GabyThe human face can express a wide range of emotions, many of which would be impossible without eyebrows. Scientists still don’t know exactly how or why those two narrow bands of dense (and sometimes sparse) hair evolved in humans. European researchers have now identified the genes that influence eyebrow shape – from thick and bushy to thin. Many of these genes are shared across populations worldwide.
Useful, yet very mysterious.
Eyebrows keep sweat and stray light out of the eyes and help people show emotion. Depending on their size and shape, they can even make someone more attractive to others. So it’s not surprising that scientists have long wondered whether eyebrow shape and thickness were shaped by natural selection or sexual selection.
Until now, there has been very little data on the genetic factors that determine eyebrow appearance. As molecular biologist Manfred Kaiser from the Netherlands points out, despite huge efforts to map the genes behind complex human traits, we still know more about genes that cause disease than about genes that influence normal appearance.
For that reason, Kaiser says the new study deepens our genetic understanding of eyebrow appearance. The number of known genes linked to eyebrow traits has increased from four to seven, creating new targets for future functional work.
Eyebrows are not only related to appearance.
Previous studies explored the genetics of eyebrow thickness in people of Latin American or Chinese descent. This new research is the first to include Europeans as well. It involved 9,948 participants divided into four ancestry groups, including people from Europe, the United States, Australia, and the United Kingdom.
Researchers identified three genes (SOX11, MRPS22, SLC39A12) that had not been reported before and that are associated with eyebrow thickness specifically in Europeans. They also found two genes (SOX2, FOXD1) that showed up in earlier studies of non-European populations. Additionally, two genes (EDAR, FOXL2) linked to eyebrow traits in non-Europeans had no significant effect in Europeans.
Kaiser says the study suggests eyebrow variation is shaped by both shared and population-specific genetic factors across continents. That underscores the need to study people from diverse ancestries to uncover the genetic basis of human traits, including—but not limited to—appearance.
The first step on the path to further study
Eyebrow thickness runs in families: it’s an inherited trait. But previous evolutionary work suggests the genes SOX2, FOXD1, and EDAR are not under strong selection pressure.
That could mean eyebrow thickness isn’t linked to survival or sexual selection. In other words, it may be a “neutral trait” not clearly tied to individual fitness or attractiveness.
As noted by the publication Sciencealert, this is an exciting discovery given how useful eyebrows are for humans. However, it’s possible researchers simply haven’t looked at the right genes yet.
The newly identified “eyebrow genes” still need follow-up studies to test for signs of natural or sexual selection. This work might also help explain why humans developed such pronounced features above the eyes in the first place.
