Evolved changes to neural systems for reactive aggression in humans and other primates

Various types of aggression are a part of how species function adaptively in their social environments. At the same time, aggression can pose a threat to societal well-being. This project uses brain imaging datasets and associated behavioral data for multiple species to examine the neurobiology of reactive aggression and investigate whether reactive aggression has been selected against in humans. Understanding how aggression may differ in humans as compared to other animals is fundamental to understanding the nature of our own species and how we fit into the animal kingdom more broadly. The project supports student training and mentoring in STEM and creates publicly available teaching materials for an undergraduate seminar course focused on improving the ability to critically evaluate scientific theories and recognize societal impacts of understanding of scientific concepts. The project tests predictions that follow from current prominent theories on the role of aggression in the evolution of humans and our closest ape relatives using unique multispecies neuroimaging datasets to examine neural circuitry supporting variation in aggressive behavior both within and across species. The investigators use existing MRI and DTI scans from chimpanzees combined with behavioral measurements in the same animals. In humans, they collect a highly validated measure of reactive and proactive aggression as well as neuroimaging data directly comparable to the chimpanzee dataset. Within each species, they examine links between aggression and (a) gray matter morphology, (b) white matter microstructure, and (c) white matter connectivity. Direct comparisons between chimpanzee, bonobo, and human brains are used to assess whether bonobos and/or humans show evolved change in neural circuits linked to individual variation in reactive aggression. Additionally, comparisons with patterns of brain organization observed in tame foxes provide a second, independent mechanism to address whether human and bonobo brains have undergone selection for reduced reactive aggression. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.