Rhedi writes to Usbek on the decline in the world’s population, especially in Europe and Asia: “It’s as if I am witnessing the aftermath of plague, and of famine” (150). Usbek replies by delineating the creationist concept of time and ponders “that such cataclysms have occurred frequently on earth, ever since the creation of the world” (152). He next writes about how the Muslim precept that a man will have at least four wives—“who are more likely to exhaust than to satisfy” (153)—must enfeeble his virility, rendering him less productive. Additionally, eunuchs and virginal female slaves all contribute to lower reproduction. In his succeeding letter, Usbek notes that Christian slaves were encouraged to reproduce and organize communities, each having a trade, thus enabling both master and slave to pursue their sexual desires without having to keep women hidden or retain many guards to watch them.

Usbek next talks about the Catholic tenet of forbidding divorce, which has negatively influenced populations as couples are forced to spend their whole life “burdened with each other” (155) instead of pursuing other people once their match is spent. He claims the Spartan practice of exchanging wives would be quite beneficial and writes that the many priests, monks, and nuns vowed to chastity in Catholicism are another cause for decreased population.