The recent discovery of a new human ancestor in the Rising Star cave system of South Africa shook the family tree. The newest member—Homo naledi—has a mash-up of ancient and modern human features, and the announcement stirred some controversy over whether the specimens are truly a new species.
H. naledi’s skull is closest to that of Homo erectus—the earliest human ancestor with many modern human traits—according to an initial study of the remains. But some of the bones in the trunk, shoulder, pelvis and femur are more similar to those of Australopithecus, an even older group of relatives known for the famed Lucy. But according to new research H. naledi's wrists, hands, feet and lower limbs are more like modern humans than these ancient ancestors.
In the first new study, a team of researchers described H. naledi feet using 107 bones, Jeremy DeSilva an anthropologist with Dartmouth College, describes in a press release. The team compared the bones from the South African cave to the foot and leg of Australopithecus sediba, an early human precursor found in a cave just a few miles from Rising Star. But H. naledi's foot looked more modern, with only subtle differences from humans today, DeSilva says.
"Homo naledi had the most human-like foot of any known early humans except for Neanderthals," he tells George Dvorsky for Gizmodo. These new members of our family tree probably "walked a lot like humans do today,” he says.
For the second paper, a research team poured over 150 hand bones. Like modern humans and Neanderthals, H. naledi sports a long, strong thumb and a robust wrist—features suitable for manipulating tools. But like Australopiths and other early human ancestors, the finger bones are longer and more curved than modern human digits. This means that tree climbing was still a large part of H. naledi’s lifestyle.
As both a walker and tree-climber, the proposed activities for H. naledi may mean that ancient humans lost their ape-like features in their feet long before they did in their upper limbs.
“There were lots of different experiments happening within hominins — it wasn’t just a linear route to how we walk today," William Harcourt-Smith, lead author of the paper on H. naledi’s feet, says in a press release.
Whether the specimens are truly another species, or an early form of H. erectus, as some experts have contended, the findings have already started to "change the human story."