On October 7, 2013, paleoanthropologist Lee Berger posted a job ad on Facebook looking for fellow scientists with a very particular set of skills: they had to have caving experience, be small enough to fit through an opening barely seven inches wide and be able to leave immediately for South Africa. Berger chose six women out of 60 applicants and sent them down a narrow channel deep inside a cave about 30 miles from Johannesburg.
Inside, they found a trove of fossilized remains belonging to a previously unknown human relative. Named Homo naledi—naledi means “star” in the local Sotho language—the ancient species could offer new insight into the story of human evolution.
“This is the first time we’ve found human fossils alone in a chamber like this in Africa,” Berger said on a conference call to members of the press on Wednesday. The discovery was announced at an official ceremony in South Africa on the morning of September 10.
Back in 2013, Berger, a researcher at South Africa’s University of the Witwatersrand, was alerted to a possible find by a pair of spelunkers visiting Rising Star Cave, a popular site for caving expeditions. Steven Tucker and Rick Hunter were exploring less-traveled sections of the well-mapped cave system and decided to try scrambling through a crevasse known as Superman’s Crawl. Once through, they discovered a small cavern filled with fossil skeletons and bone fragments. When Tucker and Hunter later sent photos and video of the site to Berger, he couldn’t believe what he was seeing, Ed Yong writes for The Atlantic.
“That evening, I couldn’t sleep,” Berger tells Yong.
The resulting find has been one of richest ever discovered in a region that was already called The Cradle of Humanity for its wealth of fossilized hominid remains. By the time Berger’s team finished their dig, they had collected about 1,550 fossil specimens belonging to about 15 individuals—more than any other ancient human dig site in Africa, Jamie Shreeve writes for National Geographic. But while Berger and his team had expected the bones to be from an early ape-like ancestor such as Australopithecus, they soon realized that this was something different—something more human.
“The message we’re getting is of an animal right on the cusp of the transition from Australopithecus to Homo," Berger tells Shreeve. "Everything that is touching the world in a critical way is like us. The other parts retain bits of their primitive past."
The fossils indicate that they belonged to an early human species that shared traits with both pre-humans like Australopithecus afarensis (the species that the skeleton nicknamed “Lucy” belonged to) and Homo erectus. The ancient species appears to have had an apelike pelvis and pronounced brow as well as small teeth, flat feet and human-like hands, Dan Vergano writes for Buzzfeed News. Homo naledi also had small brains that were about one-third the size of a Homo sapiens’.
“In a word, they are weird,” Bernard Wood, a paleoanthropologist at George Washington University who was not involved in the discovery, tells Vergano.
Those small brains pose a curious question: How did those bones end up deep inside Rising Star Cave, and why? While it appears that Homo naledi’s brains were too small to handle navigating through a pitch-black cavern, Berger believes that the skeletons were intentionally placed in the cave in a burial ritual, Yong writes.
“We found nothing else, and the only time you ever find just one thing is when humans deliberately do it,” Berger tells Yong. “I don’t see any other conclusion." According to Berger, the cave has no flowing water, and it's doubtful another type of animal could have dragged the bodies through the narrow space. Plus there are no signs the bones have been scavanged by predators.
While researchers still have much more to learn from the fossils, including precisely how old they are, in the meantime paleontologists can welcome a new member to humanity’s family tree.