New Research Expands Facial Expression Analysis to Bonobos

In a groundbreaking study published in June 2025, an international team of researchers has successfully adapted the Chimpanzee Facial Action Coding System (ChimpFACS) to include bonobos, our closest living relatives alongside chimpanzees. This research, led by Dr. Catia Correia-Caeiro from Leipzig University and the Max Planck Institute for Evolutionary Anthropology, reveals that bonobos exhibit a repertoire of 28 distinct facial movements, including 22 specific muscle actions, suggesting their facial expression capabilities are comparable to those of chimpanzees.

The significance of this adaptation lies in its potential to enhance our understanding of how these endangered great apes communicate. "This adaptation of ChimpFACS for bonobos fills an important gap in our ability to study facial expressions across different primate species," Dr. Correia-Caeiro stated. This new coding system enables systematic comparisons of facial movements not only between bonobos and chimpanzees but also with humans, shedding light on the evolutionary aspects of facial communication across primates.

The research was a collaborative effort involving institutions from Germany, Switzerland, France, the United States, and the United Kingdom, including notable participation from Harvard University and the Berlin Zoo. This international collaboration highlights the growing recognition of the importance of interdisciplinary approaches in primate research.

While bonobos demonstrate fewer facial movements than humans, they share all the facial movements identified in chimpanzees, indicating the crucial role of facial communication in the social interactions of both species. The study also has practical applications beyond academic research. According to Dr. Correia-Caeiro, understanding bonobos' facial expressions can significantly improve welfare assessments for these animals in human care settings. "By better understanding their facial expressions, we can more accurately gauge their emotional states and well-being," she added.

Historically, the Facial Action Coding System (FACS) was developed to analyze human facial expressions and has been adapted for nine other species over the years. The extension of this system to bonobos offers a standardized method for measuring and comparing facial movements across different primate species, thereby facilitating further research in primate behavior and communication.

As researchers continue to explore the complexities of primate communication, this study not only enriches our understanding of bonobos but also emphasizes the evolutionary connections among primates. Future research may focus on applying this coding system to other primate species, potentially unveiling new insights into the social dynamics and emotional expressions of these fascinating animals. The implications of these findings extend beyond academic interest, as they contribute to conservation efforts aimed at preserving the welfare of endangered species such as bonobos.

In conclusion, the adaptation of ChimpFACS to bonobos marks a significant advancement in primate research, providing a valuable tool for assessing the emotional states of these great apes. As scientists continue to unravel the intricacies of primate communication, this research underscores the importance of collaboration across disciplines and institutions in advancing our understanding of animal behavior and welfare.