By Gege Li
Modern humans have evolved stiff, arched feet for upright walking and running
An analysis of human feet and fossils has given new clues to how our feet got their stiffness, enabling us to walk and run upright.
The arches in the human foot are key to this stiffness. Other primates have flatter, more flexible feet that can bend much more than ours. Humans have two distinct arches in the middle of the foot: the medial longitudinal arch (MLA) that runs from the ball of the foot to the heel, and the transverse tarsal arch (TTA) near the ball of the foot, that runs from one side of the foot to the other .
The TTA was thought to be more involved in supporting the foot, while the MLAs main role was believed to be making the foot stiff.
But Madhusudhan Venkadesan at Yale University and his colleagues looked at the TTA and found that it is much more involved in stiffness than previously thought.
By studying two feet from human body donors, they found that cutting the tissues that run along the TTA decreased the stiffness of one foot by 44 per cent and the other by 54 per cent. This is a bigger drop than the 23 per cent difference in stiffness when they cut the MLA.
It was not a surprise that the TTA played a role, but what certainly took us by surprise is how much of a role, says Venkadesan.
The finding sheds light on how ancient humans might have walked upright despite having flat feet that lacked a distinct MLA. From looking at fossils of Homo naledi, which could walk on two legs, the researchers found that it had a human-like foot but a flat MLA. But its TTA was similar to that in modern humans, possibly compensating for this.
The finding is a game changer, says Daniel Lieberman at Harvard University. It helps explain why and how people with flat feet are able to walk just fine, and how our ancestors were able to walk for millions of years before the longitudinal arch evolved.
Journal reference: Nature, DOI: 10.1038/s41586-020-2053-y
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By Gege Li