EMILY KWONG: You're listening to Short Wave from NPR. Hey, Short Wavers, it's Emily Kwong. And today, our story starts with a TikTok-- well, really, multiple TikToks.
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SPEAKER 1: There is this meme that everything is slowly turning into a crab, including us.
SPEAKER 2: Studies have shown that numerous species of crustacean have independently evolved the flat rounded shells and tucked in tails of a typical crab.
SPEAKER 1: OK, wings have evolved four times. Crabs have evolved five.
SPEAKER 3: Scientists aren't exactly sure why this is happening, but there must be some environmental push for these crustaceans to evolve in crab form. So the ideal form is crab.
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KWONG: The comments on these videos are hilarious. People are asking, are crabs the final boss of evolution? Do aliens look like crabs? When will I become a crab? And we wanted to talk to the person whose research sparked this crab existential crisis, Javier Luque, or Javi for short. He's a senior research associate at the University of Cambridge in the UK and curator of crustaceans at their Museum of Zoology. Do you have a pet crab?
JAVIER LUQUE: I had a pet crab, a fiddler crab, a beautiful--
KWONG: Fiddler crabs are so cool.
LUQUE: --oh, they're amazing. They're so beautiful.
KWONG: Yeah, they're elegant.
LUQUE: They're elegant, so glamorous, a fascinating animal. I had one pet that was part of a research experiment we were doing. And it was fantastic. I think every person should have a crab as a pet at some point in their life.
KWONG: Yeah, definitely, definitely. What was your crab's name?
LUQUE: Little John, Juancito.
KWONG: So yeah, those viral TikToks are all based on Javi's work on carcinization, the process of crustaceans developing a crab-like body plan.
LUQUE: We have known about carcinization since the early 1900s. So this is something that the scientist called Borradaile, in 1916-- he was the one who coined the word carcinization. But it's not until 2019, when I was a researcher at Yale University that we started delving deeper into the evolution of crabs. And that's when crabs became mainstream as this incredible example of convergence and how different things that are not related directly look alike.
KWONG: Carcinization has happened not once, not twice, but at least five separate times in evolutionary history. And TikTok talked about this way less. But decarcinization, the process of losing a crab-like body, has happened even more, at least seven times throughout evolutionary history. So today on the show, to crab or not to crab, what carcinization tells us about evolution and whether humans could become crab-like, too. You're listening to Short Wave from NPR. OK, so Javier, I want to start with crustaceans. And crustaceans, of course, includes the large and diverse group known as crabs. Where do we find crabs in the world? How many are there?
LUQUE: Today there are approximately 7,500 living species of crabs all over the world. And we know approximately 3,500 fossil species. So it's between 10,000 and 11,000 fossil and living species of crabs--
KWONG: That's a lot.
LUQUE: --known to us. It's a good number. You can find them all over the world, from the North to the South Pole, from the depth of the oceans, and the trenches, to coral reefs, and shores, and beaches, and intertidal zones, fresh water, in land, in caves, in the mountains. They live under the rocks. They are conquering the world. The only thing crabs are not really doing is flying. Other than that, you can find them all over the place.
KWONG: I love that. OK, so the common denominator in a lot of your work is these species have gone through carcinization. And this, in part, happened due to something called convergent evolution, that you have so many crustaceans evolving to take on a crab-like form, to carcinize. What is convergent evolution? What happened?
LUQUE: That's a great question. Convergent evolution is the processes through which organisms that are not directly related to one another start looking alike and resembling each other, mostly because of similar lifestyles and dietary habits, and also how the environment and the lifestyle is selecting or seeking for such forms.
KWONG: So when you say lifestyles, you know, it's not like species are out here really choosing how they want to live. They just are doing their best to survive. Like, survival plays such a role in this. Like, why was it evolutionarily advantageous, given the problems that species faced 100s of millions of years ago?
LUQUE: So basically, animals are exposed to change, change in the environment, change in the conditions of the water, the ocean, the air. So as the world changes and the microworlds within our world change, the ecosystems and environments, animals need to cope with those changes by, either moving somewhere else where those changes are not happening or by changing themselves to deal with the new changing conditions.
KWONG: You sound like me talking to my therapist.
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LUQUE: Well, that's the beauty of it. part of the physical, but also mental and emotional evolution comes through change. And that change is the adaptation to those pressures from the outside world and finding the flexibility to deal with them. So that is a beautiful parallel there. And I'm happy you mentioned it because, yes, the key is change. And if we close our eyes and think of a dictionary definition of an archetypical crab, it would be a roundish animal with a flattened body that is sturdy and hard. They have a pair of big pincers, or claws in front of the body, and four pairs of walking slender legs, and teeny eyes in long eyestalks like periscopes, and a little, teeny, tiny tail underneath. So that basic combination of features has allowed them to do things in ways other crustaceans have not. For instance, if you think of lobsters and shrimp, they have long tails, fleshy, muscular, delicious tails. A big tail allows lobsters and shrimp to swim. But in the long evolutionary game, the loss of that fleshy tail into a little tiny tail that is pressed under the chest, makes the crab body way more mobile. The legs can move everywhere they want. And now they are like, OK, we don't need to swim anymore. Now we can go to other places and do things other crustaceans are typically not doing. Let's go to caves. Let's go to mountains. Let's go to mainland. Let's start climbing trees. Let's live in flowers like orchids. And that is one of the reasons why we think crabs in the last 200 million years have had an advantage in terms of success, and survivorship, and species richness compared to lobsters and shrimp.
