Figure 1. People across the globe engage in religious rituals that require a considerable amount of time or personal sacrifice. Ultraorthodox Jews spend hours every day worshiping at the Western Wall in Jerusalem (upper left). Vegans of Phuket, Thailand, perform various acts of self-torture, including bathing in hot oil, fire walking and piercing themselves with sharp implements during their annual vegetarian festival (upper right). Shiite Muslims in Karbala, Iraq, beat their backs with chains to mark the killing of one of their saints, Imam Hussein (lower left). And young Christian men in Bulgaria dive into icy waters to retrieve a crucifix to mark the feast of Epiphany Monday (lower right). From an evolutionary perspective these behaviors seem maladaptive, prompting anthropologists to ask why natural selection would favor a psychology that engages in such acts. It turns out that the answer can be found by studying the ecology of animal communication.