Archaeologists are rewriting the story of an early human child whose fossilized jaw and impacted teeth were discovered more than 40 years ago in the Ethiopian highlands. Scientists used high-tech imaging to reveal that early humans, apparently Homo erectus, inhabited this high-altitude plateau two million years ago. Their work provides more evidence that even early in our evolutionary journey, our Homo ancestors weren’t confined to warm African lowlands. Instead, they took advantage of a variety of diverse environments—a precursor of their ability to subsequently spread out across the prehistoric world.
The team analyzed the teeth and jaw as never before, and they published their findings Thursday in Science. They compared the teeth to those of other early Homo species and suggest that the child was H. erectus. That group likely made and used the abundant stone tools of the Oldowan technology found with the fossil, the authors say, as well as the more advanced Acheulean tools also found in the area, from nearly the same time period. This suggests, the authors theorize, that these early highlanders adapted quickly to a high-altitude environment.
Study co-author Margherita Mussi, an archaeologist at Sapienza University in Rome, and colleagues combined two techniques: argon-argon dating and a recently completed paleomagnetic dating analysis to fine-tune the site’s ages. The fossil and Oldowan artifacts with it had previously been dated to 1.7 million to 1.8 million years ago, but revised ages now place them at some two million years old. The team also used advanced imaging technology to study the fossil and suggest which species it represents. “This analysis gave us information inside the teeth, in extremely high detail and comparison with a lot of teeth that are already assessed as Homo erectus,” Mussi says.
Researchers couldn’t determine the child’s sex based on the ancient teeth and jaw, but since so many such fossils have been categorized as male, Mussi took the liberty of deciding the ancient child was a girl whom she affectionally nicknamed “Little Garba.”
The child’s remains were found in 1981, at an important prehistoric site known as the Melka Kunture complex. It stretches over several square miles of the Ethiopian highlands 30 miles from Addis Ababa. Over the years, previous analysis of the mandible and teeth have suggested affinities with a variety of early Homo species including not only H. erectus but also Homo habilis or Homo rudolfensis.
Determining exactly which early humans lived here involved taking the sample around the globe.
Just as H. erectus eventually migrated across much of the prehistoric world, the child’s jawbone went on its own improbable journey some two million years after its owner died. Mussi got permission from the Ethiopian government to carry the precious artifact by hand to the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The cutting-edge imaging facility’s Extremely Brilliant Source can analyze objects in detail with X-rays 100 billion times brighter than those commonly found in hospitals.
ESRF produced a suite of images showing external features of tooth surfaces like crown heights and shapes, and internal ones, like junctions between enamel and the tooth’s underlying dentine. The team compared them with features found in the known examples of various early Homo species.
That analysis, they say, suggests Little Garba was Homo erectus, the first of our ancient ancestor species to have body proportions much like our own—longer legs adapted to a terrestrial lifestyle and bigger brains. Homo erectus was also the most successful of all human species, at least so far. They survived for a staggering period of time, nearly two million years, before fading out about 110,000 years ago in their last stronghold of Java, Indonesia.
If the fossil does represent Homo erectus, it would be the first known appearance of the species in East Africa. That’s entirely plausible, since the species is known in South Africa some two million years ago. But it’s not a sure thing. Tooth morphology offers a wealth of information for determining species—but old teeth for comparison number not in the thousands or hundreds but in the tens.
“I’m not sure that we can call the species Homo erectus,” says paleoanthropologist Miriam Belmaker, of the University of Tulsa, who was not involved in the new study. “It’s of course Homo, but the jury is still out if it could be Homo ergaster, or Homo rudolfensis, which the authors simply didn’t have any teeth of to compare.”
No matter the child’s exact species, their community thrived in a high-altitude locale quite a bit different from established evolutionary hot spots like South Africa and the Great Rift Valley.
“This is 2,000 meters [6,500 feet] of elevation, and that has a lot of consequences,” Mussi explains. In the plateau’s thin air, the prehistoric climate was far different from that of the lowlands, as it remains today. “In a nutshell, it was always rather cool and rainy, and that means the vegetation was different,” Mussi says.
Work on fossil pollen by co-author Raymonde Bonnefille and others at the site has identified dozens of ancient species so far, none of which was also found on the savanna. The animals were different as well. Elephants and rhinos were found only in very small numbers, while unique subspecies distinct from those in surrounding lowlands roamed the area.
Saying that early Homo was able to adapt to this environment feels too passive for Mussi. “I would say they were taking advantage,” she says. “They were perfectly able to live in a different environment.”
“The most interesting thing in the paper, to me, is that it occurs in the highlands,” says Richard Potts, director of the Human Origins Program at the Smithsonian’s National Museum of Natural History.
“Now we know, back to two million years ago, it’s part of the array of environments that H. erectus occupied in Africa at that time,” he adds. “But also it’s the foreshadowing of all the different kinds of environments that H. erectus would move into and populate.” By about 1.7 million years ago, they were found in China at 40 degrees north latitude, a pretty cold environment. And by about the same time, they were found in the Caucasus in what is now the country of Georgia, another cooler environment where Europe meets Asia.
“If they had not been able to make use of the resources to stay in places which are cool and rainy, with different vegetation and animals, how would they have reached the Caucasus?” Mussi asks.
The fossil was found with a variety of Oldowan tools. These tool types, which our distant ancestors began making at least 2.6 million years ago, were basic, including hammerstones for bludgeoning and sharp flakes that were struck off larger cores to provide a sharp cutting edge.
But in only slightly younger layers, relating to 1.95 million years ago, researchers unearthed some of the oldest known examples of early Acheulean lithic technology. Acheulean hand axes and cleavers represent a more sophisticated type of production. They were created by taking a large stone flake and painstakingly shaping it into an ax head by repeatedly striking and breaking smaller pieces off the edges.
“I’m very impressed that the Oldowan and Acheulean tools overlapped in time and space for 200,000 years, with excellent dating,” says Belmaker. “I think that is very interesting.” She says two different early human species may have also overlapped while dwelling in these highlands, and each utilized a different toolkit. Belmaker notes that sites elsewhere in Eurasia suggest migrations by two different hominin populations, using Oldowan and Acheulean tool technologies at the same time. Something similar might have happened as humans moved into the highlands. “Early Homo was beginning to travel both north and south,” she says. “What’s nice about this paper is that it adds another dimension to this expansion, which is up.”
Potts believes that the same species, H. erectus or a very close relative, may have been present throughout. Changing tool technologies are sometimes viewed as a linear process of improvement, in which inferior older implements are quickly discarded when new, different types of tools are made, he notes. But that’s not always the reality. “Being adaptable can also mean flipping back and forth between different stone tool technologies under slightly different circumstances,” he says, “based on many factors like raw materials, conditions or how quickly food had to be processed.”
“Behaviors can be adopted in a flexible way,” he says, “and H. erectus certainly must have been that way.”
One clear aspect of Homo erectus’ flexibility was the wide variety of areas, geographical and now topographical, that they were able to call home. The species was the first great disperser in human evolutionary history and not your ordinary primate. “Not only is it bipedal, not only does it make and depend upon stone tools, but it’s also moving into all sorts of non-tropical environments,” Potts says. “Here we are really dealing with the makings of who we became.”
Editor's Note, October 13, 2023: This article originally misstated the remains were found more than a half century ago. We apologize for the error.