Gray wolves lived with ancient humans on a tiny island, upending the dog domestication debate

Between 3,000 and 5,000 years ago, two gray wolves reached Stora Karlsö, a small island in the Baltic Sea. The island has no native land mammals, so the animals almost certainly arrived by boat with people who were already using its caves.

The wolves come from Stora Förvar, a deep limestone cave that was used intensely by Neolithic and Bronze Age communities.

Through ancient DNA, bone study, and chemical clues in the skeletons, the new research shows they lived in tight contact with humans.

Ancient wolves on Stora Karlsö

The work was led by Pontus Skoglund, PhD, who heads the Ancient Genomics Laboratory at the Francis Crick Institute in London. His research uses ancient DNA to track how humans and other species have changed through time.

Stora Karlsö is only about one square mile in area, and it sits roughly three miles west of the larger island of Gotland. It lies about fifty miles from mainland Sweden, and at no point since the Ice Age has it been connected by dry land.

Archaeologists studying Gotland have shown that animals like hares, foxes, pigs, and hedgehogs were introduced by people, rather than evolving there on their own. 

On Stora Karlsö this pattern is even stronger, because the scarce mammal bones match species that humans hunted and carried.

The Stora Förvar cave holds cultural layers up to about thirteen feet thick. Those layers are packed with stone tools, pottery, and animal bones left behind during thousands of years of seasonal hunting trips.

Most of the skeletons in the cave come from seals and other marine animals. The pattern of shells and bones points to repeated seasonal visits by groups who camped in the cave while exploiting nearby marine resources.

True wolf proof

In the new study the team extracted DNA from two canid bones found deep in the cave. The animals shared genome patterns, the complete genetic instruction set in a cell, with Eurasian gray wolves and showed no sign of dog ancestry.

Using low coverage DNA data, the team measured heterozygosity, a statistic that tracks how much genetic variation an individual carries across its genome. 

One wolf had lower heterozygosity than any other ancient wolf measured so far, which hints at a small, isolated breeding group.

Measurements of the arm bone show that this Stora Karlsö wolf stood at the very small end of the size range for ancient wolves.

It was bigger than dogs of the same time in the region, but smaller than modern Scandinavian wolves measured by zoologists.

The second individual was a juvenile that died centuries earlier, during the Late Neolithic, when farmers and seal hunters were active in the Baltic. 

Together the two skeletons span several centuries of cave use, placing wolves inside a long standing relationship with people on the island.

Clues from diet and disease

Chemical tests of carbon and nitrogen, known as stable isotopes, showed that the wolves ate marine protein from seals and fish.

Their isotope values closely match those of humans from the site, pointing to deliberate feeding rather than wolves independently catching large sea animals.

One Bronze Age wolf shows clear pathology, bone damage that builds up during life, in a front leg that would have made travel painful.

An animal that could not easily chase prey across rough terrain would have struggled to survive without a steady food supply from humans.

The team considered simpler explanations, such as wolf hides brought in with fur trade or wild wolves reaching the island during rare ice conditions.

However, the mix of limb bones, the signs of injury, and the chemical data point to wolves living on the island for extended periods.

Rethinking early dog domestication

Modern dogs came from domestication, the long process where humans shape animals so they live, breed, and behave differently from their wild ancestors. 

A recent review notes that clearly identified domestic dogs appear at least fifteen-thousand years ago, well before farming spread across Europe.

Researchers debate whether wolves first approached human camps as commensal, free living scavengers that fed on leftovers, or whether people deliberately raised captured pups. 

These island wolves indicate that people could keep wild wolves inside their settlements for long periods without those animals yet showing clear dog traits.

Genetic work suggests that one dog lineage arose in northeastern Siberia twenty thousand years ago, then spread with people across the Americas.

Another ancient DNA team found that dogs today carry ancestry from at least two wolf populations, which only adds complexity.

“It was a complete surprise to see that it was a wolf and not a dog,” said Skoglund. Against that complicated background, the island wolves look like a rare snapshot of people experimenting with wolf management without fully creating dogs. 

Lessons from these ancient wolves

Modern wolf populations also show how flexible these animals can be when people reshape landscapes and food sources.

In coastal Alaska, recent research has documented wolves that feed on prey like sea otters and carry elevated mercury levels in their tissues.

On the Pacific coast of Canada, footage analyzed by a study captured a wolf hauling a crab trap rope ashore to reach bait.

That behavior may qualify as tool use, and it underlines how quickly wolves can learn new tricks when living alongside coastal communities.

The Stora Karlsö wolves add an ancient perspective to these modern cases, showing that humans have long experimented with partnerships with a large carnivore. 

“The discovery of these wolves on a remote island is completely unexpected,” said Linus Girdland-Flink, a zooarchaeologist at the University of Aberdeen.

Taken together, the anatomical, genetic, dietary, and medical clues suggest close management that resembles early steps toward domestication without yet producing true dogs. 

“The combination of data has revealed new and very unexpected perspectives,” said Jan Storå, a professor of osteoarchaeology at Stockholm University.

The study is published in Proceedings of the National Academy of Sciences.

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