0:02 Let's imagine you're lost in the
0:04 Antarctic Ocean and you make the mistake
0:06 of looking down into the water below
0:09 you. You might think all you'd see are
0:11 tiny fish or clouds of microscopic
0:13 plankton, but what you actually find is
0:16 much more terrifying. Spiders with leg
0:18 spans longer than dogs are crawling
0:20 around on the seafloor. Jellyfish with
0:22 tentacles longer than whales are slowly
0:24 drifting by. And even the most
0:26 normallooking fish are now just
0:29 abnormally gigantic.
0:32 And yes, these guys are all real. As the
0:34 freezing cold environment here has let
0:36 evolution just go completely off the
0:38 rails. This is the world of polar
0:41 gigantism. A phenomenon that most people
0:43 are totally unaware of because it only
0:45 happens in the coldest oceans on Earth.
0:47 And you'd think in [music] a place where
0:49 everything's freezing and there's barely
0:51 any food to survive that most animals
0:52 would get smaller and smaller to
0:54 conserve energy. But the complete
0:56 opposite happens. All animals in this
0:59 region turn into a sort of superersized
1:00 variant of themselves, [music] making
1:10 So why is this effect even happening in
1:12 the first place? To understand polar
1:14 gigantism, let's take a look at the most
1:16 blatant example of it, the colossal
1:19 squid. And I know what you're thinking
1:20 because most people think that the
1:22 colossal squid is a case of deep sea
1:25 gigantism, but it's actually not.
1:27 Colossal squids are found almost
1:29 exclusively in the ocean surrounding
1:31 Antarctica and swim in waters close to
1:35 or even less than 0° C. Because of the
1:37 salinity, the water won't actually
1:40 freeze at 0°. But regardless, this is
1:43 still insanely cold. And so, the squids
1:46 had to adapt. See, colossal squids are
1:47 actually a type of glass squid, [music]
1:49 which is a family named after a bunch of
1:52 translucent squids that look like, well,
1:54 glass. So, why do colossal squids look
1:57 like anything but a glass squid? Well,
2:00 this is the polar gigantism taking
2:01 effect. In an environment this cold,
2:04 [music] being see-through isn't that
2:06 useful. The colossal squid's body traded
2:09 transparency for thick flesh that's much
2:11 better for insulation, but it didn't
2:13 actually give up stealth either. Their
2:15 bodies have a reddish skin color which
2:17 will absorb any possible light from any
2:19 bioluminescent prey instead of
2:21 reflecting [music] it, which means
2:23 you'll never see it coming. When you're
2:25 this big, you don't really have any
2:27 predators besides the occasional sperm
2:29 whale. So, your body ends up being
2:32 designed for sneaking up rather than
2:34 sneaking away. But that still doesn't
2:36 answer why the colossal squids are this
2:38 huge in the first place. And the answer
2:40 isn't in the food down there, but
2:43 instead in the water itself. Cold water
2:45 holds way more oxygen than warm water
2:47 does. And for basically all animals, the
2:50 larger the body, the more oxygen their
2:52 cells need to just stay alive. In warm
2:54 waters, there just isn't enough oxygen
2:56 in the water to support super large
2:59 creatures. But when you live at 0°,
3:01 there's unlimited oxygen. And because
3:04 oxygen is everywhere, their limiter is
3:06 broken. Over millions of years, this
3:09 pushed the glass squids into giants, or
3:11 should I say colossals. And because they
3:14 then became so big, they literally left
3:16 behind their glassiness at the same
3:18 time. And since larger bodies are better
3:20 at storing heat and energy, evolution
3:22 literally forced these squids to get
3:25 bigger and bigger or die. But giant
3:27 squids don't live in the polar oceans.
