Extinct Tree-Climbing Human Walked with a Swagger

A recently unearthed extinct human species — perhaps the most primitive ever discovered — had hands and feet adapted for a life both on the ground and in the trees, researchers say.

This finding sheds light on how early humans experimented with a variety of designs, scientists added. And though the international teams of scientists are not certain how this extinct human would have walked, they say the swagger would have been quite different from ours.

Although modern humans are the only human species alive today, other human species once walked the Earth. The human lineage, the genus Homo, and its close relatives, including australopithecines such as the famed Lucy, are together referred to as hominins.

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The most recently discovered human species, Homo naledi, had a brain about the size of an orange, but it nevertheless possessed enough of a mind to perform ritual burials of its dead. More than 1,550 bones and bone fragments of H. naledi have been recovered from a cave in South Africa, the single-largest fossil hominin find made yet in Africa. Scientists have yet to pin down a date for when H. naledi lived because the nature of the cave in which it was found makes it difficult to determine the age of its fossils. [Photos: New Human Relative (H. naledi) Shakes Up Our Family Tree]

Scientists investigated the hands and feet of H. naledi to learn more about a key shift in human evolution — the move from a life of climbing trees to one spent walking on the ground. Modern humans dominate the planet partly because walking upright frees their hands for tool use, scientists have found.

The researchers analyzed more than 150 H. naledi hand bones, including a nearly complete adult right hand that was missing just one wrist bone. They found the species shared a long, robust thumb and wrist architecture with modern humans and Neanderthals, potentially giving the hand a precise, forceful grip that may have been useful for tool use.

However, its fingers were longer and more curved than most australopithecines — indeed, more curved than those of nearly any other species of early hominin. This quality hints at a life suited for moving and climbing through trees. The scientists detailed their findings on H. naledi's hands and feet online today (Oct. 6) in two papers in the journal Nature Communications.

"The tool-using features of the H. naledi hand, in combination with its small brain size, has interesting implications for what cognitive requirements might be needed to make and use tools, and, depending on the age of these fossils, who might have made the stone tools that we find in South Africa," Tracy Kivell at the University of Kent in England, lead author of one of the two H. naledi papers, said in a statement.

The scientists also investigated 107 H. naledi foot bones, including a nearly complete adult right foot. They found the ancient hominin's foot shared many features with the modern human foot, suggesting that it was well-suited for standing and walking on two feet.

"The foot is not entirely humanlike, but it's more humanlike than not," William Harcourt-Smith, a paleoanthropologist at Lehman College in the Bronx and the American Museum of Natural History in New York, told Live Science. "I think it would've been very good at walking on the ground."

However, the H. naledi foot had toes that were more curved than those of modern humans, supporting the notion that the hominin was also relatively adept at life in the trees.

"H. naledi wouldn't have been in any way as proficient as chimpanzees or much more primitive hominins at climbing trees, but it still would be better-suited than we are," said Harcourt-Smith, lead author of the other H. naledi paper.

Intriguingly, H. naledi's pelvis was more like that of australopithecines such as Lucy, flaring outward more than that of modern humans.

"This configuration moved the hip muscles away from the hip joints and gave them more leverage in walking — perhaps more of an advantage than humans have today," study co-author Jeremy DeSilva, an anthropologist at Dartmouth University, said in the statement. "Over time, the architecture of the pelvis evolved and expanded to allow the birth of larger-brained babies."

These findings suggest that early human evolution involved many experiments "on different ways to be bipedal," Harcourt-Smith said.

Scientists are still unsure how exactly H. naledi might have walked differently from modern humans. "But there's absolutely no doubt that its gait would have been different," Harcourt-Smith said.

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