The Western Hudson Bay polar bears are the most studied polar bear population in the Arctic. They are also the ones that have been most extensively filmed, photographed and marveled at, thanks to the tourism industry that has developed around the bears in Churchill, Manitoba, Canada.
Symbols of courage, resilience and strength, polar bears have been featured in decorative arts for centuries. Today, they may be best known as emblems of climate change, “charismatic victims” used to inspire people to care about our warming Earth. But not only does Ursus maritimus persist in our consciousness, polar bears—the largest bear on the planet—continue to astound us with their creativity, intelligence, patience and physiology.
For example, a recent analysis of ancient DNA from a 100,000-year-old polar bear has revealed that extensive hybridization between polar bears and brown bears occurred during the last warm interglacial period in the Pleistocene, leaving a surprising amount of polar bear ancestry in the genomes of all living brown bears today.
In another new finding, the secret to how polar bears manage to survive and thrive in one of the world’s most punishing climates comes to light: greasy hair.
A polar bear’s skull can teach us about the adaptations that help polar bears survive in the harsh Arctic environment and how the animals have evolved over time. ©Klaus Rassinger und Gerhard Cammerer, Museum Wiesbaden, Wikimedia Commons
Ancient hybridization with brown bears
Although polar bears and brown bears are distinct species with striking differences in appearance, behavior and habitats, they are closely related and can readily hybridize when their ranges overlap. Reports of hybrids have increased in recent years as the climate warms and disappearing sea ice forces polar bears onto Arctic coasts, while brown bears expand their range northward.
Previous studies of ancient DNA have shown that admixture has occurred in certain populations of brown bears at least four different times between about 15,000 and 25,000 years ago. In all cases, the direction of gene flow was from polar bears into brown bears. These mixed individuals, if they survived, did so as brown bears; perhaps because they would have had difficulty hunting successfully on the sea ice if they were not completely white. Polar bears have always been a small population with not much genetic diversity.
In 2009, the skull of a juvenile polar bear—nicknamed “Bruno” (although DNA analysis later showed it to be female)—was found on the coast of the Beaufort Sea in Arctic Alaska. An analysis by scientists from the University of California, Santa Cruz, established that Bruno belonged to a polar bear population that was ancestral to living polar bears. Finding Bruno’s skull was serendipitous. Since polar bears spend most of their lives at sea, coming across any polar bear remains is extremely unusual. Bruno’s is the only ancient polar bear skull that’s ever been recorded—and the only ancient polar bear bone known from North America.
Polar bear ancestry accounts for as much as 10% of the genomes of brown bears living today, indicating that ancient hybridization between the two species occurred, with gene flow primarily moving from polar bears to brown bears.
At some point, probably around 125,000 years ago, the polar bear lineage leading to Bruno and the brown bear lineage leading to all living brown bears crossed paths and hybridized. As a result of accessibility to Bruno’s paleogenome, the California researchers learned that polar bear ancestry accounts for as much as 10% of the genomes of brown bears living today. Their results were published in June 2022 in the journal Nature Ecology & Evolution.
This study did find some evidence of possible gene flow from brown bears into Bruno’s lineage, but the absence of admixture in polar bears today supports the idea that brown bear ancestry reduces a bear’s fitness for life as a polar bear. After diverging from brown bears about 500,000 years ago, polar bears evolved into highly specialized hunters of marine mammals on the Arctic sea ice. Brown bears, in contrast, are generalists ranging widely across Asia, Europe and North America.
Climatic shifts that have brought polar bears and brown bears together in the past include glacial periods when sea ice was more extensive, allowing polar bears to mix with brown bears in southeast Alaska, the Kuril Islands in the Russian Far East and even Ireland. The brown bears in these locations (now extinct in Ireland) acquired additional polar bear genes on top of the ancient admixture revealed by Bruno’s genome. As for what brown bears might have gained from their polar bear ancestry, scientists can only speculate. It’s possible that brown bears got something cool from polar bears, but no one knows for sure—yet.
