The Seven-million-year-old femur reigns a long and fierce scientific war over the origin of bipedalism |Science |

A new study has confirmed three features of vertical walking in Sahelanthropus tchadensis, the oldest known human, but critics have dismissed the evidence as a quadrupedal ape.

A seven-million-year-old femur reignites a long and fierce scientific war over the origin of bipedalism

New research has identified three features of upright walking in Sahelanthropus tchadensis, the oldest known hominid, but critics have dismissed the evidence as a quadrupedal monkey.

Un diminuto bulto óseo de apenas cinco milímetros ha reabierto uno de los debates más encarnizados de la historia de la paleoantropología. Un equipo de la Universidad de Nueva York ha identificado en el fémur de Sahelanthropus tchadensis tres características anatómicas que solo aparecen en los bípedos. Esta especie pudo ser el homínido más antiguo conocido, que vivió hace siete millones de años en lo que hoy es Chad. El hallazgo, publicado este viernes en Science Advances, confirmaría que los ancestros más primitivos de la familia humana ya caminaban erguidos sobre dos patas, una adaptación que hasta ahora solo se había inferido indirectamente a partir de la posición del cráneo. Y también aviva una guerra científica encarnizada que dura más de 25 años entre los que creen que el homínido podría caminar a dos patas y quienes no solo lo niegan taxativamente, sino que creen que ni siquiera era un homínido.

"The femoral tubercle is flawless in hominids and completely absent in chimpanzees," Scott Williams, an anthropologist at New York University and lead author of the study published Friday, explained to this newspaper.The small tubercle at the top of the femur is the attachment point for the largest and strongest iliofemoral ligament in the human body, which prevents the body from falling backwards when standing or walking.Williams adds: "Their presence must have occurred shortly after the evolutionary divergence from chimpanzees. In addition to the tubercle, the team identified two other pieces of evidence that they say are unequivocal: a strong flexion of the femur (the lower part of the bone is turned inward, which never happens better in apes) and a gluteal muscle."

The decision came after a 25-year scientific battle to determine whether Sahelanthropus tchadensis is bipedal or not.The bones - a femur and two ulnae - were found in July 2001 along with an impressive skeleton in the Djurab desert (Chad).They named him Toumaï, as they call babies born just before the dry season in that desert."live" in the local language.Its researchers then confirmed that it belonged to a hominid with a brain similar to that of a chimpanzee and that it was probably bipedal, judging by the placement of the spine on the head.

But the limb bones remained cataloged as "unidentified faunal remains" until 2004 when a young student, Aude Bergere, rediscovered them while searching through the collections of the University of Poitiers, France.Bergeret and the Italian paleontologist Roberto Macchiarelli analyzed the pelvis and came to an explosive conclusion: Sachelanthropus moved on all fours and was probably an ape rather than a hominid.They have been trying to publish their results for 16 years, to no avail.Bergeret was fired.

In the yearIn 2020, McChirelli was finally able to publish his review in the journal human evolution.McChirelli accused Poitier's colleagues at El Pais of "showing evidence", Kidnops calling the charge "a sad story written by the hotel's paleo anthropologists".

In 2024, Macchiarelli returned to the fray, arguing in a new study published in the Journal of Human Evolution that the trait identified by Brunet in 2022 was not diagnostic of upright walking because it also occurs in carnivores.The argument seemed solid. Poitiers, two rival teams from the same university, had the same legs and reached irreconcilable conclusions.

Williams and his team have now performed an independent analysis using 3D geometric morphometry, a technique that allows measurements of three-dimensional shapes with millimeter precision."Science works best when independent researchers have the opportunity to provide new insights," Williams explained.First, it was discovered in a high-quality model, and then confirmed in the original fossil.

However, Macchiarelli categorically rejects the existence of a femoral tubercle.In a document sent to this newspaper, Italian paleontologist Aude Bergeret attached photos of the original fossil taken in 2004 and says the area where Williams locates the nodule is "very damaged and incomplete, probably gnawed by carnivores and roughly cleaned with a mechanical cleaner."Macchiarelli adds that the research team itself acknowledged in 2022 that "there is no sign of a femur."nodules" in the original fossil and accuses Williams of only identifying it in the copies, a "very restrictive and risky analytical option."

Macchiarelli argues that "the supposed magical features represented by the femoral tubercle are highly variable in humans and often present in the remaining great apes," Macchiarelli argues.

SALVADOR Moyy agreed that the broadcast, the new researchelogy is the most important income: "The proximity is part of the following field. The billing of Bipdalism. The Catan Science is a publisher and the best of Bipelism Facts of the Factive, " Anatomical data changes did not get Bippertalism."

Williams stands by his conclusion.The result is paradoxical: Sahelanthropus looked like a chimpanzee but walked like a man."In their general surface appearance, the ulna and femur most closely resemble those of chimpanzees," admits Williams, "but each bone has one or more derived features reminiscent of later hominids."The strongly curved ulna suggests that it was an agile climber.Limb relationships between bonobos and australopithecines.But three features of the femur leave no doubt, according to the New York team: Sahelanthropus walked upright.

"I think that's exactly what we're seeing: a largely chimpanzee-like or bonobo-like ape that evolved bipedalism," Williams explains.The image that emerges is of a creature just over a meter tall and weighing 50 kilograms that walked on two feet on the ground but was still an expert tree climber."Topedalism appears to have evolved early in our lineage, but the dependence on climbing trees for food and safety continued for millions of years."he adds.

The discovery supports the hypothesis that the last ancestors of humans and chimpanzees were more similar to modern chimpanzees than to extinct Miocene apes, as defended by paleontologist Tim White, the discoverer of Lucy and Ardi.White, who currently works at the National Research Center for Human Evolution in Burgos, approved the study by Brunet and his team in 2022: "The conclusion is in line with everything we know about the first hominids: certainly not like modern chimpanzees or not like modern humans, but they have evolved into later hominids," he then announced in this newspaper.

Williams was cautious about whether his study definitively closed the debate.He admitted, "I think our study adds more weight to one side of the argument. I'm sure the case is not closed: further work and future fossil discoveries may confirm or refute our findings."Macchiarelli and his colleagues "may be wrong in some of their interpretations."

Macchiarelli, on the other hand, opposes what he considers a "discussion of interest" in the history of Sahelanthropus." The fossils and scientific discoveries are not only treasures, a common success for everyone, but for some of them can be useful business transactions to get positions, money and other influences, not only to make knowledge," he said."Paleoanthropology is deeply influenced by competition and politics.

Williams believes the fossil's history will change if the pelvis is found, and predicts it will be "shared" between Ardipithecus and chimpanzees.The missing part will solve this struggle, which has been going on for over twenty years, and will solve the problem of the origin of bipedalism.

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