Take a close look at any one of your two feet. Note the arch that spans the middle of your foot. Formed by curves in your metatarsus bones, the arch is one of the defining features of the human foot.
The curvature makes the human foot more adept for running rather than grabbing hold of tree limbs. So, from where and when did we get this podiatric feature?
Recent work by researchers at the University of Missouri and Arizona State University examining the remains of an Australopithecus afarensis, an early hominid, found a similar curvature in the extinct hominid’s metatarsus.
The remains of this A. afarensis, found in Hadar, Ethiopia, confirm that members of this species were likely responsible for ancient footprints found to have arched feet.
These footprints were discovered in Laetoli, Tanzinia and date back to 3.6 million years ago. In a paper published in Science, the group details their close examination of the fourth metatarsal of A. afarensis and how it compared with humans and other extent primates.
One of the most famous remains of A. afarensis was discovered back in 1974; given the name “Lucy” by a team who celebrated their discovery by playing and replaying “Lucy in the Sky with Diamonds,” that set of remains constituting 40 percent of the hominid’s skeleton supported the idea that bipedal walking developed before larger brain and skull sizes.
Deposits in the Hadar formation have since yielded many more hominid fossils dating back to 3.2 million years ago.
A number of other partial metatarsals have been found among them, but only a complete metatarsal, discovered in 2000, was able to address the question of whether A. afarensis had arches similar to those of humans.
This discovery also suggests that metatarsal curvature and foot arches appeared much earlier than previously suspected.
“We see humanlike arches in our genus, Homo, around 1.8 million years ago, but there has been no direct evidence from the bones earlier than this time,” wrote Carol Ward, professor of Pathology and Anatomical Sciences at the University of Missouri School of Medicine, in an email with The News-Letter.
Foot arches are especially crucial in humans, as individuals who are flat-footed tend to suffer certain physical issues due to insufficient shock absorption.
According to Ward, “arches provide shock absorption during walking and running; this is critical as we all know when people have ‘flat feet’ or ‘fallen arches’ they have a host of joint problems throughout their skeletons.”
In addition to the developments in the metatarsal bones, an additional development that led to the human feet being adept for running rather than climbing was the stiffening of the foot, where the individual bones of the feet are confined and have considerably less freedom than those of our hands.
“Also, the human feet are stiff so that when we lift our heels off of the ground the whole foot lifts up, this provides propulsion. An ape’s foot flexes in the middle,” she wrote.
The most significant finding of the study is that arched feet and bipedal motion developed much earlier than previously believed by scientists.
“This shows that the foot arches are as ancient as committed terrestrial bipedality, and supports the hypothesis that afarensis were committed bipeds like us,” Ward wrote.
She also notes that another species she is currently working with, A. anamensis, dates back even further to 4.2 million years ago, although it is not as well represented in the fossil record.
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