“We found very strong support for the idea that as species live in larger groups, their faces become more simple, more plain,” said lead author Sharlene Santana, a UCLA postdoctoral scholar in ecology and evolutionary biology and a postdoctoral fellow with UCLA’s Institute for Society and Genetics. “We think that is related to their ability to communicate using facial expressions. A face that is more plain could allow the primate to convey expressions more easily. (via Evolution is written all over your face)
There’s some fantastic facial hair in the primate world.