May 9, 2017

This Human Relative May Have Lived Alongside Our Species in Africa

A reconstruction of Homo naledi.
When the discovery of Homo naledi was announced two years ago, the news prompted both amazement and incredulity. H. naledi was described as a small-bodied hominid with a brain one third the size of that of Homo sapiens. Its remains were found within the Dinaledi Chamber of the Rising Star Cave system, which is part of the Cradle of Humankind World Heritage Site northwest of Johannesburg. Some scientists believed the researchers — who published their finds in the nascent journal eLife and worked under the glare of television cameras — played fast and loose with the truth.

Now the leader of that earlier research, paleontologist Lee Berger of the University of Witwatersrand (Wits University), and his colleagues have announced via three papers in the same journal more startling finds concerning H. naledi.

They report the discovery of a second chamber within Rising Star with abundant H. naledi fossils, including one of the most complete skeletons of an early human ever found, as well as the remains of at least one child and another adult. They further mention that dating of the site and original H. naledi remains shows these individuals were alive sometime between 236,000–335,000 years ago.

Map of the Rising Star Cave System.
Berger said the earliest fossil remains of modern humans are those from the Omo Kibish region of Ethiopia and are nearly 200,000 years old. While no Homo sapiens fossils are known from subequatorial Africa as early as this, Berger and his team now believe it is possible that some populations of H. naledi came into direct contact with modern humans or their ancestors.

“We can no longer assume that we know which species made which tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioral breakthroughs in the archaeological record of Africa,” Berger said in a statement. “If there is one other species out there that shared the world with ‘modern humans’ in Africa, it is very likely there are others. We just need to find them.”

The researchers say Rising Star Cave was dated using a combination of optically stimulated luminescence of sediments with uranium-thorium dating and paleomagnetic analyses of flowstones to establish how the cave sediments relate to the geological timescale in the Dinaledi Chamber. Uranium series and electron spin resonance dating were used to determine the estimated age of H. naledi teeth.

Geologist Hannah Hilbert-Wolf studying difficult-to-reach flowstones in a small side passage in the Dinaledi Chamber.
The second and more recently discovered room in the cave was named the Lesedi Chamber. Lesedi means “light” in the Setswana language. The researchers additionally named the near-complete H. naledi skeleton found in the Lesedi Chamber: Neo. Analysis of Neo and the other remains reveals that H. naledi had features that are shared with some of the earliest known fossil members of our genus, such as Homo rudolfensis and Homo habilis, species that lived two million years ago.

The scientists believe the approximately 5-feet-tall hominid also shared features with modern humans, such as its humanlike hands, wrists, feet, and lower limbs. H. naledi’s anatomy suggests to the researchers that it was both an effective walker and climber.

“Neo” skull of Homo naledi, frontal view.
“Lucy,” the 3.2-million-year-old skeleton of the hominid Australopithecus afarensis (left) and “Neo,” a skeleton of Homo naledi (right) that was dated as being roughly 250,000 years old.
The Lesedi Chamber is about 109 yards from the Dinaledi Chamber, where at least 15 individuals of various ages were found. Both chambers are difficult to access.

“I have never been inside either of the chambers, and never will be,” co-author John Hawks of the University of Wisconsin-Madison and Wits University said in a statement. “In fact, I watched Lee Berger being stuck for almost an hour, trying to get out of the narrow underground squeeze of the Lesedi Chamber.”

Berger eventually had to be extricated using ropes tied to his wrists.

The remoteness and distance between the cave chambers suggests to the researchers that H. naledi was caching its dead, and likely was controlling fire to see within the deep, dark cave. No tools directly associated with this species of human have been found yet, though.

Chris Stringer, a merit researcher at the Natural History Museum in London, is a leading expert on early human origins. He expressed amazement over the conclusion that H. naledi lived around 300,000 years ago.

“This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk, and hip joint,” Stringer said. “Yet the wrist, hands, legs and feet look more like those of Neanderthals and modern humans, and the teeth are relatively small and simple, and set in lightly built jawbones.”

He believes that H. naledi could be a “relic species, retaining many primitive traits from a much earlier time.” Homo floresiensis, aka the Hobbit Human that lived until relatively recently, came to his mind. The diminutive Hobbits are thought to have lived when several other species of humans were in Europe and Asia. H. floresiensis lived on the island of Flores, however, so isolation at that location could help to explain how it remained a distinct species of human.

H. naledi does not appear to have been isolated, so Stringer posed the compelling question: “How did a comparably strange and small-brained species linger on in southern Africa, seemingly alongside more ‘advanced’ humans?”

Homo naledi was very different from archaic humans that lived around the same time. Kabwe skull from Zambia, an archaic human (left) and ''Neo'' skull of Homo naledi (right).
He also questioned the theory that H. naledi cached its dead, and has not ruled out that accidental or natural processes resulted in the placement of the remains in the two remote cave chambers.

Nevertheless, Stringer said that the discovery and dating of H. naledi “remind us that about 95 percent of the area of Africa is still essentially unexplored for its fossil human record, and its history even within the last 500,000 years may well be as complex as that of Eurasia with its 5 known kinds of humans — Homo erectus, heidelbergensis, neanderthalensis, Denisovans, and floresiensis.”

Read more at Discovery News

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