Berger, a professor at the University of the Witwatersrand in Johannesburg, South Africa, had unearthed some major finds before. But he knew he had something big on his hands.
What
he didn't know at the time is that it would shake up our understanding
of the progress of human evolution and even pose new questions about our
identity.
Two years after
they were tipped off by cavers plumbing the depths of the limestone
tunnels in the Rising Star Cave outside Johannesburg, Berger and his
team have discovered what they say is a new addition to our family tree.
The team is calling this new
species of human relative "Homo naledi," and they say it appears to
have buried its dead -- a behavior scientists previously thought was
limited to humans.
Berger's
team came up with the startling theory just days after reaching the
place where the fossils -- consisting of infants, children, adults and
elderly individuals -- were found, in a previously isolated chamber
within the cave.
The team
believes that the chamber, located 30 meters underground in the Cradle
of Humanity world heritage site, was a burial ground -- and that Homo
naledi could have used fire to light the way.
"There is no damage from predators, there is no sign of a catastrophe.
We had to come to the inevitable conclusion that Homo naledi, a
non-human species of hominid, was deliberately disposing of its dead in
that dark chamber. Why, we don't know," Berger told CNN.
"Until
the moment of discovery of 'naledi,' I would have probably said to you
that it was our defining character. The idea of burial of the dead or
ritualized body disposal is something utterly uniquely human."
Standing
at the entrance to the cave this week, Berger said: "We have just
encountered another species that perhaps thought about its own
mortality, and went to great risk and effort to dispose of its dead in a
deep, remote, chamber right behind us."
"It absolutely questions what makes us human. And I don't think we know anymore what does."
The
first undisputed human burial dates to some 100,000 years ago, but
because Berger's team hasn't yet been able to date naledi's fossils,
they aren't clear how significant their theory is.
Berger tried to put the new find into perspective.
"This
is like opening up Tutankhamen's tomb," he said. "It is that extreme
and perhaps that influential in this stage of our history."
Almost human but not quite
Homo naledi is a strange mosaic of the ancient and the thoroughly modern.
Naledi's
brain was no bigger than an orange, scientists say. Its hands are
superficially human-like, but the finger bones are locked into a curve
-- a trait that suggests climbing and tool-using capabilities.
Homo
naledi was relatively big: it stood about 5 feet tall, had long legs,
and its feet are almost identical to ours, suggesting it had the ability
to walk long distances.
The braincase of a male Homo naledi is less than half the size of the modern human skull.
"Overall,
Homo naledi looks like one of the most primitive members of our genus,
but it also has some surprisingly human-like features, enough to warrant
placing it in the genus Homo," says John Hawks of the University of
Wisconsin-Madison, a senior author on the papers describing the new
species that were published Thursday.
The scientists can make these claims, in part, because of the sheer scale of the find.
In the vault at the University of Witwatersrand, hundreds of priceless specimens lie in padded cases across the room.
So
far they've unearthed more than 1,500 fossil remains in total -- the
largest single hominin find yet revealed on the continent of Africa, the
cradle of human evolution.
Underground astronauts
Gathering the fossils was dangerous work.
Berger,
a National Geographic Explorer-in-Residence, was already well-known for
his discovery of "Australopithecus sediba," another species of human
ancestor, in 2008. But this expedition would face unique challenges.
The
fossils were found at the end of a series of chambers and tight
squeezes deep underground, some 90 meters (100 yards) from the cave
entrance. To get there, scientists would have to squeeze through a
7-inch wide cave opening.
S
o Berger put out a call on social media for skinny scientists and cavers who could fit through the tiny chute and bring up the bones.
o Berger put out a call on social media for skinny scientists and cavers who could fit through the tiny chute and bring up the bones.
Within
days Berger had dozens of responses, and he eventually selected a team
of six "underground astronauts" -- all women -- to do the job.
Berger
himself could not reach the chamber where the remains lay, but he
followed all of the exploration on real-time monitors above ground and
communicated with his team.
"It
is the heart of exploration. What we are privileged enough to do is
going into the next new unexplored spaces," says Berger.
A field of bones
In the first few days of the expedition, the biggest problem was knowing where to step.
"The
first thing that you would see, especially in the early stages of the
investigation, was just bones. Bone debris everywhere," says K. Lindsay
Hunter, an American scientist and one of the "astronauts" on the Rising
Star expeditions, which were conducted in November 2013 and March 2014.
Marina
Elliott, another of Berger's astronauts, described the scene
underground as "some of the most difficult and dangerous conditions ever
encountered in the search for human origins."
Some
scientists in this field spend an entire career finding one fragment to
identify a possible new species. But early on, the team knew they had
stumbled onto something extraordinary.
Initially,
Berger thought that they might find no more than a single skeleton. But
he says that almost all the bones they found -- besides a few rodent
and bird remains that came into the cave much later -- were from Homo
naledi.
"We found everything
from infants to babies to toddlers to teens, young adults, old
individuals. It is like nothing that we could have ever imagined," says
Berger. "Homo naledi is already practically the best-known fossil
member of our lineage."
The team claims to have uncovered remains of at some 15 distinct individuals, but say this is only the beginning.
"The
chamber has not given up all its secrets," Berger says. "There are
potentially hundreds if not thousands of remains of Homo naledi still
down there."
Berger says
their discovery raises haunting questions about our deep past, and about
our very identity. Many mysteries remain, and other scientists may
well challenge some of the team's controversial conclusions. But few
will dispute that Homo naledi is truly significant.
Years
of careful exploration lie ahead. "This was right under our nose," says
Berger. "And we didn't see it. What else is out there?"
