Your Body Has Vestigial Muscles

Your body is a living museum of evolutionary history, containing several structures that have lost their original purpose. A prime example is the palmaris longus, a slender muscle running from your elbow to your wrist. You can easily check if you possess this evolutionary leftover by placing your arm on a flat surface, touching your pinky to your thumb, and slightly flexing your wrist upwards. If a tendon protrudes in the center of your wrist, you are among the roughly 85% of humans who have this muscle.

The palmaris longus is a relic from our primate (Review) ancestors, who used it to increase grip strength for climbing and moving through trees. As early humans became bipedal and less reliant on this type of locomotion, the muscle became non-essential. The fact that about 15% of the population is born without it on one or both arms, with no difference in grip or dexterity, is a clear testament to its functional redundancy. Its presence or absence is simply a result of normal human genetic variation.

Ironically, this "useless" muscle has found a surprising modern purpose in medicine. Surgeons often harvest the long, accessible tendon of the palmaris longus for use in reconstructive surgeries. It can be grafted to repair other damaged tendons or ligaments in the hand, elbow, or even the face. Because its removal has no functional consequence, it serves as a perfect spare part, a convenient piece of our evolutionary past repurposed for modern healing.