0:03 Evolution has made crabs five times. Not
0:06 five species of crabs, but five separate
0:07 times. It has turned completely
0:10 different animals into crabs. Like a
0:11 lobster looking thing evolves for
0:14 millions of years and boom, crap. Then a
0:16 different lobster looking thing that is
0:18 totally unrelated does its own thing for
0:21 millions of years and boom, also a crab.
0:24 This keeps happening. Scientists call it
0:26 carcinization, which is just a fancy way
0:29 of saying nature won't stop making
0:32 crabs. And the weirdest part, we don't
0:34 exactly know why. We have guesses, sure,
0:36 but the fact that evolution keeps
0:39 hitting the crab button over and over
0:41 suggests something about being a crab is
0:44 just superior. Crab supremacy. Are they
0:46 better than us? We're going to find out.
0:47 So, we need to talk about what's going
0:50 on here because this whole situation is
0:51 honestly pretty bizarre. And by looking
0:54 into this, I am now afraid that humans
0:56 might turn into crabs. So what is going
0:59 on? So basically carsonization means the
1:02 process of turning into a crab, which is
1:04 already kind of funny because most
1:06 scientific terms describe something that
1:08 happens once, maybe twice. This one
1:10 describes something that keeps happening
1:12 [music] over and over, which should tell
1:14 you something right there. Here's what
1:17 carcinization actually looks like. You
1:19 start with some kind of longbodied
1:21 creature. Maybe it looks sort of
1:24 shrimpish or maybe sort of lobster-ish.
1:26 It's got a long body and a big tail that
1:28 sticks out behind it. Then over millions
1:31 of years, that body gets flatter, wider,
1:33 and the tail shrinks and folds up
1:34 underneath. Suddenly, you've got
1:36 something that looks a whole lot like a
1:39 crab. Flat shell, tucked tail, and walks
1:41 around on these spled out legs. The
1:43 thing is, this isn't just happening to
1:45 one group of animals. It's happening to
1:47 completely separate groups throughout
1:49 prehistory. That's what makes it weird
1:51 because usually when you see the same
1:54 body shape evolve multiple times, it's
1:56 in really different animals. You know,
1:58 birds have wings, bats have wings, but
2:01 nobody's confused about whether a bat is
2:02 a bird. They're obviously doing
2:05 different things. But with crabs, you've
2:07 got animals in the same family doing
2:09 this, crustaceians, and they keep
2:11 landing on the exact same design.
2:13 Scientists actually have specific
2:15 criteria for what counts as being
2:17 carcinized. Your shell has to be flatter
2:19 than it is long. You need these distinct
2:22 edges on the sides. And your underside
2:24 has to be this broad fused plate. And
2:26 your abdomen, that's your tail part. It
2:29 has to fold completely under your body.
2:31 So you can't even see it from above. If
2:33 you picture a crab, that's exactly what
2:35 you're seeing. No tail hanging out, just
2:37 this discshaped body with legs. Now,
2:39 here's where this gets interesting. [music]
2:40 [music]
2:43 Not every crab is actually a crab. Yes,
2:45 this has been a crab conspiracy from big
2:47 crab government. They don't want you to
2:49 know that not every crab is actually a
2:51 crab. So, you got to hit the like and
2:52 subscribe button right now to stay
2:54 informed against the rebel crab
2:56 government. See, there are true crabs,
2:59 which scientists call brakura. And then
3:00 there are false crabs. And false crabs
3:02 aren't false because they're lying or
3:04 anything, but they're false because they
3:06 evolved the crab look, but they're not
3:08 in the true crab family. They're in this
3:10 other group called the anomeura. So
3:12 you've got hermit crabs, king crabs,
3:14 porcelain crabs, all these things that
3:16 look like crabs but technically aren't.
3:18 And both groups did [music] this
3:20 independently. True crabs evolved from
3:22 some non crab ancestor. False crabs
3:24 evolved from some other non crab
3:26 ancestor separately, which means the
3:29 crab body plan is so effective that
3:31 evolution found it at least twice just
3:33 between these two groups. And that's not
3:35 even counting all the times it happened
3:37 within each group. You can actually tell
3:39 true crabs and false crabs apart pretty
3:41 easily if you know what to look for.
