Over many hundreds of thousands of years, humans lost much of the hair on their bodies. One place we haven’t lost it is above our eyes. So, you may be wondering — why do we have eyebrows?

Experts say that eyebrows have two main purposes: keeping moisture out of our eyes and communication.

They protect our eyes from moisture and light

Physically, eyebrows are there to help keep our eyes clean and clear. They move wetness from sweat and rain away from our eyes so we can maintain our sight.

Ever notice how your eyebrow hairs grow outward, toward the sides of your face? That helps direct any moisture away from your eyes toward the side of your head. Eyebrows can also reduce the amount of light that gets into your eyes and keep dirt away from them, too.

They help us express emotions and recognize each other

Eyebrows are an important part of human expression and communication. They allow us to show our emotions. One raised eyebrow expresses skepticism or interest. Two raised eyebrows can express surprise.

Beyond looks and emotions, eyebrows are also more generally important for facial recognition. In one older 2003 study scientists asked a group of people to identify the faces of fifty famous people, such as former U.S. president Richard Nixon and actress Winona Ryder. The scientists manipulated the photos so that they’d either have no eyes or no eyebrows. Subjects could still identify the famous faces 60 percent of the time when they lacked eyes.

But when the faces lacked eyebrows, subjects could identify them just 46 percent of the time. Scientists said this indicates that eyebrows are just as important as — or maybe more important than — eyes in allowing us to recognize faces.

Scientists have established that the shape, color, and thickness of your eyebrows are inherited traits.

In one major study in 2015, scientists found a strong relationship between inheritance of specific genes and eyebrow appearance.

Four separate genes may affect eyebrow hair texture, one gene may determine eyebrow shape, five genes affect eyebrow hair color, and one gene determines whether or not you develop a monobrow.

But, environmental factors also have a lot to do with how your eyebrows look. Years of waxing or tweezing your eyebrows can permanently affect their shape. Injuries to the skin near your eyebrows can also affect hair growth and eyebrow shape.

Just as eyebrow characteristics are inherited, so are abnormalities affecting the eyebrows. One of the most common abnormalities affecting eyebrows is madarosis, or loss of eyebrows. The term madarosis can also refer to loss of eyelashes. This can be caused by many different inherited disorders.