A supposed new species of human with an exceptionally small brain and an unusual combination of both primitive and more modern human-like features has been discovered in a remote South African cave chamber, according to research published in the journal eLIFE.
Named Homo naledi, the undated new species is represented by more than 1,500 fossils that belonged to at least 15 individuals.
Estimates reveal that their brains were comparable in size to those of some of the world's first known humans, australopithecines, as well as those of today's gorillas, Chris Stringer of the Natural History Museum in London, who did not directly work on the project, told Discovery News.
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"That brain volume (about 500cc), implies significantly less brain power than recent humans," added Stringer, who authored a paper commenting on the finds.
Lee Berger of the University of the Witwatersrand, Paul Dirks of James Cook University and an international team of colleagues discovered the remains deep within the Rising Star cave system in South Africa's Gauteng province. The Dinaledi Chamber containing the fossils can only be accessed via several steep climbs and fissures.
Discovering the enormous collection of bones "was akin to (archaeologist) Howard Carter moving into Tutankhamen's tomb for the first time...seeing all of this bone material all over the floor," lead excavator Marina Elliott of Simon Fraser University recently told science teacher John Mead of St. Mark's School of Texas during a videocast recorded in the cave.
Berger and his team conclude that Homo naledi's curved fingers, shoulder, trunk and hips are, like its brain, more primitive. The wrist, hands, legs and feet, however, are similar to those of Neanderthals and our own species.
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"The foot seems structurally and functionally very human, thus implying a human-like gait," Stringer said.
He said the teeth and other features also that this human was a dexterous omnivore that must have hunted and eaten at least some meat.
Multiple mysteries currently surround the discovery. One is the age of the fossils. Berger said it is possible that the new species is more than 2 million years old, putting it fairly close to the origin of the genus Homo. On the other hand, it has not been ruled out that the fossils are less than 100,000 years old.
Yet another mystery concerns how so many Homo naledi individuals, including babies as well as adults, wound up in the chamber. One possibility is that all willingly went to the cave room, where they later succumbed to some kind of tragedy.
"I suppose it is possible that the group hid in the chamber as a refuge from something or somebody and then died there of starvation, but they would have had to access the dark zone of the cave through difficult terrain," Stringer said.
Meanwhile, some human origins experts are not convinced by the Homo naledi claims.