Unlike polar bears that are highly specialized hunters of marine mammals on the Arctic sea ice, brown bears are generalists that range widely across Asia, Europe and North America. This bear is munching on blueberries.
Bruno lived during a time of changing climate after the peak of a warm interglacial period when temperatures and sea levels were considerably higher than they are now. Similar conditions can be expected in the future because of rapid climate change, driven by the burning of fossil fuels and other human activities. As Arctic sea ice declines, many polar bear populations are already struggling to survive. If the rapid, unnatural and severe human-caused warming of the Arctic we are documenting today continues unabated, it is uncertain whether polar bears will have a sea-ice habitat to return to and survive genetically, say the scientists.
However, we shouldn’t be surprised to see gene flow occurring between what we think of as different species happening again today as the climate changes and brown bears and polar bears overlap and encounter each other again in the wild. Understanding how past changes in the climate drove interactions between organisms is critical to predicting how current changes will create new admixtures, increase disease transmission, or impact natural resources or society, conclude the scientists.
Fur with anti-icing properties
After some “polar sleuthing,” which involved scrutiny of hair collected from six polar bears in the wild, scientists from Trinity College Dublin’s School of Chemistry and AMBER Research Center in Ireland and the University of Bergen in Norway found that hair sebum (or grease)—which is made up of cholesterol, diacylglycerols and fatty acids—makes it very hard for ice to attach to polar bears’ fur. These findings were published in the international journal Science Advances in January 2025.
Sebum, fatty lubricant matter secreted by sebaceous glands of the skin, found in polar bear fur is the key component that gives the bears their anti-icing properties, which come in handy when hunting seals on ice platforms.
To conduct this study, the researchers measured ice adhesion strength, which is a useful measure of how well ice sticks to fur; hydrophobicity, which dictates whether water can be shed before it freezes; and freezing delay time, which simply shows how long it takes for a drop of water to freeze at certain temperatures on a given surface. They then compared the performance of the polar bear hair with that of human hair and two types of specialist, human-made “ski skins.”
The sebum quickly jumped out as being the key component giving the anti-icing effect, since the adhesion strength was greatly impacted when the hair was washed. When washed and the grease largely removed from it, polar bear hair performed similarly to human hair, to which ice sticks easily whether it is washed or greasy. In contrast, unwashed, greasy polar bear hair made it much harder for ice to stick.
That finding led the team to perform a detailed chemical analysis of polar bear sebum. As well as identifying its key components, the scientists were surprised to find squalene was absent. This fatty metabolite is present in human hair and in the hair of other aquatic animals, such as sea otters, which suggests its absence in polar bear hair is very important from an anti-icing perspective.
Despite spending extensive periods in water at subzero temperatures, polar bears don’t suffer from ice accumulation. Their “fur grease” provides a natural route for easily shedding ice.
This work not only represents the first study of the composition of polar bear fur sebum, but it also resolves the question of why polar bears don’t suffer from ice accumulation. Despite having thick layers of insulating blubber and fur and spending extensive periods in water at subzero temperatures, polar bears have a natural route in their fur for easily shedding ice when it forms.
These natural lipid coatings produced by polar bears will help us develop new, more sustainable, anti-icing coatings that may replace problematic forever chemicals, such as PFAS, that have been previously used. They may also have a suite of unrelated applications, with a similar concoction of artificially-made sebum promising to be useful as an anti-ice surface coating or in next-gen ski skins used by skiers and snowboarders.
This isn’t the first time that animals living in polar habitats have emerged as a source of inspiration for the development of new anti-icing materials. For example, it was recently discovered that the hierarchical structure of Gentoo penguin feathers gives the birds anti-icing properties.
The hierarchical structure of Gentoo penguin feathers afford the birds anti-icing properties that rely on feather structure rather than on a preening oil coating.
These interesting discoveries also help us better understand the ecology of both polar bears and native Inuit populations. One of the polar bear’s main hunting strategies is “still hunting,” where the animal remains motionless beside a breathing hole on sea ice waiting for seals to surface. Still hunting frequently develops into an “aquatic stalk,” with the polar bear using its hind paws to slide into the water to pursue its prey; and the lower the ice adhesion, the less noise generated and the faster and quieter the slide.
