2 hikers crawled through an impossibly tiny cave and discovered a new human ancestor that defies everything scientists know about evolution

The recent discovery of bones from a previously unknown human ancestor in a cave in South Africa adds a tantalising new piece to the puzzle of human evolution.

A couple of cavers stumbled across the remains of at least 15 individuals in South Africa’s Cave of Stars. The species, which is named Homo naledi (‘naledi’ means ‘star’ in the South African language Sotho), had a small brain, yet remarkably humanlike features. And the bones appear to have been deposited in the cave intentionally, a sign that this human ancestor may have ‘buried’ its dead.

The findings, which were described today in two studies in the journal eLife, have scientists intrigued.

“Anytime we add a twig onto the branch of our family tree it’s exciting,” anthropologist Briana Pobiner of the Smithsonian Institution National Museum of Natural History, who was not involved in the research, told Business Insider.

H. naledi has a combination of traits that’s different than any scientists have seen before, and while they don’t know how old it is, “this species is potentially related to the earliest members of our own genus, Homo,” Pobiner said.

An unlikely find

The cave where the bones were found lies in a region of South Africa known as the Cradle of Humankind, because so many fossils of early human ancestors have been found there. According to National Geographic, the cave is a popular climbing spot, but the chamber where this archaeological windfall lay is incredibly hard to get to, and the bones would probably not have been found if it weren’t for two cavers, Steven Tucker and Rick Hunter, who were exploring it two years ago.

To get to the chamber, they first had to squeeze through a narrow passage known as Superman’s Crawl, because in order to fit through you have to keep one arm pressed against your body and raise the other one above your head like the famous comic book hero.

Then, the cavers had to drop 40 feet down a narrow, pitch-black chute. At the bottom, they found a trove of bones, strewn about as if they had been tossed in there on purpose. They knew they had found something exciting, as scientists would later confirm.

Lee Berger, a paleoanthropologist at South Africa’s University of Witswatersrand, led the investigation of the bones. He was too big to get inside the cave himself, so he recruited some skinny female scientists to retrieve the bones, while he directed the operation aboveground.

The team recovered 1550 human ancestor fossils, including bones and teeth — the most specimens of a single ancestral human species ever found in Africa.

Tantalising questions

The new species lies somewhere along the evolutionary tree between Australopithecus afarensis (which contains the famous remains of Lucy) and Homo erectus (an extinct great ape species that walked upright).

“It could be an ancestor of Homo erectus,” Pobiner said, “or an evolutionary cousin, a shared common ancestor. It’s hard to know yet.” In some ways it’s more primitive than other human ancestors, and in some ways more modern, she added.

The new species had humanlike hands, wrists and feet, but more primitive shoulders, torso and pelvis. It also had a much smaller brain than modern humans.

What’s especially curious, though, is that the bones appear to have been intentionally dumped in the cave. Pobiner thinks this is the most likely interpretation, because if the bones fell in accidentally, they would have found the remains of many other animals as well.

However, the bones don’t appear to have been buried ceremoniously. It seems more likely that these early human ancestors dumped them there to keep away predators which might be attracted by the dead bodies, Pobiner said. This suggests these individuals may have lived within a small area, unlike many early human ancestors, which were hunter-gatherers, she said.

Big findings like this are often published in well-known journals like Science or Nature, but Berger may have decided to publish in the journal eLife because it’s open-access (meaning it’s available to the public without a subscription), Pobiner thinks. Part of Berger’s strategy is “to make the findings and research as widely accessible as possible,” she said.

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