This week researchers announced a possible new addition to our family tree, introducing the world to Homo naledi, a strange, human-like species with a mix of modern and primitive features. The stunning discovery of 1,500 fossils­—which got a much-needed assist thanks to social media—was detailed in the open-access journal E-Life and led by paleoanthropologist Lee Berger from the University of the Witwatersrand in South Africa.

The fossils were found in 2013 by two amateur cavers spelunking through the recesses of the Rising Star cave system, located 30 miles northwest of Johannesburg. The fossil-rich region has been called the “Cradle of Humankind” thanks to the past discovery of extinct hominins. The two spelunkers came upon an unknown chamber near the back of the cave system, located by a steep, rocky area known as Dragon’s Back. Shimmying through the narrow entrance, less than 8-inches wide, the men dropped nearly 30 feet into the chamber below. They were shocked by what was found—hundreds of fossilized remains covering the chamber floor. They contacted Berger, who has been credited with several key finds in the region in recent years, including the discovery of the species Australopithecus sediba in 2008.

Composite skeleton of Homo naledi, surrounded by fossil fragments. (Credit: Robert Clark/National Geographic, Lee Berger/University of the Witwatersrand)
Composite skeleton of Homo naledi, surrounded by fossil fragments. (Credit: Robert Clark/National Geographic, Lee Berger/University of the Witwatersrand)

After initially sending his teenaged son (who had worked with his father on the discovery of Au. sediba) into the chamber, Berger realized he needed to call in additional—tiny—help. A Facebook group was created, looking for skinny scientists with advanced degrees or higher in paleontology or related fields who also had significant caving experience. More than 50 people applied, with six young women—who Berger dubbed the “Underground Astronauts”—meeting the unique criteria. Over the course of two weeks, the women, working in cramped conditions, painstakingly extracted the fossilized remains from what was now known as the Dinaledi Chamber. In all, nearly 1,500 fossils and more than 200 teeth were recovered from the chamber—the remains of at least 15 individuals, including men, women and children.

Eager to start studying the massive haul, Berger once again turned to social media for help, putting out a call for additional scientists. The new recruits, including several researchers in the early stages of their careers, were put to work examining fossils for specific body parts, at cleverly-dubbed workstations such as Hand Land and Tooth Booth. Almost immediately the researchers began to notice startling irregularities. Some body parts combined physical traits from several known species in a way never before seen. And when the physiology of those body parts was fully assembled, Homo naledi (“naledi” means “star” in a local dialect) was a most striking creature indeed.

The "Underground Astronauts" pose with Rick Hunter and Steve Tucker, who discovered the Dinaledi Chamber. (Credit: Elizabeth Fitzgerald/National Geographic)
The “Underground Astronauts” pose with Rick Hunter and Steve Tucker, who discovered the Dinaledi Chamber. (Credit: Elizabeth Fitzgerald/National Geographic)

H. Naledi was slight, standing no taller than 5 feet and weighing less than 100 pounds. Its brain was about as big as an orange, or one-third the size of modern humans, and it had a wide, flattened pelvis and shoulders similar to the more apish Australopithecus. Yet its skull, jaw, teeth, feet and thumbs were remarkably similar to modern humans. H Naledi likely walked much like us, but its dramatically curved fingers indicate that it was just as adept at climbing trees.

Dating the fossils to accurately place them in the evolutionary tree has proved to be difficult. Most fossilized remains are found between layers of volcanic ash or sedimentary rock, which can be radiometrically dated based on its rate of decay. The Rising Star cave provided no such clues, with the fossils buried in shallow, mixed sediment or lying exposed on the chamber floor. Researchers admit that the lack of an accurate age complicates news of the discovery. According to Berger, “If our present understanding of the time frame of the genus Homo is right, then naledi must be somewhere older than 2 million years as a species, in its origins.” It’s possible, however, that the fossils could be less than 100,000 years old. The team notes that the Dinaledi Chamber has only been partially excavated, and that additional, extensive studies at the site will likely continue for years.

H. naledi's hands, with with curved fingers. (Credit: Robert Clark/National Geographic, Lee Berger/University of the Witwatersrand)
H. naledi’s hands, with with curved fingers. (Credit: Robert Clark/National Geographic, Lee Berger/University of the Witwatersrand)

So if the cave remained inaccessible for thousands of years or more, how did H. naledi get there in the first place? The lack of teeth marks, damage to the bones or animal remains in the cave rules out the possibility that carnivores dragged the creatures in. There’s also no sand or sedimentary evidence that would indicate that the bodies were washed into the cave by water, leading researchers to believe that the chamber was likely used as a ceremonial burial pit of sorts. That’s a trait that, until now, had been attributed only to more advanced species such as Homo sapiens and possibly Neanderthals, making the H. naledi find even more significant. As Berger noted, “Only humans do that,” going on to say, “You’re faced with a remarkable situation of a small-brained primitive hominid that is almost certainly deliberately disposing of its dead in a sort of repeated ritualized fashion, in an underground chamber. That alone is remarkable.”