ExtinctZoo - Why Animals Are White In The Arctic But Not In Antarctica

Episode Date: April 1, 2026

If convergent evolution has taught us anything, its that some designs work over and over again, which is why its a bit strange that two places, the Arctic and Antarctic that are both known for being endless cold, have animals that look very different, right?

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that sometimes it looks like they have an invisibility cloak on when standing in the snow. Then we have penguins who are fashionable, um, I mean, tuxedo-colored. In other words, white but also black, making their coat stick out quite a bit more. And yet, at the same time, both live in some of the coldest, most snow-and-ice-covered places on earth. But one animal looks like it would design to disappear into a snowstorm, while the other looks like it's perpetually on its way to a fancy dinner. So, what gives? How can two animals living what appears to be the exact same frozen hellscape, just in polar opposite ends of the world, no, pun intended, end up with completely different color choices. And the answer is that they're not actually living in the same environment at all,

not even close. And once you understand this, and why, the whole thing starts to make a lot more sense. Now, most people know the Arctic isn't a continent, hopefully, but what they might not know is that it's basically a frozen ocean with a broken ring of land around it. Eurasia, North America, Greenland, they all form this jagged necklace around a relatively shallow and less salient ocean that freezes over, creating walkways for anything with legs. In over thousands of years, wolves, Hairs, reindeer, musk oxen, and a whole bunch of other animals have simply walked through these ice bridges, making themselves at home at various places in the area. In simpler terms, the Arctic is basically a cold frozen ocean surrounded by land.

And Arctic, on the other hand, the complete opposite. It's an actual continent being a massive dome of rock and ice, which is completely surrounded by the southern ocean. And that ocean has been swirling around the continent for about 30-ish million years thanks to the circumpolar current, which form in the Drake Passage and Tasmanian Passage opened up. And this is important because the current essentially acts like a biological moat, resulting there being no land mammals for a very, very long time, as there simply is no way to cross. Well, at least if you want to stay alive, that is.

And so the south is a frozen island in the middle of an ocean fortress, unlike the Arctic, which is again a frozen ocean, surrounded by land. Opposites. And if that wasn't enough of a difference, there's also the whole altitude situation. The Arctic Ocean sits at sea level because, well, you know, it's an ocean. While Antarctic, on the other hand, is a high plateau, with the average elevation, you know, should be in 2,500 meters or 8,000 feet, with some parts of the area reaching more than 4,000 meters or 13,000 feet above sea level. And so the air is thinner, drier, and the wind can

scream across that plateau at over 100 miles per hour, or 160 kilometers an hour, with temperatures diving below negative 60 degrees Celsius or minus 76 degrees Fahrenheit in winter in certain areas. So when we talk about the poles, we're talking about two completely different types of places with two completely different types of cold. And so when you consider all of this, the costume choices start making sense, because color in animals is almost never about looking pretty. Well, sometimes it is, looking at you peacocks, but usually it's more about eating without being eaten. And so, in the Arctic, where temperatures are a bit more livable and accessible, you've got quite a bit more diverse when it comes to life. And with diversity, it also means more opportunity and threats.

So if a hare is not trying to become lunch for an owl, or if an owl doesn't want its chicks to be eaten by a fox, blending into the background is literally life or death, a get food or a bee food kind of situation. And biologists call this phenomena background matching, which is a type of camouflage. Shocking, I know. And a snow-covered landscape is the ultimate canvas for background matching. And so predators and prey in the north have evolved to either vanish into it or see through the disguise of those trying to vanish, usually both. But in the water, the optical environment flips completely.

Light scatters, predators can attack everything from above, below, or the side, and there's no true fixed background because everything moves. And therefore, the best way to disappear into a column of water is to erase your outline, which usually in this case means darkening your back to match the abyss below, enlightening your belly to match the glowing surface above. And this two-tone paint job is called countershading. And fun fact, it was actually described over a century ago by a painter of all things, which is quite fitting.

And this shading choice is a fan favorite being used by a plethora of different marine creatures, penguins, orcas, sharks, and more. They all use the same general principle. So background matching solved the problem of disappearing on a white field of snow, while countershading solves the problem of vanishing into the deep blue. And because the denizens of the Arctic stick mostly to land, and residents of Antarctica, mostly to the ocean, the default palette at each pole is completely different. But here's where things get switched up of it.

