong to different settlements."[385] Among the Kandhs, according to Colonel Macpherson, "marriage cannot take place even with strangers who have been long adopted into, or domesticated with, a tribe;" and the Cis-Natalian Kafirs are reputed to "dislike marriage between persons who live very closely together, whether related or not."[386] Further proof is derived from the fact that "many peoples have a rule of exogamy, which does not depend on kinship at all." Piedrahita, in the seventeenth century, "relates of the Panches of Bogota that the men and women of one town did not intermarry, as they held themselves to be brothers and sisters, and the impediment of kinship was sacred to them; but such was their ignorance that, if a sister were born in a different town from her brother, he was not prevented from marrying her."[387] So also the "Yaméos, on the river Amazon, will not suffer an intermarriage between members of the same community 'as being friends in blood, though no real affinity between them can be proved;'" and the Uaupés, of the same region, "do not often marry with relations, or even neighbours, preferring those from a distance, or even from other tribes."[388]

The great variation in the extent of prohibited degrees found among nations is "nearly connected with their close living together." Savage and barbarous peoples, "if they have not remained in the most primitive social condition of man, live, not in separate families, but in large households or communities, all the members of which dwell in very close contact with each other." Such are the house-communities of the American aborigines, found everywhere, from the "long houses" of the Iroquois to the vast pueblos or "cities" of Mexico and Yucatan;[389] the "joint undivided families" of the Hindus and Southern Slavs;[390] and the trevs or clan households of ancient Wales, comprising four generations living in one inclosure, whose members are forbidden to intermarry.[391] It is significant that in all such cases we find extended prohibitions of close intermarriage, which do not exist "where the family lives more separately." In fact, there is a marked tendency, amounting almost to a law, that the larger the family or clan group, the wider is the circle of forbidden degrees; and, on the contrary, the more isolated and dispersed the manner of life, the greater is the liberty of matrimonial choice.[392]

In the same way prohibition of marriage on the ground of "affinity" or "spiritual relationship" may take place. "By association of ideas" the "feeling that two persons are intimately connected in some way" may "give rise to the notion that marriage or intercourse between them is incestuous." A strong argument is also derived from the "classificatory system of consanguinity." Tylor has shown that this system and the system of exogamy are, in most cases, found together. They are the "two sides of one institution."[393]

But a deeper and still more interesting question remains: "How has this instinctive aversion to marriage between persons living closely together originated?" We cannot help feeling that through his masterly solution of this difficult problem Westermarck has at last brought us very near to the truth. He finds the key to it in the biological law of similarity.[394] It is demonstrated that a "certain degree of similarity as regards the reproductive system of two individuals is required to make their union fertile and the progeny resulting from this union fully capable of propagation." But the similarity must not be too close. A certain amount of differentiation is requisite; but the differentiation must not be too great.[395] There must be homogeneity combined with heterogeneity. Among domestic animals close interbreeding, it is well known, leads to infertility and degeneration; and Darwin's researches prove that self-fertilization in the vegetable kingdom produces the same results.[396] There is abundant evidence tending to show that what is true of plants and the lower animals is true also of man. "Taking all these facts into consideration," says Westermarck, in closing his argument, "I cannot but believe that consanguineous marriages, in some way or other, are more or less detrimental to the species. And here, I think, we may find a quite sufficient explanation of the horror of incest; not because man at an early stage recognized 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; and those of our ancestors who avoided in-and-in breeding would survive, while the others would gradually decay and ultimately perish. Thus an instinct would be developed which would be powerful enough, as a rule, to prevent injurious unions. Of course it would display itself simply 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 the feeling from the predecessors from whom he sprang, or whether it was developed after the evolution of distinctly human qualities, we do not know."[397]

Exogamy appears, then, to be the result of natural selection, arising "when single families united in small hordes. It could not but grow up if the idea of union between persons intimately associated with one another was an object of innate repugnance." Conversely, the law of similarity enables us to understand the coexistence of clan-exogamy and tribal endogamy. The one springs from a horror of sexual union between persons who are too near; the other arises in a dislike of connection between those who are too remote. Among primitive men, and sometimes even among those well advanced in civilization, there exists a shrinking from physical contact with strange races only less violent than the aversion which the dread of incest excites. But this prejudice yields to the sympathy produced by the growing similarity of interests, ideas, sentiments, and general culture among men. Sympathy, upon which affection mainly depends, has widened the sphere of sexual selection.[398]

IV. THE PROBLEM OF THE SUCCESSIVE FORMS OF THE FAMILY

From the preceding analysis it will appear, we trust, that scientific examination of the problems of kinship and exogamy has disclosed something of the real origin of the laws which govern human sexual relations. The searching criticism to which the theory of polyandry has been subjected, in connection with the opposite custom of polygyny, carries us still nearer the truth. For, in the light of recent research, it does not seem entirely hopeless to discover a trace of the actual sequence in which, according to natural law, the general forms of marriage and the family have been evolved.

According to McLennan, it will be remembered, polyandry originates in a scarcity of women due to female infanticide; and it is a universal phase of social progress through which transition is made from promiscuity and the system of kinship in the female line to the paternal system and higher types of family life. Furthermore, he seems to think, though on this point he is not very clear,[399] that polygyny may grow out of polyandry through the practice of capturing wives. This theory has by no means gone unchallenged.[400] It has been shown, in the first place, that the extent to which the custom of polyandry has prevailed is greatly exaggerated. Though it is found among various peoples in different parts of the world, its occurrence is on the whole comparatively rare; and the practice is much less extended than that of polygyny. Its former existence cannot be inferred from such customs as the niyoga and the levirate; for these are capable of simpler explanation.[401] It is highly probable, as Starcke urges, that they are merely expedients for procuring an heir or for conveniently regulating the succession to property and authority,[402] particularly in the joint family; but there is no good reason to doubt that Spencer's explanation is adequate in some cases. "Under early social systems," he declares, "wives, being regarded as property," are inherited like other possessions.[403] The procuring of an heir through a brother or some other third person harmonizes with the "juridical character of fatherhood among primitive men."[404]

Again, not only is the general extent of polyandry limited, but even where it exists it is confined in almost every case "to a very small part of the population."[405] It is sometimes restricted to the poorer classes, sometimes to the rich; and nearly always it is found side by side with polygyny or monogamy. There is another limitation, already noticed, which tells very strongly against the theory of its origin in promiscuity. Polyandry usually shows a tendency in the direction of monogamy. Sometimes each of the husbands lives with the wife during a certain period, while the others are absent; or frequently, "as one, usually the first married, wife in polygynous families is the chief wife;" so also, "one, usually the first, husband in polyandrous families is the chief husband." In him authority and the property are vested, and all the children, even, are feigned to be his.[406]