Animals exhibit an astonishing variation in their behavior, yet little is known about the neural mechanisms that generate this diversity. To gain insight into mechanisms of behavioral evolution, we have begun to translate neurogenetic tools from D. melanogaster to closely related Drosophila species, allowing us to directly compare homologous neural circuits and pinpoint sites of adaptive change. In recent work, we compared pheromone-processing pathways in D. melanogaster and D. simulans to define how these sister species endow the same pheromone, 7,11-hepatcosadiene, with the opposite behavioral valence to underlie mate discrimination. Our results reveal that species-specific pheromone responses can emerge from conservation of the sensory periphery and diversification of central circuitry, and demonstrate how variation at discrete nodes in neural circuits can contribute to behavioral evolution. We are now taking advantage of the rapid evolution of female pheromones in the Drosophila genus to examine how parallel changes in mating behaviors have been independently implemented in different species, shedding light on the types of changes that are possible and preferable within brain circuits.