Researchers have uncovered the skulls of two individuals belonging to the species Homo erectus—one of our ancient ancestors—alongside various types of stone tool of differing complexity at a site in Ethiopia, casting new light on the use of technology by early humans.
According to a study published in the journal Science Advances, the finds further refute the "single species/single technology" idea of early Homo—the group of species which includes modern humans and several extinct relatives, such as H. erectus.
In the fields of paleoanthropology and archaeology, stone tools are classified according to their complexity and the time period in which they were used.
So-called Oldowan (or Mode I) tools date back to more than two-and-a-half million years ago and are primitive in nature—usually stones that have had just a handful of flakes chipped off. These were succeeded by Acheulean (or Mode II) tools, which appeared later, around 1.7 million years ago. These are more complex—for example, stones that have been shaped on both sides by human hands, such as prehistoric hand axes.
Some researchers have previously proposed that H. erectus invented Mode II tools, although there is debate among experts.
In the traditional "single species/single technology" view, each early hominin species, like H. erectus, only used stone tools that were either Mode I or Mode II.
However, the authors of the latest study say their finds support the idea that H. erectus in Africa invented Mode II tools, indicating they used both Mode I and Mode II technologies concurrently over hundreds of thousands of years.
The team, led by Sileshi Semaw from the Centro Nacional de Investigación sobre la Evolución Humana in Spain, uncovered H. erectus skulls from two individuals at two different locations within an archaeological site in Gona, northern Ethiopia. This is where the oldest known Oldowan tools have been found.
The researchers dated one of the skulls, dubbed BSN12, to around 1.26 million years ago, while the other, known as DAN5, appears to be between 1.6 and 1.5 million years old.
"At each site, we found H. erectus cranial fossils in direct association—i.e. found right next to and within the same strata—with both simple Mode I stone tools and more complex Mode II stone tools such as hand-axes and picks, purposefully shaped," Michael Rogers, one of the authors of the study from Southern Connecticut State University, told Newsweek in an email.
"Archaeologically, our study is noteworthy for 1.) documenting the direct association of hominin crania with both kinds of stone tools at multiple sites and 2.) raising the possibility that some H. erectus populations, at least at times, did not make Mode II tools, or made them rarely," Rogers said. "For example, the younger BSN12 site has very few Mode II artifacts, and we could have very easily missed them, which would have led us to interpret the site as a 'Mode I' site."
According to Rogers, this indicates that some populations of H. erectus made Mode I stone tools extensively and sometimes exclusively, depending on the need, availability of stone, and local traditions. Furthermore, the findings suggest that there was not a simple replacement of Mode I tools by Mode II technology once H. erectus appeared on the scene, which is what many experts had thought.
"Discovered first in Indonesia in the 1890's, [H. erectus] have since been found at many sites in Eurasia and Africa, and lasted an incredibly long time, from around 1.8 to 0.3 million years ago," Rogers said. "They are usually described as large-bodied—some as tall as us—with modern limb proportions and bigger-brained.
"They are also credited with inventing controlled fire, wooden spears, and cumulative culture. Some researchers consider H. erectus to be, in a broad sense, the immediate ancestor of us, Homo sapiens."
He continued: "Anatomically they were essentially the same as us today from the neck down—some even had brain sizes that approach ours—and behaviorally they may have been the first to use technology (that is, stone tools, but probably also wooden tools) habitually. Earlier hominins made and used stone tools, but H. erectus may have been the first to start depending on them,' he said.
Robert Goodby, a professor of Anthropology at Franklin Pierce University who was not involved in the latest research, said the study contributes "significant new data" to the growing understanding of the evolution of the genus Homo.
"For many years, paleoanthropologists had embraced a simplistic one-to-one correlation of tool traditions and species, with Oldowan tools associated with early Homo and the more advanced tools of the Acheulian tradition associated with the larger-brained Homo erectus," he told Newsweek.
"While it has long been recognized elements of the Oldowan tradition continue into the early Homo erectus period, this study tells us just how long this persistence was, reflecting technological practices that endured for almost 1.5 million years and a relatively slow rate of evolutionary and behavior change that contrasts sharply with the explosive behavioral changes accompanying the appearance of modern H. sapiens 40,000 years before present," he said.
However, Bernard Wood, Professor of Human Origins at the George Washington University, who was also not involved in the research, was more sceptical of the paper. He said that while it provided "important new evidence," the finds were "not well-interpreted."
"[The study] suggests that hominins did not abandon the use of more primitive tools, even though they knew how to make more sophisticated stone tools," he told Newsweek. "The authors assume the hominins—H. erectus—manufactured the stone tools. The tools could have been manufactured several hundreds of years before or after the individuals whose bones are at the site were there."
Nevertheless, the study also sheds light on the physical characteristics of Homo erectus, given that the DAN5 cranium—a female—is the smallest skull of this species found to date in Africa, the researchers said. This indicates that H. erectus was physically more variable than previously thought, and that a large brain was not necessarily required to be a member of it. The authors suggest that this could be evidence of sexual dimorphism—when the two sexes of a species display different characteristics beyond their differing sexual organs.
"For decades, and perhaps as recently as a decade ago or so, paleoanthropologists had thought of Homo erectus as exhibiting less sexual dimorphism than earlier hominins, based on the skeletal samples that had been measured," Rogers said. "In just the last 10 to 15 years, though, with the discovery of a few smaller H. erectus crania—including the DAN5 cranium record-breaker—this view will certainly get a second look.
"If H. erectus is confirmed to be significantly sexually dimorphic throughout its long tenure, then the decrease in dimorphism among modern humans would be a more recent phenomenon, with interesting social implications," he said.
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