In a report published in the journal Nature this week, scientists found a greater diversity in the genes that determine facial structure than any other type of genes in the human body.
A team led by Michael Sheehan, a postdoctoral fellow at the University of California, Berkeley, analyzed dozens of face and body measurements in a U.S. Army database. They found that the ratio of most body parts were consistent (for example, Leonardo da Vinci famously illustrated how average arm span correlates to average height). Face parts, however, are not so predictable.
The team then looked at the genomic sequences of 836 people of European, African, or Asian origin from the 1000 Genomes Project, focussing on 59 stretches of DNA linked to facial features. They found that these sequences were more variable than the rest of the genome, and more variable than sequences associated with height.
The team also compared modern human DNA to that of Neanderthal and Denisovan, our closest known relatives in the genus Homo. In both modern and ancient DNA, two genes – one which determines nose shape and the other the distance between chin and bridge of nose – had similar levels of variability. This, the team suggests, shows that facial diversity evolved before modern humans did.
So why is individual facial identity more of a feature for humans than other animal species?
Sheehan isn’t sure, but suggests that our facial diversity could have evolved as a survival advantage, conveying an ability to distinguish friend from foe and recognize places within a hierarchy – in the same way that many social insects recognize each other by their diverse coloring. However, it could equally have arisen just by chance.
Another intriguing question is to what degree are human faces around the world a mosaic of modern and archaic genes?
As your early modern humans ancestors dispersed around the globe from 60,000 years ago, did their facial features begin to adapt purely to the new environments they found themselves in? Or, if they interbred with now extinct hominins en route, is it the vestiges of a Neanderthal brow-ridge or a Denisovan nose you are seeing in the bathroom mirror?