Heritability of gray matter volume and asymmetry in chimpanzees (Pan troglodytes) and their association to cognitive abilities and tool use.

Genetic studies have increasingly identified key mechanisms that underlie individual and phylogenetic variation in behavioral and brain phenotypes. Here, we used quantitative genetics to estimate heritability in whole brain and region-specific variation in gray matter in a sample of captive chimpanzees. We included the contributions of sex and age to individual variation in gray matter as well as their association with cognition and motor functions and found small to moderate heritability in average gray matter volume in the majority of brain regions. By contrast, weaker estimates of heritability were found when considering asymmetries in gray matter across brain regions. Age was inversely associated with gray matter volume for the frontal lobe and the basal forebrain after accounting for sex and relatedness of the chimpanzees. Chimpanzees that had higher cognition scores were found to have greater leftward asymmetries in the regions comprising the frontal lobe and basal forebrain component. Further, chimpanzees with better performance on a tool use task had higher gray matter volumes in the frontal and basal forebrain regions. However, no genetic associations were found between tool use performance or cognition and the average frontal or basal forebrain gray matter volumes or asymmetry.