Somewhere along the evolutionary line that split polar bears from brown bears, a gene called APOB picked up mutations that changed how the animals clear cholesterol from their blood. That single shift helped make possible a life built almost entirely on seal blubber, and it is one of dozens of genetic changes researchers have now mapped across the polar bear genome. Taken together, the findings show that the species underwent intense natural selection on the systems that manage fat, blood flow, and body heat. The pressing question, as Arctic sea ice shrinks roughly 13 percent per decade according to the National Snow and Ice Data Center, is whether those deep adaptations can buffer an animal whose hunting platform is disappearing beneath it.
Genetic evidence built over a decade
The most detailed picture comes from a 2014 population genomics analysis published in Cell that compared whole genomes of polar bears and brown bears. Now more than a decade old, the study remains the most comprehensive genomic comparison of the two species published to date. The team, led by Shiping Liu, found strong signatures of positive selection concentrated in lipid metabolism and cardiovascular pathways, with APOB as a standout target. “Polar bears have undergone a remarkable genetic transformation in a very short evolutionary time,” Liu and colleagues wrote, noting that the changes clustered in genes central to cholesterol transport and cardiac function. APOB encodes a protein that packages and transports cholesterol, a function that matters enormously for a predator whose meals are dominated by the blubber of ringed and bearded seals. The same study flagged heart development genes as another category under active selection, suggesting the bears’ circulatory systems were reshaped in tandem with their ability to process fat.
A parallel 2014 paper in Genome Biology and Evolution, also among the most thorough genomic analyses of polar bear adaptation available, confirmed that polar bears carry genome-wide signatures of bioenergetic adaptation. That work, led by Andrea Welch, zeroed in on mitochondrial and nuclear gene interactions governing cellular respiration and heat generation, offering a molecular explanation for how a 450-kilogram mammal maintains core body temperature on wind-blasted sea ice. Welch and colleagues described the pattern as evidence that “the polar bear lineage has experienced selection on genes involved in the electron transport chain,” linking dietary fat processing to the metabolic furnace that keeps the animals warm. The bioenergetic findings dovetail with the Cell paper: the same dietary fats that demand specialized cholesterol processing also fuel the heat production that sustains polar bears in extreme cold.
Adaptation was not limited to single-letter changes in DNA. A 2019 study in the Proceedings of the National Academy of Sciences documented gene copy-number variation linked to the high-fat seal diet. Entire segments of DNA were duplicated or deleted as polar bears diverged from brown bears, and those structural differences clustered in regions showing signs of recent positive selection, not random genetic drift.
A follow-on analysis in Scientific Reports explored where the raw material for these changes originated. The researchers reported that selection acted on both standing genetic variation, diversity already present in the ancestral population before the species split, and on mutations that arose afterward. That mix matters: populations that can recruit pre-existing variants tend to adapt faster than those waiting for new mutations to appear, which may help explain how polar bears specialized so rapidly despite a relatively recent divergence from brown bears, estimated at roughly 500,000 years ago.
A subpopulation surviving without sea ice
In 2022, a NASA-funded survey published in Science revealed a previously unknown subpopulation of polar bears in Southeast Greenland. These bears live in a region where sea ice is available for only about 100 days a year, far less than most polar bear habitat. Instead of following the retreating ice edge, they hunt from freshwater glacial ice that calves into steep fjords.
The discovery drew wide attention, including coverage in Nature, because it demonstrated that at least some bears have found a behavioral workaround for habitat loss. But the scientists behind the study were careful to temper expectations. Lead author Kristin Laidre noted that the glacial fjords are geographically boxed in by mountains and fast currents, the population is small, and the habitat type is rare even within Greenland. As of June 2026, no researcher involved has described it as a climate refuge for the species at large.
What the data do not yet show
No published study has connected specific mutations, including APOB variants or mitochondrial changes, to measured hunting success or thermoregulation in free-ranging bears. The genomic signatures are statistical inferences drawn from comparing populations; they reveal which genes appear to be under selection, not how individual animals perform differently because of those genes. Closing that gap would require pairing genetic sampling with field measurements of metabolic rate, kill success, and body condition across bears carrying different alleles.
The Southeast Greenland group adds another open question. No paired genomic sampling has been published to determine whether the same lipid and cardiovascular loci flagged in broader studies are under selection in this specific subpopulation. Without that data, it is unclear whether their survival reflects genetic adaptation, behavioral flexibility, or the fortunate geography of glacial fjords.
Recent work on transposon activity, sometimes called “jumping genes,” has found differences among Greenland polar bear subpopulations living in distinct climate zones. Transposons can reshape gene regulation and generate new variation, but the study relied on limited samples and lacked longitudinal tracking of whether those differences translate into survival or reproductive advantages. The findings hint at another mechanism of genetic change without yet proving functional consequences.
Copy-number variation results, while well documented between polar and brown bears, were generated using older genome assemblies. No whole-genome resequencing of the Southeast Greenland bears has been published to test whether the same structural variants appear there or whether new ones have emerged in response to recent ice loss.
Specialists on a shrinking stage
The genomic studies converge on a clear narrative: polar bears are the product of intense selection on fat processing, cardiovascular function, and energy balance. The Cell paper, the Genome Biology and Evolution analysis, and the PNAS copy-number work each provide independent lines of evidence pointing at the same biological systems. That convergence is compelling. But it mainly describes how polar bears adapted to the historical Arctic over thousands of years, not how they are adapting right now to an ice platform that is vanishing within decades.
With a global population estimated at roughly 22,000 to 31,000 and an IUCN status of Vulnerable, polar bears face a mismatch between the pace of environmental change and the pace of evolution. The traits that made them supreme Arctic predators, a metabolism tuned to seal fat, a body built to conserve heat, a life cycle timed to sea-ice formation, are the same traits that make them vulnerable when that niche erodes. Evolution built a specialist, and specialists rarely pivot quickly.
To move from inference to prediction, researchers need finer-grained data: repeated sampling of known individuals, high-quality genome assemblies for multiple subpopulations, and long-term monitoring that tracks survival, reproduction, and movement alongside genetic change. Only then will it be possible to judge whether the subtle shifts now detectable in polar bear DNA represent the opening moves of a new adaptive response or the lingering imprint of an Arctic that is already slipping away.
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*This article was researched with the help of AI, with human editors creating the final content.