3:43 True crabs have four pairs of walking
3:45 legs that you can see. False crabs look
3:47 like they only have three pairs because
3:49 that fourth pair is tiny or hidden
3:51 somewhere. But both of them have that
3:54 same general vibe. Flat, wide, hard
3:56 shell, no visible tail. Because it's a
3:58 really clear example of something called
4:00 convergent evolution. That's when
4:02 different animals evolve the same
4:03 solution to the same [music] problem.
4:05 Except usually conversion evolution
4:08 happens across really different groups.
4:09 But this is all happening with
4:11 crustaceans, which is much weirder cuz
4:13 it means there's something about that
4:15 crab shape specifically that keeps
4:17 working. Something about having a flat
4:20 body and a tucked tail solves problems
4:23 that long body crustaceians run into.
4:25 And look, evolution doesn't have a goal.
4:27 It's not sitting over there going,
4:29 "Let's make crabs." Or maybe it is. We
4:31 should be scared. It's just random
4:33 mutations and the ones that help you
4:35 survive stick around. But when you see
4:36 the same thing happen five separate
4:38 times, you start to think maybe it's not
4:40 that random. Maybe there's something
4:42 about the way crustaceian bodies are
4:44 built that makes turning into a crab
4:46 kind of inevitable if you're in the
4:48 right situation. Because here's the
4:50 thing, these crabshaped animals are
4:54 everywhere now. Oceans, rivers, beaches,
4:56 and they've been succeeding for hundreds
4:58 of millions of years. So whatever
5:00 advantages the crab shape gives you,
5:02 they're not small. They're big enough
5:04 that evolution keeps finding the shape
5:06 over and over in different time periods,
5:09 whether it's right now or in ancient
5:10 prehistory in different parts of the
5:12 world with different starting animals.
5:14 The scientist who coined the term back
5:18 in 1916, his name was Lancelot Boradale.
5:20 Of course, his name was Lancelot because
5:21 why not? Anyways, he described
5:24 Carsonization as basically taking a long
5:26 buddied crustation and squashing it down
5:28 and widening it out until it looks like
5:30 a crab, which is pretty much exactly
5:32 what happens. The back end shrinks, the
5:34 front end spreads out. You end up with
5:36 something that can scuttle around
5:38 sideways and hide under rocks. So,
5:40 that's what's happening. Evolution keeps
5:41 turning things into crabs because
5:43 apparently being a crab works really
5:45 well. But saying it happened multiple
5:48 times doesn't quite capture how many
5:50 times it has actually happened. And when
5:52 I say multiple times, I mean it's
5:55 honestly kind of absurd. Five times at
5:57 least, but probably more. Scientists are
5:59 still arguing about the exact number,
6:00 which is kind of funny because you would
6:02 think how many times did this happen
6:04 would be a straightforward question. But
6:06 evolution doesn't exactly leave
6:07 receipts. So, they're working backwards
6:09 from what they can see now and what they
6:12 can find in fossils. The first group is
6:14 true crabs. Rachura. These are your
6:16 classic crabs. The ones that showed up
6:18 first in the fossil record around 200
6:19 million years ago in the Jurassic
6:22 period. Somewhere back then, some
6:23 long-bodied crustaceian ancestor
6:26 flattened out and tucked its tail under
6:28 and boom, true crab. Every single modern
6:30 true crab, and there are thousands of
6:32 species of these, comes from that one
6:35 original shift. So, that's one time.
6:37 Then you've got king crabs. And king
6:38 crabs are fascinating because they're
6:40 enormous, right? They're the ones you
6:43 see in seafood restaurants that cost a
6:45 ridiculous amount of money. But they're
6:47 not actually true crabs. They're false
6:49 crabs, and they evolved from hermit
6:51 crabs. Yes, those little guys that carry
6:53 shells around. At some point, a group of
6:56 hermit crabs got too big for shells,
6:58 stopped using them, and their bodies
7:00 hardened up and flattened out into
7:02 something that looks a whole lot like a
7:04 regular crab. Except here's the weird
7:06 part. If you look at a king crab's
7:09 anatomy, it's still asymmetrical inside.
