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. In our project, we focus 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. Although bonobos and chimpanzees diverged from each other only 1-2 mya, they show considerable differences in social cognition. Studies in bonobos suggest that they have higher social sensitivity and are better at tasks that require social tolerance and cooperation. However, to date very little is known about the mechanisms underlying these behavioral differences. To further our understanding of the evolutionary origins of human sociality, we study variation in candidate genes that are crucial in the regulation of the social brain. We report newly identified differences in the genes coding for the receptors for vasopressin (AVPR1A), oxytocin (OXTR), serotonin (HTR1A), dopamine (DRD2), estrogen (ER1 and ER2) and androgen (AR) based on high-resolution whole genome data for 20 unrelated bonobos and 57 chimpanzees. We examine the impact of non-synonymous nucleotide substitutions on protein function and structure, and discuss their potential relevance for reported differences in social cognition between the two species.