16. _Of marriage between blood-relations, in regard to which the present law could not bind the men of the earliest ages._ As, therefore, the human race, subsequently to the first marriage of the man who was made of dust, and his wife who was made out of his side, required the union of males and females in order that it might multiply, and as there were no human beings except those who had been born of these two, men took their sisters for wives,--an act which was as certainly dictated by necessity in these ancient days as afterwards it was condemned by the prohibitions of religion. For it is very reasonable and just that men, among whom concord is honourable and useful, should be bound together by various relationships; and that one man should not himself sustain many relationships, but that the various relationships should be distributed among several, and should thus serve to bind together the greatest number in the same social interests. "Father" and "father-in-law" are the names of two relationships. When, therefore, a man has one person for his father, another for his father-in-law, friendship extends itself to a larger number. But Adam in his single person was obliged to hold both relations to his sons and daughters, for brothers and sisters were united in marriage. So too Eve his wife was both mother and mother-in-law to her children of both sexes; while, had there been two women, one the mother, the other the mother-in-law, the family affection would have had a wider field. Then the sister herself by becoming a wife sustained in her single person two relationships, which, had they been distributed among individuals, one being sister, and another being wife, the family tie would have embraced a greater number of persons. But there was then no material for effecting this, since there were no human beings but the brothers and sisters born of those two first parents. Therefore, when an abundant population made it possible, men ought to choose for wives women who were not already their sisters; for not only would there then be no necessity for marrying sisters, but, were it done, it would be most abominable. For if the grandchildren of the first pair, being now able to choose their cousins for wives, married their sisters, then it would no longer be only two but three relationships that were held by one man, while each of these relationships ought to have been held by a separate individual, so as to bind together by family affection a larger number. For one man would in that case be both father, and father-in-law, and uncle[181] to his own children (brother and sister now man and wife); and his wife would be mother, aunt, and mother-in-law to them; and they themselves would be not only brother and sister, and man and wife, but cousins also, being the children of brother and sister. Now, all these relationships, which combined three men into one, would have embraced nine persons