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A controversial femur suggests that the human family already walked on two legs seven million years ago

2022-08-24T20:26:18.805Z


The bone was discovered in 2001 in Chad and since then it has been the subject of a fierce war between scientists from the same university


Humanity still does not know from what creatures it arose.

The human family split from the chimpanzee family between 6 and 10 million years ago.

That last common ancestor is an enigma, but a seven-million-year-old femur now illuminates that dark period of evolution.

The bone, found in Central Africa in 2001, indicates that the oldest members of the human family - beings weighing 50 kilos and just over a meter tall, belonging to the species

Sahelanthropus tchadensis

- already possessed one of the most characteristic of people: they walked on two legs.

The femur has been involved in one of the fiercest wars in the history of paleoanthropology.

The bone turned up alongside numerous animal fossils on July 19, 2001 at the Toros-Menalla site in Chad, but was overshadowed by the discovery of a majestic seven-million-year-old skull.

The director of the excavations, the French paleontologist Michel Brunet, from the University of Poitiers, proclaimed that they had found "the beginning of the lineage of the human being".

The skull, as its discoverers then explained, belonged to a hominid with a brain similar in size to that of a chimpanzee, but which was already possibly bipedal, judging by the place of insertion of the vertebral column in its head.

That individual was baptized

Toumaï

, as they call in that desert of Chad the babies that are born just before the dry season.

It means “hope to live” in the local language.

The new species was recorded as

Sahelanthropus tchadensis

.

The real soap opera began in 2004, when a young student, Aude Bergeret, came across the femur in a collection of indeterminate animal bones at the University of Poitiers.

Suspecting that it could be from

Toumaï

's left leg or from another specimen of the same species, and given that Michel Brunet was excavating in Chad, the student showed the femur to another professor at the same institution, the Italian Roberto Macchiarelli.

After a preliminary analysis, both concluded that the

Sahelanthropus tchadensis

moved on all fours and were far from the human family.

They failed to publish their results until 2020.

Two three-dimensional models of the analyzed femur (left) and another two of each ulna.Franck Guy / CNRS – University of Poitiers

A new, more exhaustive study of the same femur defends the opposite: the

Sahelanthropus tchadensis

did walk on two limbs “usually”.

The work is published this Wednesday in the journal

Nature

, a showcase of the best world science.

The species thus joins later ones that also moved on two legs at the beginning of the human family, such as

Orrorin tugenensis

, which lived in what is now Kenya about six million years ago, and

Ardipithecus ramidus

, which walked some 4.4 million years ago by present-day Ethiopia.

Paleontologist Guillaume Daver is one of the co-directors of the new study at the University of Poitiers.

His team does not believe that the ability to walk on two legs arose independently in different species.

Daver argues that the most logical thing is that "this behavior appeared only once throughout human evolution: either it was inherited from the last common ancestor or it arose soon after the divergence between chimpanzees and humans."

The collective imagination, influenced by religious stories, perceives evolution as a straight path from the primitive quadrupeds to the perfection of the human being, but reality is more like a leafy tree with branches that intersect in a confusing way.

Chimpanzees, which are rather quadrupedal, may be descended from a creature that was rather bipedal.

Or not.

One of the living legends of paleoanthropology, the American Tim White, has moved to Spain this year to join as a scientist affiliated with the National Center for Research on Human Evolution, in Burgos.

In 1979, he was one of the researchers who presented the world with the remains of

Lucy

, a meter-tall australopitheca that showed that human ancestors already walked on two legs more than three million years ago in what is now Ethiopia.

In 2009, White announced another landmark discovery: the skeleton of

Ardi

, a female of a new extinct species found in Ethiopia,

Ardipithecus ramidus .

, able to walk upright on the ground 4.4 million years ago and also to move agilely through the branches of trees by means of a huge opposable thumb on the foot.

Artistic recreation of the modes of locomotion of 'Sahelanthropus tchadensis'. Sabine Riffaut, Guillaume Daver, Franck Guy / CNRS – University of Poitiers

Tim White blesses the new study, in which he has not participated.

Sahelanthropus tchadensis

did

walk on two legs.

"Their conclusion is fully consistent with everything we know about early hominins: they were definitely neither like modern chimpanzees nor modern humans, but had already evolved in the direction of later hominins from the last common ancestor we shared with chimpanzees." today," says White, who uses the word hominids to refer exclusively to bipedal primates.

The Italian Roberto Macchiarelli, however, charges against his colleagues at the University of Poitiers.

In his opinion, the new study "omits indications" that the

Sahelanthropus tchadensis

were quadrupedal and its authors "lie" about the origin of the femur.

“[The student] Aude Bergeret saved the bone from destruction in 2004 and they don't even mention her.

They fired her and seized the material.

Taking more than 20 years to carry out an analysis is a new world record”, criticizes Macchiarelli.

The atmosphere inside the University of Poitiers is explosive.

The co-directors of the new work, Guillaume Daver and Franck Guy, defend themselves against the accusations.

They claim that Macchiarelli and Bergeret concluded that

Sahelanthropus tchadensis

were quadrupedal from a preliminary analysis of the femur, based primarily on photographs taken before the adhering sediments were cleaned from the bone.

Michel Brunet, head of the team that discovered the remains in 2001, began digging in the inhospitable desert of Chad in 1994. Today he is 82 years old and says he did not want to participate in the new analysis.

“There has been too much strange behavior around these fossils since their discovery.

Since I am a young paleontologist, I value and need more tranquility and greater intelligence to enjoy science”, he jokes.

The Djurab desert, in Chad, where the fossils of the 'Sahelanthropus tchadensis' were found. CNRS – University of Poitiers

Brunet justifies the delay of more than two decades.

"My team was just doing more digging in Chad and waiting for more fossils to turn up," he says.

The rest, he says, is "a sad tale written by couch potato paleoanthropologists, with a lot of unacceptable behavior," a clear allusion to Roberto Macchiarelli and Aude Bergeret.

The former student, today director of the Jacques de La Comble Natural History Museum in Autun (France), declines to assess the new study.

“For my part, I am glad that, after all this time, there can finally be a scientific debate about the femur,” replies Bergeret.

In addition to the controversial femur, the new work analyzes two ulnae - the bones of the forearm - also found at the same site in Chad in 2001. While the characteristics of the femur suggest that

Sahelanthropus tchadensis

walked the ground on two legs, the two ulnae suggest that they could also climb trees with agility.

In the opinion of evolutionary biologist Daniel Lieberman, of Harvard University (United States), it is not a definitive verdict.

“The Sahelanthropus

femur

does not present compelling evidence of bipedalism, but it is more like that of a bipedal hominid than that of a quadrupedal ape,” he says in a separate commentary published in the journal

Nature

.

The scenario of human evolution is now left with

Sahelanthropus

walking on two legs and climbing trees seven million years ago, perhaps similar to how

Ardipithecus ramidus

would have done 4.4 million years ago in what is now Ethiopia. .

The rest of the story is better known.

Australopithecines, other members of the human family, evolved about three million years ago and perfected their two-legged walk, until members of the genus

Homo

emerged , such as modern humans, capable of even running the 100 meters in less than 10 seconds.

After decades of controversy and risky excavations in the Chadian desert, veteran Michel Brunet believes that this may be the end point of the debate about whether

Sahelanthropus tchadensis

walked on two legs: “In scientific terms, this is definitely the end of the debate, but we'll see, because all this is also a human story”.

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Faith of errors

In a first version of this article it was said that Roberto Macchiarelli was never able to personally analyze the femur, but he was able to do a preliminary examination in 2004.

Source: elparis

All news articles on 2022-08-24

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