How the humble eyebrow has shaped human history

When you think of eyebrows, it’s hard not to picture Eugene Levy of the American Pie franchise. Or Cara Delevingne. Perhaps even the now-infamous ‘Scouse brow’, crayoned emblem of Liverpudlian street style. What doesn’t come to mind is, er, the whole of human evolution. Although if this most recent study is anything to go by, that could all change…

Researchers at the University of York have found that “highly mobile eyebrows” may just have played a crucial role in human survival. Moveable eyebrows facilitate a readily available spectrum of communication tools, in turn allowing humans to establish broad social networks.
In particular, eyebrows come in handy when expressing more nuanced emotions, such as sympathy or acknowledgment. Think about it: you can howl in pain or shriek with laughter, but there are few outward expressions of, say, mild concern available to a person. You’re not going to omit a bellow or a groan – these things would suggest disproportionate distress. Sometimes a simple raising of the eyebrows is the most socially viable response one can proffer.

The study sheds light on an age-old debate as to why our ancestors had such pronounced brow ridges, while ours are typically much flatter. Researchers looked at a particular species of archaic hominin, known as Homo heidelbergensis, which roamed Earth between 600,000 and 200,000 years ago. Discounting popular explanations for the protruding ridge, such as skull-stabilisation when chewing, the scientists posited that the facial characteristic owed its prominence to a “sexually dimorphic display and social signalling.” The idea was borrowed from studying other animals, namely mandrills (a species of monkey found in West Africa), whose dominant males grow brightly coloured facial swellings in order to indicate status.

Senior author of the paper, Paul O’Higgins, Professor of Anatomy at York University said: “We used modelling software to shave back Kabwe’s (a fossilised skull) huge brow ridge and found that the heavy brow offered no spatial advantage as it could be greatly reduced without causing a problem. Then we simulated the forces of biting on different teeth and found that very little strain was placed on the brow ridge. When we took the ridge away there was no effect on the rest of the face when biting.”

He went on to explain: “Since the shape of the brow ridge is not driven by spatial and mechanical requirements alone, and other explanations for brow ridges such as keeping sweat or hair out of eyes have already been discounted, we suggest a plausible contributing explanation can be found in social communication.”

The evolutionary transition to flatter, more vertical brows facilitated a friendlier display of emotions, “which helped [modern humans] form social bonds between individuals”. The process accelerated in the past 20,000 years, as humans switched from a predominantly hunter-gatherer society to an agriculturalist one. The latter lifestyle, the team pointed out, requires less variety in both diet and physical effort.

Co-author of the paper, Dr Penny Spikins from York University’s Department of Archaeology, shed some light on the versatility of eyebrows: “Eyebrow movements allow us to express complex emotions as well as perceive the emotions of others. A rapid “eyebrow flash” is a cross-cultural sign of recognition and openness to social interaction and pulling our eyebrows up at the middle is an expression of sympathy. Tiny movements of the eyebrows are also a key component to identifying trustworthiness and deception. On the flip side it has been shown that people who have had botox which limits eyebrow movement are less able to empathise and identify with the emotions of others.”

Their evolutionary role, she stresses, was pivotal: “Eyebrows are the missing part of the puzzle of how modern humans managed to get on so much better with each other than other now-extinct hominins.”

Forget integrity, or generosity of spirit. Those are *so* 20,000 years ago. The key to a healthy social life lies with a handsome pair of brows. Ready, get set, groom.