Humans need food, sleep, safety, love, purpose. Psychologist Abraham Maslow ordered our needs into a hierarchy. This week, TED speakers explore that spectrum of need, from primal to profound. Guests include psychologist Margie Lachman, neuroscientist Russell Foster, computer security expert Bruce Schneier, journalist Sebastian Junger, activist Caroline Casey, and psychologist Mihaly Csikszentmihalyi. (Original broadcast date: April 17, 2015)