One can easily observe a huge diversity in how their faces appear

Jan 12, 2012 10:38 GMT  ·  By

Evolutionary “detectives” at the University of California in Los Angeles (UCLA) recently took it upon themselves to identify the reasons why primates exhibit such a wide array of facial features. In order to do that, they analyzed the faces of 129 male primates of different species.

The test “participants” were collected from Central and South America. Biologists then set out to create a map of how their facial features evolved from a common ancestor, which roads this evolution took, and what the factors that influenced it were.

Details of their investigation appeared in the January 11 early online issue of the esteemed scientific journal Proceedings of the Royal Society B. The group says that the research stretches back more than 24 million years into the past.

For this study, primates were selected both from species that tend to live gregariously, in groups that can reach up to hundreds of individuals, and from those where individuals would much rather keep to themselves. Differences in social behavior are thought to have an influence on facial features.

“If you look at New World primates, you're immediately struck by the rich diversity of faces. You see bright red faces, moustaches, hair tufts and much more,” UCLA associate professor of ecology and evolutionary biology Michael Alfaro explains.

“There are unanswered questions about how faces evolve and what factors explain the evolution of facial features. We're very visually oriented, and we get a lot of information from the face,” adds the expert, who was also the senior author of the study.

Each of the faces included in the study was divided into 14 regions, each of which was then color-coded based on skin and hair tone, overall anatomy and other criteria. Each of the primates then received a facial complexity score.

These scores were then related to the each primate's physical environment. Variables such as exposure to sunlight and average temperature were considered as well. “We found very strong support for the idea that as species live in larger groups, their faces become more simple, more plain,” Sharlene Santana says.

The UCLA postdoctoral scholar in ecology and evolutionary biology was the lead author of the new study. Santana is also an Institute for Society and Genetics postdoctoral fellow. “We think that is related to their ability to communicate using facial expressions,” she says,.

“A face that is more plain could allow the primate to convey expressions more easily,” the expert concludes.