7:11 Most of their organs are lopsided
7:13 because hermit crabs have asymmetrical
7:15 bodies so they can coil into the spiral
7:18 snail shells. And king crabs never fully
7:20 lost that. So they're scuttling around
7:22 looking like crabs, but internally
7:23 they're still kind of hermit crabs,
7:25 which is honestly pretty strange when
7:26 you think about it. Third, you've got
7:28 porcelain crabs. They are small,
7:30 delicate, flat little things you find on
7:33 rocky shores. They look like crabs. They
7:35 act like crabs, but they're actually
7:37 more closely related to squat lobsters
7:39 than [music] to true crabs. They show up
7:42 in fossils around 150 million years ago,
7:44 which means they independently became
7:45 crabshaped during the age of [music] the
7:48 dinosaurs, completely separate from true
7:50 crabs. Fourth, there's this group called
7:53 stone crabs. And I'm not talking about
7:55 the ones that you eat. I'm talking about
7:57 Lis Herta, which is this hairy crab from
7:59 the Indo-Pacific that looks so much like
8:02 a true crab that people called it a
8:04 stone crab. But it's not. It's another
8:06 false crab, another independent
8:08 evolution of the crab shape. And fifth,
8:11 you've got coconut crabs. Now, coconut
8:13 crabs are technically hermit crabs, but
8:14 they're hermit crabs that said, "Forget
8:16 the shell." As adults, they don't use
8:18 shells. They just walk around with their
8:20 hard, flat bodies, climbing trees, and
8:23 cracking open coconuts with their claws.
8:25 They can even weigh up to 9 lb. And
8:27 they're the largest land arthropod on
8:29 Earth. And they're basically crabs now,
8:30 even though they start life as
8:32 shellwearing hermits. They also have
8:34 been known to eat humans. But let's not
8:36 talk about that for too [music] long or
8:37 else big crab government is going to get
8:39 me. So that's five clear cases where
8:41 evolution looked at a non- crab and
8:44 turned it into a crab. But there's more
8:45 because scientists have found extinct
8:47 groups of crustaceans that also went
8:49 crabshaped. There were these things
8:51 called cyclia [music] in the triacic and
8:53 Jurassic periods that looked strikingly
8:55 crabish even though they weren't even in
8:57 the same lineage as modern crabs. And
8:59 within the groups I just mentioned,
9:01 there are subgroups that might count as
9:03 separate instances, too. Some
9:05 researchers think true crabs might have
9:07 evolved the crab shape twice within
9:09 their own family tree. Some think there
9:10 are more false crab evolutions we
9:13 haven't fully documented yet. The fossil
9:15 record isn't complete and genetic data
9:17 is still being analyzed. And every few
9:19 years, someone finds a new weird crab
9:21 fossil that changes the count. But the
9:23 point is, evolution has run this
9:25 experiment at least five times that
9:27 we're sure about. Five separate lineages
9:29 of crustaceians starting from different
9:31 ancestors ending up with the same
9:34 general body plan. Flat shell, tuck
9:36 tail, sidewalking legs. And these didn't
9:38 happen all at once. They have been
9:40 spread over hundreds of millions of
9:42 years. Which means this isn't some fluke
9:45 or one-time accident. This is a pattern.
9:47 Nature keeps making crabs because
9:50 something about being a crab means you
9:53 get to live longer. So when did exactly
9:55 all of this start? Well, way earlier
9:57 than you would think. The first real
9:59 crabs show up around 200 million years
10:01 ago in the early Jurassic period.
10:03 Dinosaurs are just starting to become a
10:05 thing on land. And down in the ocean,
10:07 something's busy flattening itself out
10:10 and tucking its tail under. Just quietly
10:11 becoming a crab while the rest of the
10:13 world is focused on giant reptiles. For
10:16 a while, not much happens. Crabs exist.
