If you’ve ever noticed someone with a small mark or tiny hole near their ear and assumed it came from an injury, it’s actually something different. It’s a genetic trait—and here’s what it may mean.

According to American researcher Neil Shubin, in his book Your Inner Fish, this unusual feature could be linked to human evolution. He suggests that, at some point in our distant past, humans shared traits with fish, and this mark may be a leftover sign of that connection.

Only a small portion of the population has this feature. It appears near where the ear meets the head and typically forms during the early stages of fetal development.

This condition is known as a preauricular sinus. It’s not dangerous, not a disease, and doesn’t affect a person’s health. Instead, it’s simply a harmless physical trait that may reflect our evolutionary history.

Interestingly, the percentage of people with this mark varies by region:Africa: About 10% of the population, the highest rate globallyAsia: Around 4%United Kingdom: Approximately 0.9%United States: About 0.1%, the lowest reported rate

Some theories suggest that this small opening could be a remnant of structures similar to gills from ancient ancestors, hinting at humanity’s evolutionary link to aquatic life.

While this idea remains a theory, the mark itself is completely normal—and simply another fascinating detail of human biology.