Throughout their evolution, humans hadn’t always had the thin eyebrows they have today. Some early hominin species had prominent ridges on the skull in the area of their brows. This made the scientists wonder why our ancestors had thick eyebrows, and why we evolved a thinner version. A recent research revealed the thick ridges played an important social role.
Why did ancient hominins have thick ridges on their skulls?
Humans look pretty different from their ancestors, such as Homo erectus or Neanderthals. One big difference consisted in the shape of their skulls, and the thin versus thick ridges above the eyes. The easiest explanation offered a physiological perspective on this difference.
Scientists suggested these thick ridges connected the eye sockets of the early hominins with the inside of their skulls. Also, the ridges must have had a protective purpose. The thick layer of bones should keep the skull safe from powerful bites, or allow the hominins to take punches in the face without serious brain damage.
However, researchers wondered if this was the only explanation. To find out, they digitally produced a skull model belonging to an extinct hominin species. This species was called Homo heidelbergensis. Then, they used the same computer program to modify the eyebrow ridges.
These ridges might have played a social role
For each ridge they tested, they looked what it would happen if the skull received bites of different strengths. They came up with an interesting result. The thick ridge didn’t offer much protection against bites, and it didn’t help much with connecting the eye sockets and the brain cage. This is how the researchers came up with the social hypothesis.
Primates also have thick ridges near their brows, which help them send dominance messages. Therefore, early hominins might have been in a similar situation. As humans started evolving, they also evolved more sophisticated mechanisms of communication. As the frontal ridges got thinner, humans could start moving their eyebrows up and down, and send more subtle messages.
However, the study has its limitations. The skull the researchers used for the model lacked a mandible. This means the results could have been different if they used a full skull. However, the findings are still valuable and relevant. The study has been published in the journal Nature Ecology & Evolution.
Image source: Wikimedia Commons