Nervous systems are complex networks, composed of neurons in various brain regions that are interconnected by synaptic connections and inter-regional pathways. While much effort has been expended to map the connectome of humans and a few model organisms, a more systematic comparative acquisition and analysis of connectomes across many species is lacking so far. Hence, the evolutionary processes that have shaped connectome architecture are largely unknown. Here, we address this gap in knowledge by generating connectivity data from a large set of mammalian species in order to allow comprehensive and comparative network analysis as well as to relate network features to evolutionary anatomic and behavioral adaptations. Lead by experts in magnetic resonance imaging, network theory and behavior, this interdisciplinary team will a) create a unique unprecedented data base of mammalian connectomes (covering 5% of all mammalian species), acquired using cutting-edge diffusion imaging and tractography; b) configure and deploy network analysis techniques to mine these data and discover patterns that trace the evolution of the connectome across species; and c) formulate and test specific hypotheses that illuminate evolutionary patterns in the relation between brain connectivity and behavior. The project will thus create a first-of-its-kind opportunity to study the evolution of the connectome across the mammalian class. RELEVANCE (See instructions): Complex brain networks enable and support human cognition and behavior. This project will reveal principles of network organization across a broad range of species in the mammalian class, including those of commonly used model organisms such as non-human primates and rodents. The resulting knowledge will illuminate the evolutionary origins of brain networks and thus provide new insights into their neurobiological function and dysfunction in humans.