A reconstruction of Homo naledi’s head by paleoartist John Gurche, who spent some 700 hours recreating the head from bone scans. The find was announced by the University of the Witwatersrand, the National Geographic Society and the South African National Research Foundation and published in the journal eLife. (Photo by Mark Thiessen/National Geographic)

A new species of human relative, called Homo naledi, has been discovered deep in a cave in South Africa, it was announced Thursday morning at a press conference in Johannesburg.

Video shows female scientists and experienced cavers recovering fossil remnants of new species of human relative in November 2013 at the Cradle of Humankind Heritage Site in South Africa. The women were chosen via social media because they were slender enough to move through the cave's narrow passageways to get to the fossil chamber, 100 yards from the cave entrance. (NOVA/National Geographic)

[Full story: Fossils found in African cave are new species of human kin, say scientists]

Three men who led the expedition took part in a Q & A with the National Geographic Society about how the fossils were found, their excavation and their two-year analysis by teams of international experts as to their place in human evolution. Below is a selection of those questions and answers from Lee Berger, an archaeologist and the leader of the expedition, John Hawks, an anthropologist and Paul Dirks, a geologist:

1) Why is the combination of features in naledi unusual or unexpected?

Until recently, most anthropologists believed that brain size and tool use emerged together with smaller tooth size, higher-quality diet, larger body size and long legs. In this view, transformations in the body in early Homo were tied to changes in behaviour that influenced diet and the brain.

H. naledi shows that these relationships are not what anthropologists expected. It has small teeth and hands that seem to have been effective for toolmaking but also a small brain. It has long legs and humanlike feet but also a shoulder and fingers that seem effective for climbing

[Ancient shoulders show signs of humanity’s ape-like past]

What happens if H. naledi is very old? Or very young?

If it turns out that H. naledi is old, say older than around 2-million-years, it would represent the earliest appearance of Homo that is based on more than just an isolated fragment. On the other hand, if it turns out that H. naledi is young, say less than 1-million-years old, it would demonstrate that several different types of ancient humans all existed at the same time in southern Africa, including an especially small-brained form like H. naledi.

[Scientists find the oldest-ever hand bone to resemble a modern human’s]

Given its primitive skeletal adaptations, this might have profound implications for the development of the African archaeological record. It would also have profound implications for our understanding the origins of complex behaviours previously thought to arise only with the origins of hominins not very different from our own species as recently as 350,000 years ago...The youngest individual died near or at the time of birth, the oldest was an old adult individual with extremely worn teeth. Out of the 15 individuals found so far, eight were children of various ages and five definitely adults, with two either young adults or older adolescents.

A composite skeleton of H. naledi’s overall body plan and an illustration of how it compares to Homo species such as H. erectus and australopithecines such as Lucy. (Skeleton: Stefan Fichtel/National Geographic Body Comparison Painting: John Gurche; Sources: Lee Berger and Peter Schmid, Wits; John Hawks, University of Wisconsin-Madison)

2) What are some of the broader implications of H. naledi?

It is clear that we have missed some key transitional forms in the fossil record, as H. naledi represents an unexpected combination of australopith-like and human-like features that, until now, was entirely unknown to science.

This serves to highlight our ignorance about our own genus across the span of the African continent. There are obviously many unknown fossil species yet to be discovered. In addition, we must recognise that some species of ancient humans exhibited very human-like behaviors, which in turn will have profound implications for the archaeological record.

Anthropologist Marina Elliott (left) and paleontologist Ashley Kruger explore a side chamber in the Rising Star cave where more than 1,500 fossil elements of a new species, Homo naledi, were discovered. (Elliot Ross/ National Geographic)

3) How were the fossils found?

Two cavers, Rick Hunter and Steven Tucker, when probing a narrow fracture system to the back of the cave system found the entrance into the Dinaledi Chamber, [the name given to the area where the fossils were discovered.] When they showed pictures of the fossils to Pedro Boshoff another caver and geologist, he recognised the fossils as potentially significant and alerted Professor Lee Berger to the find. Further detailed investigations followed, which quickly demonstrated the significance of the find.

[Scientists discover a new human ancestor that roamed with ‘Lucy’]

4) Why are there no other fossils apart from the hominins?

The cave chamber in which the fossils occur is very inaccessible now and has always been very inaccessible. To get into the chamber involves a steep climb up a sharp lime stone block called “the Dragon’s Back”, and a drop down a narrow crack. All this has to be done deep inside the cave, in the dark zone in the total absence of light. No other large animals, apart from H. naledi ever found their way this deep into the cave.

A composite skeleton of H. naledi is surrounded by some of the hundreds of other fossil elements recovered from the cave. (National Geographic/National Geographic)

5) Do the hominin fossils occur as complete skeletons?

Remains are currently found in partly articulated, disarticulated and fragmentary states. This includes delicately articulated remains of hands and feet. This suggests that bodies entered the cave whole but disarticulated after deposition as a result of reworking of the sediments in which the fossils were originally deposited.

Sedimentological evidence suggests that bodies were brought into or dropped into the cave chamber, landing in muddy sediment on the floor. Whole bodies probably ended up within the muddy sediments of the Dinaledi Chamber, but over time, sediments drained out of the chamber through holes in the

chamber floor. As a result, some of the fossils were redistributed across the chamber floor, and ended up lying as dispersed fragments across the floor.

6) How did the hominins find their way into the Dinaledi Chamber?

This is a puzzling question. Our geological investigation indicates that the Dinaledi Chamber was always in the dark zone, and the route to get there was probably very complex involving navigating difficult terrain. This suggests that they may have used fire to guide them into the cave.

7) Why are there so many hominins in the Dinaledi Chamber?

This is the big question. Our investigations show that the bodies came in whole. They were probably deposited over a period of time and entered the chamber using the same entrance as today. So far we have found no evidence on any the bones for any form of trauma as a result of a fall, or due to predators. So far we have also not found any evidence of cannibalism like cut-marks, like on some of the hominin assemblages in European caves. All this is very hard to explain and suggests that at some point H. naledi entered the cave on purpose to deposit bodies in the Dinaledi Chamber.

To find out more, you can now stream the full Nova/National Geographic documentary on the discovery online.

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