3:30 So, how did they get so big? See, the
3:32 deep sea gigantism effect does have some
3:34 relevance here. And this is why giant
3:37 squids are so giant. Colossal squids, on
3:39 the other hand, live even deeper than
3:42 giant squids. So, the deep sea gigantism
3:44 also plays a bit of a role, but they
3:46 didn't get so big solely because of the
3:48 deep. And most of it is because of the
3:51 cold. Colossal squids are actually a
3:53 rare case of double crossover gigantism,
3:55 combining both polar and deep sea
3:58 gigantism into making one really big
4:00 creature. And this is likely why
4:02 colossals are the largest invertebraes
4:04 on Earth. And while not technically
4:06 longer than the giant squid, they are
4:09 much heavier, being over 1,000 lb, which
4:12 is double the weight of a giant squid.
4:13 But this is just one case of polar
4:16 gigantism. It doesn't necessarily prove
4:18 that cold [music] water is creating
4:20 giants. But take a look at this guy.
4:22 This is a normal sea spider that's found
4:24 in a coral reef. These guys aren't
4:26 actually real spiders since they're pink
4:28 nogginids, but these sea spiders are
4:31 about 1 to 2 cm across. This is about
4:33 the same size as your normal house
4:35 spider, but find this same animal in the
4:38 Antarctic Ocean, and it looks like this.
4:41 This spider is over 2 ft across and is
4:43 the exact same family as the other tiny
4:46 spider I just showed you. So, what's
4:48 going on here? Well, the exact same
4:50 rules that turned glass squids into
4:52 colossals have forced these spiders to
4:54 grow bigger. Cold water means more
4:56 oxygen, and these guys literally breathe
4:58 through their legs. You can already see
5:01 how freakishly long they are. So that
5:03 basically means a ton of oxygen is
5:05 coming in. But what can they do now that
5:07 they're so big? Well, unlike crabs or
5:09 lobsters, giant sea spiders aren't
5:12 brawlers, but they are predators. They
5:14 creep across the seafloor on those
5:16 massive legs, using them almost like
5:18 stilts to step over sponges, corals,
5:20 [music] and starfish. They then often
5:22 use their long proboscus like a straw,
5:24 piercing something like a starfish and
5:26 then sucking out its insides like a
5:29 milkshake. But again, this is the
5:31 Antarctic Ocean, so the starfish are
5:34 also ginormous. I know what you're
5:36 thinking. That barely looked like a
5:38 starfish, but this is a real starfish.
5:41 Just this one has over 50 arms instead
5:43 of the normal five. Antarctic starfish
5:46 are on another level of freaky because
5:48 they didn't just grow larger, but also
5:50 evolution literally started stacking on
5:52 as many arms as it felt like. Most
5:55 normal starfish are actually predators,
5:57 too, and will eat the insides of things
5:59 like clams. But Antarctic starfish are
6:01 so brutal, they'll literally eat other
6:04 starfish as well. Whoever has the most
6:07 arms wins, I guess. Antarctic starfish
6:09 can also live over 40 years on average,
6:11 which is way longer than the 5-year
6:14 lifespan that warm water starfish have.
6:17 And yes, this is polar gigantism at play
6:19 that forced these cute creatures to
6:21 develop into gigantic freaks. Funny
6:24 enough, the effect of polar gigantism is
6:26 so powerful that it's also created the
6:29 longest animal on Earth, the lion's mane
6:31 jellyfish. Compare this length to a blue
6:33 whale, and you can see the lion's mane
6:36 is notably longer. Of course, the blue
6:38 whale has more mass, but this still goes
6:40 to show the sheer scale of polar
6:42 gigantism because if you compare a
6:45 jellyfish in the same genus as a lion's
6:47 mane, like the blue jellyfish, you can
6:49 see just how much smaller they are. Blue
6:51 jellies live in warm water. And because
6:53 of that, we're never forced to become
6:56 massive. So, after seeing all these
6:58 oversized monsters of the deep, you're
7:00 probably wondering how high oxygen alone
7:02 could allow these things to go off the
7:04 rails. And while that is a large part of
7:06 the reason, it's not the [music] full answer.