10:18 They're doing their crab thing, but
10:20 they're not exactly taking over. Then
10:22 you hit the late Jurassic about 150
10:25 million years ago and suddenly crabs are
10:27 everywhere, specifically in reef
10:29 environments. Coral reefs are expanding
10:30 and there are all these little cracks
10:33 and hiding spots and crabs just explode
10:35 in diversity. Scientists call this the
10:37 first big crab radiation, which sounds
10:39 dramatic, but it really just means a
10:41 bunch of new crab species showed up at
10:43 once. But the Cretaceous period is
10:44 really when [music] things start to get
10:48 genuinely wild. This is 145 to 66
10:50 million years ago. And paleontologists
10:52 actually call this the Cretaceous Crab
10:54 Revolution, which is a great name for a
10:56 band, but it is also an accurate
10:58 description of what happened. Something
11:00 like 80% of modern crab families
11:02 originated during this time. Most of the
11:04 crabs you see today can trace their
11:06 family tree back to the Cretaceous. This
11:08 is also when crabs started developing
11:10 their really nasty traits. Strong claws
11:12 that could crush shells. Some of them
11:14 became specialized predators that would
11:16 hunt down snails and clams and just
11:18 crack them open. There's this fossil
11:20 crab called Mega Xantho, and it had
11:22 these toothy ridges on its claws
11:24 specifically for breaking shells. So,
11:25 crabs weren't just scuttling around
11:27 anymore. They were actively haunting
11:29 things and doing it pretty well. And
11:31 then crabs started leaving the ocean,
11:33 which seems ambitious for an animal that
11:35 breathes through gills, but they made it
11:37 work. They moved into fresh water, and
11:38 some of them started hanging out on
11:41 beaches. A few really bold ones went
11:42 into the forests. And we know this
11:45 because in 2021, scientists found a crab
11:48 preserved in amber. Yes, amber, which is
11:50 fossilized tree resin. You find
11:52 mosquitoes in amber. You find ants in
11:54 amber. You don't find crabs in amber
11:56 because crabs don't hang out in trees.
11:58 Except apparently 100 billion years ago
12:00 they did, which is a thought that should
12:03 terrify you. This tree crab is called
12:06 Cretuspara Antha. Do not clock me on
12:07 that name. I don't know how to say it.
12:09 And it is tiny. But the fact that it
12:11 exists at all means crabs were exploring
12:14 land way earlier than anyone thought.
12:16 We're talking 50 million years earlier
12:17 than the previous estimate. So, while
12:19 T-Rex is still tens of millions of years
12:21 away from even existing, crabs are
12:23 already climbing around in forests
12:25 getting stuck in tree sap. Now, my
12:27 favorite prehistoric crab is this thing
12:29 called Cali Chimeriia Perplexa. And
12:32 perplexa is right because this crab is
12:35 genuinely perplexing. It's 95 million
12:37 years old. And when scientists found it,
12:39 they didn't know what to do with it
12:41 because it doesn't look like a crab.
12:43 It's got these huge eyes with no
12:45 sockets, paddle-shaped legs for
12:47 swimming, and a long tail that sticks
12:48 out behind it, which is one of the
12:51 things crabs specifically don't have.
12:53 Tell me this thing does not look like
12:56 Paris the Pokémon, like without the
12:58 mushrooms. It's like a one to one. I
13:00 feel like scientists actually called it
13:02 the strangest crab that ever lived. Its
13:05 name means perplexing beautiful chimera,
13:07 which is a very fancy way of saying we
13:08 have no idea what the we're looking at
13:11 because Cali Chamaria kept a bunch of
13:13 features that you normally see only in
13:15 baby crabs. It's like it just never grew
13:17 up and it was only the size of a quarter
13:19 and it swam around in open water, which
13:22 is not standard crab behavior at all.
13:23 What this tells us is that the
13:25 Cretaceous wasn't just crabs perfecting
13:27 the crab shape. It was crabs trying out
13:30 every possible variation. Some worked,
13:31 some didn't, but they were
13:33 experimenting. And then the dinosaurs
13:35 went extinct 66 million [music] years
13:37 ago, and crabs just kept going. They
13:39 didn't even slow down. Fast forward to
13:41 today, and you've got crabs that are
13:44 genuinely absurd. The Japanese spider
13:48 crab has legs that span 13 ft. 13 ft. It
13:50 is the largest arthropod on the planet,
13:53 and it is just a crab that decided to
13:55 get really, really big. It lives in deep
13:57 water near Japan and can live for a
13:59 hundred years, which is a long time to
14:01 be a spider crab. On the opposite end,
14:03 you've got pea crabs are the size of,
14:05 well, who could have guessed, a carrot?
14:07 No, it's a pee. They're the size of a
14:08 pee. Uh, they're a few millimeters
14:10 across. They live inside oysters and
14:12 muscles and just steal food from their
14:14 hosts. Their bodies are soft because
14:15 they don't need armor when they're
14:17 living inside someone else's shell. So,
14:19 you've got the full range, giant crabs,
14:22 tiny crabs, and everything in between.
