When and how do we start walking? — Rayssa, age 11, Newark, New Jersey.
This is an important question because many anthropologists see bipedalism — which means walking on two legs — as one of the defining characteristics of “hominids,” or modern humans, and their ancestors.
But it is difficult to give a simple answer because bipedalism did not appear overnight. It was the result of a gradual evolution that began many millions of years ago.
And of course there are no videos of the first person who walked upright. So how do scientists try to answer questions about how humans moved in the remote past?
Fortunately, the shape of a creature’s bones and the way they fit together can tell the story of how that body moved when it was alive. And anthropologists can find other evidence in the landscape, for example, that indicates how ancient peoples walked.
In 1994, the first fossils of a hitherto unknown hominid were found in Ethiopia. The anthropologists responsible for the discovery described the remains as that of an adult woman, and decided to call the species the Ardipithecus ramidus, nicknamed “Ardi”.
Over the next ten years, more than one hundred fossils of the Ardi species were found and dated between 4.2 million and 4.4 million years ago.
When scientists examined this collection of bones, they identified certain features that indicated bipedalism. The foot, for example, had a structure that allowed us to take steps with the impulse of the toes, as we do today, which apes that walk on four legs do not.
The shape of the pelvic bones, the way the legs were positioned under the pelvis, and the way the leg bones fit together also suggested that they walked upright.
Ardi may not have walked exactly as we do today, but bipedalism, as a normal form of movement, seems to be a feature of these fossils from 4.4 million years ago.
Anthropologists had already found almost 40% of the complete skeleton of a species of hominid that lived about 1 million years after Ardi, also in Ethiopia.
Because of its similarity to other fossils found in southern and eastern Africa, they called the species the Australopithecus afarensis, which in Latin means “southern ape from a distant region”.
The remains found were also female, so they nicknamed her “Lucy” after a Beatles song (“Lucy In The Sky With Diamonds”) popular at the time.
Several other fossils of this species — more than 300 individuals — were added to the group, and today researchers know a lot about Lucy and her relatives.
Lucy had a partial but well-preserved pelvis, which was how anthropologists knew she was female.
Her pelvis and thigh bones fit together in a way that showed she walked upright on both legs. No foot bones were preserved, but later discoveries of A. afarensis include feet and also indicate bipedal walking.
In addition to fossil remains, scientists have found other notable evidence of how Lucy’s species has moved in the Laetoli region of Tanzania.
Under a layer of volcanic ash that dates back 3.6 million years ago, anthropologists have found fossilized footprints on what had once been a wet surface of volcanic ash.
The tracks extend for nearly 30 meters, and 70 individual prints indicate the presence of at least three individuals walking upright on two feet.
Given the presumed age, the owners of the footprints were likely Australopithecus afarensis.
The footprints prove that these hominids walked on two legs, but the walk looks a little different from ours today. Still, Laetoli provides solid evidence of bipedalism 3.5 million years ago.
A hominid with an anatomy so similar to ours that we can say that it walked like us only appeared in Africa 1.8 million years ago.
O Standing man it was the first to have long legs and shorter arms that would make it possible to walk, run and move across the Earth’s landscapes as we do today.
O Standing man it also had a much larger brain than earlier bipedal hominids, and it manufactured and used stone tools called Acheulean instruments.
Anthropologists consider the Standing man our close relative and one of the first members of our own genus, Homo.
So, as you can see, the human walk took a long time to develop. It appeared in Africa over 4.4 million years ago, long before tool manufacturing began.
Why do hominids walk upright? Perhaps this allowed them to spot predators more easily or run faster, or perhaps the environment changed and there were fewer trees to climb, as early hominids did.
In any case, humans and their ancestors began walking very early in their evolutionary history.
Although bipedalism came before toolmaking, upright posture freed their hands to make and use tools, which has become one of the hallmarks of humans like us.
*Jan Simek is Professor of Anthropology at the University of Tennessee, USA.
This article was originally published on the academic news site The Conversation and republished here under a Creative Commons license. Read the original version here (in English).
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