Old school

Homo erectus study reveals 4 new facts about this ancient human

Paleontologists are finally shedding light on this oft-forgotten human ancestor.

The Gona site in Afar, Ethiopia is a hotbed of anthropological discovery. It is also, quite literally, hot. But the inhospitable climate, paleoanthropologist Sileshi Semaw tells Inverse, is likely why the archeological record there is so well-preserved and pristine. The site is untouched by development; its inhabitants are nomadic pastoralists whom, Semaw says, "understand the value of the antiquities," and protect the site.

The value of these antiquities to science, and for our own origin story, is considerable: In a study published Wednesday in the journal Science Advances, Semaw, director of the Gona Paleoanthropological Research Project, and his team describe the discovery of Homo erectus skull fragments and tools.

The treasure trove of artifacts serve as clues to what life was like for this ancient human species — and dispel old and tired theories about its behavior.

Homo erectus lived between about 1.89 million years to 110,000 years ago. It is the longest surviving of our human ancestors, and is credited as the earliest hominin to have modern human-like physical qualities.

Despite their long reign on Earth, paleoanthropologists are still striving to understand what day-to-day life was really like for Homo erectus — as well as what eventually killed them off.

Special skulls

The findings at Gona — which is home to hominin fossils dating back 6 million years — help flesh out our understanding of Homo erectus. The team, working through 104 degrees Farhenheit days, made two crucial discoveries that form the basis of this study: Two skull fragments and an array of different tools.

One of the skull fragments dates to 1.26 million years ago, and the other to between 1.6 to 1.5 million years ago. Curiously, the older skull is smaller and more slender than the other — it is also the smallest Homo erectus skull found in Africa yet, Semaw says.

Co-authors Sileshi Semaw (right) and Michael Rogers (left) with the smaller skull.Michael Rogers

The small skull reinforces the idea that Homo erectus may have been sexually dimorphic, meaning that the males were larger than the females.

It is also similar to some of the Homo erectus skulls found in the country Georgia, suggesting Homo erectus was "mobile and probably may have returned to Africa from Georgia," Semaw says.

Isotope analysis of this skull's molars revealed further insight into Homo erectus' life: It likely had a varied, omnivorous diet, dining on eggs, insects, plants, and more.

Tool flexibility

Near the skulls, the team also found tools representing two types of Stone Age technology. Dating of the sediments on the tools suggests they were used at about the same time the owners of the skulls once lived.

Oldowan, or Mode 1, tools appeared around 2.6 million years ago. These widely used stone tools are simple in design — a sharpened rock, with a few flakes chipped off. Some researchers believe these tools were subsequently replaced by a more sophisticated tool technology known as Acheulian, or Mode 2, Semaw explains. That technology shows up in the archeological record about 1.75 million years ago, and is characterized by distinctive oval and pear-shaped "hand-axes."

The discovered Acheulian stone tools. Michael Rogers

The discovery and age of the Oldowan and Acheulian tools at Gona, Semaw says, clearly shows that the Oldowan tools continued to be manufactured and used by Homo erectus after the invention of the Acheulian tools. Rather, they were seemingly used side-by-side, implying Homo erectus had "behavioral flexibility," Semaw says.

The discoveries paint a very different picture of this ancient human to previous research, which posited they weren't really one for making or using a diverse array of tools — a lack of ingenuity that may have driven their downfall.

Instead, these findings suggest the species was behaviorally flexible and diverse — an early human who migrated and innovated.

For Semaw, the next Homo erectus mystery he wants to solve is the function of their hand axes and cleavers. The early examples found in Gona are crudely made — but later hand axes made by Homo erectus are symmetrical, thin, and well-shaped. In fact, they are so aesthetically pleasing, that it' difficult to say if they were truly made for butchery. Understanding the culture of Homo erectus, Semaw says, "would be awesome."

Abstract: Although stone tools generally co-occur with early members of the genus Homo, they are rarely found in direct association with hominins. We report that both Acheulian and Oldowan artifacts and Homo erectus crania were found in close association at 1.26 million years (Ma) ago at Busidima North (BSN12), and ca. 1.6 to 1.5 Ma ago at Dana Aoule North (DAN5) archaeological sites at Gona, Afar, Ethiopia. The BSN12 partial cranium is robust and large, while the DAN5 cranium is smaller and more gracile, suggesting that H. erectus was probably a sexually dimorphic species. The evidence from Gona shows behavioral diversity and flexibility with a lengthy and concurrent use of both stone technologies by H. erectus, confounding a simple “single species/single technology” view of early Homo.

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