14:24 Then there's the coconut crab, which I
14:26 mentioned earlier, which is nine pounds,
14:28 lives on land, and climbs trees, and has
14:30 claws strong enough to crack open
14:32 coconuts and also strong enough to hurt
14:34 you pretty badly if you bother it. There
14:36 are stories of coconut crabs stealing
14:38 camping gear, which is both impressive
14:39 and deeply annoying if you're the
14:42 camper. And in 2005, scientists found
14:45 the yeti crab deep sea covered in hair.
14:46 Actually, it's bristles, but they look
14:48 like hair. So, everyone calls it the
14:50 yeti crab. And it doesn't eat the hair.
14:52 It eats the bacteria that grows on the
14:54 hair. It's farming bacteria on its own
14:56 arms, which is a weird way to make a
14:58 living, but it works. The range of crabs
15:01 today is honestly kind of ridiculous.
15:03 Mountain streams, deep ocean trenches,
15:06 coral reefs, beaches, rainforests, your
15:08 local motel. Some are carnivores, some
15:11 are filter feeders, some are herbivores.
15:12 They figured out how to survive
15:14 basically everywhere. Which brings us
15:16 back to the question we started with.
15:18 What is it about being a crab that makes
15:20 this possible? Scientists don't actually
15:22 know for sure. And I know that's a
15:23 disappointing answer, but it's the
15:25 honest one. They have theories, good
15:27 theories, but nobody's proven exactly
15:29 which one is right or if it's all of
15:30 them at once. The first theory is
15:32 protection. Crabs have a thick shell on
15:34 top and their tail is folded underneath
15:36 the shell. So, there's no soft exposed
15:39 belly for a predator to bite. Compare
15:41 that to a lobster where the entire tail
15:42 is just hanging out in the open. It
15:44 makes for an easy target. Crabs fix that
15:46 problem by tucking everything away.
15:48 You're basically a rock with legs.
15:50 you're pretty hard to eat. The second
15:52 theory is stability. Crabs are wide,
15:54 flat, and low to the ground. You can
15:56 wedge yourself into a crack in a reef
15:58 and just stay there. Predators cannot
16:00 flip you over, can't pull you out, and
16:02 you're firmly planted, and if you need
16:04 to move, you're not going to tip over
16:06 because your center of gravity is
16:08 basically on the floor. The third theory
16:10 is the sideways thing. Most crabs walk
16:12 sideways. There's actually a reason for
16:14 that. If a predator comes at you, you
16:16 can dart left or right without having to
16:18 turn your whole body around. Your eyes
16:20 stay pointed at the threat while you're
16:22 escaping, which is genuinely smart if
16:24 you think about it. Most animals have to
16:25 turn and run, which means they're not
16:27 looking at the danger anymore. Crabs
16:29 don't have that problem. And the fourth
16:30 theory, and this one's interesting, is
16:33 that the crab body plan is versatile.
16:35 Once you get rid of that big tail, your
16:36 legs can evolve to basically do
16:38 anything. Some crabs have paddle legs
16:40 for swimming. Some have digging legs for
16:42 burrowing. Some have thick walking legs
16:45 for land. The crab shape is a base model
16:47 that you can modify. And evolution loves
16:49 things that it can modify because that
16:51 means you can adapt to new environments
16:53 without starting from scratch. There's a
16:56 researcher named Javier Lu who studies
16:58 crabs. Yes, he's the crabs guy. And he
17:00 pointed out that having a big lobster
17:02 tail actually limits what the rest of
17:04 your body can do. You're hauling this
17:06 huge tail around. So that constrains
17:08 your options. Get rid of the tail and
17:09 suddenly you've got room to try new
17:12 things. The fifth theory is hiding. A
17:14 flat body fits under rocks. It fits in
17:15 coral. Fits in places where a
17:17 long-bodied animal can't go. And if
17:19 predators can't reach you, you don't get
17:21 eaten. Simple. But here's the thing that
17:23 nobody wants to admit. These are all
17:26 guesses. Educated guesses, sure, but
17:27 still guesses. Because the real answer
17:29 is probably some combination of all
17:31 these things. And it probably varies
17:33 depending on which group of crabs we're
17:35 talking about. Maybe one group became
17:37 crabs because of predator pressure.
17:38 Maybe another group became crabs because
17:40 it let them invade new habitats.
