The fossilised remains of a previously unknown species of human has been discovered inside a cave in South Africa.

Named Homo naledi, the species has been assigned to the genus Homo, to which modern humans also belong.

Scientists unearthed more than 1,500 bones belonging to at least 15 individuals which are yet to be dated

They say they could be anything between 20,000 and two million years old.

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Meet the ancestors: Named Homo naledi, the species has been assigned to the genus Homo, to which modern humans also belong. Scientists unearthed more than 1,500 bones belonging to at least 15 individuals (pictured)

The discovery came about thanks to a tip-off from cavers two years ago, who had glimpsed what looked like human remains through a crack in a limestone wall.

The bones were located in the Rising Star cave system in South Africa's Gauteng province, part of the Cradle of Humankind World Heritage Site, in a remote chamber that can only be accessed via several steep climbs and fissures.

The chamber, situated down a narrow 40ft (12 metre) chute, measures around 30 feet (9 metres) long and just a few feet wide.

It is not yet clear how more than a dozen H. naledi skeletons - ranging from babies to elderly individuals - ended up in a remote region of a large cave.

The researchers have not ruled out the possibility of the bodies being disposed of in the cave deliberately, or a catastrophic 'death trap' scenario in which the humans entered the cave and all died of an unknown cause.

New member of the family: The finding has provided a challenge for the scientists who have been tasked with the bones' analysis, Dr Stronger added: 'Some of Homo naledi's features, such as its hands, wrist and feet, are very similar to those of modern humans' (reconstruction of new species Homo naledi pictured)

H. naledi's overall body plan is illustrated right and an how it compares to Homo species such as H. erectus (centre) and australopithecines such as Lucy (far left)

Scientists say that many more examples of the new species may lay uncovered in the remote cave system

Researchers said 'Some of Homo naledi's features, such as its hands (pictured), wrist and feet, are very similar to those of modern humans.

If the burial scenario is correct, the creatures would have introduced artificial light into the caves in the form of torches as the narrow passages are entirely devoid of light.

The bones are in phenomenal condition - with even the delicate inner ear bones of the new species lying intact.

Professor Chris Stringer, Research Leader in Human Origins at the Natural History Museum in London, said: 'The deep cave location where the bones were found suggests that they may have been deposited there by other humans, indicating surprisingly complex behaviour for a 'primitive' human species.'

Scientists say that many more examples of the new species may lay uncovered in the remote cave system.

The finding has provided a challenge for the international team of scientists who have been tasked with analysing and aging the bones, Dr Stronger added: 'Some of Homo naledi's features, such as its hands, wrist and feet, are very similar to those of modern humans.

HOW A NEW SPECIES WAS DISCOVERED South Africa Deputy President Cyril Ramaphosa, left, shakes hand with Steven Tucker, right, by Lee Berger, a professor at the University of the Witwatersrand Jagged rocks hooked into Steven Tucker's overalls as he squeezed through a crack deep in a subterranean cave. Upon emerging at the other end, he saw he was in a chamber dripping with stalactites. Then his headlamp shone onto a bone. Then more bones, and half of a skull. It was the night of September 13, 2013, and Tucker and his caving partner had just discovered the remains of what scientists would later determine to be a new member of the human family tree. Tucker was only trying to get out of fellow caver Rick Hunter's way, inching to the side, on a different intended route when he stepped into the crack in the network of caves known as Rising Star. He'd heard of the crack before, but despite having been down this cave more than 20 times before, he had never noticed it, nor known of any other caver who had ventured down it. He shone his headlamp down the dark crevice, and couldn't see where it ended. He knew of at least one other caver who also stared down the crack, and decided it was too dangerous. He began to lower himself, feet-first, into the narrow vertical opening. 'It's exciting to find something new,' Tucker, now 27, told The Associated Press on Thursday, trying to explain why he took the risk. Tucker, just wiry enough to fit, followed the crack deeper into the earth for nearly 13 yards (12 metres). 'It's 7 inches (18cm) wide, with these jagged rocks, sticking into you from all sides. And suddenly at the bottom, it opens up into a large chamber with really stunning stalactites hanging from the ceiling,' Tucker said, hunching his shoulders and jutting his elbows out as he re-enacted the descent. The discovery came about thanks to a tip-off from cavers two years ago, who had glimpsed what looked like human remains through a crack in a limestone wall (fossil site marked far right) 'Underground astronaut' Marina Elliott is pictured working in a tight area of the Rising Star cave located outside of Johannesburg, South Africa, where H. naledi, a new species of human relative, was discovered The 50,000-hectare (123,550-acre) area of hilly grasslands where the two were spelunking is recognized as the Cradle of Humankind, featuring a network of caves that has yielded nearly 40 percent of known hominid fossils, according to the University of the Witwatersrand in Johannesburg. But the bones in this particular chamber had apparently remained undiscovered until Tucker entered it. Inside what is now known as the Dinaledi chamber, Tucker's headlamp illuminated pure white rock formations. Tucker and Hunter, who also braved the narrow chute, were excited to find new caving terrain. Then they saw the bones scattered on the chamber floor. 'You could see half of a skull sticking out of the floor,' Tucker said. 'Of course, at that time we had no idea what we had found. ... What interested us at first was the fact that these were quite large bones. How does something that has no lights, no protective equipment like we had get in here?' An almost complete mandible told the cavers that they had found something almost human. Their camera battery had died so a week later they made their way through the cave again, and photographed their find. They sent the photos to geologist Pedro Boshoff, who alerted paleontologist Lee Berger, who went onto become the lead paleontologist on the discovery of Homo naledi. It was only when the cavers saw Berger's excitement that they realized just how big their discovery was. At the press conference announcing the discovery of Homo naledi, a potential new member of the human family tree, Tucker was joined by other cavers who volunteered on the excavation for nearly two years. Berger called them 'underground astronauts.' Advertisement

'On the other hand, the species' small brain and the shape of its upper body are more similar to a prehuman group called australopithecines.'

