Early Human Foot Bones Shed Light On Walking and Tree Climbing Abilities

Homo naledi, a new, extinct human ancestor was recently discovered in a South African cave. Now, a month later, we have a better understanding of how our relatives walked upright and swung from tree to tree. 

After more than 1,550 fossils were excavated from Rising Star cave, researchers determined that the feet were the most human-like body part of H. naledi. Although, it turns out they didn't use them to walk in quite the same fashion modern humans (Homo sapiens) do today, according to a news release.

Researchers examined 107 foot bones, from which they found that H. naledi was well adapted for standing and walking on two feet, but that it was also well-adapted to climbing trees. To better understand the climbing strategy of H. naledi, researchers also examined their hand bones. This study sheds light on the skeletal form and function that may have characterized our ancestors. 

"Homo naledi's foot is far more advanced than other parts of its body, for instance, its shoulders, skull, or pelvis," William Harcourt-Smith, lead author of the new paper and a resident research associate in the American Museum of Natural History's Division of Paleontology, said in the release. "Quite obviously, having a very human-like foot was advantageous to this creature because it was the foot that lost its primitive, or ape-like, features first. That can tell us a great deal in terms of the selective pressures this species was facing."

While H. naledi's foot appeared to be more similar to human bones, there were two areas that still resembled chimpanzee bones. For instance, H. naledi's foot was more curved and their feet were generally flatter than those of modern humans. Although they are considered bipeds for their ability to walk upright, these differences suggest that our ancestors were not quite rid of their tree-climbing days. Researchers also used clues provided by H. naledi's long and curved fingers and more ape-like shoulder joints to confirm this.

"This species has a unique combination of traits below the neck, and that adds another type of bipedalism to our record of human evolution," Harcourt-Smith said in a statement. "There were lots of different experiments happening within hominins--it wasn't just a linear route to how we walk today. We are a messy lineage, and not just in our skulls and our teeth. We're messy in the way we moved around."

The H. naledi fossils have yet to be dated, so the researchers are still unsure how this form of bipedalism fits into the evolution of humans.

Their findings were recently published in the journal Nature Communications.  

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