Functional candidate gene studies and the evolution of behavior in primates: Lessons from the MAOA gene Timothy K. Newman1 1Laboratory of Neurogenetics and Laboratory of Clinical & Translational Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health Abstract Most candidate genes associated with behavioral and psychiatric disorders in humans have homologues in the rhesus macaque genome, an important animal model in behavioral, psychiatric and pharmacological genetics research. Some genes, including monoamine oxidase A (MAOA), serotonin transporter (5-HTT) and dopamine receptor D4 (DRD4), contain functional polymorphisms that originated prior to the common ancestor of catarrhines, and show evidence of having been under positive selection in humans. The enzyme, reuptake pump and receptor protein products of these genes are critical components in a complex neurotransmission pathway that underlies normal and pathological variation in a wide range of affective behaviors. Here, I will focus on my recent work investigating the influence of a functional polymorphism in the MAOA gene on aggression, impulsivity, age of dispersal and acquired dominance in male rhesus macaques. I then present data on the distribution of this polymorphism across a number of primate and non-primate species, examining the dynamics of this system in a broader evolutionary framework. Finally, I hope to demonstrate the translational capacity of the rhesus model in investigating the role of “ancient” and novel monoaminergic gene polymorphisms on aggressive and impulsive behaviors, while emphasizing the value of cross-species comparative analyses of functional gene regions.