What is the point of eyebrows? Why do they get bushy in old age?

Eyes and EyebrowsEyebrows are one of the most characteristic features of our faces. They can be things of beauty and objects of disgust, coming in all manner of shapes and sizes: high arched, low arched, bushy, monobrow and handlebar, to name just a few.

There isn’t one reason for why we have peculiar tufts of hair just above our eyes. One of the most popular explanations is that eyebrows protect our eyes from moisture, usually sweat and rain, from getting into our eyes. The curved shape of the eyebrows and the direction of their hairs ensure that beads of liquid flow outwards along the ridge of the eyes, or down the gap between them to flow over the nose. Additionally, eyebrows can provide some shade for our eyes from sunlight and can catch debris, such as small pieces of dandruff, from falling directly into our eyes.

Another purpose for eyebrows is that they allow us to communicate non-verbally, through the use of facial expressions. Scientists who study non-verbal communication believe that eyebrows allow us to express a range of emotions including happiness, surprise and anger because they exaggerate our facial expressions.

Recent research has suggested that eyebrows may also act as a biological ‘ID card’, helping us to recognise each other from afar. Eyebrows stand out against the forehead and don’t change much over time, making them ideal for the brain to use as a means to identify friend from foe. In a 2003 study performed by researchers from MIT, volunteers were asked to identify celebrities with either their eyes or their eyebrows digitally edited out. The subjects were able to recognise the celebrity 46% of the time with their eyebrows edited out and 60% of the time when the celebrities didn’t have eyes in the picture.

And if you’re wondering why older people have longer eyebrow hair, then take a more careful look – it’s generally only men who have wild and bushy brows in older age. For women, eyebrows can often stop growing altogether with age (requiring a pencilled substitute!) due to the fall in female sex hormones after the menopause. Men, on the other hand, often have testosterone levels that remain pretty constant up until the age of 70 and later, helping to continue healthy eyebrow growth. Interestingly, the hormone testosterone also has the effect of causing baldness while stimulating nose and ear hairs to grow outrageously long. Call it God’s sense of humour.

So rather than just being random clumps of facial hair, we are reliant on eyebrows to protect our eyes and help us to communicate with each other… if you know what I mean (Cue: cheekily raised eyebrow)?

Answer by Nathan Beal

Photo credit: Amanda Palmer Eyes on Flickr

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Article by Nathan Beal

January 15, 2015

Nathan is currently in the throes of a PhD in Computational Chemistry at the University of Manchester. When he’s not behind a computer, he’s outside enjoying the sights of the city. A fan of The Walking Dead, he has a strange apathy to all things football-related.

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