On April 11th, 2018 we learned about

Homo sapiens got a social boost by giving up bony eyebrows

You may have your mom’s hair, or your dad’s eyes, but how about humanity’s eyebrows? As much as you may hear about big brains or opposable thumbs, anthropologists believe that our flat, fuzzy eyebrows may be a uniquely human trait. What’s more, they may have given us an edge over other hominids with bonier brows.

Benefits of a big brow

Older ancestors, like Homo heidelbergensis, generally had brows closer to what you find on other primates. Even as their heads became taller in relation to their face, they still had a prominent ridge of bone protruding above the eye sockets. That may have provided a bit of protection and shade for their eyes, but researchers have now ruled out other structural benefits. Computer simulations have found that reducing these bits of bone had no ill-effect on a virtual H. heidelbergensis‘ bite strength, nor would it make more space for a larger brain case in the skull.

Even if a smooth brow doesn’t impede an individual’s ability to bite down, it doesn’t explain how it benefited modern Homo sapiens enough to spread throughout our gene pool. It wasn’t worse than a bony brow, but how was it better? Some pitting along the brows of H. heidelbergensis provided clues, as it was remarkably similar to microscopic craters found on display features in other primates. Dominant male mandrills, for instance, have these pits on the sides of their muzzles where they grow colorful tissue to express their social status to their potential rivals and mates. Seeing these pits on the side of H. heidelbergensis‘ brow ridge suggests that that feature may have started a similar function for our ancestors, signaling fitness and status as a display structure.

Making friends with fuzz

That kind of communication is may have started human ancestors down the road to our modern eyebrows built from hair and muscle. It’s easy to take them for granted, but the movement of eyebrows plays a big role in how we express emotion and intent to people around us. We can even communicate these feelings when drawing an abstract face with simple dots for eyes, as long as the brow lines slope up, down, or asymmetrically. Some expressions, like a quick lifting of both brows to express recognition or openness, are understood by humans around the world.

It’s thought that the role of this kind of social communication became incredibly important as humans banded together to start farming forming settlements thousands of years ago. Those developments would require more trust and cooperation with other individuals, and would have depended on clear communication. Being able to form social bonds, both with close kin and newcomers, would have allowed humans to help each other through difficult circumstances. It seems there was no better way to build a friendship than by moving articulated tufts of hair up and down over your eyes.

Source: Research to raise a few eyebrows: Why expressive brows might have mattered in human evolution by University of York, Phys.org

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