The DAN5 female cranium of H. erectus.
The DAN5 female cranium of H. erectus.
Image: Michael J. Rogers, Southern Connecticut State University

Archaeologists in Ethiopia have uncovered skull fragments and tools belonging to Homo erectus, one of the most successful hominins to have ever lived. Importantly, the newly discovered stone tools came from two different technological traditions, highlighting the diversity and flexibility of these extinct hominins.

When it comes to extinct human species, Neanderthals tend to hog the spotlight. But another group of early humans, Homo erectus, is equally deserving of our love and attention.

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H. erectus emerged in Africa some 2 million years ago—a debut that happened some 1.7 million years before the appearance of our species, Homo sapiens. It’s not clear if we’re directly descended from this species (Homo heidelbergensis is a more likely candidate), but we most certainly share a common ancestor. As a hominin, H. erectus was quite successful, with a geographical range that extended into Eurasia and Indonesia and a tenure that finally ended between 117,000 and 108,000 years ago.

The dearth of fossil evidence has made it challenging for archaeologists to study this species, but new research published today in Science Advances is putting these remarkable people into clearer focus. The new paper was led by Sileshi Semaw from the National Center for Research on Human Evolution in Spain and the Gona Paleoanthropological Research Project in Ethiopia.

Stone tools found at the DAN5 site in Ethiopia.
Stone tools found at the DAN5 site in Ethiopia.
Image: Michael J. Rogers, Southern Connecticut State University

Skull fragments from two individuals were recently uncovered in Gona, Afar, Ethiopia, alongside associated stone tools—a rarity in archaeology. Even rarer is the discovery of stone tools hailing from two different technological traditions, a finding that’s upsetting a conventional notion that associates single human species with single stone tool technologies. The finds are also shedding new light on the eating habits of H. erectus and the physical differences that existed between males and females.

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The skull fragments were found at two different sites located 5.7 kilometers (3.5 miles) apart: Dana Aoule North (DAN5) and Busidima North (BSN12). The female skull fragment, designated DAN5/P1, was dated to 1.26 million years old, and the male skull fragment, BSN12/P1, was dated to between 1.6 million and 1.5 million years old.

Map of the Gona study area.
Map of the Gona study area.
Image: Michael J. Rogers, Southern Connecticut State University
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Archaeologists and anthropologists characterize early stone tools based on their level of sophistication and the time period in which they were constructed. So important are stone tools to archaeology that entire hominins and cultural subgroups are identified according to their mode of lithic industry. The Clovis people of North America are a good example—a group of humans literally known by their iconic Clovis Points.

Of relevance to the new study, the authors reference Mode 1 tools, in which several pieces are knapped off a stone to produce sharp edges, and Mode 2 tools, which are more complex, having all sides flaked off to produce a pear-shaped hand-axe. Mode 1 tools are also referred to as Oldowan and Mode 2 tools as Acheulian.

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Existing archaeological evidence suggests H. erectus built Mode 2 tools, while previous hominin groups invented and used Mode 1 tools. The new study, however, suggests H. erectus used both Oldowan and Acheulian stone tools over the course of hundreds of thousands of years, which upsets the single species/single technology view of early humans.

“The evidence from Gona suggests that H. erectus had population-level behavioral diversity and flexibility, with a lengthy and concurrent use of both Mode 1 and Mode 2 technologies,” wrote the authors in the new study.

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The researchers attributed the variability in stone technology to a number of factors, such as proximity to raw materials, changes to the environment over time, population, size, and the degree of contact with other groups. The new paper is also significant in that it documents the presence of hominin skull fragments with both kinds of stone tools at multiple sites.

Michael Rogers, a researcher from the Department of Anthropology at Southern Connecticut State University and a co-author of the new paper, said the single species/single technology perspective of early Homo likely dates back to Mary and Louis Leakey’s discoveries of Homo habilis and basic stone tools at Tanzania’s Olduvai Gorge in the 1960s.

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“Mary Leakey called these simple stone tools ‘Oldowan,’ and [they] are now recognized as the earliest known habitually used tools used by our ancestors, the oldest of which are dated to 2.6 million years ago at sites such as Gona and Ledi in Ethiopia,” Rogers told Gizmodo. “Later, when Homo erectus was discovered in Africa, a hominin with a larger brain size than H. habilis, it was recognized that a more sophisticated tool was often found in indirect association—these are the larger, purposefully shaped hand-axes and picks of Acheulian (Mode 2) technology.”

