Newly discovered fossil discoveries in Africa have pushed back the age we know modern humans roamed the Earth by roughly 100,000 years—and injected profound doubt into what we thought we knew about where humanity first arose.
"This material represents the very roots of our species—the oldest Homo sapiens ever found in Africa or elsewhere," said Jean-Jacques Hublin, an anthropologist at the Max Planck Institute for Evolutionary Anthropology, in a press conference this week. Hublin was the lead researcher for one of the two studies published on the discoveries in yesterday's issue of the journal Nature.
Up until now, the oldest definitive modern human fossils were known to be around 200,000 years old, and had been found in modern-day Ethiopia. These discoveries helped cement the dominant theory among anthropologists in recent decades that modern humans, Homo sapiens, evolved in East Africa and then migrated north into Asia and Europe. This region has therefore been dubbed the “cradle of humankind” (though South Africa also lays claim to the title).
"Our results challenge this picture in many ways," Hublin said. The fossils his team studied come from a cave in central Morocco, thousands of miles away from East Africa. They suggests that, by 300,000 years ago, modern humans had already spread across Africa. Recall that the continent that was much easier to cross then, with lush grasslands and lakes residing where the forbidding Sahara Desert lies today.
What’s still not clear, Hublin said, is where exactly in Africa Homo sapiens first evolved. Further fossil discoveries, he says, will need to settle that.
The site of these discoveries is not new. Hominid remains were actually stumbled upon there in the 1960s by miners looking for the crystalline mineral barite, and were studied at the time by anthropologists. However, this was still early on in the history of dating technology, Hublin says, and the miners didn't practice good archaeology in recovering the remains. Therefore researchers couldn't accurately date the bones, and could only estimate an age of at least 40,000 years old from radiocarbon dating. In 2006, an attempt to date one of the fossils with a newer dating technique called electron spin resonance yielded an age of 160,000 years old—closer, but also inaccurate.
In the meantime, the attention of the anthropology world turned to Ethiopia, where Richard Leakey and other scientists were thrilling the world with discoveries of the oldest Homo sapiens —or so they thought—at around 195,000 years old.
But Hublin wasn’t finished with the Moroccan site. He returned to explore it several times in the 1980s and 90s, before launching a full-scale excavation of the undug areas in 2004. His team eventually found tooth and skull remains, which to Hublin seemed to display an odd mix of strikingly modern human features with primitive skull shapes.
Found in the sediment layer of dirt with the bones was a trove of flint tools, some of which had been charred from fire. This proved a key lead, Hublin says, because it allowed his team to use an analysis technique called "thermoluminescence dating" that relies on accumulated radiation to date when the tools had last been burned. Presumably, that date would tell them when the humans at the site lit fires where the tools had been discarded on the ground.
The results revealed that humans had lived there roughly 300,000 years ago, as reported in the second study published in Nature. "These dates were a big 'wow,' I would say," Hublin said. "Very early in the process we realized this site was much older than anyone could imagine."
Turning to the bones themselves, Hublin's team used another form of radiation dating to pinpoint one of the recovered teeth to a jaw-dropping 286,000 years old. The remaining challenge, however, was to identify these fossils as clearly being Homo sapiens. Using advanced imaging technology to 3D scan and measure the recovered skulls, the researchers were able to create full facial reconstructions, showing striking similarity to the appearance of humans today.
The hat would be necessary, because the major noticeable difference between these Homo sapiens and us is a differently shaped head, caused by a brain that was as large as ours, but longer and less round. Rounder brains are a major feature of modern humans, though scientists still can’t say exactly how it changed the way we think. "The story of our species in the last 300,000 years is mostly the evolution of our brain," Hublin says.
For Zeray Alemseged, a paleontologist at the University of Chicago who wasn't involved in the recent studies, Hublin's work is a "very important discovery."
"They’re placed at a critical time period when the earliest members of our species could have evolved," he told the Atlantic, "and they’re critical for better understanding the patterns of physical and behavioral evolution [among humans] across the African continent."
Paleoanthropologist Rick Potts, who leads the Smithsonian Institution's Human Origins Program and also wasn't involved in these studies, isn't quite convinced yet.
"This view promoted by Hublin is by no means a slam dunk, but it is feasible," Potts told the Washington Post. He cited concerns about linking newly discovered materials with those from the more haphazard 1960s digs, as well as whether thermoluminescence was the best dating method to use in this region. "It will doubtless be tested over and over by further African fossil discoveries in this important time period," he said.