Human faces vary so much that it isn't difficult to identify a person from another. Even look-alike twins have distinct facial features that make it easier for their family and friends to tell them apart.
It is clear that the uniqueness of each person's face offers some benefits. Imagine having friends and family members who look exactly like you or meeting a group of people who appear to be clones of each other. Researchers of a new study, however, have set out to investigate whether the individually unique facial characteristic of humans has developed by chance or it is a result of evolutionary selection. Findings of the study suggest that humans evolved to be as individually unique as possible.
For their study published in the Nature Communications on Sept. 16, Michael Sheehan and his colleague Michael Nachman, both from the Museum of Comparative Zoology and Integrative Biology of the University of California, compared the variations in human faces with those found in other parts of the body using the U.S. Army Anthropometric Survey (ANSUR) data.
They found that the facial traits of humans are more variable compared with other body traits. People who have longer arms, for instance, tend to have longer legs as well but people who have a wider nose do not necessarily have longer noses, suggesting that the variation in human faces has been enhanced by evolution.
"Here we demonstrate that faces evolved to signal individual identity under negative frequency-dependent selection," the researchers wrote. "Faces show elevated phenotypic variation and lower between-trait correlations compared with other traits."
The researchers also found the same genetic pattern when they analyzed and compared the DNA of hundreds of individuals from different parts of the world. They observed that the dissimilarity in the genetic regions associated with facial traits varied more than in other regions indicating this variation in facial features is evolutionarily advantageous.
"Genetic variation tends to be weeded out by natural selection in the case of traits that are essential to survival," Nachman said. "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."
Sheehan and Nachman also compared the genomes of modern humans with those of the Neanderthals and Denisovans and observed the same genetic variation.
"Genetic variation maintained by identity signalling tends to be shared across populations and, for some loci, predates the origin of Homo sapiens," the researchers wrote.
