Face it. If we all looked the same, our world would be pretty boring. Fortunately every human face has its own unique features, and for that, we can thank evolution.
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Credit: UC Berkeley.
According to a new study, evolution has favored humans with distinctive facial features because it is beneficial for people to be able to recognize each other, and be recognizable.
"If everyone looked more or less the same there would be total chaos," study co-author Dr. Michael J. Sheehan, a postdoctoral fellow in the University of California, Berkeley’s Museum of Vertebrate Zoology, told The Huffington Post in an email. "It would be really hard to tell the difference between members of your family, different people at work, friends and neighbors versus total strangers, etc. Of course, it may still be possible to figure out who is who after talking with them for a bit but think of how taxing that would be."
For the study, Sheehan and his colleagues examined body measurements collected in 1988 from white and black men and women in the army. The researchers looked at how much facial traits -- like distance between the pupils and nose width -- varied across the sample, in comparison to other body traits like forearm length.
What did the scientists find? Facial traits varied more than body traits, and the most variable traits were found in the "triangle region" between the eyes, nose and mouth. They also found that facial traits varied independently from each other. For instance, no link was found between how far apart your eyes are and how wide your nose is. The findings suggest that facial variation was enhanced by natural selection, according to the researchers.
Next, the researchers analyzed variation in the genomes of more than 1,000 people around the world. They looked specifically at genetic regions associated with face shape, and found more variation among these regions compared to genes that code for traits like height.
“Genetic variation tends to be weeded out by natural selection in the case of traits that are essential to survival,” study co-author Dr. Michael Nachman, a population geneticist and professor of integrative biology at the university, said in a written statement.“Here it is the opposite; selection is maintaining variation. All of this is consistent with the idea that there has been selection for variation to facilitate recognition of individuals.”
Of course, it's not just humans who develop distinctive traits, which the researchers call "identity signals," to distinguish themselves from the rest of the pack. Other animals, such as wasps, also recognize each other by face, while some animals rely on traits such as distinctive calls, scent markings, egg coloration, and more to signal who they are.
Identity signals help animals defend their territory and signal dominance, according to the researchers. They also help social animals, like humans, determine whom they should invest time and energy in to help, whom to reward, and whom to punish.
Why do humans tend to use faces to recognize each other, as opposed to other traits? For starters, humans evolved from other primates who were highly visual and less scent-oriented than other mammals. The researchers hypothesize that looking closely at the face instead of another area of the body to determine identity allows primates to see where another animal is looking, and keep track of the other animal's mouth to see whether or not the animal will bite.
“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,” Sheehan said in the statement.
The study was published online on Sept. 16 in the journal Nature Communications.