Why do we have eyebrows, and how do they help our vision?

10 March 2020

Author: Kate Green


The origin of our brows


Humans didn’t always have eyebrows. Hundreds of thousands of years ago, we used to be covered in hair all over, before gradually evolving over the years to exist mostly hairless. We did, however, keep a strip of hair above each eye, in the form of eyebrows, along with a good covering on our scalps, and eyelashes. But what was there before these isolated tufts on our faces?


Humans used to have an even more prominent brow ridge which jutted out, shielding your eyes from sweat and rain. This ensured that your vision was kept clear, no matter what the weather conditions or hunting environments were. We rely on our vision more than we do on any of the other five senses, making preserving its function even more crucial. The brow ridge served the same purpose that our eyebrows do now, but evolution had other ideas.


Social function of eyebrows


Aside from keeping moisture out of your eyes, eyebrows are actually also essential for communication. The movement and position of your eyebrows plays a key part in conveying a range of emotions, like surprise or disgust, and it’s also particularly useful for people who use sign language, to complement their hand signs. Experts believe that the ability to convey subtle emotions to each other allowed humans to build strong friendships and relationships, aiding their survival. This perhaps encouraged the development of a taller skull and more mobile eyebrows over the years, to help bring unfamiliar social groups together.


Facial recognition


Lots of us like to change the appearance of our eyebrows, whether that’s plucking, dyeing, or tattooing them on. But did you know that eyebrows are also essential for recognising faces? A study in 2003 presented participants with photos of celebrities and famous figures, some with their eyes edited out, and others with their eyebrows digitally removed. When the famous faces were presented without eyes, 60% of the participants recognised them. However, when they were without eyebrows, only 46% of the participants identified them correctly. This would suggest that brows are even more important than other facial features for us to recognise people we know!


Protecting our eyes

Your eyebrow hairs grow outwards, pointing towards the side of your face. Not only does this allow you to smooth them out neatly in one direction and keep them looking fleeky, but it directs all moisture away from your eyes. This can include both rain and sweat, but particularly the latter as its high salt content can really irritate our eyes. Eyebrows can also shade light from your eyes, keeping your pupils at an appropriate size and ensuring too much brightness doesn’t damage your eyes. If we hadn’t developed eyebrows over hundreds of thousands of years, scientists believe we might have grown really thick eyelashes to serve the same purpose, brushing dust and moisture away from our eyes. Alternatively, we may have developed a more prominent brow bone, jutting even further over our eyes for protection.


It appears to be the crucial social and communicative function of eyebrows that aided their development, serving multiple purposes in our day to day lives.

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