'Highly mobile eyebrows' helped humans to evolve and survive, scientists find | London Evening Standard

Highly expressive eyebrows may have played a crucial role in helping humans to survive, scientists have found.

Our early ancestors sported a pronounced brow ridge, which was “a permanent signal of dominance and aggression”, new research from the University of York suggested.

But modern humans evolved to adopt a smooth forehead with more visible, “mobile” eyebrows capable of expressing subtle emotions, the study revealed.

These brows offer key communication skills for establishing large social groups, according to the researchers, which may have set us apart from our now-extinct sister species the Neanderthals.

Scientists used modelling software to examine the purpose of brow ridges (Paul O'Higgins , University of York)

Using 3D engineering software, the researchers studied the brow ridge of a fossilised skull, known as Kabwe 1, to better understand its purpose.

It belonged to one of our distant extinct ancestors - Homo heidelbergensis, who lived between 600,000 and 200,000 years ago.  

Scientists discounted two theories commonly put forward to explain protruding brow ridges: that they were needed to fill the space where the flat brain cases and eye sockets of the species met, and that the ridge helped to stabilise their skulls from the force of chewing.

They decided that a possible explanation for the skull shape could be social communication.

Senior author of the paper, Paul O’Higgins, Professor of Anatomy at the University of York, said: “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.”

According to the researchers, modern humans evolved communicative foreheads over the past 100,000 years, beginning as a side-effect of our faces getting gradually smaller.

Co-author of the paper, Dr Penny Spikins from the Department of Archaeology at the University of York, said the adaptation may have been key to our surviving over other human species.

She said: “Modern humans are the last surviving hominin. While our sister species the Neanderthals were dying out, we were rapidly colonising the globe and surviving in extreme environments.”

Hominins are the group consisting of modern humans, extinct human species and all our immediate ancestors.

Dr Spikins added: “This had a lot to do with our ability to create large social networks – we know, for example, that prehistoric modern humans avoided inbreeding and went to stay with friends in distant locations during hard times.”

The archaeologist said eyebrow movements “allow us to express complex emotions as well as perceive the emotions of others”.

She said: “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. “

The research, which contributes to a long-running academic debate about why anatomically modern humans evolved flatter foreheads, was published in the journal Nature Ecology and Evolution.

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