Why did humans evolve to have such different faces?

Dogs sniff each other's butts, penguins call to reconnect with their long-lost partners and humans use facial recognition to tell each other apart.

The ability to recognise human faces is a crucial element in the functioning of human society. It is only possible because we evolved faces that are very different from one another, and cognitive abilities that allow us to link faces to information about individuals.


A study published in Nature Communications last week provided some insight into the evolutionary mechanisms that gave humans more diverse facial features than other animals.

The study found that there is massive variation in facial traits in humans, such as the distance between the eyes, compared to other body parts. For example, while relatively short people are likely to have shorter arms and shorter legs, facial features do not follow the same patterns.

The most variable traits were found to be situated within the triangle of the eyes, mouth and nose.

Behavioral ecologist Michael Sheehan, a postdoctoral fellow in UC Berkeley in the US who worked on the study, said, “[In the study] we asked, ‘Are traits such as distance between the eyes or width of the nose variable just by chance, or has there been evolutionary selection to be more variable than they would be otherwise; more distinctive and more unique?’”

The researchers analysed genetic data from the 1000 Genome project, which has sequenced more than 1,000 human genomes, in conjunction with measurements of the human body. They found that the relationship between genes and body traits such as height were reliable but the influence of genes on facial features was more erratic.

Humans on average can tell apart faces with 97.53 per cent accuracy (although, interestingly, machines are catching up - facebook's face recognition software, DeepFace, can now achieve almost the same level of accuracy).

However, there are a small number of people with a disorder called prosopagnosia, more commonly known as face blindness, who fail to recognise their own or other people's faces. This disorder can cause significant difficulties in social situations - it can be excruciatingly awkward but also, potentially, quite dangerous.

This study provides insight into why humans are generally so good at teling each other apart and future study in this area might help explain why some people lack this ability.

"Individual recognition is really important, in some ways so important that sometimes we don't realise how we recognise individuals," study co-author Michael Sheehan, a postdoctoral fellow at University of California in the US told The Washington Post. "It's so ingrained within us."