Plantaris Became Obsolete

The plantaris is a small calf muscle that modern humans barely use, but anatomists think our primate ancestors once used it more effectively for grasping with their feet. In humans, it now contributes only weakly to plantar flexion and knee flexion, and its function is so minor that surgeons can remove its long tendon for reconstruction with little deficit. The muscle is absent altogether in about 8 to 12 percent of people, which has helped fuel arguments that humans may be evolving away from it.

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