Homo erectus has shaped the history of our ancestors for almost a million and a half years, but this early person still poses a number of puzzles. Now two new finds of Homo-erectus fossils in Ethiopia are shedding new light on its anatomical diversity and the development of its tool technology. The two skulls found a few kilometers apart vary greatly in size and robustness – which speaks for clear gender differences or other intrinsic variations. At the same time, finds of stone tools prove that these early humans apparently used primitive and advanced techniques at the same time.
The Homo erectus was the first early human to leave Africa and penetrate far into Southeast Asia. Fossil finds prove that he lived in Georgia around 1.8 million years ago and occurred on the island of Java a good 1.6 million years ago. His species stayed there for almost one and a half billion years until a good 100,000 years ago. This early man probably owed his success to several technological innovations: he could have been the first of our ancestors to use fire regularly. He was also the first to develop complex stone tools of the so-called Acheuléen style. Its predecessors and the first representatives of its kind worked stones only on one side and with a few strokes. The result was the simple boulders of the Oldowan culture, which differed little from unprocessed boulders. In contrast, the tools of the Acheuléen: They were chipped off on both sides so that hand wedges and rectangular cutters with sharp edges were created.
Two skulls with remarkable differences
Now Sileshi Semaw from the CENIEH research center in Burgos, Spain, and his colleagues have discovered two new Homo-erectus specimens. These are two skulls that were found just a few kilometers apart at Gona in the Afar triangle in Ethiopia. Although this area is considered a cradle of mankind and scientists have found many relics of prehistoric people there, finds of Homo-erectus fossils from this area are rather rare. Dating shows that the rather small, dainty “DAN5” baptized skull is around 1.5 to 1.6 million years old. The BSN12 skull is around 1.25 million years old and significantly larger and more robust. “The new relics show a measure of biological variation that has never been seen in Africa before,” said co-author Scott Simpson of the Cleveland Museum of Natural History. “The small size of the DNA5 skull is particularly noteworthy.” With an internal volume of 590 cubic centimeters, it is the smallest Homo-erectus skull found in Africa to date – and also significantly smaller than most of this type of skull known from Asia.
But how do these differences come about? “The anatomical variation in these specimens can be interpreted in different ways,” say Semaw and his colleagues. For one thing, DAN5 could have more primitive traits due to its older age, including the smaller brain volume. “Alternatively, the differences in size and anatomy that we observe in the Gona specimens could also be a consequence of gender differences within this species,” said the researchers. This assumption of sexual dimorphism is supported by earlier fossil finds in the Georgian Dmanisi Cave, where scientists had found erectus skulls of almost the same age with a surprisingly wide range of sizes and features.
Tools of two technology stages
But the new finds from Ethiopia are particularly interesting for one reason: Together with the skulls, the researchers have also discovered several stone tools at both sites. Some of these tools were made using the older Oldowan technique and were more like rough-hewn river pebbles. In the same find layer, Semaw and his team also came across hand axes and hand axes that had already been produced using the more modern Acheuléen technology. Traces of cuts on the leg bone of an antelope and the foot bone of an elephant show that the early humans used these tools to cut prey. It is not clear whether they hunted them themselves or whether they only used fresh carcasses found in the savannah. The crucial point, however: The simultaneous occurrence of Oldowan and Acheuléen tools indicates that the technological development of the Homo erectus was less straightforward than previously thought.
“Although most researchers in our field assume that the Acheuléen technology replaced the former Oldowan around 1.7 million years ago, our research now shows that the older technology remained widespread throughout the Paleolithic period,” says the co-author Michael Rogers from Southern Connecticut State University. “It does not support the simple view that a hominin type used only one tool technology. Instead, the history of human development is much more complicated. ”According to the researchers, this suggests that Homo erectus was more flexible and versatile in its use of tools than previously thought. Depending on the intended use and the raw material available, this early human could have decided whether a simple Oldowan tool was sufficient or whether he needed a more complex, more elaborate hand ax or a hand ax.
Source: Sileshi Semaw (CENIEH, Burgos) et al., Science Advances, 2020; doi: 10.1126 / sciadv.aaw4694