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 site, about
30 miles northwest of Johannesburg, 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, he said.
In an
announcement made Thursday, Sept. 10, 2015, scientists say the fossils revealed
the new member of the human family tree. The expedition team was led by Lee
Berger of the university.
The researchers
announced the discovery Thursday in the journal eLife and at a news conference
in the Cradle of Humankind, a site near the village of Magaliesburg. 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.
