Primates & Facial Expression Complexity
Primates have been relying on facial expressions to delineate friends from predators for thousands of years and new research purports that increasing group size puts more pressure on the evolution of coloration across different sub-regions of primates’ faces.
International Business Times reports on these new findings from biologists from the University of California Los Angeles.
“Social pressures have guided the evolution of the enormous diversity of faces we see across the group [Old World African and Asian primates species] ,“ Michael Alfaro, an associate professor of ecology and evolutionary biology in the UCLA College of Letters and Science and senior author of the study commented. Unlike solitary species like orangutans, Old World species can live in groups of up to 800 members. Larger groups let member species develop “more communication avenues” and “a greater repertoire of facial vocabulary.”
The scientists divided photos of primate faces into several regions, and classified each face’s color, hair and skin. Each face was assigned a score based on the total number of different colors on its facial regions. The biologists then determined how the complexity scores were related to social variables including environmental factors like geographic location, canopy density, rainfall and temperature.
“We found that for African primates, faces tend to be light or dark depending on how open or closed the habitat is and on how much light the habitat receives,“ Alfaro said. “We also found that no matter where you live, if your species has a large social group, then your face tends to be more complex.”
The team discovered that primates’ facial complexity is determined by the size of its social group and within the Old World group, they found that different primate groups used their faces differently. For instance, great apes had plainer faces than monkeys. One reason behind this could be attributed to facial expressions.
The biologists hope that these findings might shed some light on the evolution of human faces as well.