Try a little tenderness: Investigating the evolution of empathy through comparing consolation and reassurance in our closest relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes)

Abstract

Empathy—the ability to share, understand, and respond to the emotions and states of others—is often considered a cornerstone of the human experience. As our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) are often used as models for the evolution of human behaviour, and comparative research often seeks to identify interspecific variation. However, comparisons often consist of single groups of small captive populations, and recent investigations have indicated substantial within-species differences in bonobo and chimpanzee cognitive and emotional behaviour. In this thesis, to contribute to the investigation of empathy’s evolution, I provide the first comprehensive systematic comparison of sanctuary-living groups of bonobos and chimpanzees regarding their use of reassuring body contact during two periods of social tension: post-conflict consolation and pre-feeding affiliation. Using a combination of naturalistic observations and an experimental method, I show the Pan apes share similar tendencies to engage in consolation and pre-feeding reassurance, including the use of genital contacts during social tension. Instead, considerable variation lies at the individual, dyadic, and group levels. Two bonobo communities varied in consolatory tendencies, and whilst younger individuals offered consolation more than older individuals, young male chimpanzees consoled more than other chimpanzees. Results also indicate that contact affiliation around feeding is associated with reduced conflict and promotes an individual’s access to a competitive feeding zone. Furthermore, contact affiliation between socially central sex pairings in each species—bonobo females, and chimpanzee males—were associated with group-level social tolerance, indicating that reinforced affiliative bonds between dominant individuals in both species promotes more crowded, peaceful feeding. My findings support considering individual variation and multiple groups of diverse populations when making species-level comparisons in ethology. A bottom-up approach assessing species- and group-specific abilities could reveal the ancient ancestry of empathy, and what factors promote or inhibit its emergence.