This year in Japan, the number of people killed or injured by bear attacks set an all-time high. As climate change has reduced food sources such as beechnuts, bears have more frequently come down into residential areas. Warming caused by humans has come back as a boomerang in the form of 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 on by humans, they eliminated potential conflict by evolving genetically to reduce aggression in order to survive. Bears living in the Arctic changed their genes from carnivory to herbivory to survive. What have humans done to bears' genes?
◇ Reduced aggression as isolation began 2,000 years ago
Researchers in the Department of Life Sciences and Biotechnology at the University of Ferrara in Italy said in the international journal Molecular Biology and Evolution on the 15th (local time) that "bears living near villages in Italy have, over more than 2,000 years, undergone genetic changes that made them smaller and less aggressive, minimizing conflict with humans."
The team compared the genes of the Apennine brown bear (Ursus arctos marsicanus), found only in central Italy, with 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 has remained completely isolated since Roman times.
The isolation of Italy's brown bears was caused by humans. Andrea Benazzo, the corresponding author of the paper, said, "The decline and isolation of the Apennine brown bear population was likely due to the spread of agriculture in central Italy, which increased deforestation and population growth."
The researchers analyzed at the genetic level how bears on the brink of extinction survived. As expected, the isolated Apennine brown bears showed reduced genetic diversity and higher inbreeding rates than other European brown bears. Yet these changes actually helped the bears survive. The team said that, in the Apennine brown bears' evolutionary process, genes associated with reduced aggression were selected.
Humans both imperiled bears and enabled them to survive to this point. As humans encroached on habitats, the number of brown bears fell and their genetic diversity declined, raising the risk of extinction. But in that process, unintended genetic mutations reducing aggression appeared in bears. As a result, conflict with humans decreased, allowing them to survive, albeit in isolation.
Giorgio Bertorelle, a co-author of the paper, said, "Interactions with humans are mostly a threat to the survival of wildlife, but they can also promote the evolution of traits that reduce conflict." The team noted that, for this reason, care is needed to ensure such genetic variants are not diluted during population restoration. In other words, releasing bears into the wild to boost numbers should not lead to a resurgence of aggression and renewed conflict with humans.
◇ Arctic bears that switched to herbivory as seal hunting became difficult
Polar bears (Ursus maritimus) in Greenland have also had their genes altered by humans. A team led by Simone Immler, a professor in the School of Biological Sciences at the University of East Anglia (UEA), and Dr. Alice Godden said in the international journal Mobile DNA on the 12th (local time) that "polar bears in southeastern Greenland show genetic mutations that appear to be adaptations to warming."
Polar bears are the largest terrestrial carnivores and apex predators. 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 in the ocean—for seals to surface to breathe. However, as climate change rapidly reduces sea ice, hunting opportunities have plummeted. Godden predicted, "If current conditions persist, more than two-thirds of polar bears will disappear by 2050."
Earlier, scientists at the University of Washington discovered an isolated population of polar bears in southeastern Greenland and reported it in Science. These bears were less dependent on sea ice than those elsewhere. Southeastern Greenland is warmer than the northeast and has less sea ice. 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 genes different from those in the northeast for survival. 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.
Dr. Barbara McClintock first discovered jumping genes in corn and won the 1983 Nobel Prize in physiology or medicine. The scattered dark-red kernels like blemishes on yellow corn are due to jumping genes.
Bears have changed their own genes to find a way to live in the face of human threats. 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 their extinction risk has declined," adding, "We must do everything we can to reduce 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