17:42 Evolution doesn't follow a script. It
17:44 just does what works in the moment. Or,
17:46 and what the elite won't tell you is
17:48 that it's big crab lobbying the
17:50 government to make more crabs. They
17:51 don't want this leaked, but I have to
17:53 tell people. There's also this idea that
17:55 maybe being a crab isn't the advantage
17:57 by itself. Maybe it's what being a crab
17:59 allows you to do next. You become a
18:01 crab, and now you can evolve better
18:04 claws or faster legs or whatever. The
18:06 crab shape opens doors. It's not the end
18:08 goal. It's just a really useful starting
18:10 point for other changes. What we do know
18:12 is that when something evolves five
18:14 separate times, there's a reason.
18:16 Natural selection doesn't keep picking
18:18 the same option unless that option is
18:19 working. And crabs are everywhere.
18:21 They're in every ocean, every kind of
18:23 habitat, and they're thriving. So,
18:24 whatever the crab shape is doing for
18:26 them, it's enough. But scientists are
18:28 still studying this. They're looking at
18:30 crab DNA to find patterns. They're
18:32 comparing Carsonized crabs to their non-
18:34 crab relatives to see what's different.
18:36 testing whether crabshaped animals
18:38 actually survive predators better or
18:40 reproduce more or whatever. The research
18:42 is ongoing and every few years someone
18:45 finds a new fossil that changes part of
18:47 the story. So the answer to why does
18:48 this keep happening is we don't know
18:50 yet, but we're working on it. In the
18:53 meantime, evolution is probably busy
18:55 making another crab somewhere. But now I
18:56 should mention that evolution doesn't
18:59 just turn things into crabs. Sometimes
19:01 it does the opposite. There's actually a
19:03 term for when crabs stop being crabs.
19:05 decarcenization, which is exactly what
19:07 it sounds like. A crab-shaped animal
19:09 evolves back into something that's not
19:11 crabshaped. And this has happened at
19:13 least seven times that scientists know
19:15 about. Take frog crabs. These are true
19:18 crabs, proper members of the brachiier
19:19 family, but they've gone and made
19:21 themselves longer and narrower again.
19:23 They borrow into sand on the ocean
19:25 floor. Apparently, being flat and wide
19:26 wasn't working for that. So, over time,
19:28 they stretched back out. Their shells
19:30 got longer and their tails unfolded a
19:32 bit. They're still crabs technically,
19:34 but they're crabs that decide to undo
19:36 some of the crabness. Mole crabs did
19:38 something similar. These are the little
19:40 guys you find on beaches that burrow
19:41 backwards into the sand right when the
19:44 waves wash up, and they basically turn
19:46 themselves into torpedoes. Smooth,
19:49 streamlined, barely any legs, no big
19:50 claws. They don't look like crabs at
19:52 all. They look like someone tried to
19:54 design the least crab thing possible
19:56 while still technically being a crab.
19:57 And it works for them because they need
20:00 to dig fast and filterfeed in the surf.
20:02 But the really interesting case is the
20:04 whole hermit crab situation. Hermit
20:06 crabs originally gave up being crabs so
20:08 that they could live in shells. They let
20:10 their abdomen stay soft and coiled so
20:12 they could fit into snail shells. That's
20:14 decarcinization. Then later, king crabs
20:16 evolved from hermit crabs and went back
20:18 to being crabshaped. That's
20:20 recarcenization, I guess. So, you've got
20:22 crabs that become not crabs that became
20:24 crabs again. It's always crabs. It's
20:26 crabs all the way down. And you could
20:28 still see the evidence of this in king
20:29 crab anatomy because, as I mentioned,
20:31 their insides are asymmetrical. Their
20:33 reproductive organs are lopsided because
20:35 their ancestors spent millions of years
20:38 twisted up inside spiral shells. King
20:40 crabs never fully corrected that.
20:41 They're wearing the evolutionary history
20:43 of their hermit crab phase on the
20:46 inside. So, why would any animal stop
20:48 being a crab if being a crab is so
20:50 great? Well, turns out being a crab is
20:51 great for a lot of things, but not
20:54 everything. If like if a crab runs into
20:56 its natural predator, a cooking pot,
20:58 it's going to die. That's a case where
21:00 you would not want to be a crab. If
21:01 you're trying to burrow straight down
21:03 into sand really fast, being flat and
21:05 wide is actually bad. You want to be
21:07 narrow and streamlined. If you're
21:09 carrying around a borrowed shell for
21:10 protection, you don't need a thick hard
21:12 shell of your own. You can save the
21:15 energy and just stay soft. Evolution
21:16 doesn't care about being consistent. It
21:18 just does whatever helps you survive
21:21 right now. If being a crab helps, great.