KWONG: All very delicious, by the way. OK, let's move on to your more recent work. I'm really excited about this because in August, so just last month, you released a paper analyzing all the crab fossils we know about and putting them together like a puzzle, helping to trace the grand ultimate history of crabs. Can you talk about that?
LUQUE: So in this paper you're talking about that we published in Palaeontologia Electronica, reassessing, re-evaluating the fossil record of crabs for the study of the molecular divergence time estimation. So how old are these branches splitting from one another? We did a very rigorous study of which groups can we say, beyond a doubt or with a lot of confidence, that they actually belong to the branches they belong.
KWONG: So what was the first crab?
LUQUE: So the oldest true crab that we know today, its name is Eocarcinus praecursor, which means the early crab from the dawn of life and the precursor to any other crabs.
KWONG: What a name.
LUQUE: It's an ancestral crab? It's a beautiful name. It's an animal that is approximately 180 million years in age, really old. It lived in the Jurassic Period in England, here where I am right now.
KWONG: So if you were to put this ancestral crab in the tank with Juancito-- your little crab-- he could say, like, you're my great, great, great, great, great, great, great, great, great, great, great, great, great, great, great great grandfather, right?
LUQUE: If Juancito knew about the crab tree of life, and he has read some of our papers, he would say, you are my great, great, great, great, great, great, great, great, great grandcousin.
KWONG: Oh, which is still great. We love cousins.
LUQUE: Oh, yeah, we do. So the thing about evolution and the fossil record is that it's easy sometimes to fall under the idea that every fossil is the direct ancestor of other branches. But it doesn't work that way. So a fossil is not the father, or the mother, or the parent of a branch necessarily. They are relatives of this family. But you don't have necessarily the straight genealogical life. So that's why I say cousins, or uncles, or family, instead of father, mother, or parent. So Eocarcinus was the grand, grand, grand, grand, grand, grandrelative of every modern crab known today.
KWONG: Yeah, you mentioned earlier that there are some species that have, however, decarcinised, meaning they lost their crab-like form. Why did evolution do that? Why would it make something become crab-like and then nix it later?
LUQUE: Brilliant, brilliant question. Because evolution is not set. Evolution is not fixed. But it's opposite, quite dynamic and variable. Not every combination of changes or features are optimal for what you do. So if you are a swimming animal like a penguin, your anatomy, all of the Lego pieces you are building, is not the same as if you are an ostrich, that you need to run really fast, but you have almost no wings. And if you are a pelican, or a cormorant, or an albatross, your body form needs to be different, that is good to fit the flying that you do.
KWONG: Yeah. Since you work on timescales that are so large, my last question for you is-- you know, we're living among crabs, among many crab-like creatures-- would it be possible for the human species to ever split off in such a way that we-- we-- could become crabs, crab-like, crab-like? I'm learning.
LUQUE: Crab-like. (LAUGHS) I don't think we are going to become crabs. And I don't think crabs will be the answer to all forms. But certainly, for this group of crustaceans, it is a fascinating, wonderful, functional, practical way of getting the most out of their environments, avoiding dehydration, desiccation, resistance to predation, and exploiting resources in different ways.
KWONG: Evolution's like, pick a strategy. You can't have it all. You can't-- you can't do everything. You've got to specialize.
LUQUE: But you can divide and conquer. So that is the beauty of evolution. These splits in the branches of the tree of life allow different branches to try different combinations and have a fail an error, like trial and error.
KWONG: You-- I just want to say, Javi, you are, like, a sensational, not only scientist but science communicator. And just thank you so much for bringing your work to Short Wave. It's been so good to talk to you.
LUQUE: Oh, thank you very much. It has been a pleasure to me to chat with you all. And I hope that this is just an appetizer for people to get more excited about crab evolution and why evolution is so obsessed with crabs.
KWONG: Kids ask the best questions. And on October 15th, to celebrate our fifth birthday, we are taking questions from any Short Waver who is five years old. Record your best questions and your name in a voice memo and send it to shortwave@npr.org, or ask your parent to do it. And we may answer it in a birthday episode. Thanks so much. This episode was produced by Hannah Chinn and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. James Willetts was the audio engineer. Beth Donovan is our senior director. And Collin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. And thank you for listening to Short Wave from NPR.
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