Ancient lessons of bipedal locomotion | Science and life

Among animals, only man knows how to constantly walk on two legs. Of course, there are also jerboas and kangaroos, but they do not walk, they jump; for various reasons, they cannot move their legs one by one. Some monkeys can walk on their hind legs for quite a long time. But, one way or another, natural upright posture, or bipedalism, is an exclusively human ability. It is believed that the ancestors of people got to their feet only once, and this happened about 6 million years ago, after which their body began to adapt to a new way of movement. (Actually, the ancestors did not immediately become erect, and their bipedalism improved along with constructive anatomical changes.) The ability to keep the body straight, moving on two legs, appeared even before the human ancestors began to enlarge their brains and they learned how to make tools.

The most famous evidence of upright walking is the footprints found at Laetoli in northern Tanzania. They were found there back in the 70s of the last century. However, the footprints in Laetoli were of different types. Some of them, the most famous, are from legs that are very similar to those of modern people. But there were others, strange in shape, that betrayed a special manner of walking: they were left by someone who put their legs crosswise, that is, with each step, the leg went forward and sideways, crossing the line of movement. According to one of the versions, these traces were left by some ancient relative of man, a primate from the Hominin subfamily, but not the one that left other, “normal” traces. According to another hypothesis, they were left by a bear, who decided to walk on its hind legs. The comparison with the bear may seem surprising – after all, the human footprint is different from the bearish one. But, firstly, traces in Laetoli were not left by people, not Homo, and some great apes, albeit more humanoid than chimpanzees. Secondly, these tracks are several million years old. Thirdly, the bear’s legs are so arranged that the trace of the bear’s right foot is somewhat similar to the trace of the primate’s left foot. And in this case, you do not need to rack your brains over the strange gait crosswise.

The strange footprints were forgotten for a long time, until new footprints in the same spirit were excavated in Laetoli, and these new footprints make it possible to assert with a high degree of certainty that they were still left by human relatives. Employees Dartmouth College, Ohio University and other research centers describe in Nature signs indicating that bipedal primates have left strange footprints. The thumb (first) toe and the second toe are almost the same in length, while the thumb pressed on the ground more than the second; the trace from the toes inextricably passes into the trace from the rest of the foot; primate heel mark is wide. At the same time, the big toe is so long that its owner could easily grab something with his foot, as modern monkeys do. In general, the tracks are unusually wide and at the same time short, which makes them unlike the tracks of any other hominins.

a) Cross tracks from Laetoli; b) the usual trail from Laetoli; c) a strange trail from Laetoli, shorter and wider; d) bear trail; f) chimpanzee footprint. (Photo: Nature, 2021).

Australopithecus left other traces in Laetoli Australopithecus afarensis, who is considered the ancestor of all other hominins, including humans. But the strange traces, old and new, were clearly not left by him. There are also other ancient humanoid footprints of 3.4 million years old found in Ethiopia – they differ from the Australopithecines and are somewhat similar to the strange footprints from Laetoli. Perhaps their traces from Ethiopia were left by the same species of humanoid hominins, which could stand on “grasping” hind legs and put them crosswise so as not to lose balance. Maybe these were different types. Or maybe they were left by some unusual Australopithecus afarensis… However, the authors of the work are inclined to believe that the unusual traces were left not by Australopithecus, but by someone else. In other words, not only those great apes whose descendants gave rise to humans, but also their relatives, experimented with upright walking – however, what kind of relatives they were, we do not yet know.

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