Rethinking primate facial expression: a predictive framework

Primate facial expression has long been studied within a framework of emotion that has heavily influenced both theoretical approaches and scientific methods. For example, our understanding of the adaptive function and cognition of facial expression is tied to the assumption that facial expression is accompanied by an emotional internal state, which is decipherable by others. Here, we challenge this view and propose that facial expression should also be conceptualised as an indicator of future behaviour as opposed to current emotional state alone. We also advocate the use of standardised, objective methodology (FACS) to avoid making assumptions about the underlying emotional state of animals producing facial expressions. We argue that broadening our approach to facial expression in this way will open new avenues to explore the underlying neurobiology, cognition and evolution of facial communication in both human and non-human primates.