Human ancestors that buried their dead
A cave crammed with fossil remains of a previously undiscovered human ancestor suggests that these primitive people were burying their dead.
The new species has been given the name Homo naledi, which in a local language means "star", as a nod to the place of its discovery, within the Rising Star cave near Johannesburg.
More than 1500 fossil specimens have since been recovered from the site, which was first uncovered in 2013 by two amateur cavers.
A massive international effort ensued following the discovery, which involved job adverts calling for suitably qualified individuals who were also physiologically capable of sliding through passageways just inches across to reach the cavern containing the remains and retrieve them.
Fifteen skeletons have been retrieved so far, yielding complete hands and feet. This sort of anatomy is almost never found in the fossil record, because the tiny bones are so easily washed away by rain, or lost when scavengers pick over bodies.
Reassembling the skeletons show that these primitive individuals would have stood about 1.5 metres tall, they had heads and brains about one third the size of our own, their shoulders were adapted for climbing and the pelvis is relatively wider than that of a modern human.
But thereafter the differences become less apparent. The teeth of H. naledi are similar in size to our own, although they are still different in overall shape, reflecting a different diet. These creatures walked on two legs, their feet are nearly identical to ours, and their hands would pass as human with the exception that the fingers are more curved and their thumbs would have delivered an extremely powerful grip.
More remarkable is that the bones are not encased in rock but were found lying on the surface material of the cave floor. Many of the remains were also found in articulation, situated as they would have been during life.
A painstaking scrutiny of the specimens has failed to turn up any signs of trauma or cannibalism, there are no wild animal remains found alongside the Homo naledi fossils to account for them being in the cave, and analysis of the sediment in the cave has ruled out a flash flood washing the bones into the hole. Moreover, the cave they were found in is not thought to have changed or been reconfigured by geological events at any recent point.
According to lead researcher Lee Berger, who is based at the University of Witwatersrand in South Africa, "these hominids may have been burying their dead."
With their combination of features, these new fossils could sit very early in the story of human evolution, perhaps as far back as 2.5 million years, or they could be much more recent, at 100,000 years, and perhaps represent an offshoot of the human evolutionary arrow.
Obtaining the ages of the remains, which have been published this week in the journal eLife, is therefore critical at the moment though the team don't have a date.
According to study co-author Charles Musiba from the University of Colorado, "the geology of the cave is extremely complex. It's a painstaking job reconstructing the deposition history and the time line, and unfortunately we're not there yet, but we're working on that."