Posted on behalf of Nadia Drake.
Picture this scene: it’s 1.8 million years ago in the southern reaches of the Caucasus Mountains and a powerful feline, an ancestor of the modern jaguar, has just made a kill. The predator retreats to a secluded gully where it can feed on the bloodied carcass at its leisure. Suddenly a volley of rocks rains down, delivering painful blows and forcing the big cat to abandon its dinner and withdraw. Moments later, a band of prehistoric humans scrambles down the gully to claim the prize. Chalk up another victory for the diminutive scavengers whose relatives will one day take over the planet.
The scenario is speculative, but based on evidence unearthed at the Dmanisi excavation site in the Republic of Georgia and presented earlier this month at a meeting of the Society for American Archaeology in Sacramento, California.
Reid Ferring, a geoarchaeologist at the University of North Texas, has championed the idea, which arose from his ongoing interest in the numbers and arrangements of stones found at the dig. The stones or ‘cobbles’ are intriguing, he says, because they are otherwise nonexistent in the layers of volcanic sediment that encase the ancient site. “There’s no possible way they got there naturally,” he says of the nearly 200 stones he’s studied.
Ferring realized the stones in the gullies were of appropriate size for throwing, which might shed light on the survival strategy of the small hominins who first occupied Dmanisi, the location of the oldest known Homo fossils outside of Africa.
“There are a lot of carnivores in the Dmanisi assemblage, much higher than we see in most other archaeological sites,” Ferring explains. “Where do humans fit in?”
One answer might be that the small hominins who lived there stuck together for protection and threw rocks to pilfer food from local carnivores. Stone-throwing has previously been suggested as an adaptation for early human ancestors in Africa, but has not figured prominently in discussions of Eurasian populations.
In one small gully section, Ferring found nearly 75 cobbles clustered near human fossils and carnivore bones. But farther from the gullies, he found almost no cobbles – just stones showing evidence of being flaked for tool usage. The cobbles’ association with the gully boneyard provides the context Ferring needs to support the hypothesis that imported stones played a role in prehistoric scavenging.
Ferring acknowledges the evidence is circumstantial, but there is plenty of it. His hypothesis offers a glimpse into what life may have been like at Dmanisi, now one of the most important windows into the first known epoch of human migration out of Africa.
Located under the visible remains of a medieval fortress, the Dmanisi excavation (right) has yielded artifacts from several eras of human occupation, with older material particularly well preserved under more recent volcanic deposits. Within these layers, archaeologists in 1991 discovered the oldest hominin fossil outside Africa: a 1.77-million-year-old jaw bone belonging to Homo erectus. Skulls and long bones found since then have allowed scientists to build a picture of the small, mobile human relatives living at Dmanisi. Now, interpretive analyses at the site are adding to the understanding of early human migration, adaptations, and behavior, said paleoanthropologist David Lordkipanidze, director of the Georgian National Museum, who coordinates work at Dmanisi.
“In Dmanisi, [early humans] are very well adapted to the environment,” Lordkipanidze says. “They had exactly enough brain capacity, exactly the anatomy and features to be adaptive, and the capacity to produce stone tools.”
Ferring’s work represents just one facet of ongoing efforts to interpret the finds at Dmanisi, which Harvard University archaeologist and curator Ofer Bar-Yosef likens to a paleolithic bus station. “People come to it and then spread into Eurasia, some go to Europe, some go to other parts of Asia,” says Bar-Yosef, who was not involved in Ferring’s work. He says the idea that the stones were used for driving off carnivores is compelling, but adds that there may have been other reasons why the stones were brought there. “My suggestion is that some of the stones were used to pound meat,” he says, an essential activity prior to the use of fire for cooking flesh.
Ferring agrees, explaining that the larger rocks at the site were likely tools used for pounding flesh, cutting meat, or smashing bones – but that the smaller stones might have served a different purpose: aiding in aggressive scavenging and tipping the scales toward success for the “small, first colonists of Eurasia.”
Since its discovery, Dmanisi has provided a crucial signpost for dating the human exodus from Africa. More recent work by Ferring and others now suggests the site can shed light on early social behavior and adaptations among human ancestors.
“More and more, colleagues are interested in adaptation, behaviour, social organization, evolution of the social brain,” says Bar-Yosef. “But the essentials – chronology, detailed information from the sites –- are critical if we are to evaluate or reconstruct how these hominins adapted themselves to environments entirely different from the African savanna.”
Ferring says he and his colleagues will continue building the case for early stone-throwing at Dmanisi by excavating additional areas at the site – away from the gullies – and tracking associations between cobbles, flaked stones, and bones. Ferring hopes the site will answer questions about how Homo erectus found food, a missing piece in the picture of early human adaptations and behaviors. “It’s a tough nut to crack,” he says. “But Dmanisi provides us with one of the strongest chances to look at context that has ever been recovered.”