The first human? Homo naledi, a new branch of the human family tree. National Geographic. |
Dawn of Humanity. Video. NOVA. PBS, September 10, 2015. Also here.
Homo Naledi, New Species in Human Lineage, Is Found in South African Cave. By John Noble Wilford. New York Times, September 10, 2015.
Naledi Fossils: This Face Changes the Human Story. But How? By Jamie Shreeve. National Geographic, September 10, 2015.
Naledi Fossils: Mystery Lingers Over Ritual Behavior of New Human Ancestor. By Nadia Drake. National Geographic, September 15, 2015.
In this
artist’s depiction, Homo naledi
disposes of its dead in South Africa’s Rising Star cave. Though such advanced
behavior is unknown in other early hominins, the scientists who discovered the
fossils say no other explanation makes sense. ART BY JON FOSTER. SOURCE: LEEBERGER, WITS
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Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. By Lee R. Berger et al. eLife, September 10, 2015.
Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. By Paul H.G.M Dirks et al. eLife, September 10, 2015.
The many mysteries of Homo naledi. By Chris Stringer. eLife, September 10, 2015.
Wilford:
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.
Tracy
Kivell of the University of Kent, in England, an associate of Dr. Berger’s
team, was struck by H. naledi’s “extremely curved fingers, more curved than
almost any other species of early hominin, which clearly demonstrates climbing
capabilities.”
William
Harcourt-Smith of Lehman College, another researcher at the Museum of Natural
History, led the analysis of the feet of the new species, which he said are
“virtually indistinguishable from those of modern humans.” These feet, combined
with its long legs, suggest that H. naledi was well suited for upright
long-distance walking, Dr. Harcourt-Smith said.
In an
accompanying commentary in the journal, Chris Stringer, a paleoanthropologist
at the Natural History Museum in London, found overall similarities between the
new species and fossils from Dmanisi, in the former Soviet republic of Georgia,
dated to about 1.8 million years ago. The Georgian specimens are usually
assigned to an early variety of Homo erectus.
Much
remains to be discovered in the Rising Star Cave, like determining the ages of
the fossils and the evolutionary position of H. naledi in the genus Homo and
the human family tree. The discovery chamber has not given up all of its
secrets. “There are potentially hundreds if not thousands of remains of H.
naledi still down there,” Dr. Berger said.
At the news conference in South Africa on Thursday announcing the findings, Dr. Berger said: “I do believe that the field of paleoanthropology had convinced itself, as much as 15 years ago, that we had found everything, that we were not going to make major discoveries and had this story of our origins figured out. I think many people quit exploring, thought it was safer to conduct science inside a lab or behind a computer.” What the new species Naledi says, Dr. Berger concluded, “is that there is no substitute for exploration.”
At the news conference in South Africa on Thursday announcing the findings, Dr. Berger said: “I do believe that the field of paleoanthropology had convinced itself, as much as 15 years ago, that we had found everything, that we were not going to make major discoveries and had this story of our origins figured out. I think many people quit exploring, thought it was safer to conduct science inside a lab or behind a computer.” What the new species Naledi says, Dr. Berger concluded, “is that there is no substitute for exploration.”