We thus see that the great majority of savages extend their idea of incest much further than we do. The reason of this has been much discussed. It was formerly said that consanguineous marriage was contrary to the commandments of God; that it offended the natural sentiment of modesty; that it obscures relationship, etc. Nowadays, it is said to be injurious to posterity. Ethnography teaches us, however, that these statements are of little value.
Along with the exogamy of many tribes there is among other savages a system of endogamy, described by MacLennan; this is the prohibition of marriage between different clans. Spencer and MacLennan have different explanations of this custom which seem hardly natural. Westermark appears to be nearer the truth in remarking as follows: The sexual appetite, especially in man, is excited by new impressions and cooled by habit. It is not the fact of a man and woman being related, but intimate companionship since youth, which produces in them a repugnance to sexual union. We find the same repugnance between adopted brothers and sisters and between friends who have been intimate since childhood. When, on the contrary, brothers and sisters or near relatives have been separated from each other since an early age, they often fall in love with each other when they meet later on. There is, therefore, no innate or instinctive repugnance to incest in itself, but only against sexual union between individuals who have lived together since childhood. As it is parents and their children who are usually in this situation, everything is explained simply and clearly.
The causes of exogamy are explained in the same way, by the fact that members of the same clan often live together in close intimacy. It is the small clans, formed of thirty or fifty individuals of a few families living together, which have the most severe laws against incest or endogamy. Where the families live in separate homes, such prohibitions do not exist. The Maoris, who are endogamous, inhabit villages which are widely separated, and marriage between relations is allowed. Endogamy generally exists where the clan life is little developed, and where relatives know and see little of each other. The aversion to marriage between persons living together has thus created prohibition of marriage between relations as well as that of marriage between members of the same clan. It is the same reason which has led to the prohibition of marriage between brothers-and sisters-in-law, between brothers and adopted sisters, etc. In people living in small communities, endogamy does not appear to have ever existed.
Incest between relatives living together appears to have everywhere the same natural cause—the scarcity of women in isolated families living in remote districts. There is also a psycho-pathological form of incest associated with morbid appetites in the families of degenerates. In animals living alone and whose families break up very rapidly (cats for example) incestuous unions, between parents and young, for instance, are quite common.
Let us now consider the scientific side of the question. We see everywhere that sexual union between quite distinct animal species gives no result. At the most, certain closely allied species, such as the ass and the horse, the rabbit and the hare, give progeny which are themselves sterile (mules, etc.). The feebleness and sterility of hybrids derived from widely separated races or nearly allied different species proves the deficiency in vital force of the offspring of fundamentally dissimilar procreators. But, on the other hand, the dangers of continuous consanguineous reproduction are no less evident. Perpetual unions between brothers and sisters for several generations, lead to degeneration of the race. For example, the still-births will be 25 per cent. instead of 8 per cent., which is the figure in ordinary crossings. The prejudice against consanguineous unions may, however, depend on the accumulation of certain pathological defects.
Westermark admits that it is difficult to show clearly that consanguineous marriages are prejudicial in man. The consanguinity which causes evil effects in animals concerns long-continued unions between parents and children or brothers and sisters. But this never occurs in man. Animals and plants may be perpetuated for many years in the closest consanguinity without degeneration resulting. Among the Persians and Egyptians, intimate unions have existed for a long time without producing degeneration.
On the other hand, breeders of animals tell us that a single drop of new blood (or rather sperm) is enough to counteract all the evil effects of consanguinity. In man the most frequent incests are always interrupted by some other union. The Ptolemies, who nearly always married their sisters, nieces or cousins, lived long and were far from being sterile. In Ceylon, the Weddas perpetuate their consanguineous unions; insanity is rare among them, but they are small, unfruitful and tend to become extinct.
In Europe, the question of marriages between first cousins has been much discussed, and it has been constantly attempted to prove that they are injurious. Nevertheless, when we examine the question impartially, we always find that the prejudices against them do not arrive from consanguinity, but from certain pathological defects, such as insanity, hemophilia, etc., which are naturally perpetuated by consanguineous unions when they are accumulated in one family, as well as when two insane persons of different families marry. Therefore it is not consanguineous unions in themselves (which are always accidental in man and interrupted by others) but the hereditary reproduction of pathological defects, often of blastophthoric origin, which are the real cause of the evil. Statistics have clearly proved that marriage between first cousins plays no part in the causes of insanity.
Influenced, no doubt, by general opinion, Westermark tries to believe in some instinctive repulsion of man for consanguineous unions. If in modern society such unions, perpetuated between parents and children, brothers and sisters, were still produced as in animals I should agree that they might be injurious to the species; but, considering how cosmopolitan and mixed is our modern society, I cannot make the concession. On the contrary, I maintain that the isolated unions which still take place between relatives in civilized countries are so exceptional that they do not present the least danger, excepting among the families of degenerates. It is therefore only a question of superstition. What we have to guard against are unions between pathological individuals and blastophthoric influences. We must not forget that many degenerates and idiots have a great pathological tendency to incest, and this is no doubt why the effect has been confounded with the cause.
Westermark himself gives us a striking example. Since the most remote times the inhabitants of the Commune of Bats, composed of 3,300 persons, have intermarried; yet this population is very healthy and vigorous and shows no sign of degeneration. On the other hand, we have seen that contrasts produce a mutual attraction in the domain of love, while strong resemblances rather repel. Bernardin de St. Pierre has said that love is created by contrasts; the greater the contrast the greater the love. Schopenhauer remarks as follows: "Every individual seeks in the opposite sex peculiarities which contrast with his own; the most masculine man seeks the most feminine woman, while small and feeble men love large and strong women; people with short noses prefer long ones, tall and thin men prefer short and stout women. All this increases fecundity." Thus instinct is sufficient to protect humanity against consanguinity, each sex instinctively seeking the contrasts which consanguinity diminishes.