Human evolution; our feet differ from apes. (Introduction)

by David Turell , Wednesday, February 26, 2020, 20:13 (1730 days ago) @ dhw

Our foot is stiffer and exerts more force:

https://phys.org/news/2020-02-overlooked-arch-foot-key-evolution.html

"long-overlooked part of the human foot is key to how the foot works, how it evolved, and how we walk and run, a Yale-led team of researchers said.

"The discovery upends nearly a century of conventional thinking about the human foot

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"When humans walk and run, the front of each foot repeatedly pushes on the ground with a force exceeding several times the body's weight. Despite these strong forces, the human foot maintains its shape without severely bending. Such stiff feet—unique to humans among primates—were important for the evolution of bipedalism. (my bold)

"What makes human feet so stiff? According to conventional thinking, it's mainly the longitudinal arch of the foot. This arch runs from heel to forefoot and is reinforced by elastic tissues underneath it. The arch and tissues create a bow-and-string structure that for nearly a century was considered the main source of the foot's stiffness.

"But the foot has a second arch that runs across the width of the midfoot, known as the transverse arch. Venkadesan and his colleagues investigated the transverse arch, which had not been studied previously. They performed a series of experiments,using mechanical mimics of the foot, cadaveric human feet, and fossil samples from long-extinct human ancestors and relatives (hominins). Their results show that the transverse arch is the main source of the foot's stiffness.

"The reason the transverse arch is so important can be found in your wallet. Take out a dollar bill, hold it at one end, and the dollar flops around. But press your thumb down to give the dollar some curvature, and it stands out straight.

"'That type of effect also works in the foot," said Venkadesan, assistant professor of mechanical engineering and materials science. "It's not as simple as a sheet of paper because there are many other tissues and structures in the foot, but the principle turns out to be the same."

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"'We found that transverse springs, which mimic tissues spanning the width of your foot, are crucial for curvature-induced stiffness," said Ali Yawar, a Ph.D. student in Venkadesan's lab. "So we expected that stiffness would decrease in real human feet if we were to remove the transverse tissues and leave everything else untouched."

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"We found that the transverse arch, acting through the transverse tissues, is responsible for nearly half of the foot's stiffness, considerably more than what the longitudinal arch contributes," said Carolyn Eng, an associate research scientist in Venkadesan's lab.

"These results may also explain how the 3.66 million-year-oldAustralopithecus afarensis, the same species as the fossil Lucy, could have walked and left a human-like footprint despite having no apparent longitudinal arch. Working with Andrew Haims, a professor at the Yale School of Medicine, the researchers developed a new technique to measure transverse curvature using partial skeletons of the foot. By applying this technique to fossil samples, includingA. afarensis, they traced how the transverse arch evolved among early hominins.

"'Our evidence suggests that a human-like transverse arch may have evolved over 3.5 million years ago, a whole 1.5 million years before the emergence of the genus Homo, and was a key step in the evolution of modern humans," Venkadesan said". (my bold)

Comment: we are as different from apes in our physical attributes as in our special brain. Note my bolds: Stiffness developed long before true Homo species arrived. I view this as God pre-planning our appearance as He managed evolution. From the Darwin standpoint, why should Lucy develop a stiff foot she didn't really need when she existed? She could run faster which tells us she was designed to be able to save herself on the ground by running. This means she was designed with the ability to protect her on the ground from the beginning of her species appearance. Not a slow Darwinian adaptation.