As to how H. naledi held on to its distinctive characteristics while living cheek-by-jowl with other human species, Prof Hawks said: "It's hard to say it was geographic isolation because there's no boundary - no barrier. It's the same landscape from here to Tanzania; we're in one continuous savannah, woodland-type habitat.
He added that the human-sized teeth probably reflected a diet like that of modern humans. In addition, H. naledi had limb proportions just like ours and there is no apparent reason why it could not have used stone tools.
"It doesn't look like they're in a different ecological niche. That's weird; it's a problem. This is not a situation where we can point to them and say: 'They co-existed because they're using resources differently',"
A new haul of ancient human remains has been described from an important cave site in South Africa.
Despite showing some primitive traits it lived relatively recently, perhaps as little as 235,000 years ago.
The researchers say that finding the remains of multiple individuals in a separate chamber bolsters the idea that Homo naledi was caching its dead. If correct, this surprising - and controversial claim - hints at an intelligent mind and, perhaps, the stirrings of culture.
By dating the site, researchers have sought to clear up some of the puzzles surrounding the remains.
In 2015, Prof Berger told BBC News that the remains could be up to three million years old based on their primitive characteristics. Yet the bones are only lightly mineralised, which raised the possibility that they might not be very ancient (although this is not always an accurate guide).
In order to arrive at an age, the team dated the bones themselves, sediments on the cave floor and flowstones - carbonate minerals formed when water runs down the wall or along the floor of a cave.
Several techniques were used: optically stimulated luminescence to date the cave sediments, uranium-thorium dating and palaeomagnetic analyses for the flowstones and combined U-series and electron spin resonance (US-ESR) for dating three naledi teeth.
By combining results together, they were able to constrain the age of the Homo naledi remains to between 236,000 and 335,000 years ago.
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