Page 184 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms
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                                Chapter 8
likely that the last common ancestor of all great apes expressed similar behaviors in response to conspecifics.
Other important findings in this dissertation relate to the influence of social and contextual factors on emotion perception. Specifically, there are crucial differences in how these factors affect human and bonobo attention for emotions, how they modulate mimicry in orangutans. Attention for emotions in humans and bonobos is affected by familiarity, or more specifically, by whether the emotional expressions come from group mates or unfamiliar others (Chapter 2). As for orangutans, familiarity with individuals does not appear to impact the occurrence of contagious yawning (Chapter 5), but social closeness (or distance) does impact the occurrence of self- scratch contagion in stressful situations (Chapter 6). These findings highlight once again that context and social factors have an interactive effect on attention and mimicry. For instance, different evolutionary environments may have contributed to shaping the sensitivity to emotions of others, such that humans are more tuned to the ingroup, and bonobos more to the outgroup (Hrdy & Burkart, 2020).
Bonobos are remarkable in their xenophilic tendencies, which likely arose due to bonobos’ relatively stable feeding environment (Hare et al., 2012). With less competition over valuable resources such as food, there was also less need to fight over these resources, which over time led to selection against aggressive tendencies. Crucially, this allows bonobos to have relatively peaceful interactions with strangers and even share food with them (Tan et al., 2017; Tan & Hare, 2013). In contrast, humans (and chimpanzees) had to adapt to more arduous environments and faced more severe competition over food and resources. Aggressive tendencies would therefore be beneficial for both species to protect the group (Bowles, 2009; Hare et al., 2012). Following this line of thought, as orangutans tend to affiliate with others less often compared to for instance bonobos, their perception of emotional expressions may also be less affected by socially close others, or only be affected by seeing unfamiliar or socially distant others. While this remains an open question for future research, I can at least say that our findings support the idea that self-scratch contagion in orangutans is affected by social distance, or specifically, having a weak social bond with the observed self-scratching individual(s).
In addition to an evolutionary account, contextual factors likely exert a great influence on emotion perception. For instance, recent findings show that bonobos and chimpanzees preferentially attend to high-ranking familiar individuals compared to unfamiliar individuals (for bonobos, these high-ranking familiar individuals were females, and for chimpanzees, males) (Lewis et al., 2021). Importantly, the researchers
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