Monogamous marriage changes men psychologically, even hormonally, and has downstream effects on societies. Although this form of marriage is neither “natural” nor “normal” for human societies-and runs directly counter to the strong inclinations of high-status or elite men — it nevertheless can give religious groups and societies an advantage in intergroup competition. By suppressing male-male competition and altering family structure, monogamous marriage shifts men’s psychology in ways that tend to reduce crime, violence, and zero-sum thinking while promoting broader trust, long-term investments, and steady economic accumulation. Rather than pursuing impulsive or risky behaviors aimed at catapulting themselves up the social ladder, low-status men in monogamous societies have a chance to marry, have children, and invest in the future. High-status men can and will still compete for status, but the currency of that competition can no longer involve the accumulation of wives or concubines. In a monogamous world, zero-sum competition is relatively less important. So, there’s greater scope for forming voluntary organizations and teams that then compete at the group level.