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