September 10, 2015 1:27 pm
Deep within a South African cave palaeontologists have found a burial chamber full of bones of primitive humans previously unknown to science.
The hominids seem to have placed the bodies of their deceased there over many years — the first time such a ritual practice has been observed in a species other than our own Homo sapiens and Neanderthals.
The remarkable discovery of Homo naledi, as the new species is called, was announced at the University of the Witwatersrand in Johannesburg and associated press briefings in the UK. Details of the fossils, which are an extraordinary mosaic of primitive and modern features, are published in eLife and National Geographic.
An international team of 60 scientists has worked intensively on characterising the bones of 15 individuals removed from the Rising Star cave 50km from Johannesburg since the initial discovery in 2013.
“With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage,” said professor Lee Berger, the project leader. The species is named after its discovery site; naledi means star in the local Sesotho language.
Yet many mysteries remain — above all, the age of the fossils. The usual geological dating techniques have not yet given a result, leaving open the possibility that Homo naledi might have lived as long as 2.5m years ago or at the other extreme just tens of thousands of years ago.
“Homo naledi is similar to modern humans in some ways, such as the shape of its hands, wrist and feet,” said Professor Chris Stringer, head of human origins research at the Natural History Museum in London. “On the other hand, Homo naledi’s small brain [just a third the size of an adult brain today] and the shape of its upper body are more reminiscent of prehuman and very early human species such as Homo habilis, which lived more than 1.5m years ago.
“Based on these features, Homo naledi could be one of the earliest species of human yet discovered, or a species that retained many features from an earlier stage of human evolution,” Prof Stringer added.
The fossils — of babies, children, young and old adults — lay in an isolated chamber 90 metres from the cave entrance. In contrast to all other hominid archaeological sites discovered so far, there were no animal fossils associated with the bones, which bore no marks of carnivores, scavengers or natural processes such as running water that might have carried the Homo naledi remains into the cave.
“We explored every alternative scenario, including mass death, an unknown carnivore, water transport from another location or accidental death in a death trap, among others,” said Prof Berger.
“In [rejecting] every other option, we were left with intentional body disposal by Homo naledi as the most plausible scenario.”
This “ritualised behaviour”, as the palaeontologists call it, means repeated activity and does not necessarily imply any religious context. The hominids may have wanted to dispose of their death in an isolated cave for practical reasons such as hygiene.
Because the 18cm opening into the cave is so narrow, much of the excavation was carried out by six slim women who responded to Prof Berger’s call on social media for “underground astronauts” willing and able to squeeze through the hole. Prof Berger pointed out that much more is left to be discovered in the Rising Star cave.
“This chamber has not given up all of its secrets,” he said. “There are potentially hundreds if not thousands of remains of Homo naledi still down there.”