These facts of ape etiquette would, to use an Elizabethan phrase, have been ‘nuts’ to Mr. Atkinson, and prove that sexual separation of the children is a very early institution. In Australia, New Caledonia, and other countries, brothers and sisters must not even speak to each other, and must avoid each other utterly. Thus the danger and ‘sin’ of the most innocent intercourse between brothers and sisters is emphasised; much more awful, then, are matrimonial unions of brother and sister. ‘The extension’ (of this idea) ‘by the use of relationships produces the various forms of exogamy,’ says Mr. Crawley.[44] There are difficulties here; for example, Mr. Crawley tells us that incest did not ‘need prevention,’ though the rules of brother-and-sister avoidance seem really to mean that it did, or was thought to do so (but perhaps only superstitious dread of ordinary intercourse caused the rule?), and though we know of regions where such incest, in early youth, is said to be universal.[45] ‘Such incest,’ says Mr. Crawley, ‘is prevented by the psychological difficulty with which love comes into play between persons either closely associated, or strictly separated before the age of puberty....’[46] Now we know that lust does come into play--for example, among the Annamese--between brothers and sisters not closely separated; and we also know that, the more persons are ‘strictly separated,’ the more does the novelty and romance, when they do meet, produce natural attraction, as between Romeo and Juliet. Incest among the young is really prevented by the religious horror with which, by most peoples, it is regarded; as well as, among the civilised, by the constant and sacred familiarity of family life. The bare idea of it can only occur, as a desirable notion, to a boyish revolutionary, like Shelley, or to minds congenitally depraved. Again, men and women of the same totem have no ‘avoidances’ forced upon them, as far as I know (and, as they may not marry, this is an oversight); yet their marriages are as terribly sinful as marriages between brother and sister of the full blood. Mr. Crawley writes, ‘Obviously the one invariable antecedent in all exogamous systems, indeed in all marriage systems, is the prohibition of marriage “within the house.”’ But, we reply, A (a male) and B (a female), of the same totem, may never have been in the same house, or in the same degree of latitude and longitude, before they met and fell in love. As to ‘house,’ houses they may have none. Yet their union is a deadly sin. Mr. Robertson Smith is said to have ‘set the question in the right direction,’ when he wrote, ‘whatever is the origin of bars to marriage, they certainly are early associated with the feeling that it is indecent for house-mates to intermarry.’[47] But what is early need not be primary.