Acting on a tip from spelunkers two years ago, scientists in South Africa
discovered what the cavers had only dimly glimpsed through a crack in a
limestone wall deep in the Rising Star Cave: lots and lots of old
bones.
The
remains covered the earthen floor beyond the narrow opening. This was,
the scientists concluded, a large, dark chamber for the dead of a
previously unidentified species of the early human lineage — Homo
naledi.
The new hominin
species was announced on Thursday by an international team of more than
60 scientists led by Lee R. Berger, an American paleoanthropologist who
is a professor of human evolution studies at the University of the
Witwatersrand in Johannesburg. The species name, H. naledi, refers to
the cave where the bones lay undisturbed for so long; “naledi” means
“star” in the local Sesotho language.
In two papers
published this week in the open-access journal eLife, the researchers
said that the more than 1,550 fossil elements documenting the discovery
constituted the largest sample for any hominin species in a single
African site, and one of the largest anywhere in the world. Further, the
scientists said, that sample is probably a small fraction of the
fossils yet to be recovered from the chamber. So far the team has
recovered parts of at least 15 individuals.
“With
almost every bone in the body represented multiple times, Homo naledi
is already practically the best-known fossil member of our lineage,” Dr.
Berger said.
The finding, like so many others in science, was the result of pure luck followed by considerable effort.
Two
local cavers, Rick Hunter and Steven Tucker, found the narrow entrance
to the chamber, measuring no more than seven and a half inches wide.
They were skinny enough to squeeze through, and in the light of their
headlamps they saw the bones all around them. When they showed the
fossil pictures to Pedro Boshoff, a caver who is also a geologist, he
alerted Dr. Berger, who organized an investigation.
Just getting into the chamber and bringing out samples proved to be a huge challenge. The narrow opening was the only way in.
Paul
Dirks, a geologist at James Cook University in Australia, who was lead
author of the journal paper describing the chamber, said the
investigators first had a steep climb up a stone block called the
Dragon’s Back and then a drop down to the entrance passage — all of this
in the total absence of natural light.
For
the two extended investigations of the chamber in 2013 and 2014, Dr.
Berger rounded up the international team of scientists and then
recruited six excavating scientists through notices on social media. One
special requirement: They had to be slender enough to crawl through
that crack in the wall.
One
of the six, who were all women and were called “underground
astronauts,” was Marina Elliott of Simon Fraser University in British
Columbia. She said the collection and removal of the fossils involved
“some of the most difficult and dangerous conditions ever encountered in
the search for human origins.”
Besides
introducing a new member of the prehuman family, the discovery suggests
that some early hominins intentionally deposited bodies of their dead
in a remote and largely inaccessible cave chamber, a behavior previously
considered limited to modern humans. Some of the scientists referred to
the practice as a ritualized treatment of their dead, but by “ritual”
they said they meant a deliberate and repeated practice, not necessarily
a kind of religious rite.
“It’s
very, very fascinating,” said Ian Tattersall, an authority on human
evolution at the American Museum of Natural History in New York, who was
not involved in the research.
“No question there’s at least one new species here,” he added, “but there may be debate over the Homo designation, though the species is quite different from anything else we have seen.”
A
colleague of Dr. Tattersall’s at the museum, Eric Delson, who is a
professor at Lehman College of the City University of New York, was also
impressed, saying, “Berger does it again!”
Dr.
Delson was referring to Dr. Berger’s previous headline discovery,
published in 2010, also involving cave deposits near Johannesburg. He found many fewer fossils that time, but enough to conclude that he was looking at a new species, which he named Australopithecus sediba.
Geologists said the individuals lived 1.78 million to 1.95 million
years ago, when australopithecines and early species of Homo were
contemporaries.
Researchers
analyzing the H. naledi fossils have not yet nailed down their age,
which is difficult to measure because of the muddled chamber sediments
and the absence of other fauna remains nearby. Some of its primitive
anatomy, like a brain no larger than an average orange, Dr. Berger said,
indicated that the species evolved near or at the root of the Homo
genus, meaning it must be in excess of 2.5 million to 2.8 million years
old. Geologists think the cave is no older than three million years.
The
field work and two years of analysis for Dr. Berger’s latest discovery
were supported by the University of the Witwatersrand, the National
Geographic Society and the South African Department of Science and
Technology/National Research Foundation. In addition to the journal
articles, the findings will be featured in the October issue of National Geographic Magazine and in a two-hour NOVA/National Geographic documentary to air Wednesday on PBS.
Scientists
on the discovery team and those not involved in the research noted the
mosaic of contrasting anatomical features, including more modern-looking
jaws and teeth and feet, that warrant the hominin’s placement as a
species in the genus Homo, not Australopithecus, the genus that includes
the famous Lucy species that lived 3.2 million years ago. The hands of
the newly discovered specimens reminded some scientists of the earliest
previously identified specimens of Homo habilis, who were apparently among the first toolmakers.
At a news conference on Wednesday, John Hawks of the University of
Wisconsin, Madison, a senior author of the paper describing the new
species, said it was “unlike any other species seen before,” noting that
a small skull with a brain one-third the size of modern human
braincases was perched atop a very slender body. An average H. naledi
was about five feet tall and weighed almost 100 pounds, he said.
Source: John Noble Wilford
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