A recent study, published in Nature Ecology and Evolution claims that eyebrows that are mobile help people with non-verbal communication, which is one of the traits that make us the most advanced human species to ever exist. In contrast, the Neanderthals' jutting brow was used for displays of dominance and sexual attraction instead, similar to the function of a stag's antlers.
"Sexually dimorphic display and social signaling is a convincing explanation for the jutting brows of our ancestors," said Paul O'Higgins, senior author and professor of Anatomy at the University of York.
"Their conversion to a more vertical brow in modern humans allowed for the display of friendlier emotions, which helped form social bonds between individuals".
Around 100,000 years ago, human groups began to diversify their social networks, which is why it made evolutionary sense to prioritize emotional responses over violent adaptations. Scientists claim that it is around this point in history that human being began to develop smaller and flatter brow ridges, as well as the mobile eyebrows that we still have today.
According to co-author Penny Spikins from the Department of Archaeology at the University of York, "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 empathize and identify with the emotions of others."
While this study is not a hundred percent conclusive, it does go to show that at some point in history, our ancestors decided to voluntarily self-domesticize in order to get on better with the people around them, which is something that modern humans can learn a lot from!