Ancient Human Ancestor, Sahelanthropus tchadensis, May Have Walked Upright 7 Million Years Ago
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A groundbreaking new study suggests the earliest known human ancestor, Sahelanthropus tchadensis, possessed the ability to walk upright, pushing back the timeline for the evolution of bipedalism. This discovery, published in Science Advances, challenges previous assumptions about our evolutionary origins and offers compelling evidence that walking on two legs developed surprisingly early in the human lineage.
The fossilized remains of S. tchadensis were first discovered in the Djurab Desert of Chad in the early 2000s. The hominid, dating back approximately 7 million years, exhibited a blend of ape-like and hominid characteristics, sparking a decades-long debate among scientists regarding its locomotion.
The Long-Standing Debate Over Bipedalism
For the past two decades, the scientific community has grappled with the question of whether S. tchadensis was capable of upright walking. Earlier research largely indicated a quadrupedal movement pattern, similar to that of modern apes who utilize knuckle-walking. However, this new analysis presents a compelling counterargument.
New Evidence from Ulna and Femur Analysis
This latest research departs from previous studies that primarily focused on the skull. Instead, scientists meticulously examined the ulna (forearm) and femur (thigh bone) of S. tchadensis. Through advanced analytical techniques and comparative studies with other species, including Australopithecus – famously represented by the “Lucy” skeleton discovered in Ethiopia in 1974 – researchers have uncovered significant anatomical clues.
Key Anatomical Indicators of Upright Walking
The study identified several key features indicative of bipedalism. Crucially, researchers pinpointed a specific attachment point for the iliofemoral ligament, which connects the pelvis to the femur. This ligament is a defining characteristic of hominids and essential for stable, upright walking.
Furthermore, the team detected a femoral torsion unique to hominids, which orients the legs forward and facilitates efficient walking. The presence of gluteal muscles similar to those found in early hominids – responsible for hip stabilization and locomotion – also supports the bipedalism hypothesis. Additionally, S. tchadensis exhibited a relatively longer femur in proportion to its ulna, a trait more commonly observed in bipedal species.
Revealing Proportions: A Shift from Ape-Like Structure
A fundamental difference between apes and hominids lies in their body proportions. Apes typically have long arms and short legs, while hominids possess comparatively longer legs. While the legs of S. tchadensis were shorter than those of modern humans, they demonstrably differed from the leg structure of apes, exhibiting proportions more akin to Australopithecus – often referred to as “Lucy.”
“We are faced with compelling evidence that S. tchadensis could walk on two legs, which shows that bipedalism evolved early in our lineage and from an ancestor very similar to today’s chimpanzees and bonobos,” stated a co-author of the study, an anthropologist at New York University.
An Ongoing Scientific Discussion
While this new research provides strong evidence for bipedalism in S. tchadensis, the debate is not entirely settled. One researcher at the University of Barcelona, who was not involved in the study, believes this represents the “oldest known demonstration of bipedalism, being very close to the evolutionary division into the two lines that gave rise to chimpanzees and humans.”
However, a director of the Human Evolution Laboratory at the University of Burgos cautioned that the available fossil remains are not yet conclusive enough. “If the fossils themselves serve to say one thing and the opposite, it is that they are surely insufficient,” he noted.
Despite the ongoing discussion, this latest study significantly strengthens the case for S. tchadensis as a pivotal figure in the early evolution of humankind, suggesting that the ability to walk upright emerged much earlier in our ancestry than previously thought.
