Augustine of Hippo, Against Two Letters of the Pelagians I.31: Thirdly, of Conjugal Intercourse

“We say,” says he, “that the sexual impulse—that is, that the virility itself, without which there can be no intercourse—is ordained by God.” To this I reply that the sexual impulse, and, to make use of his word, virility, without which there can be no intercourse, was so appointed by God that there was in it nothing to be ashamed of. For it was not fit that His creature should blush at the work of his Creator; but by a just punishment the disobedience of the members was the retribution to the disobedience of the first man, for which disobedience they blushed when they covered with fig-leaves those shameful parts which previously were not shameful.