You see, more than 20 species in the Northern Hemisphere undergo what's basically a biannual wardrobe change. Arctic foxes, snowshoe hairs, stouts, willow termigans, and more, all swap their winter whites for a different colored summer sweater, and then back again. And that makes sense, seeing that being fully white in the summer, in other words, when the snow is already melted, is not the greatest of ideas. And so this begs the question of, is this change actually related to the snow itself? Like, does the animal see the snow falling and think,

Oh yes, time to change my clothes. I've heard white is in fashion now. No, no they don't. What's actually happening is that their bodies run on an internal calendar that measures day length, or rather the amount of light within a day, something which is called photoperiod. And so as autumn days get shorter, photoreceptors in the retina feed information to the body, which, depending on the animal, will trigger downstream effects of different hormones that ultimately affect coat color, density, shedding, etc. For example, in canids, the change of photoperiod

triggers the pinail gland to change its output of melatonin, which in turn inhibits the production of prolactin, and thus leading to the production of white winter fur. So when prolactin levels dip in autumn, the pigments that make a hair summer coat brown basically shut down. So as the animal molds, the new fur that grows in is non-pigmented. And then when spring returns and days get longer, the switch lifts back and melanin pumps back into the follicles, and thus the browns and grays return, which are much more fitting when their environment returns, well, to said browns and grays, instead of pure white. And for tens of thousands of years, this system has worked perfectly. The rhythm of light and darkness match the rhythm of snow arriving. But needless to say,

our arch nemesis, climate change, has thrown a wrench into that elegantly simple arrangement. As unfortunately now, winter now arrives later and melts earlier in many northern regions, leaving white animals stranded against brown or gray background. In a study of snowshoe hairs have found that increased mismatches of fertile environment, meaning wearing white on bare ground or brown on snow, leads to significantly lower survival rates, with survival rate each week decreasing by up to 12% for when they don't have the proper coat. And that's each week that is. The silver lining, if you can call it that, is that natural selection will push hairs to adjust.

Individuals whose molt timing better match the snow should have higher reproductive success, simply by the precedent of actually surviving. The question is, though, can they adapt fast enough? Now, interestingly, not all animals follow this simple white, then brownish flip-flop scheme. For instance, about 1% of Arctic foxes belong to what biologists call the Blue Morph, which is that instead of bleaching to white in winter, these animals stay smoky charcoal or bluish gray color year-round. And the reason why it comes down to a tweak of a single gene called MC1R. Wireless can feel like a world of traps, but not with visible.

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Known as the Melodicortin 1 receptor. And so two amino acid substitutions change how it functions and prevent the shutdown of melanin production in winter. And because the trait is dominant, a fox only needs one, copy of the quote unquote blue allele to keep its dark coat. And this is especially intriguing as it almost acts like niche partitioning within the same species, as blue morphs have found to be more common on rocky coasts, where snow cover is patchy and the backdrop is modeled rather than pristine white. This also means that while dark fox trotting over snow might look like a target, it never has to endure the opposite problem of looking like a ghost on bare ground. And who knows? As the Arctic warms and

snow arrives later and melts earlier, the relative advantage of staying dark may grow, thus spurring on increases in the blue morph. But as always, natural selection will balance the cost and benefits depending on local conditions. Now at this point, I do have to be honest with you guys. There is one thing I fail to mention, which is that Arctic animals don't actually have white fur, rather it just appears white to us. Take the polar bear, for example. Under a microscope, each long guard hair is actually clear, not white, and has a hollow core. And so when sunlight hits those transparent fibers, structures and the hair scatter light in all directions, something physicists call me scattering, which makes the hair look white without actually having a white pigment.

So, yeah, the bear isn't white. It just looks white because of how light bounced around inside and off its fur. Funny enough, underneath all that optical trickery, the polar bear's skin is dark, near Jet Black, being packed with e-melanin, the same pigment that the hair and fox used to change their fur back to brown. And another fun fact is that there has never been a confirmed albino polar bear, as far as I can find, despite it looking somewhat albino to begin with.

And as I hinted at, what we call their fur is actually, two layers of fur, a dense undercoat, and then longer guard hairs, which all covers up to 10 centimeters or four inches of fat around their body. And this all leads to insulation so good that adult polar bears actually overheat more easily than they get cold, despite again living in one of the coldest places on earth. In a warm days, they'll sprawl out on the ice to cool down or just take a dip in the freezing cold water. Obviously though, unlike the others we talked about, polar bears, despite being an arctic mammal, do not change their fur color. And that's a reflection that generally speaking the polar bear prefers being on the sea ice rather than land for as long as it's

