Why the long face? Human faces evolved to reveal emotions and communicate

A new review published in the journal Nature Ecology and Evolution suggests that a combination of biomechanical, physiological and social influences have helped shape the modern human face — transforming it from ape-like to a softer and more refined morphology.

There have been many reasons suggested for this change by evolutionary biologists. But Paul O'Higgins, one of the authors of the review, suggests that we have underemphasized how important human sociality has been in this evolutionary change. 

The human face has evolved to express a range of emotions in order to help us with social communication, O'Higgins told Bob McDonald from Quirks & Quarks. And that has been vital to the development of our species.

The evolution of the human face

Fossil evidence shows that the human face has changed greatly in the last 20,000 years.

Before then, diet, climate and environment were the primary factors that shaped our face, according to O'Higgins, a professor of anatomy at the University of York in England.

But in the last 10,000 years, humans have transitioned away from hunting and gathering to an agricultural lifestyle. They started forming communities, and with that, the human face has shrunk significantly in size and turned more friendly and baby-like.

"The new idea is that social faces are important," said O'Higgins. "We, as modern humans, rely heavily on face reading."

Fossil records indicate that Neanderthals and other related hominims looked very similar to us, but they had very large faces with prominent brow ridges and large features including a big nose, big eyebrows and large jaws that were pushed forward.

But the modern human face is much smaller.

"There's a reduction in the middle portion of the face and the brow ridges, which is important for facial signalling," said O'Higgins.

"By losing the brow ridges and developing that baby forehead with mobile eyebrows, you can suddenly express much more subtle things."

The importance of a social face

According to O'Higgins, these changes have helped us with social communications, and were driven by our need for good social skills.

Over the last 80,000 years, as humans moved out of Africa, we've had to depend more and more on each other in order to survive in new environments. In order to do that, it became important that we communicate our feelings.

"Our face has become less robust and more baby-like through evolution. And that opens up the opportunity for communication. People are more likely to communicate with creatures that appear to be empathic than aggressive."

The transition to smaller eyebrows with a flat forehead freed up our eyebrows to move up and down to communicate all kinds of emotions.

These changes made it possible for humans to express more than twenty kinds of emotions including subtle ones like recognition and sympathy. And this made it easy for us to work together in groups and help each other, which has helped make us so successful as a species, said O'Higgins.

"This sort of communication seems to be extremely important for us to have developed into this sort of complex, technological creature that we are today."

In the future, O'Higgins believes the human face will continue to become more baby-like with increasingly pre-processed foods and a sedentary lifestyle.