That small groove running from your nose to your upper lip is called the philtrum, and while it serves little purpose in humans today, it may be a reminder of a sensory world our ancestors left behind.

In dogs and many other mammals, the philtrum helps channel moisture from the mouth toward the nose, helping keep the nose damp. That moisture traps scent molecules from the air, improving the animal's ability to detect and analyze odors.

Humans have the same facial feature, but it no longer appears to play a significant role in smell.

Scientists believe this reflects a broader evolutionary shift. Over millions of years, primates increasingly relied on vision, especially color vision, while some aspects of the sense of smell became less important. As a result, humans accumulated hundreds of inactive odor-detecting genes that no longer function.

The evidence of that change is still written into our DNA and, perhaps, right in the middle of our faces.

The next time you notice the small groove above your lip, you may be looking at a leftover piece of sensory equipment from a time when our ancestors depended far more on smell than we do today.