Culture is a central theme in understanding variation between human societies and a hallmark of the human species. In recent years, culture has been identified in non-human animals as well. These accounts, however, merely evidence cultural traditions (i.e. delineated behaviours like cracking nuts with wooden instead of stone tools), while human cultures also differ from one another in terms of group-level sociality, i.e. the very proclivity to be near and interact with others. Importantly, in humans, it is not any cultural tradition, but this group-level sociality (henceforth "social culture") that results in marked variation in the expression of adaptive behaviour, e.g. cooperation. My project investigates whether differences in sociality across great ape populations can be understood in terms of "social culture" (e.g. by focusing on genetics), and whether these differences explain variation in cooperation. I will study both sanctuary- and zoo-housed populations of bonobos and chimpanzees. I will test the hypotheses that great ape groups differ in their sociality, that this variation can be ascribed to "culture", and that social groups are better poised to cooperate. Chimpanzees and bonobos are our closest living relatives, having diverged from the human lineage only 5–8 mya. As such, both species form a unique window into our evolutionary past, i.e. into gaining an understanding of the behavioural phenotype of our last common ancestor and identifying uniquely human traits.