Page 17 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

has undergone unique changes: adaptations that made survival in their separate social 1 and physical environments possible. Nevertheless, comparisons between species
make it possible to get some sense of what our common ancestor may have lived and
behaved like. If a specific characteristic is found in all the species that are compared,
this may suggest a common evolutionary origin (Wilson, 2021). There are likely a lot of commonalities to be found in the behavior and cognition of great apes and humans. In this dissertation, the focus lies on two great ape species that can provide us with unique insights into the evolution of emotions, and specifically on how emotions are perceived: bonobos (Pan paniscus) and orangutans (Pongo pygmaeus).
Bonobos are known for their relatively tolerant nature, as well as their usage of sexual behaviors to reduce tension in their group, strengthen bonds with other females, and form new relationships with unfamiliar individuals (De Waal, 1988; Furuichi, 2011). Endemic to a small area in the Democratic Republic of the Congo, bonobos live in fission-fusion groups where males have life-long residency in the group and females disperse to other groups when they reach sexual maturity (Hohmann et al., 1999). Like all apes, bonobos are endangered, with a minimum estimated wild population of about 15.000-20.000, and around 225 individuals living in zoos across the world (Fruth et al., 2016). Though current research efforts into the psychology of bonobos are growing, we still understand relatively little about their social cognition. In stark contrast with their more territorial cousins, chimpanzees (Pan troglodytes) (Wilson et al., 2014), as well as ancestral humans (Bowles, 2009; Wrangham & Glowacki, 2012), bonobos show remarkable xenophilic tendencies. Females of different groups show high social tolerance and tend to affiliate with each other rather than fight (Furuichi & Thompson, 2007). Even within their social groups, bonobos show high levels of affiliation and cooperation, and low levels of aggression. Moreover, neuroscientific studies on the brains of bonobos have found that the brain structures involved in emotion processing and regulation are bigger in volume and have more dense connections in bonobos compared to other great apes, thus making them an important referential model for the evolution of social cognition in ancestral humans (Issa et al., 2019; Rilling et al., 2012; Stimpson et al., 2016).
Native to Borneo and Sumatra, orangutans are arboreal apes that lead a semi- solitary existence that is highly unusual among the great apes (Delgado & Van Schaik, 2000; Galdikas, 1985; Mitra Setia et al., 2009). Occasional social associations among individuals do occur, but not frequently (Singleton et al., 2009; Van Schaik, 1999). It is during these temporary formations of small groups that orangutans have the opportunity for socializing, playing, and mating. The formation of these parties, as well
The mechanisms of emotion perception
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