Scientists claim to have discovered a new species of human relative, deep in a South African cave.

The scientists who discovered the new species, Homo naledi, spoke at the British Science Festival in Bradford and the find is reported in two papers published in the free-to-access scientific journal eLife.

The fossils were discovered in an unexplored chamber at the back of the Rising Star cave, near Johannesburg. The new species was named after the cave – “naledi” means “star” in Sesotho, a local South African language.

To reach the fossils, explorers had to squeeze through a small fissure, before descending down a long, narrow chute to the Dinaledi chamber, 40 metres below the surface.

Marina Elliott is one of the six “underground astronauts” who were selected after responding to a global call on social media for experienced cavers who could fit through the 7-inch-wide cave opening.

She said, “It was an incredible experience. It’s a twenty minute journey in and out of that cave and we spent 7 hours in the Dinaledi chamber.”

The women recovered more than 1,550 pieces of bone belonging to at least 15 individuals of the same species. The bones appear to be from infants, children, adults and one very old adult.They indicate that H. naledi stood about 1.5 metres (5 feet) tall and weighed about 45 kilograms (almost 100 pounds). From stud of its limbs, the scientists say that H. naledi probably walked upright on two legs, but was also well adapted to climbing trees.

“H. naledi has extremely curved fingers, more curved that almost any other species of early hominin, which clearly demonstrates climbing ability,” said Dr Tracy Kivell of the University of Kent, UK, who was part of the team which studied the hands.Its hands, too, are modern, their shape is well-suited to making basic tools.

The true significance of the find may be in the sheer quantity of fossils recovered. “With almost every bone in the body represented multiple times, H. naledi is already practically the best-known fossil member of our lineage,” said Professor Lee Berger, of the Evolutionary Studies Institute at the University of the Witwatersrand, South Africa, who led the two expeditions that discovered the fossils.

Professor Mark Maslin, University College London, UK, who wasn’t involved in the discovery, agrees. 

“This discovery is only one of four places in the world where we have a large population of hominins.  That means that not only can we determine a new species, but we can discover information about the differences between individuals within that species, for example, the difference between genders, and growth patterns in children.”

The location of the find has led the researchers to believe that this primitive species intentionally deposited the bodies of their dead in the cave, a form of behaviour previously thought to be unique to humans.

Professor Mark Maslin said, “This discovery, along with lots of other evidence that has been appearing recently, suggests that our early ancestors were much more human-like than we give them credit for.”

Although the size of the discovery so far is virtually unprecedented, much remains to be discovered in the Rising Star cave. “This chamber has not given up all of its secrets,” Professor Lee Berger said. “There are potentially hundreds if not thousands of remains of H. naledi still down there.”