麻豆传媒

A treasure trove of ancient human remains discovered in a cave in South Africa could give us a new picture of human evolution 鈥� and evidence of a previously undiscovered species.

Lee Berger at the University of聽the Witwatersrand in Johannesburg and his colleagues call the cave simply UW 105 because it is the 105th site they have identified. It is a short walk from the Rising Star cave, where his team discovered a new species called Homo naledi in 2013. The following year, the group found a fragment of a lower jaw with a聽single tooth in UW 105. They聽belonged to a hominin, but at the time the Rising Star excavation was a priority.

Then covid-19 happened and gave the team an opportunity to聽gather remains from UW 105. Berger estimates that his team has found between 100 and 150 pieces of bone there in the past few months, including bits of skull, shoulder blades, teeth and聽limb bones. He says there are at least four individuals, of聽which one seems to be an adult and two are juveniles.

They aren鈥檛 modern humans,聽nor are they 贬.听苍补濒别诲颈 or Australopithecus sediba, the聽other species Berger鈥檚 group聽has聽discovered. The teeth are too big for that.

Berger says the teeth look similar to a molar found in the nearby Gondolin cave thought to belong to Paranthropus robustus, a big-bodied hominin that lived between 1 and 2聽million years ago. Its big teeth聽may have been used for chewing tough plants like grass.

Large teeth have been thought of as 鈥減rimitive鈥�, so聽this聽might suggest that the聽owners of the big teeth in聽UW聽105 belong to an early species, but Berger says estimating age based on shape is 鈥渁 fool鈥檚 errand鈥�. Evolution doesn鈥檛 go in straight lines, he says, so sometimes seemingly primitive traits can emerge in recent species. He points to 贬.听苍补濒别诲颈, which had a skull only聽slightly larger than that of聽a聽chimpanzee, yet which lived聽just聽250,000 years ago.

Instead, Berger is waiting for聽the results of independent dating analyses. The fossils all聽originated in a layer of rock in聽the cave that is covered by聽flowstone: a layer formed when聽minerals were deposited by flowing water. It should be聽possible to determine the聽flowstone鈥檚 age, giving a聽minimum age for the fossil-bearing rock.

It is too early to say whether the remains are of a new species of early human or a known one, but they seem unlike anything else known. Tracy Kivell at the University of Kent, UK, one of Berger鈥檚 regular collaborators, says that both the back and front teeth are large 鈥� unlike with P. robustus, which only had聽big back teeth. Also, the bones from the rest of the body are relatively small, suggesting a聽slim build 鈥� which is unusual for聽a big-toothed hominin.

鈥淭o me, that suggests a different way of adapting to聽one鈥檚 environment,鈥� says Kivell. 鈥淓ven if they look fairly similar, things that adapt to their environment in different ways are probably different species. Based on the little information we have for now, I聽would say it鈥檚 looking like it鈥檚 heading in that direction.鈥�

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