This year, Japan set a record for the most people ever killed or injured by bear attacks. Because food sources like beech nuts decreased due to climate change, bears have more often come down into villages. Warming caused by humans has boomeranged back as bear attacks.
Italy is different. It faces the same climate crisis, but bears living in the Apennines rarely attack people. Pushed to the brink of extinction early by humans, they eliminated the potential for conflict by undergoing genetic changes that reduced aggression to survive. Bears living in the Arctic changed their genes from carnivory to herbivory to survive. What have humans done to the bears' genes?
◇ Aggression decreased as isolation began 2,000 years ago
Researchers in the Department of Life Sciences and Biotechnology at the University of Ferrara in Italy said, "Italian bears that live near villages minimized conflict with humans by becoming smaller and less aggressive through genetic changes over the past more than 2,000 years," according to a study published on the 15th (local time) in the journal Molecular Biology and Evolution.
The team compared the genes of the Apennine brown bear (Ursus arctos marsicanus), found only in central Italy, with those of other European brown bears. Previous research found that the Apennine brown bear split from other European brown bears 2,000 to 3,000 years ago and remained completely isolated after the Roman era.
The isolation of Italian bears was caused by humans. Andrea Benazzo, the corresponding author of the paper, said, "The population decline and isolation of Apennine bears were likely due to the spread of agriculture in central Italy, which increased forest clearing and population growth."
The researchers analyzed at the genetic level how bears on the brink of extinction survived. As expected, the isolated Apennine bears had lower genetic diversity and higher inbreeding than other European brown bears. But these changes actually helped the bears survive. The team said genes associated with reduced aggression were selected during the Apennine bear's evolution.
Humans both put bears in danger and enabled them to survive until now. As humans encroached on habitats, brown bear populations decreased and genetic diversity declined, raising the risk of extinction. But in that process, unintended genetic mutations that reduced aggression in bears appeared. As a result, conflict with humans decreased, allowing them to survive, albeit in isolation.
Giorgio Bertorelle, a co-author of the paper, said, "Interaction with humans is usually dangerous to the survival of most wild animals, but it can also promote the evolution of traits that reduce conflict." The researchers noted that in this respect, care is needed to ensure such genetic variants are not diluted during population recovery. In other words, releasing bears into the wild to boost numbers must not lead to renewed aggression and trigger conflict with humans.
◇ Polar bears switched to herbivory as seal hunting became difficult
Polar bears (Ursus maritimus) in Greenland also had their genes changed due to humans. A team led by Simone Immler, a professor in the School of Biological Sciences at the University of East Anglia (UEA), and researcher Alice Godden said, "Polar bears living in southeastern Greenland show genetic mutations that appear to be adaptations to warming," in a study published on the 12th (local time) in the journal Mobile DNA.
Polar bears are the largest land carnivores and the top predators in the food chain. But their survival is threatened as sea ice is rapidly shrinking due to abrupt climate change. Polar bears hunt by waiting on sea ice—floating pieces of ice on the ocean—and seizing the moment when seals surface to breathe. However, climate change is rapidly reducing sea ice, sharply cutting hunting opportunities. Godden predicted, "If current conditions persist, more than two-thirds of polar bears will be gone by 2050."
Earlier, scientists at the University of Washington discovered an isolated group of polar bears in southeastern Greenland and published their findings in Science. Their dependence on sea ice was lower than in other areas. Southeastern Greenland has less sea ice because temperatures are higher than in the northeast. The University of East Anglia team collected blood from polar bears in northeastern and southeastern Greenland and compared their genes.
Polar bears in the southeast had different genes from those in the northeast to survive. As sea ice disappeared and seal hunting became difficult, changes appeared in genes related to fat processing. The researchers said this shows polar bears are gradually adapting to a plant-based diet instead of carnivory.
The team said the genetic changes in polar bears occurred over the past 200 years. Such rapid genetic shifts were made possible by so-called "jumping genes." As the name suggests, these genes can easily change position within DNA over short periods.
Barbara McClintock first discovered jumping genes in corn and received the 1983 Nobel Prize in physiology or medicine. The scattered dark-red kernels embedded like blemishes in yellow corn are caused by jumping genes.
Bears changed their own genes to find a way to live in the face of human threats. But that does not absolve humans of responsibility. The University of East Anglia team said, "This study offers hope for polar bears, but it does not mean the extinction risk has decreased," adding, "We must do everything we can to cut carbon emissions and slow the pace of warming."
References
Molecular Biology and Evolution (2025), DOI: https://doi.org/10.1093/molbev/msaf292
Mobile DNA (2025), DOI: https://doi.org/10.1186/s13100-025-00387-4
Science (2022), DOI: https://doi.org/10.1126/science.abk2793