Inuit people optimize their hunting strategies to mimic the polar bear method of still hunting. Inuit hunting stools are sometimes shod with polar bear fur on the feet to avoid noise when moving on the ice. And people sometimes wear “polar bear trousers,” ensuring the entire contact area with the ice is covered in low-ice-adhesion polar bear fur for optimal noise reduction.
Notably, the traditional Inuit preparation method protects the sebum on the fur by ensuring the hair-covered side of the skin is not washed. This is unlike, for example, a fox skin, which would traditionally be cleaned by rubbing the hair side with soapstone or dry clay.
Inuit people model their hunting strategies on the polar bear method of “still hunting.” They sometimes wear trousers made from polar bear fur, ensuring that their contact area with the ice is covered in a low-ice-adhesion material that is also optimal for noise reduction.
Polar bear population declines due to “energy deficit”
Unfortunately, such fun and informative discoveries about polar bears may not go on forever. In another January 2025 study, this time published in the journal Science, researchers from the University of Toronto Scarborough developed a model that demonstrates that population decline in polar bears is the result of the bears not getting enough energy, and that’s due to a lack of food caused by shorter hunting seasons on dwindling sea ice. A loss of sea ice means bears spend less time hunting seals and more time fasting on land, which negatively affects the bears’ energy balance, leading to reduced reproduction and cub survival and, ultimately, population decline.
The “bio-energetic” model developed by the researchers tracks the amount of energy the bears are currently getting from hunting seals and the amount of energy they need to grow and reproduce. What’s unique about the model is that it follows the full life cycle of individual polar bears—from cub to adulthood—and compares it to four decades of monitoring data from the Western Hudson Bay polar bear population between 1979 and 2021. During this period, the polar bear population in this region has declined by nearly 50%. The monitoring data shows that the average size of polar bears is also in decline. The body mass of adult females has dropped by 86 pounds and that of one-year-old cubs by 47 pounds over a 37-year period.
The researchers’ model provides a close match to the monitoring data, meaning it provides an accurate assessment of what is happening and will continue to happen to the polar bear population if it keeps experiencing sea-ice loss and a greater amount of time in energy deficit. The model, however, goes one step further than saying there’s a correlation between declining sea ice and population decline. It provides a mechanism that shows what happens when there is less ice, less feeding time and less energy overall. When the numbers are run, there’s a near one-to-one match to what’s seen in real life.
Polar bear cubs face the brunt of climate-induced challenges. Shorter hunting periods cause mothers to produce less milk, which jeopardizes their young ones’ survival. Mothers now are also having fewer cubs.
Sadly, cubs face the brunt of these climate-induced challenges. Shorter hunting periods result in mothers producing less milk, which jeopardizes cub survival. The cubs face reduced survival rates during their first fasting period if they fail to gain enough weight.
Mothers are also having fewer cubs. Monitoring data shows cub litter sizes have dropped 11% compared to almost 40 years ago, and mothers are keeping their cubs longer because they aren’t strong enough to live on their own. And, simply put, the survival of cubs directly impacts the survival of the population.
Western Hudson Bay has long been considered a bellwether for polar bear populations globally; and as the Arctic warms at a rate four times faster than the global average, the researchers warn of similar declines in other polar bear populations. This model basically describes their future, they say.
Many Inuit hunters consider polar bears to be the most intelligent animal in the Arctic. For the rest of us, polar bears represent courage, resilience and strength. The saying is trite but true: polar bears are on thin ice. Let’s not lose them on our watch.
Polar bear proficiencies and product ideas
An Arctic icon, polar bears have also played roles in art, conservation and politics. We’re lucky to have them still among us. Bruno’s ancient skull has given us insights not only into present-day polar bear physiology but that of all living brown bears. And today’s polar bears have provided inspiration for the creation of new products for anti-icing and better traction on ice and snow.
But the warming of the Earth that our activities have caused could spell the end for polar bears. Let’s not lose them now—on our watch.
Here’s to finding your true places and natural habitats,
Candy
