“Do men need to cheat on their women?” a Playboy headline asked in the summer of 1978. Their not-so-surprising conclusion: Yes! Science says so! The idea that men are promiscuous by nature, while women are chaste and monogamous, is an old and tenacious one. As far back as Darwin, scientists were churning out theory and evidence that backed this up. In this episode, Annie and Elah go back to the 1970s and 1980s, when feminism and science come face to face, and it becomes clear that a lot of animals—humans and bluebirds included—are not playing by the rules.