7:08 answer.
7:10 Because the water is so cold, metabolism
7:13 also slows down massively. And so much
7:15 so that large bodies actually become
7:17 more efficient. They burn less energy
7:20 per raw animal mass. On top of this, the
7:23 cold ocean is actually extremely stable,
7:25 [music] which I know is weird because I
7:27 just showed you a bunch of the giant
7:28 monsters it has, [music] but the
7:30 temperature barely changes here. The
7:32 pressure is constant and predators are
7:34 rare. There's nothing forcing these
7:37 animals to stay small and fast. They can
7:39 afford to be massive, slow, and built
7:41 like tanks, exactly like how the
7:44 colossal squid developed its strategy.
7:46 But you're probably wondering, if the
7:48 cold makes things bigger, then a polar
7:50 bear is a case of polar gigantism
7:51 [music] since they're way bigger than
7:54 normal bears or penguins since, to be
7:56 fair, they're way larger than normal
7:59 birds. The thing is, polar gigantism
8:01 only works for cold-blooded animals,
8:02 which are creatures that let the
8:04 environment control their body
8:05 temperature and get their oxygen
8:07 directly from the water. For them,
8:10 colder water means more oxygen, slower
8:12 metabolism, and zero energy wasted on
8:14 generating heat. Warm-blooded animals,
8:16 though, are stuck with a different
8:18 problem. They have to burn energy
8:20 constantly just to stay warm, no matter
8:23 how cold the water or air gets. The
8:25 bigger they get, the more calories they
8:27 need. And in the polar region, there
8:28 simply isn't enough food to support
8:31 something that massive. Every extra
8:33 pound of body mass comes with a huge
8:35 metabolic cost. So even if they're not
8:38 necessarily gigantic, why are they still
8:40 big? This has to do with something
8:43 called Bergman's rule. Bergman rule says
8:45 that in all climates, warm-blooded
8:47 animals do get bigger, but not because
8:49 of oxygen. It's because larger bodies
8:52 lose heat slower. That's why polar bears
8:54 are way bigger than other bears. and
8:56 emperor penguins dwarf tropical birds.
8:58 The extra body mass helps them hold on
9:01 to warmth longer, like having a built-in
9:03 insulation. But there's a limit. Being
9:05 warm-blooded means you're constantly
9:07 burning energy to stay alive. So getting
9:10 too big becomes a massive liability. The
9:12 bigger you are, the more food you need,
9:14 and in the polar regions, food is
9:16 already scarce. This is the same reason
9:19 woolly mammoth got so big, but never
9:21 totally out of control. So, while
9:23 Bergman's rule gives you bog for warmth,
9:24 it never lets you go full [music]
9:27 colossal squid mode that polar gigantism
9:30 gives. On a much smaller scale, even
9:32 plankton have their colossal [music]
9:34 versions. Antarctic copods are basically
9:36 the polar's gigantism version of
9:38 plankton [music] and are nearly 10 times
9:40 heavier than tropical cop pods. For
9:43 reference, most copods are so small you
9:45 can barely see them without a microscope
9:47 [music] since they're usually not even a
9:49 millimeter. Antarctic coat pods can
9:51 reach up to a centimeter long, big
9:53 enough that you could actually see
9:55 swimming with the naked eye. This
9:57 obviously isn't really monstrous like
9:59 colossal squids are, but in the eyes of
10:01 plankton, these things are absolute
10:04 behemoths. But here's the weirdest part.
