Human feet evolved to have a “unique” arch more than 3.5 million years ago, which made it possible to walk and run on two legs, scientists have said.
And experts believe the discovery shows a “key step” in human evolution and may help to improve the design of robotic feet.
The so-called transverse arch, which run across the width of the midfoot, is absent in other primates such as chimpanzees and gorillas which have flat, and more flexible, feet.
Mahesh Bandi, an associate professor at the Okinawa Institute of Science and Technology Graduate University in Japan, who co-led the study, added: “Having a firm understanding of how the human foot works has several real-world applications.”
Anthropologists have long debated how the structure of the human foot creates the stiffness that is essential for upright walking.
While most studies have focused on the longitudinal arch, which runs from the heel to the ball of the foot, the role of the transverse arch has been overlooked.
To investigate whether the transverse arch creates stiffness, a team of engineers, which included scientists from the University of Warwick, performed bending tests on human feet and examined fossil samples of human ancestors and relatives.
They also created computer simulations and plastic models of the midfoot and measured how much force was required to bend them.
The results, published in the journal Nature, showed the transverse arch to be responsible for “more than 40%” of foot stiffness.
Just as bending a sheet of paper parallel to the width stiffens it lengthways, the researchers believe the transverse arch may have a similar role in feet.
The team believe their findings may explain how Australopithecus afarensis, a human relative which lived around 3.66 million years ago, could generate footprints like humans, despite having no apparent longitudinal arch.