social rights and duties which are associated not with a common descent but with close living together. Dr. Frazer asks, — " If the root of the whole matter is a horror of marriage between persons who have always lived with each other, how comes it that at the present day that horror has been weakened into a mere general preference for marriage with persons whose attractions have not been blunted by long familiarity ? . . . Why should the marriage of a brother with a sister, or of a mother with a son, excite the deepest detestation, . . . while the origin of it all, the marriage between housemates, should excite at most a mild surprise too slight probably to suggest even a subject for a farce, and should be as legitimate in the eye of the law among all civilised nations as any other marriage ? " For my own part, I believe that marriage between a man and his foster-daughter, or between a foster-brother and a foster-sister, in case the social relations between them have been exactly similar to those of blood-relatives of corresponding degrees, would cause more than a mild surprise, and appear unnatural and objectionable. I do not deny that unions between the nearest blood-relatives inspire a horror of their own, but it seems quite natural that they should do so considering that from earliest times the aversion to sexual intercourse between persons living closely together has been expressed in prohibitions aga'nst unions between kindred. Such unions have been stigmatised by custom, law, and religion, whilst much less notice has been taken of inter- course between unrelated persons who may occasionally have grown up in the same household. Nor can it be a matter of surprise that the prohibitory rules so commonly refer to marriages of kindred alone. Law only takes into account general and well- defined cases, and hence relationships of some kind or other between persons who are nearly always kindred are defined in terms of blood-relationship. This is true not only of the pro- hibitions of incest, but of many duties and rights inside the family circle.
Dr. Frazer raises another objection to my theory. He argues that, if exogamy resulted from a natural instinct, there would be no need to reinforce that instinct by legal pains and penalties ; the law only forbids men to do what their instincts incline them to do, and hence we may always safely assume that crimes forbidden by