And we see that, since the human race has increased and multiplied, this is so strictly observed even among the profane worshippers of many and false gods, that though their laws perversely allow a brother to marry his sister, yet custom, with a finer morality, prefers to forego this licence; and though it was quite allowable in the earliest ages of the human race to marry one's sister, it is now abhorred as a thing which no circumstances could justify. For custom has very great power either to attract or to shock human feeling. And in this matter, while it restrains concupiscence within due bounds, the man who neglects and disobeys it is justly branded as abominable. For if it is iniquitous to plough beyond our own boundaries through the greed of gain, is it not much more iniquitous to transgress the recognised boundaries of morals through sexual lust? And with regard to marriage in the next degree of consanguinity, marriage between cousins, we have observed that in our own time the customary morality has prevented this from being frequent, though the law allows it. It was not prohibited by divine law, nor as yet had human law prohibited it; nevertheless, though legitimate, people shrank from it, because it lay so close to what was illegitimate, and in marrying a cousin seemed almost to marry a sister,—for cousins are so closely related that they are called brothers and sisters, and are almost really so. But the ancient fathers, fearing that near relationship might gradually in the course of generations diverge, and become distant relationship, or cease to be relationship at all, religiously endeavoured to limit it by the bond of marriage before it became distant, and thus, as it were, to call it back when it was escaping them. And on this account, even when the world was full of people, though they did not choose wives from among their sisters or half-sisters, yet they preferred them to be of the same stock as themselves. But who doubts that the modern prohibition of the marriage even of cousins is the more seemly regulation,—not merely on account of the reason we have been urging, the multiplying of relationships, so that one person might not absorb two, which might be distributed to two persons, and so increase the number of people bound together as a family, but also because there is in human nature I know not what natural and praiseworthy shamefacedness which restrains us from desiring that connection which, though for propagation, is yet lustful, and which even conjugal modesty blushes over, with any one to whom consanguinity bids us render respect?