By Jamie Shreeve,
National Geographic PUBLISHED THU SEP 10 17:01:00 EDT 2015 1
Scientists reacted with a mix of awe and exasperation to the news Thursday of the discovery of fossils in South Africa that are said to define a new species of human ancestor, Homo naledi.
The awe was inspired mostly by the sheer number of fossils—more than 1,500 bones, all of them from a remote chamber in the cave system called Rising Star, 30 miles northwest of Johannesburg.
“It’s a stunning collection of bones, unlike any we’ve seen before,” said Carol Ward, a paleoanthropologist at the School of Medicine at the University of Missouri.
Like other scientists, however, Ward tempered her enthusiasm with frustration at the discovery team’s decision to publish before more information could be gathered—most importantly, on the age of the bones.
While primitive in some respects, the face, skull, and teeth show enough modern features to justify H. naledi’s placement in the genus Homo.
Artist Gurche spent some 700 hours reconstructing the head from bone scans, using bear fur for hair. Homo naledi sports a bizarre mixture of primitive and modern traits.
It has a tiny ape-like brain perched on a body proportioned much like a small modern human; it has ape-like shoulders and torso, curved fingers for climbing trees—and a remarkably human foot. The mix hints at a species close to the origin of the genus Homo, between two million and three million years ago.
But dating fossils solely by what they look like is a highly risky business. Traits from a primitive ancestor can be retained in a skeleton alongside ones that have evolved toward a more modern form. The fossils could be much younger or—less likely—much older than their morphology suggests.
MORE ABOUT THE FIND This Face Changes the Human Story.
But How? In East Africa, datable volcanic ash layers provide “time stamps” that have allowed the age of famous hominin finds, such as the 3.2-million-year-old Lucy skeleton, to be determined precisely.
In contrast, South African cave finds are notoriously difficult to place in time. Often the age is estimated from the types of extinct animal bones found in the same deposits. But aside from an owl bone and a few rodent teeth, no other animal bones were found in the cave chamber that yielded the Homo naledi fossils. Until the fossils’ age is known, some scientists say, their real value to science hangs in limbo.
“Without a date, these fossils are more curiosities than game-changers,” said William Jungers, a paleontologist at the State University of New York, Stony Brook.
“Where they fit in the family tree will be influenced by their age—they’re a twig, looking for a trunk.”
Some prominent researchers even question the conclusion that the fossils represent a new species.
“From what is presented here, the [fossils] belong to a primitive Homo erectus, a species named in the 1800s,” Tim White of the University of California at Berkeley told the Associated Press.
The Sum of Its Parts A composite skeleton reveals H. naledi’s overall body plan. Its shoulders, hips, and torso hark back to earlier ancestors, while its lower body shows more humanlike adaptations. The skull and teeth show a mix of traits.