Could a marriage policy first pursued by the Catholic Church a millennium and a half ago explain what made the industrialized world so powerful—and so peculiar?
Around 597 a.d., Pope Gregory I dispatched an expedition to England to convert the Anglo-Saxon king of Kent and his subjects. The leader of the mission, a monk named Augustine, had orders to shoehorn the new Christians into Church-sanctioned marriages. That meant quashing pagan practices such as polygamy, arranged marriages (Christian matrimony was notionally consensual, hence the formula “I do”), and above all, marriages between relatives, which the Church was redefining as incest. Augustine wasn’t sure who counted as a relative, so he wrote to Rome for clarification. A second cousin? A third cousin? Could a man marry his widowed stepmother?
He could not. Pope Gregory wrote back to rule out stepmothers and other close kin not related by blood—another example was brothers’ widows. He was lax about second and third cousins; only the children of aunts and uncles were off-limits. By the 11th century, however, you couldn’t get engaged until you’d counted back seven generations, lest you marry a sixth cousin. The taboo against consanguineous family had expanded to include “spiritual kin,” who were, mostly, godparents. (It went without saying that you had to marry a Christian.) Pope Gregory and Augustine’s letters document a moment in a prolonged process—begun in the fourth century—in which the Church clamped down, and intermittently loosened up, on who could marry whom. Not until 1983 did Pope John Paul II allow second cousins to wed.