In this episode, Keith introduces me to his theory of human sociability. As he sees it, human relationships can be seen on a spectrum of playing and fighting. Playing is a cooperative activity with an agreed-upon set of rules. Sometimes play is pure fun, and sometimes winning/losing dynamics are painful. But any engaged activity under an external set of rules is considered play. Fighting is trying to dominate the other, with little or no regard for a shared set of rules. Three outcomes of fighting are domination, submission, or a shift to cooperation (play). Both playing and fighting are human superpowers that can be used for better or worse. Dr Keith and I explore the play/fight current through all of humanity, delivering surprising insights into intimate relationships, politics, and evolution.