Sleep is essential to cognitive function and health in humans, yet the ultimate reasons for sleep - that is, 'why' we sleep - remains mysterious. This course integrates research findings from human sleep studies, the ethnographic record, and the ecology and evolution of mammalian and primate sleep to better understand sleep along the human lineage and in the modern world. Students will learn how to use 'wearable' technology, such as actigraphy, for scientific research. The goal of the course is to empower students with the theoretical and technological tools to be able to not only critically assess their own sleep-wake behaviour and performance but also popular generalizations about how to maximize long-term health outcomes.