It all boils down to a technicality: while eyebrows and eyelashes are hair that grows on the face, they are not facial hair. We can all agree that the eyebrows, the stripe of thick and delicate hairs that follows the edge of the eyebrow above the eye, are an absolute difference between humans and non-human primates. This is because human beings have little facial hair coverage, making the stripe of hair on the crest of the brow remarkable, especially since it exists in all genders. Other primates have increased musculature around the brow region, which indicates greater control of the eyebrows compared to other mammals, and some (especially some species of guenons) have different colors in the hair on the forehead, which can functionally imitate human eyebrows (Emery 2000).
Primates seemed to have developed strong eyebrows and musculature, but human development isolated the eyebrows and lost most of the rest of their facial hair. It is not known when exactly eyebrows developed. Have you noticed how the brow hairs grow out to the outside, to the sides of the face? This helps draw moisture away from the eyes and onto the side of the head. Eyebrows can also reduce the amount of light that enters the eyes and also keep dirt away from them.
Brow gels aren't just reserved for eyebrows. They can also be used to tame unruly baby hair. If you touch your face, you might feel some small, furry hairs on your cheeks and forehead. However, the hair on the eyebrows is usually a little thicker.
The most common explanation, dating from the Greek doctor Herophilos, is that eyebrows prevent sweat and dirt from entering the eyes, something that is necessary in human beings, since there is no other hair that covers the face or an eyebrow that protrudes properly. Some people have the talent to raise just one eyebrow at a time or to have their eyebrows do a kind of dance. Four different genes can affect the texture of eyebrow hair, one gene can determine the shape of the brow, five genes affect the color of eyebrow hair, and one gene determines whether or not an eyebrow develops. As human beings have had to deal with ever larger social groups, any clue to identify individuals is useful, and eyebrows seem to stand out especially.
This effect was found to be stronger than when the eyes were removed from the image and the eyebrows remained intact. One of the purposes of eyebrows is to prevent things like rain or sweat from running down the forehead and reaching the eyes. The face, especially looking into another person's eyes, is a particularly prominent emotional feature in humans, and eyebrows offer a way to communicate complex emotional states, along with other characteristics. The eyebrows also draw attention to the eye, a key means of expressing emotions and communicating, and can help to follow the eye (Emery 2000).
The human eyebrow, with its contrasting hair, accentuates the movement of the eyebrow, making it more noticeable (such would also be true for Guenon's orange eyebrow). Most of us are familiar with how our own eyebrows look like but what about other people? Scientists have established that shape, color and thickness of eyebrows are hereditary traits. It is believed that these traits are passed down from generation to generation through our genes. Generally speaking, most people's eyebrows will grow back if they are plucked or waxed but how fast they grow will depend on your age and overall health.
In conclusion, it is clear that eyebrows play an important role in our lives. They help us express emotions and communicate with others as well as protect our eyes from dirt and moisture. They also help us identify individuals in large social groups. Understanding how our eyebrows work can help us take better care of them.