Why are the faces of primates (and people!) so dramatically different from one another?
Biologists working as "evolutionary detectives" studied the faces of 129 adult male primates from Central and South America in search of some answers, and discovered that faces they studied evolved over at least 24 million years.
Science Daily quotes evolutionary biologist Michael Alfaro as saying, "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. 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."
Some of the primate species the team studied are solitary, while others live in groups that can include dozens or even hundreds of others. Science Daily quotes evolutionary biologist Sharlene Santana as saying, "We found very strong support for the idea that as species live in larger groups, their faces become more simple, more plain. 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.
"Humans have pretty bare faces, which may allow us to see facial expressions more easily than if, for example, we had many colors in our faces."
The discovery that faces are more simple in larger groups came as a surprise. Santana says, "Initially, we thought it might be the opposite. You might expect that in larger groups, faces would vary more and have more complex parts that would allow one individual to identify any member of that group. That is not what we found. Species that live in larger groups live in closer proximity to one another and tend to use facial expressions more than species in smaller groups that are more spread out. Being in closer proximity puts a stronger pressure on using facial expressions."
The website quotes geneticist Jessica Lynch Alfaro as saying, "This finding suggests that facial expressions are increasingly important in large groups. If you’re highly social, then facial expressions matter more than having a highly complex pattern on your face." In other words, a plain face is easier to "read"–something that may be a necessity when dealing with the strangers present in a large group.
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