available. And unfortunately, that availability is now changing due to declining sea ice coverage. And I have to emphasize this unfortunate part because not only is the environment they're made for changing, but more and more polar bears and their cubs are dying in the journey across the Arctic, looking for the sea ice, drowning at sea or suffering from eventual starvation or weakening due to the prolonged journey to find said ice. With a 2016 study projecting decline in population over 30% in three generations, with another study concluding that polar bears may become regionally extinct by 2050 if trends continue. So, not good. On a somewhat happier note, we have the unit that is the musk fox, a shaggy little big guy that looks like they stepped

straight out of the Pleistocene, and in a sense they did, as they're basically relics of a world of mammoths and saber-toothed cats. But unlike its Ice Age brethren and the polar bear, they are doing just fine, being classified under least concern by the IUCN. And as opposed to, well, a lot of other arctic animals, musk oxen are not white and are in fact similar to the polar bear, but just in an opposite way, meaning they don't bother changing color at all. Instead, their dark coats stay dark, with them having long outer guard hairs that hang like a curtain almost to the ground, and then a soft insulating inner coat called Kivuut, which is not only stronger and warmer than sheep's wool, but also softer than Kashmir.

But anyways, now that we've established what the arctic animals look like, or generally look like, let's slip the map upside down and look at the south. And as mentioned before, the animals that dominate Antarctica are mostly marine. And guess what? Their colors reflect that. For instance, Emperor Penguins, Tuxedo, black jacket, white shirt. And when in the water, if you look at them from above, their backs blend with the dark ocean. But if you're below them, their bellies merge with a bright surface.

Class of countershading. But that might not be the only reason here. As for anyone who seen happy feet, you know that emperer penguins endure the Antarctic winter by huddling tightly together, as males incubate their eggs with their feet under folds of skin, which, for nearly two months that is, without feeding, while the females are off at sea getting some milk in six, i.e. fish. In understandably, when you're standing on the coldest place on earth trying to heat up an egg, warmth is pretty important. And that's where their tuxedo might have a second use. And I say might because this is somewhat disputed, but the idea is that

by positioning their back towards the winter sun, the black portion of the plumage absorbed more solar radiation than the white side, and thus warming them up. Contrary to that is that the plumage is so dense that the heat on the black feathers is not even able to reach the skin. So, the verdict's still out there. But regardless, the tuxedo is in fashion. And it's not just the emperor penguin who finds a tuxedo fashionable. King, Adelae, chin strap, and gentu penguins all follow the same basic pattern, but with tweaks for their particular stylistic choices.

For example, chin strap penguins of a distinctive black line under their chins, hence chinstrap, well, Gantos of white bonnet patches. So, very fashionable bunch. Now, unlike the Arctic, and the end. Antarctica does not have any permanent terrestrial vertebrates that we can use for pure comparisons. However, it does share a group of mammals that do enjoy the solid ground occasionally in both areas. Seals. But what's interesting about this group is that even seals follow the Arctic and Antarctic differences in a sense.

For instance, leopard seals, the biggest true Antarctica resident and formidable predators in their own right, are darker on the top side and of a pale belly on the underside, once again to blend the shifting water column. Now, seals that live near Santa Claus are numerous, and we can't really give a blanket description on their coloring. But interestingly, seal pups, which live on land if they're old enough, have found out significant differences in colors depending on where they live, with seal pups that are purely white generally being found in Arctic seals, not Antarctic, which is not too surprising considering the largest fully terrestrial animal in the Antarctic is an insect, while the Arctic instead houses

the largest terrestrial carnivore, period, who would be all too happy to turn you into a tasty snack. And studies do back this up, with one study from 2012, reporting strong evidence that seal pups have white pellage in the Arctic regions due to them being subject to more terrestrial predation. On the flip side, pups that have more darkish colorations are found in species without as many terrestrial predators. So, generally, arctic animals are more white and Antarctic animals are more fashion-oriented. But of course, like any good rule, there are exceptions. Take the snow petrel, the small Antarctic seabird that is as pure white as any arctic animal. And then in addition, crab-eater seals, which are found in Antarctica, do actually develop a blondeish white coat, which then switches back to dark later on. But interestingly enough, that happens in the summer, not in the winter.

Yet regardless, at the end of the day, it comes down to this. The Arctic is a frozen ocean framed by land and populated by animals that evolved under the gaze of predators and prey on snow. And so in that world, survival means turning off the pigmented winter to blend in. Antarctica, on the other hand, is a continent surrounded by water and dominated by creatures for whom the ocean is, Numero uno. And so erasing a silhouette than a column of water is infinitely more important than blending in the snow or predation risk on land is much less common. So the next time you see a polar bear, because you know they're just so common to see, don't forget to give it pity that nature couldn't have deigned to give it a bit more drip. Thanks for watching,

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