Why are some species monogamous, and others polygamous? Hans Hofmann is trying to understand the ecological and molecular basis of divergent social organizations. He’s also trying to decipher the most basic molecular and hormonal mechanisms underlying social behavior in individuals. In dozens of aquarium tanks in his lab, African cichlid fishes jockey for turf, sometimes threatening to head-butt one another as they test territorial boundaries. The fish are ideal for studying social organization and behavior, because of their recent evolutionary radiation that has resulted in hundreds of species that behave differently. Hofmann will tell us what he’s learned so far—and where the research is headed.