Seven Million Years Ago, the Oldest Known Early Human Was Already Walking

The answer to when early humans deviated from apes and started their own evolutionary path may be found in a broken leg bone.

Two decades ago, a find suggested that early humans walked on two feet. The new analysis makes a strong case for the existence of a species that walked on two legs. The oldest known hominin is the group consisting of modern humans, extinct human species and all of our immediate ancestors, and it is thought to be the result of bipedalism.

If the species's ancestors led to Homo sapiens, it would be our oldest non-Ape Ancestor. While the fossil femur seems to have supported the demands of upright walking, it still spent a lot of time in the trees. Some three million years ago, the species used a grasping climbing technique to support a hybrid lifestyle.

It lived during the time when humans branched off from the apes. Two decades ago, fossils were found at the Toros- Menalla site. The Touma, meaning "hope of life" in the local Goran language, is a new species.

Daniel Lieberman, who wasn't involved in the new study, says it looks like an ape. The skull of the species is larger than that of a chimp. It has a number of key features that make it look like it is on the human line. Lieberman says that the most important feature is that it looks like a biped. There is evidence of bipedalism in the skull. The passage through which the brain connects with the spine is the same as it is in humans and other upright walkers.

Some experts don't agree with the idea of bipedalism. The femur is one of the bones that scientists have taken nearly two decades to describe.

The bones were found near the skull, but they weren't initially seen as part of the fossils. Scientists don't know if the limb fossils are from the same person as the skull, but they do know that the bones are from the same primate.

It was difficult to analyze the femur because the bone is missing the joints on each end and there was a debate about whether it was bipedal. If the femur was adapted for bearing all the body weight on one leg at a time, it would be obvious. If alignment kept body weight beneath the center of gravity, it was a sign of bipedalism.

According to co-author Jean-Renaud Boisserie of the Université de Poitiers, it was difficult because the bone had been gnawed on. A lot of information was preserved both on the external and internal structures that were scanned.

Boisserie and colleagues compared more than 20 characteristics of the femur and forearm bones with a sample of living apes. They compared external shapes, curves, internal structures and thicknesses to see if the bone had the same characteristics as those known to be well suited to the demands of force, balance and other requirements of upright walking. There were many similarities between the femur of S. tchadensis and other hominin species. According to Boisserie, the most parsimonious interpretation of the results is that the hominins share the same evolutionary history, but with different types of motor skills.

The authors did everything they could to find out if it is a biped or not. Daniel Lieberman says that they make a compelling case. Was it smoking gun evidence on its own? It's absolutely not. It should end the debate about whether this is a biped.

The debate will probably continue. Two years ago, a study in the Journal of Human Evolution suggested that the same femur belonged to someone who wasn't habitually bipedal. The new analysis is very different from the old one. John Hawks, who studies human evolution at the University of Wisconsin–Madison and was not involved in either femur study, has questioned whether the skull and teeth of a person are upright hominin. Since the fossil in question was discovered two decades ago, the connection between the analyses is a little frustrating. He says that the two teams that collected data from the femur disagreed about what the femur showed. The same piece of bone is being looked at by two people. They disagree about this. There would be no reason for this disagreement if both groups could just release surface 3-D and internalCT scans so that we can all look at it.

The analysis of the ulnae, the larger of the two forearm bones, shows that the arms were very apelike. The species was very good in the trees.

Boisserie suggests that this lifestyle could have been useful in the environment of Toros-Ménalla. In the northern Chad Basin, there was a patchwork of forest cover, palm groves and less forested areas. It had resources from a variety of environments at its disposal.

The analysis of the ulnas and the demonstration that Sahelanthropus also lived or moved in the trees made me happy. The evidence shows that hominins may have been adapted to move in and out of the trees for four million years.

The debate over bipedalism is just one part of a larger and still more intriguing question; is the oldest known member of our human lineage?

Some scientists don't think the species is a hominin. Scientists are debating if the fossils are from an individual who lived after the divergence of hominins and apes or if they are from someone who lived just before. If the latter is an ancestral descendant of either chimps or humans, or even a close relative which is actually ancestral to neither, that's right.

The leg bones of ancient skeletons show that two-legged walking might have evolved differently, several times. It is possible that ancient bipedal walkers are not ancestors of the later hominins who refined that ability.

As shown in earlier studies of the skull, reduced canine teeth that restructured the mouth are two of the adaptation that all later hominins share. One of the earliest known hominins, Ardipithecus Ramidus, which lived about 4.5 million years ago, shares some of the same characteristics.

What are the chances that 7 to 4.5 million-year-old apes in Africa have both of these characteristics? "Do you know what I'm asking?" All three of them are hominins, according to the authors. It might have been the closest we could get to the evolutionary branching event that led to us.