Researchers discovered two canid remains, dating back roughly 3,000 to 5,000 years, with grey wolf ancestry on the Swedish island Stora Karlsö. This prompted them to pose the question: were wolves under human control in prehistoric Scandinavia?
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The remains were discovered in the Stora Förvar cave, an archaeological site on the island frequently used by seal hunters and fishers in the Neolithic and Bronze Ages. These are not the first remains found in this cave – previously found in the layers were scattered human remains and a domestic dog.
Stora Karlsö is a small island of just 2.5 square km, located in the Baltic Sea, about 5km west from the larger island Gotland and around 80km east of mainland Sweden – both islands were never connected to the mainland, so they don’t have any native terrestrial mammals.
The group of researchers published their findings about these canid remains in the journal Proceedings of the National Academy of Sciences. While the paper emphasises other explanations are possible, it could be likely that the wolves were brought to the island by humans and were possibly under their control.
Dog domestication
Dogs were domesticated from a currently-unidentified wolf population at least 15,000 years ago, but the specifics of that process are widely debated and poorly understood. There are two possible ways this domestication might have occurred: “commensal pathway”, suggesting that wolves self-tamed by settling among human populations as an adaptive strategy; and the “direct pathway”, suggesting humans deliberately domesticated wolf pups.
It’s hard to explicitly determine what happened because no dog remains clearly dating back to the early stages of domestication are currently known. What we do know are the early indicators of domestication: close and continuous association with humans or archaeological sites, dietary shifts, reduced body size and genetic diversity decline.
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The clues
It’s been previously proven that differentiating between wolves and early domestic dogs based on morphology (the form and structure of an organism) is difficult, so the researchers turned to genetics. By analysing the remains of the two canids found on Stora Karlsö, they determined that both specimens were genetically wolves.
The wolves were relatively small – bigger than any known prehistoric dog, but smaller than a sample of modern Scandinavian wolves and at the lower end of the size range of wolves of the Pleistocene and Holocene periods.
One of the wolves also demonstrated particularly low genetic diversity, which is usually observed in small and isolated populations or selectively bred ones.
An isotope analysis also revealed something interesting about the wolves’ diet – it was rich in marine protein, such as seals and fish. This contrasts with the dog previously found in the cave, whose diet was primarily based on terrestrial resources consistent with the diet of dogs and humans of the period, from the nearby island Öland.
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While marine diets in wolves have been previously observed in populations from Alaska and British Columbia, there is no record of such diet in wolves from prehistoric Scandinavia. This sustained access to marine resources further points towards the wolves’ dependency on local humans.
“The discovery of these wolves on a remote island is completely unexpected,” said one of the study’s lead authors, Linus Girdland-Flink from the University of Aberdeen.
“Not only did they have ancestry indistinguishable from other Eurasian wolves, but they seemed to be living alongside humans, eating their food, and in a place they could have only have reached by boat. This paints a complex picture of the relationship between humans and wolves in the past.”
The implications
The researchers have emphasised that although all the above-mentioned factors occurring together point towards the possibility of these prehistoric humans controlling wolves in some capacity, other scenarios – such as the wolves somehow naturally spreading to the island – are possible.
Still, the findings offer new insight into a possibly forgotten chapter in the history of the co-existence of humans and wolves that might not have as much to do with the modern domesticated dog as previously thought.
Read the full findings here.
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Top image: view from the cave Stora Förvar on the island of Stora Karlsö in Sweden. Credit: Jan Storå/Stockholm University
