Discover how a simple test on your wrist with your pinky can reveal fascinating evidence of human evolution via the presence of this tendon.

Many internal and external features we possess are merely remnants inherited from our ancestors. These traits often no longer serve a practical purpose in our modern lives. As people 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 instance, the curious phenomenon of goosebumps

This isn’t just a random occurrence. Our mammalian ancestors had a way of dealing with cold temperatures. Goosebumps helped them increase their surface area to retain heat. When we’re cold, a muscle attached to our arm hairs contracts, making the hairs stand upright and creating bumps on our skin.

While this response no longer serves a significant purpose in our lives today, it still reminds us to grab a coat on a chilly day. We can observe modern mammals engaging in this biological instinct, such as a pigeon puffing up its feathers to stay warm on a cold winter day. If that isn’t evidence of evolution, what is?

But there is one trait that clearly shows proof of evolution: The most compelling evidence lies within our arms, specifically in our tendons. One tendon, which has gradually phased out in 10-15% of the human population, highlights that humans are still evolving.

This tendon is connected to an ancient muscle called the palmaris longus.

This muscle was essential for arboreal primates, such as lemurs and monkeys, to help them move from branch to branch. As humans and ground-dwelling apes like gorillas no longer rely on this muscle or tendon, both species have gradually lost this function.

However, evolution moves slowly, so nearly 90% of humans still have this vestigial trait, passed down from our primate ancestors. To see 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 this tendon, congratulations—you’re showing an evolutionary change! The presence or absence of this tendon is a fascinating connection to our ancestral past, with those who have it carrying a tangible link to our evolutionary history. Conversely, those without it represent clear evidence of ongoing human evolution.