Discover how a simple test involving your wrist and pinky finger can provide fascinating insight into human evolution through the presence of a specific tendon.

Many internal and external features we possess are remnants inherited from our ancestors, traits that no longer serve a practical purpose in our modern lives. While we no longer need to scavenge for food or live as nomads, we still carry these almost obsolete characteristics, passed down from a time when they were essential for survival.

Take, for example, the curious phenomenon of goosebumps. This isn’t just a random occurrence. Our mammalian ancestors used goosebumps to help them deal with cold temperatures. The reaction increased their surface area, allowing them to retain heat. When we’re cold, a muscle attached to our arm hairs contracts, causing the hairs to stand upright and creating bumps on the skin.

Though this response no longer serves a major function today, it still reminds us to grab a coat on a chilly day. Modern mammals, such as pigeons puffing up their feathers to stay warm on a cold winter day, continue this instinctive behavior. If that’s not evidence of evolution, what is?

However, one particular trait offers more direct proof of our evolutionary journey: the presence of a tendon in our arms. This tendon, which has gradually disappeared in 10-15% of the human population, demonstrates that humans are still evolving.

The tendon is connected to an ancient muscle called the palmaris longus. This muscle was crucial for arboreal primates, like lemurs and monkeys, helping them swing from branch to branch. As humans and ground-dwelling apes, such as gorillas, no longer rely on this muscle or tendon, its function has gradually diminished.

Evolution, however, is a slow process, so nearly 90% of humans still retain this vestigial trait, inherited from our primate ancestors. To check if you have this tendon, place your forearm on a table with your palm facing up. Touch your pinky finger to your thumb and slightly lift your hand off the surface. If you see a raised band in the middle of your wrist, you have the tendon connected to the palmaris longus.

If you don’t see the tendon, congratulations—you’re showing evidence of an evolutionary change! The presence or absence of this tendon is a tangible link to our ancestral past, with those who have it carrying a piece of evolutionary history. On the other hand, those without it represent clear evidence of ongoing human evolution.