Whatever observations may have been made, the prohibition of incest is in no case founded on experience. Had the savage man discerned that children born of marriage between closely related persons are not so sound and vigorous as others, he would scarcely have allowed this knowledge to check his passions. Considering how seldom a civilised man who has any disease, or tendency to disease, which is likely to be transmitted to his descendants, hesitates to marry an equally unhealthy woman, it would surely be unreasonable to suppose that savages have greater forethought and self-command.[1900] But even if we admit that man originally avoided marriage with near kin from sagacious calculation, and that he did this during so long a period that usage grew into law, we do not advance a step further. All the writers whose hypotheses have been considered in this chapter, assume that men avoid incestuous marriages only because they are _taught_ to do so. “It is probable,” says Mr. Huth, “that, if brothers and sisters were allowed to marry, they would do so while yet too young.”[1901] But though law and custom may prevent passion from passing into action, they cannot wholly destroy its inward power. Law may forbid a son to marry his mother, a brother his sister, but it could not prevent him from desiring such a union if the desire were natural. Where does that appetite exist? The home is kept pure from incestuous defilement neither by laws, nor by customs, nor by education, but by an _instinct_ which under normal circumstances makes sexual love between the nearest kin a psychical impossibility. An unwritten law, says Plato, defends “as sufficiently as possible,” parents from incestuous intercourse with their children, brothers from intercourse with their sisters: “ἀλλ’ οὐδ’ ἐπιθυμία ταύτης τῆς συνουσίας τὸ παρ ‘παν εἰσέρχεται τοὺς πολλοὺς”—“nor does even the desire for this intercourse come at all upon the masses.”[1902] CHAPTER XV PROHIBITION OF MARRIAGE BETWEEN KINDRED (_Concluded_) It has been asserted that, if there be really an innate horror of incest, it ought to show itself intuitively when persons are ignorant of any relationship. But ancient writers state that, in Rome, incestuous unions often resulted from the exposure of infants who were reared by slave-dealers. Not long ago Selim Pasha unwittingly married his sister, who, like himself, had been a Circassian slave. The story told in the ‘Heptameron’ of a double incest was probably true, and became widely spread; and so on. Man has thus no horror of marriage with even the nearest kindred if he is unaware of their consanguinity; consequently, Mr. Huth concludes, there is no innate feeling against incest.[1903]