10:06 Not everything in the polar oceans got
10:08 the gigantism effect. A select few
10:10 animals actually got the complete
10:12 opposite from an effect called polar
10:15 dwarfism. While this is extremely rare
10:17 and the majority of animals got the
10:19 gigantism effect, some Antarctic fish
10:21 species like certain ice fish and snail
10:23 fish are noticeably smaller than their
10:25 relatives in warmer waters. In these
10:28 extreme environments, food isn't always
10:30 available year round. So, evolving a
10:32 smaller body means they can reach
10:34 adulthood faster, reproduce sooner, and
10:36 survive longer periods of scarcity. When
10:38 food is only available for a few months
10:40 out of the year, staying small can
10:42 literally be the difference between life
10:44 and death. And having a much faster
10:46 reproduction cycle will ensure your
10:49 species survived. Not really as sick as
10:51 turning into a giant sea monster, but
10:53 still an interesting way evolution made
10:56 them develop. But a weird side effect of
10:58 the cold is that it doesn't just change
11:00 what evolves. It changes how fast
11:02 evolution itself occurs. In the polar
11:05 ocean, everything runs in slow motion,
11:07 which means chemical reactions slow
11:09 along with metabolism and reproduction.
11:12 A single generation of some Antarctic
11:14 animals can take decades to complete
11:17 since, as I mentioned, even starfish are
11:19 now surviving decades instead of just a
11:21 few years. This makes evolution take
11:24 much longer, and it already takes
11:26 millions of years. Many of these species
11:28 are basically living fossils, almost
11:30 identical to their ancestors that swam
11:33 under the Antarctic ice tens of millions
11:36 of years ago. Some sea spiders, urchins,
11:39 and fish lineages have barely changed
11:41 since before humans even existed. With
11:43 no drastic seasons in the Antarctic,
11:45 species here have stayed practically
11:48 frozen in time for millions of years.
11:50 The environment barely changes, so
11:53 evolution never needed to either. Every
11:55 creature here is fine-tuned for a world
11:57 that's stable, predictable, and cold,
11:59 which has worked flawlessly for millions
12:02 of years, literally. But that stability
12:05 is exactly what makes the Antarctic so
12:07 fragile. When your entire ecosystem
12:09 depends on everything staying the same,
12:11 even a small shift can break it. The
12:13 moment the environment starts to change,
12:15 the rules that built these giants start
12:18 to collapse. Because being a super mega
12:20 frost giant sounds really awesome until
12:23 it suddenly isn't. Polar giants have one
12:25 massive weakness, and it's that they're
12:27 all built for stability, not change.
12:30 Their entire existence depends on water
12:32 that stays freezing, dense, and packed
12:35 with oxygen. Take that away, and the
12:37 whole system collapses. Warmer water
12:40 holds less oxygen, metabolism speeds up,
12:42 and suddenly those massive bodies
12:44 becoming a liability. The animals that
12:46 once ruled the frozen deep start
12:49 suffocating in their own size. Bring any
12:51 of these monsters into a fun, friendly
12:53 tropical ocean, and they will literally
12:55 die from the sunshine. This is already
12:58 happening, too. As the oceans warm,
13:00 oxygen levels are dropping fast, and the
13:02 creatures that evolve to thrive in the
13:04 cold are running out of room to survive.
13:06 Studies have shown that sea spider
13:08 maximum sizes are actually dropping in
13:10 areas where the water is getting
13:12 slightly warmer. And although they're
13:14 much harder to study, this means that
13:16 eventually colossal squids could become
13:19 uncalos or just die altogether. And
13:21 while I would never actually want to
13:23 encounter one of these giant monsters
13:25 face to face, it's kind of sad to think
13:27 about. These creatures are living relics
13:29 from a different world. And regardless,
13:31 they're basically zero threat to us
13:33 anyways. Total human deaths from
13:36 colossal squids is zero because no one's
13:39 ever been attacked by one. But anyways,
13:41 the effect that cold has on evolution is
13:42 perhaps one of the strangest and most
13:45 unexpected reasons for gigantism. Freeze
13:48 the ocean and life won't die. It just
13:51 gets giant. Thanks for watching and if
13:53 you want to see a video about the
13:55 world's deadliest jellyfish, check it
13:57 out here. The most dangerous one isn't