Study co-authors Michael Rogers (left) and Sileshi Semaw (right) holding the DAN5 cranium.
Study co-authors Michael Rogers (left) and Sileshi Semaw (right) holding the DAN5 cranium.
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This story, at least at a basic level, makes intuitive sense: the bigger the brains, the better the technology. What’s more, the extensive time range of both H. erectus and Acheulian stone tools, which lasted for more than a million years (from 1.7 million to 300,000 years ago), served to reinforce this simple correlation between early human species and stone technology, explained Rogers. As more fossils and artifacts are being discovered, however, archaeologists are realizing that “the story of early human technology is not quite so simple,” said Rogers, even if the broad outlines of the story are still largely valid.

Key to the new discovery was in demonstrating that the fossils and stone tools belonged together. This proved to be a rather straightforward process at the BSN12 site, in which the skull fragment and two Acheulian tools were covered in the same volcanic ash. The scientists subsequently found additional artifacts, namely the Mode 1 tools, within the same ash layer.

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As for the DAN5 site, however, that required more “patience” and literally years of hard work, according to Rogers. The skull fragment was found in association with Mode 1 tools, but the Mode 2 artifacts were found nearby on the surface and could not immediately be linked to the fossil. A subsequent dig just 50 meters (164 feet) away revealed more Mode 2 tools in the ground layer but not immediately next to the skull fragment. Undaunted, the researchers continued over many years to scan the site surrounding the cranium, eventually finding both Mode 1 and Mode 2 artifacts.

This discovery is also adding new color to our conceptions of Early Stone Age cultural traditions, both in terms of how they originated and how they were maintained over extensive periods of time. As Rogers explained, the new evidence suggests local populations of H. erectus in Gona built both Mode 1 and Mode 2 stone tools, but given the broader archaeological record in Africa from 1.7 million to 1 million years ago, it’s wholly plausible that different groups of H. erectus may or may not have even made Mode 2 stone tools.

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“The fact that the Mode 2 tradition seems to be conserved over such a long time, and over long distances, raises questions about the functionality of Mode 2 stone tools, strength of cultural traditions, and the degree of interactions between wide-ranging groups,” Rogers told Gizmodo. “It’s remarkable that the Mode 2 tradition was passed down successfully over thousands of generations, especially in light of the variability that we are now seeing in the paleoanthropological records.”

The implication of these findings, said Rogers, is that we require a better understanding of the “conditions under which certain Early Stone Age artifacts were created,” be they environmental, functional, social, or cultural factors.

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Teeth from the DAN5 cranium.
Teeth from the DAN5 cranium.
Image: Scott W. Simpson, Case Western Reserve University

The skull fragments themselves provided new clues about the sexual dimorphism that existed in H. erectus, that is, physical differences between males and females. The female skull, DAN5/P1, is smaller and slimmer compared to those of males. The skull was determined to belong to a young adult, given that all her molars had erupted and that some teeth exhibited signs of wear (she even had a wisdom tooth, which typically comes in around age 18 in modern humans).

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Interestingly, DAN5/P1 is now the smallest H. erectus cranium ever found in Africa, pointing to significant physical variability in the species as a whole. Which makes sense, as the authors wrote in the study:

The broad dispersion and probable low population density of H. erectus created opportunities for developing regional anatomical [physical differences] due to periods of interrupted gene flow [i.e. group isolation]. As shown by recent studies of ancient DNA, hominins can and will recognize each other as viable mates even after many hundreds of thousands of years of separation, such that a temporary interruption in gene flow does not necessarily result in speciation.

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An isotopic analysis of a tooth taken from the DAN5/P1 fossil points to a diverse omnivorous diet. These humans likely consumed plants, eggs, insects, and browsing herbivores. Rogers told Gizmodo that this particular population of H. erectus appears to have acquired its food from a forested environment, which was unexpected, since the species adopted a grassland-oriented diet elsewhere in East Africa. Again, “our study documents more physical and behavioral variability than we had seen before,” said Rogers.

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It’s important to point out that this was the culmination of years of work. Discoveries like these don’t happen overnight; they require tremendous amounts of physical and mental labor.

“We owe a debt of gratitude to our Afar colleagues, with whom we’ve worked for more than 20 years at Gona,” Rogers told Gizmodo. “They are the ones who find most of the fossils and artifacts, excavate most of the sites, and sift through most of the sediments in search of our common ancestry.”

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George is a senior staff reporter at Gizmodo.

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