'While we do not yet know the exact age of the bones, the discovery of so many fossils belonging to at least 15 individuals is remarkable.

'The mixture of features in H. naledi highlights once again the complexity of the human family tree and the need for further research to understand the history and ultimate origins of our species.'

HOMO NALEDI: WHAT WE DO - AND DON'T - KNOW ABOUT THE SPECIES Named Homo naledi, the species has been assigned to the genus Homo, to which modern humans also belong. It is not yet clear how more than a dozen H. naledi skeletons - ranging from babies to elderly individuals - ended up in a remote region of a large cave. The researchers have not ruled out the possibility of the bodies having been disposed of in the cave deliberately, or a catastrophic 'death trap' scenario in which the humans entered the cave and all died of an unknown cause. The age of the the skeletons are also yet to be determined. 'Some of Homo naledi's features, such as its hands, wrist and feet, are very similar to those of modern humans. 'On the other hand, the species' small brain and the shape of its upper body are more similar to a prehuman group called australopithecines'. Advertisement

The bones were located in the Rising Star cave system in South Africa's Gauteng province in a remote chamber that can only be accessed via several steep climbs and fissures (arrangement of fossils pictured)

Scientists say that the mixture of features in H. naledi (pictured) highlights the complexity of the human family tree and the need for further research to understand the history and ultimate origins of our species

HOMO NALEDI'S STRANGE HYBRID HUMAN FEATURES Features similar to modern humans Shape of skull Shape and structure of feet Shape and structure of hands, palms and wrists Long legs Features similar to australopithecines Size of skull 'Flared' hips Curved fingers useful for climbing trees Shoulders suggest swinging from trees Advertisement

Homo naledi may shed light on the transition from australopithecines (fossil pictured) - that emerged around four million years ago - to humans. Some of Homo naledi's features, such as its hands, are very similar to those of modern humans. But the species' small brain are more similar to a prehuman group

WHERE DOES HOMO NALEDI FIT IN? THE COMPLEX EVOLUTION OF MAN 55 million years ago - First primitive primates evolve 15 million years ago - Hominidae (great apes) evolve from the ancestors of the gibbon 8 million years ago - First gorillas evolve. Later, chimp and human lineages diverge 5.5 million years ago - Ardipithecus, early 'proto-human' shares traits with chimps and gorillas 4 million years ago - Australopithecines appeared. They had brains no larger than a chimpanzee's. Homo naledi bears some similarities to this species 2.8 million years ago - LD 350-1 appeared and may be the first of the Homo family 2.7 million years ago - Paranthropus, lived in woods and had massive jaws for chewing 2.3 million years ago - Homo habalis first thought to have appeared in Africa 1.8 million years ago - Homo ergaster begins to appear in fossil record 1.6 million years ago - Hand axes become the first major technological innovation 800,000 years ago - Early humans control fire and create hearths. Brain size increases rapidly 400,000 years ago - Neanderthals first begin to appear and spread across Europe and Asia 200,000 years ago - Homo sapiens - modern humans - appear in Africa. Homo naledi bears similar hands and wrists to modern humans 40,0000 years ago - Modern humans reach Europe Advertisement

It is hoped Homo naledi will shed light on the transition from australopithecines to humans, helping uncover how humans fit into the framework of the natural world over the course of their evolution.

Some images included in this article feature in the October issue of National Geographic magazine

Australopithecines emerged around four million years ago and had a brain no larger than a chimp's.

The species is epitomised by 'Lucy', a skeleton discovered in Ethiopia in 1974. About a million years passed before Homo erectus, or modern man, began to emerge and much of how human evolution played out over this time remains shrouded in mystery.

Scientists admit that it could take decades before they are able to identify who Homo naledi really was and how he fits into our complex evolutionary tree.

Professor Stringer added: 'The mixture of features in H. naledi highlights once again the complexity of the human family tree and the need for further research to understand the history and ultimate origins of our species.'

Casts of Homo naledi fossils will be unveiled at the Natural History's after-hours Science Uncovered event on 25 September and will then go on permanent display in a new Human Evolution gallery opening at the Museum at the end of November.

At the event, they will be alongside the reconstructed skeleton of a recently discovered australopithecine species from South Africa: Australopithecus sediba.

Comparing the characteristics of these ancient species reveals how humans have changed over millions of years.

Details of the find feature in the paper Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.

The bones were located in the Rising Star cave system in South Africa's Gauteng province, part of the Cradle of Humankind World Heritage Site, in a remote chamber that can only be accessed via several steep climbs

The bones (jawbone pictured) were located in the Rising Star cave system in South Africa's Gauteng province, part of the Cradle of Humankind World Heritage Site, in a remote chamber that can only be accessed via several steep climbs and fissures

Peering inside the cave: The chamber, situated down a narrow 40ft (12 metre) chute, measures around 30 feet (9 metres) long and just a few feet wide, National Geographic reported

Casts of Homo naledi fossils (3D printed cast of skull pictured) will soon be displayed alongside the reconstructed skeleton of a recently discovered australopithecine species from South Africa