this argument, Pius XI repeats that the conjugal act is intrinsically tied with procreation, but also acknowledges the unitive aspect of intercourse as licit. The encyclical affirms the Church's opposition to adultery and divorce, and speaks out against the eugenics laws, popular at that time, that forbade those deemed "unfit" from marrying and having children. Pope Pius XII Pope Pius XII in the years 1939-1942 delivered a series of lectures to the newly married couples of Rome which for decades became the basis for marital instruction in the US. Like Popes before him, and following the teachings of the Council of Trent, Pope Pius explained in Sacra virginitas that virginity is superior to marriage. He also rejects the view that the human body needs fulfillment of the sexual instinct for the sake of one's mental or physical health, or for the harmony of one's personality. In this context he criticized the cult of the body and disorderly love of oneself. Ethics In a 1951 speech to midwives, Pius XII stressed the inviolability of the human body as a creation of God and stated his opposition to all forms of genetic mercy killings. The right to life comes directly from God, not from the parents. He rejected any kind of sterilization as well. Like Pius XI, he extolled the sanctity of the sacrament of marriage, a place for peace and love, requiring often heroism by both partners. Parents have a role, not only to give physical love, but also to give spiritual life to their offspring. Pius criticized the traditional male role in marriage, stating that while the male member is head of the family, he should also participate in domestic chores, especially within families, where the mother is working full-time. Pius XII demands equal pay for equal work. Family planning Regarding natural family planning methods, Pope Pius XII distinguished between engaging in sexual intercourse during infertile days and the specific selection of these days for intercourse. He argued that, if a marital partner entered marriage with the intention to have intercourse only during infertile days in order to avoid having offspring, the marriage contract itself would be invalid. If, on the other hand, the marital partner has intercourse during infertile days only occasionally but not exclusively, then the marriage is legitimate. The intention, not the actual use of marital rights, is decisive. Pius XII illustrates this with the notion that