Scientists say they've discovered a new member of the
human family tree, revealed by a huge trove of bones in a barely
accessible, pitch-dark chamber of a cave in South Africa.
The creature shows a surprising mix of human-like
and more primitive characteristics — some experts called it "bizarre"
and "weird."
And the discovery presents some key mysteries: How
old are the bones? And how did they get into that chamber, reachable
only by a complicated pathway that includes squeezing through passages
as narrow as about 7½ inches (17.8 centimeters)?
The bones were
found by a spelunker, about 30 miles (48 kilometers) northwest of
Johannesburg. The site has yielded some 1,550 specimens since its
discovery in 2013. The fossils represent at least 15 individuals.
Researchers
named the creature Homo naledi (nah-LEH-dee). That reflects the "Homo"
evolutionary group, which includes modern people and our closest extinct
relatives, and the word for "star" in a local language. The find was
made in the Rising Star cave system.
The creature, which evidently
walked upright, represents a mix of traits. For example, the hands and
feet look like Homo, but the shoulders and the small brain recall Homo's
more ape-like ancestors, the researchers said.
Lee Berger, a professor at the University of the Witwatersrand
in Johannesburg who led the work, said naledi's anatomy suggest that it
arose at or near the root of the Homo group, which would make the
species some 2.5 million to 2.8 million years old. The discovered bones
themselves may be younger, said Berger, an American.
At
a news conference Thursday in the Cradle of Humankind, a site near the
town of Magaliesburg where the discovery was made, bones were arranged
in the shape of skeleton in a glass-covered wooden case. Fragments of
small skulls, an almost complete jawbone with teeth, and pieces of
limbs, fingers and other bones were arrayed around the partial skeleton.
Berger
handed a skull reconstruction to Deputy President Cyril Ramaphosa, who
kissed it, as did other VIPs. Berger beamed throughout the unveiling.
The
researchers also announced the discovery in the journal eLife. They
said they were unable to determine an age for the fossils because of
unusual characteristics of the site, but that they are still trying.
Berger
said researchers are not claiming that neledi was a direct ancestor of
modern-day people, and experts unconnected to the project said they
believed it was not.
Rick Potts, director of the human origins program at the
Smithsonian Institution's Natural History Museum, who was not involved
in the discovery, said that without an age, "there's no way we can judge
the evolutionary significance of this find."
If
the bones are about as old as the Homo group, that would argue that
naledi is "a snapshot of ... the evolutionary experimentation that was
going on right around the origin" of Homo, he said. If they are
significantly younger, it either shows the naledi retained the primitive
body characteristics much longer than any other known creature, or that
it re-evolved them, he said.
Eric Delson of Lehman College in New
York, who also wasn't involved with the work, said his guess is that
naledi fits within a known group of early Homo creatures from around 2
million year ago.
Besides the age of the bones, another mystery is
how they got into the difficult-to-reach area of the cave. The
researchers said they suspect the naledi may have repeatedly deposited
their dead in the room, but alternatively it may have been a death trap
for individuals that found their own way in.
"This
stuff is like a Sherlock Holmes mystery," declared Bernard Wood of
George Washington University in Washington, D.C., who was not involved
in the study. Visitors to the cave must have created artificial light,
as with a torch, Wood said. The people who did cave drawings in Europe
had such technology, but nobody has suspected that mental ability in
creatures with such a small brain as naledi, he said.
Potts said a deliberate disposal of dead bodies is a feasible
explanation, but he added it's not clear who did the disposing. Maybe it
was some human relative other than naledi, he said.
Not
everybody agreed that the discovery revealed a new species. Tim White
of the University of California, Berkeley, called that claim
questionable. "From what is presented here, (the fossils) belong to a
primitive Homo erectus, a species named in the 1800s," he said in an
email.
At the news conference in South Africa, Berger disputed that.
"Could this be the body of homo erectus? Absolutely not. It could not be erectus," Berger said.
