Tulane University paleoanthropologist Trenton Holliday helped to discover a new species related to humans during a dig that began two years ago in a nearly inaccessible South African cave.
The discovery is the cover story of the October issue of National Geographic magazine and made headlines worldwide when it was announced Thursday by the National Geographic Society and its partners, Wits University in Johannesburg, and the National Research Foundation’s South African Department of Science and Technology.
But the work has been going on for more than two years.
In 2013 and 2014, Holliday flew to South Africa to work on the dig, located in the Rising Star Cave system northwest of Johannesburg.
The group was unusually young: Out of the roughly 40 researchers on the international team led by Wits professor Lee Berger, many were either Ph.D. students or new Ph.D. graduates. Holliday, 49, held what he calls a “middle management” role on the team: not a youngster nor the leader, but one of fewer than a dozen team leaders.
The new species was dubbed Homo naledi. “Naledi” means “star” in some South African languages, so it was named for the cave system it was found in.
It’s in the same genus as humans, who are classified as Homo sapiens, but it’s unclear where the new guy, Homo naledi, fits in the family tree.
One of the most startling parts of this discovery is that it seems these human ancestors — or at least relatives — were using a remote, dark cave chamber to intentionally deposit the bodies of their dead — infants, children, adults and the elderly.
That’s a ritualistic behavior previously believed to be limited to far more modern humans. “It’s definitely not a behavior I’ve seen in any animals other than us,” Holliday said.
Before this dig, the earliest undisputed evidence of humans burying their dead was from a site in Israel that is perhaps 90,000 to 120,000 years old, said Holliday, who estimates that these fossils may be 2 million years old, though they haven’t been officially dated.
In some ways, the new discovery confounds the classic evolutionary image from science classrooms that starts with an apelike creature walking on all fours on the left-hand side and ends up with a modern man on the right-hand side. In the images, as man evolves, he turns into Homo erectus, Neanderthal man and Cro-Magnon man. He gets less hairy and walks more upright. In the most recent stages, it’s clear that he can use tools, since he’s shown with a spear in his hand.
But in reality, the evolution may not be so linear, as the new discovery shows. “The more fossils we find, the less linear things seem to be,” Holliday said.
Some parts of H. naledi — its skull, hands, teeth and feet, for instance — are more like modern humans than more recent human ancestors. Its feet look more likely to walk than climb, which jibes with its long leg bones. And its hands and pinky fingers are opposable, in a way that is tool-ready. But the fingers are long and curved, which is how fingers look in animals that climb a lot, Holliday said.
When compared with modern humans, H. naledi has brow ridges, which modern humans tend not to have, and its brain is much smaller. A modern human brain measures about a quart and a half, but these brains are less than half that size. On average, it seems as though H. naledi stood about 5 feet tall and weighed about 100 pounds.
Holliday did not work on the fossil site itself, which is in a remote cave chamber that was inaccessible to him and most members of the team.
Berger recruited a team of six petite women scientists because they were small enough to crawl through a tunnel that included two small openings, one less than 10 inches high and another about 8 inches wide, said Holliday, who worked to analyze the fossils in a massive bank vault constructed off-site.
Though the team has removed only a small part of the fossils in the chamber — an area about 6 feet by 3 feet and 8 inches deep, Holliday estimates — the discovery is considered the single largest find made in Africa of a fossil hominin, an extinct relative of humans.
All told, what’s been removed from the cave includes 1,550 numbered fossil elements from at least 15 individuals. “It’s an amazing collection,” Holliday said.
Still unclear is where H. naledi lived, if indeed the species did simply use the cave as a burial ground. To date, researchers have found no indication that they lived in the cave itself. “We’ve found no evidence of fire, no stone tools,” Holliday said.
Holliday brought no bones of the newly discovered species to Tulane with him; scientists these days generally leave fossils in the country where they’re found.
Yet because Berger, the expedition’s leader, is emphatic about giving the general public access to fossil sites, New Orleanians can take a look at H. naledi for themselves, through 3-D digital replicas made of the recent finds.
“If you had a 3-D printer, you could make yourself a copy of the skull,” Holliday said.