Humans Evolved Distinct Faces to be as Unique as Possible

Human faces vary widely; some have wider set eyes while others have narrower ones, and noses come in all shapes and sizes. Yet why do human faces vary more widely than those of other animals? Scientists have now taken a closer look and have found that our varied faces are the result of evolutionary pressure to make each of us as unique and easily recognizable as possible.

"Humans are phenomenally good at recognizing faces; there is a part of the brain specialized for that," said Michael Sheehan, one of the researchers, in a news release. "Our study now shows that humans have been selected to be unique and easily recognizable. It is clearly beneficial for me to recognize others, but also beneficial for me to be recognizable. Otherwise, we would all look more similar."

In order to examine what causes humans to look so different, the researchers turned to the U.S. Army database of body measurements that was compiled from both male and female personnel in 1988. The scientists conducted a statistical comparison of facial traits of European Americans and African Americans, including forehead-chin distance, ear height, nose width and distance between pupils, with other body traits, such as forearm length and the height at waist. In the end, the researchers found that facial traits are more varied than others, and that facial traits are independent of bodily traits. For example, someone with longer arms doesn't necessarily have a longer nose.

"All three predictions were met: facial traits are more variable and less correlated than other traits, and the genes that underlie them show higher levels of variation," said Michael Nachman, one of the researchers. "Lots of regions of the genome contribute to facial features, so you would expect the genetic variation to be subtle, and it is. But it is consistent and statistically significant."

Because of the genomic variation, it's likely that the facial variation is evolutionary advantageous. While genetic variation tends to be weeded out by natural selection, you see the opposite when it comes to facial variation. This, in particular, is consistent with the idea that humans have been selected for variation.

"Clearly, we recognize people by many traits-for example their height or their gait-but our findings argue that the face is the predominant way we recognize people," said Sheehan.

The findings are published in the journal Nature Communications.