© Oxford University Press 2017. The self-domestication hypothesis (SDH) suggests bonobo psychology evolved due to selection against aggression and in favour of prosociality. This hypothesis was formulated based on similarities between bonobos and domesticated animals. This chapter reviews the first generation of quantitative research that supports the predictions of the SDH. Similar to domestic animals, bonobos are prosocial towards strangers, are more flexible with cooperative problems, are more responsive to social cues and show expanded windows of development compared to their closest relatives, chimpanzees. A preliminary comparison of bonobo and chimpanzee infants suggests that when hearing a stranger, bonobos have a xenophilic response while chimpanzees have a xenophobic response. The chapter explores why the research with bonobos has implications for theories of both human and animal cognitive evolution, and why bonobos will be central in studying evolutionary processes that lead to cognitive change.