Page 185 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

report differences not only between the species but also between the different populations that were tested. One population of chimpanzees lived with only one resident male whereas the other population had multiple males and females. The females from the first population showed a bias towards outgroup males rather than the familiar male, likely due to the difference in social environments. In the studies on emotion-biased attention in bonobos and humans, we aimed to provide more context to the emotional expressions on our stimuli by including whole-body expressions and by embedding expressions into scenes. Nevertheless, we did not yet look at how contextual factors that the participants find themselves in may affect their attentional bias. Future work should aim to consider these contextual factors more closely, and steps into this direction have already been made. See for instance work by Bethell et al. (2012) on how emotional states affect social attention in macaques. Moreover, we did consider contextual factors in our studies on mimicry with orangutans, and indeed see that for instance stress can affect the occurrence of self-scratch contagion in this species. As a comparison, a next step could be to look into how stress or tension affects the occurrence of self-scratch contagion (or other forms of mimicry) in bonobos and humans.
Finally, in addition to familiarity and context as moderators of emotion
perception, I wish to highlight one more example, namely similarity. Specifically,
similarity in facial or bodily expressions of emotions. The form and potentially
also meaning of emotional expressions are, to some degree, shared between
primates (e.g., Darwin, 1872; Preuschoft & van Hooff, 1995). Thus, due to a common
heritage, it is conceivable that humans and great apes show an attentional bias
towards some of the other species’ emotional expressions, or that mimicry can
occur between different species. For humans, we indeed found an attentional bias
towards bonobo expressions in Chapters 3 and 4, but for bonobos, we could not 8 confirm an attentional bias towards human expressions (Chapter 2 and 4). Given
the evidence at hand, only humans may be sensitive to the feelings and needs of other species, with one explanation being that humans often ascribe human-like characteristics to other animals (Williams et al., 2020). However, it is more likely that our studies did not have enough power to detect an effect, given our small bonobo sample size. The evolutionary continuity between expressions of emotions in hominids remains an active topic of research (e.g., Waller et al., 2020), and future work could tackle the current knowledge gap by for instance measuring whether different species have similar implicit associations with emotional expressions of conspecifics and heterospecifics (e.g., humans or other closely related species), for
General discussion
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