We’ve evolved to consider sex, the researchers argue, as a game of finite resources. For our ancestors, multiple sexual partners meant things could get knotty when it came to proving whose kids were whose. For women who depended on men for their livelihoods (and the livelihoods of their offspring), that uncertainty meant losing out on the support of their male partners. Bad news. For men, it meant investing in the well-being of children they hadn’t necessarily fathered. Also bad news.

The connection between sexual behavior and morality, then, may have come about as a way of keeping a gender-based social order intact. “Through moralizing,” the researchers wrote, “individuals can promote behavior which serves their own personal and coalitional interests.” Back in the day, judgment was a form of defense.