Finally, there was one meta-justification for birth control that brought together the others in a dense, actionable nugget: “modern life” or “the times.” For Americans asking themselves whether to have two children or three, or any children at all, modernity was a bleeding reality, not an academic abstraction. The demand for smaller families seemed to spring from history itself—from the faster, riskier, more open-ended world that had replaced the “old-fashioned” world of one’s parents, grandparents, and ancestors. Rationality (or greed), pragmatism (or faithlessness), mastery of fate (or hubris): Americans disagreed passionately about whether birth control was part of the good or the bad in modern life, but they agreed that history itself seemed to demand ever-tighter control over fertility. The best-adapted people always seemed to have the smallest families.

The idea that the olden days were friendlier to families is hardly airtight as empirical history. Demographers have documented steep drops in fertility rates among illiterate Bulgarian peasants, for example, and stable high ones in industrial England. In the United States, birth rates began to drop in a period when huge majorities still lived in rural areas, women lacked independence, secondary education was rare, churches were strong, contraceptives were rudimentary, child mortality was high (about 20 percent), and nonfamily farm labor did not come cheap. After World War II, fertility climbed in the United States—though not because Americans suddenly desired large families; the Baby Boom was a result of more Americans deciding to have small or medium-size families rather than none at all. To this day, no one has succeeded in writing a formula for higher or lower fertility: There is no single explanation, only possibilities of varying likelihood.