Cross-Cultural and Cross-Species Comparisons of Mutual Gaze and Infant Emotion: Challenging WEIRD and BIZARRE Assumptions

In this study of mutual gaze (MG) and emotion, using multiple groups of chimpanzee infants to compare with multiple groups of human infants, we provide a methodology to assess two deeply rooted assumptions: 1. Psychological outcomes in chimpanzees are uninfluenced by socio-ecological conditions; and 2. Samples from humans living in Western, middle-class families settings are adequate representatives of humankind. Even though MG is widely viewed as foundational for social cognition, and gaze becomes coordinated with emotion around 1-yr of age, these topics have rarely been studied in 1-yr-old chimpanzees. We studied four diverse chimpanzee groups, i.e., 1-yr-old infants living at Chester Zoo (n=4); in Gombe National Park (n=12); at Primate Research Institute (PRI, n=3); and in a human home (n=2), compared to three diverse groups of human 1-yr-olds: urban-UK (n=8); subsistence farming-Nso (n=12); and foraging-Aka (n=10). MG occurred 22% of the time and did not differ across groups or species. We found no species differences in any infant Emotion or in any MG-Emotion co-occurrence pattern. In three of five types of MG-Emotion co-occurrence, the PRI chimpanzee infants differed from at least one of the other chimpanzee groups (we reject assumption #1) and the UK infants differed from at least one of the other human groups (we reject assumption #2). We conclude there are meaningful influences of socio-ecology on the functions of some social cognition outcomes, and, thus, it is necessary to sample multiple diverse groups to detect true species differences.