21:23 If unbeing a crab helps, also great.
21:25 Neither one is permanent. Meanwhile,
21:26 scientists are still trying to map out
21:29 the full crab family tree, and they're
21:31 running into problems because about half
21:33 of the branches are basically unknown.
21:35 They don't have genetic data for a lot
21:37 of groups. Fossils are incomplete, and
21:39 every time someone digs up a new
21:41 prehistoric crab, it changes part of the
21:44 picture. In 2021, a team of researchers
21:45 published this big analysis trying to
21:47 nail down exactly how many times
21:50 carcinization happened and when. are
21:52 using DNA sequencing now trying to find
21:54 genetic patterns that show up every time
21:56 something becomes a crab because if
21:58 there are specific genes that get turned
22:00 on or off during carcinization that
22:02 would explain why it keeps happening.
22:04 Maybe it's just an easy switch for
22:06 crustaceian bodies to flip. People
22:08 always ask if everything is eventually
22:09 going to become a crab. And the answer
22:13 is sadly no. Don't worry, you're not
22:15 going to wake up a crab as much as I
22:17 would like you to. This only happens to
22:18 crustaceians because their bodies are
22:20 built in a modular way. They've got
22:23 segments that they can arrange. Humans
22:24 don't have that. Neither do most
22:27 animals. You can't turn a mammal into a
22:28 crab. The body plan doesn't work that
22:31 way. Well, not yet, that is. But within
22:32 crustaceations, yeah, we'll probably see
22:34 more carcinization in the future because
22:36 if it keeps working, there's no reason
22:39 to think evolution is done making crabs.
22:41 Give it another 50 million years, and
22:43 some shrimp lineage that hasn't tried it
22:45 yet probably will. Right now, there are
22:47 thousands of crab species all over the
22:49 planet. Deep ocean vents where the water
22:51 is boiling hot. Antarctic waters where
22:53 everything is frozen. Coral reefs,
22:56 rivers, forests, deserts. Somehow, some
22:57 crabs can hold their breath and climb
23:00 trees. Some crabs live their entire
23:02 lives in pitch black caves. Some crabs
23:04 are transparent. There are crabs that
23:06 have symbiotic relationships with sea
23:08 enemies that carry them around in their
23:10 claws for protection. I actually own
23:12 some in my fish tank behind me. They're
23:14 really cute, but they tried to pinch me
23:16 once. One species of crab, and I'm not
23:19 making this up, farms algae gardens on
23:22 its back. It plants algae in its shell
23:24 and tends to it and then eats it later.
23:27 That is agriculture. Yes, crabs invented
23:29 farming. It's not advanced farming, but
23:31 still, humans didn't invent that. Crabs
23:33 did. The crabs are rising up. They are
23:35 learning. The range of what crabs can do
23:37 is genuinely impressive when you lay it
23:39 all out. And that's probably the real
23:40 answer to why carcinization keeps
23:43 happening. The crab body plan is a Swiss
23:45 Army knife. It works in enough different
23:47 situations that evolution keeps coming
23:49 back to it. Not because it's perfect,
23:51 but because it's good enough for most
23:52 things and flexible enough to be tweaked
23:54 for specific things. Scientists are
23:56 going to keep studying this. They're
23:57 going to find more fossils, sequence
24:00 more DNA, and run more comparisons
24:02 between crabshaped and non- crabshaped
24:04 crustaceations. Eventually, we'll have a
24:06 more complete answer, but for now, we've
24:07 got a pretty good idea of what's
24:09 happening, even if we don't know every
24:11 detail of why. So, in the end, are
24:13 humans turning into crabs? Not yet, that
24:15 is. But hey, maybe in a 100 million
24:17 years they can come back to this video
24:19 and say, "Damn, look at this dummy. He
24:21 thought we weren't going to be crabs."
24:23 But meanwhile, it was always crabs. It
24:24 was crabs all along. If you enjoyed
24:25 watching this video, make sure to give
24:27 it a like and comment down below what
24:28 your favorite part was. And if you would
24:30 like to learn any other topics that
24:31 relate to prehistory. If you don't want
24:33 to miss any of our future uploads, make
24:34 sure to hit the subscribe button and hit
24:36 the hype button to make sure this video
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