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Despite the way our species evolved away from climbing trees to walking on flat ground, some people are still walking around with chimp-like feet.

As much as eight percent of humans may have feet that are "flexible", according to a study in The American Journal of Anthropology.


This is surprising, because part of the reason our feet work so well is that they don't bend in the middle -- it gives us support as we stroll. While we have joints in the middle of our feet, we don't have a "midtarsal break" because our ligaments are stiff and act to keep it rigid.

Chimp feet, on the other hand, retain similar bone structure but have softer ligaments that make tree-climbing (and anything that involves grasping with feet) easier.

Anthropologist Jeremy DeSilva and occupational therapist Simone Gill looked at 398 people as they walked up and down barefoot in the Boston Museum of Science. They filmed the feet up close to see what midtarsal flexibility there was, and found 32 of the participants -- or nearly one in 13 -- "possessed both elevated lateral midfoot pressures and even exhibit midfoot dorsiflexion characteristic of a midtarsal break". That is, they have bendy feet, like chimps.


The owners of the monkey feet didn't look like they were walking noticeably different to the casual observer, nor did they tell DeSilva or Gill that they felt like they could notice the bending of their feet as they walked. However, people with the midtarsal break had much flatter feet than normal.

Whether the difference confers any advantages -- beyond making it easier to pick stuff up with one's feet, or climb trees -- is unclear. DeSilva told New Scientist that he believed, because flexible feet should pose a disadvantage for humans who only use their feet for walking, it might be a reemerging trait caused by new lifestyle variations (like wearing shoes) that mean the feet ligaments fail to become as rigid.

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