The difference in cognition between humans and apes is not simply a greater degree of general intelligence, but rather a quantitative difference in social cognition. Social cognition comprises the ability to understand and respond to social responses of others. This concept includes social skills related to self-knowledge and theory of mind, which indicates the ability to understand the emotions and behavior of a person from their perspective. This project focuses on our closest living evolutionary relatives: bonobos and chimpanzees. These two species diverged from the human lineage only 5-8 mya. This makes them keystone species for investigating our own evolutionary past and identifying unique human traits. Bonobos and chimpanzees diverged from each other between 1-2 mya, but show considerable differences in social cognition. Studies in bonobos have shown that they have higher social sensitivity and are better at tasks that require social tolerance and cooperation. To date, very little is known about the mechanisms behind these behavioral differences. Therefore, this study aims to contribute to our understanding of the evolutionary origins of human sociality by studying the genetic mechanism underlying these differences in these two closely related ape species. More specifically, I aim to investigate variation in candidate genes that play an important role in the regulation of the social brain, and how they impact sociability, cooperation and social tolerance.