There are profound differences in behavior among individuals of a species and across species. Much effort has been devoted to the observation and theory of behavioral variation, but the molecular, genetic, and neurobiological mechanisms that generate and maintain such diversity are largely unknown. My lab studies the mechanisms of behavioral variation from genetic and neurobiological angles – by identifying specific genes involved and how they impact the brain, and by characterizing functional variation in neuronal circuits. We then analyze the common themes that emerge to describe the evolution of behavior. Our work focuses mainly on Peromyscus mice and Siamese fighting ‘betta’ fish. In addition to our work on behavior, we work on selected projects on broader aspects of evolutionary genetics and on select evo-devo questions in these and other models.