The function of the eyebrows has been the subject of debate among experts for decades. One of the most widespread and accepted hypotheses maintains that it is, fundamentally, protective elements of the eyes. Thus, they would help keep dust, rain or sweat at bay. They also play an important role in non-verbal communication. When we hold them up, for example, our facial expression denotes astonishment; if we frown, we show disagreement or even aggressiveness. Well, a team of researchers from the Department of Archeology of the University of York, in the United Kingdom, maintains that this aspect is much more relevant than what has been believed so far and that, in fact, the eyebrows have played a role. determining role in the survival of our species .
In a study published in the journal Nature ecology & evolution , these scientists indicate that one of the features that distinguishes us from other hominins – bipedal, upright walking hominins – of the Middle Pleistocene – between 780,000 and 126,000 years ago – is that we lack the marked arc superciliary that characterizes our ancestors. On the contrary, modern humans have a much flatter and more vertical forehead and eyebrows with greater mobility. As they explain, the presence of the aforementioned superciliary arch in archaic species of the genus Homo has raised doubts among paleontologists. Some point out that its peculiar morphology is the result of the spatial relationship between the orbits and the upper part of the skull. Others, that this anatomical structure is greatly influenced by the way of chewing.
But what are they for?
These specialists assure, however, that there is no evidence that this has been the case, and that both approaches could be wrong. To determine this, they digitally recreated a fossil Homo heidelbergensis skull known as Kabwe 1. This is between 300,000 and 125,000 years old, and was discovered in what is now Zambia in 1921. The three-dimensional reconstruction of the piece showed that the prominences bones are larger than would have been necessary if their primary function had been to protect the eye sockets or skull. Likewise, it seems to rule out its relationship with chewing.
“The computing tool we used allowed us to find out that it did not offer a certain spatial advantage, as it could be greatly reduced without causing difficulties. Then we simulated the biting of different teeth and found that there was hardly any tension exerted on this part. Furthermore, when we removed it, we observed that there were no effects on the rest of the face during chewing ”, explains professor of anatomy Paul O’Higgins, one of the signatories of this essay.
Friendlier faces
As our ancestors became more sociable, they experienced a progressive flattening of the forehead. It is a kind of side effect of another phenomenon: the reduction in size that the human face has experienced in the last 100,000 years. This process, which has accelerated since our ancestors stopped being hunters and gatherers to become farmers, made the eyebrows more visible. According to O’Higgins and his collaborators in a statement, everything indicates, then, that its main function has to do with the expression of emotions. “The more vertical forehead of modern humans allowed them to subtly display friendly emotions. These surely reinforced the bonds between the individuals ”, says O’Higgins.
For archaeologist Penny Spikins, who has also participated in this initiative, “the eyebrows are the missing pieces to understand how modern humans managed to get along better with others than other now extinct hominids.”
Reference: Supraorbital morphology and social dynamics in human evolution . Ricardo Miguel Godinho et al. Nature Ecology & Evolution (2018) . DOI: 10.1038 / s41559-018-0528-0
Image: CC0 / Paul O’Higgins – University of York
