Page 178 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 8
Detecting and correctly recognizing emotional expressions is pivotal to social life, as these expressions guide our thoughts and behaviors, and enable us to understand others’ feelings and intentions. They are at the basis for complex phenomena such as empathy (De Waal & Preston, 2017; Koski & Sterck, 2010) and cooperation (Boone & Buck, 2003), which have long been considered to be uniquely human. However, when and why did our high sensitivity to emotions evolve, and are the processes that govern emotion perception truly unique to our species? Do emotions mean anything to other animals? One way to go about answering these questions is to reconstruct the lives of our ancestors, but this is difficult. The fossil record of early humans is sparse (Andrews, 2020) and fossilization of brain tissue is extremely rare. Nevertheless, our closest living relatives, the great apes, offer us an invaluable window into the past, allowing us to indirectly infer the social and cognitive characteristics of extinct humans and other apes (e.g., Wilson, 2021).
Studying great apes can not only inform us about our evolutionary past but can also provide a stepping stone towards understanding the evolutionary pressures that shaped the expression and processing of emotions throughout the animal kingdom. Here, it is important to remember that the social and cognitive abilities of hominids are just examples that are part of a diverse collection of exceptional skills that organisms can develop to deal with the social and physical demands of their specific environments (i.e., “There is not ‘one cognition’”, Bräuer et al. (2020)). That said, directly comparing different species is challenging. Preferably, we would measure emotion perception using the same method for all species involved, without neglecting species-specific characteristics that may impact the expression of emotion perception (for instance, if one species expresses emotions mainly through facial expressions and another species expresses them mainly through vocal signals, using the same testing method may not be optimal). Based on the literature on cognition and behavior in great apes, it is reasonable to assume that there is at least some continuity between how humans and great apes express and perceive emotions (Kret et al., 2020; Nieuwburg et al., 2021). Following this assumption, the studies reported in this dissertation focused on several unconscious and automatic mechanisms underlying emotion perception that can be studied similarly across humans and great apes: attention, spontaneous mimicry, and implicit associations.
The goal of this dissertation was to take a closer look at the differences and similarities in emotion perception in humans, bonobos, and orangutans. Specifically, we examined emotional modulation of attention (Figure 1i) and spontaneous mimicry (Figure 1ii), and developed a method that could potentially probe implicit
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