When we think of rare physical traits, we often imagine striking features that catch the eye. Yet some unusual traits are so small they often go unnoticed—even by those who have them. One example is the tiny hole or dimple near the top of the ear called a preauricular sinus.

A preauricular sinus, also known as a preauricular pit or fistula, is a small congenital opening formed during early fetal development around the sixth week of gestation. It occurs when parts of the ear fail to fully fuse and is often hereditary, running in families. The sinus can appear on one or both ears, though having it on both sides is rare.

For most people, a preauricular sinus is harmless and causes no problems. However, it can sometimes become infected, leading to swelling, redness, or pain. Infections are typically treated with antibiotics. If infections happen repeatedly, minor surgery may be recommended to remove the sinus entirely. Doctors advise keeping the area clean and monitoring it for signs of irritation.

Beyond its medical aspects, the preauricular sinus highlights the fascinating ways small genetic variations contribute to our individuality. Some researchers, including evolutionary biologist Neil Shubin, speculate that these tiny holes might be evolutionary remnants of fish gills, hinting at our distant aquatic origins—though this remains a theory without solid proof.

Despite the speculation, the condition itself is generally harmless and poses no health risks for most people. These small ear dimples quietly remind us of our shared biology and the intricate history written in our bodies. They’re subtle traces of evolution and development, showing how even the tiniest features tell a story about who we are.