You're Dead to Me – Curious Cases Takeover: “Why Do So Many Animals Turn Into Crabs?”
Podcast: You’re Dead to Me (BBC Radio 4)
Episode: Hannah Fry and Dara Ó Briain introduce Curious Cases
Date: October 8, 2025
Episode Overview
In this special crossover episode, Greg Jenner hands over the “You’re Dead to Me” feed to the hosts of BBC Radio 4’s Curious Cases, Dr. Hannah Fry and comedian Dara Ó Briain. The pair, joined by evolutionary experts and the director of a crab museum, tackle an internet-fuelled biological question: Why does evolution keep producing crabs (a phenomenon known as carcinization)? Humorous, fact-filled, and full of sideways banter, this episode explores evolutionary convergence, the true—and false—crabs of the crustacean world, and why pop culture can’t get enough of these quirky creatures.
Key Discussion Points & Insights
1. Setting the Stage: “Everything Becomes a Crab” Meme
[01:08–04:03]
- Hannah and Dara discuss the cultural fascination with crabs and how the meme that “everything evolves into a crab” (carcinization) has seized the internet—and even science museums.
- Dara recounts a recent Natural History Museum exhibit speculating about possible alien body plans, noting, “The only really recognizable thing was a crab. They said, yeah, yeah, there'll definitely be a crab.” (Dara Ó Briain, 05:01)
2. The Central Question: Is Crab Evolution a Trend?
[05:34–07:19]
- Listener question: Why have so many different species independently evolved into crab-like forms? Is the “crab” the ideal shape, and could humans one day become crabs?
- Hosts introduce three guests:
- Prof. Matthew Wills (Evolutionary Palaeobiology, Bath)
- Dr. Joanna Wolfe (Evolutionary Biologist, Harvard & Santa Barbara)
- Ned Sysat Williams (Director, Crab Museum Margate)
3. What Is a Crab, Anyway? True vs. False Crabs
[08:16–13:11]
- Dr. Wolfe clarifies the difference between “true” crabs (Brachyura, ~8,000 species) and “false” crabs (Anomura, e.g., hermit crabs, king crabs, squat lobsters).
- Ned and Joanna note the confusion in taxonomy and why we sometimes label things with “crab” in the name that really aren’t crabs.
- “Hermit crabs are like my favorite crab, and they're not a crab.” (Dara Ó Briain, 11:00)
- “A crab is a made-up word… horseshoe crabs are not crabs, neither are they horses or shoes, but we still recognize them for the wonderful beings they are.” (Ned Sysat Williams, 23:17)
4. Carcinization & Convergent Evolution Explained
[13:03–22:48]
- Carcinization: multiple, independent lineages (at least five times) have evolved the “crab” body plan—broad, flat shells and tucked-under abdomens.
- Prof. Wills uses the lobster as an example, showing how evolving into a crab results in sacrificing mobility (the ability to flick away backwards) in exchange for better armor and compactness.
- Not every animal can or will become a crab; convergent evolution requires pre-existing body plans and environmental pressures.
- “You have to be in an environment where [crab shape is] an advantage… and have all the building blocks.” (Matthew Wills, 15:42)
- Carcinization is remarkable, but not unique—there are memes for crabs, fewer for e.g. dolphin/shark convergence.
5. Are Humans Next?
[19:13–19:34]
- Fry presses Wills: if enough time passes, will everything become a crab?
- “No.” (Matthew Wills, 19:32)
- The meme is fun, but oversimplifies the science.
6. The Flexibility—and Limits—of Evolutionary Trees
[19:40–22:48]
- Genomics—versus older comparative anatomy—has overturned much mammalian taxonomy: “Horses are more closely related to bats… Elephants and Sirenians (manatees) are cousins.” (Matthew Wills, 21:14)
- Convergence means wildly different animals can look and act similarly without being closely related.
7. Crabs: Why So Cool?
[23:38–25:12]
- Ned extols crabs as underestimated, ecosystem engineers whose burrowing supports mangroves and coastal life.
- “Without crabs, mangroves choke and mangroves die. So crabs are ecosystem engineers.” (Ned Sysat Williams, 24:20)
- Crabs exhibit fascinating, sometimes bizarre behaviors—wearing hats (jellyfish, sea anemones), living inside sea urchins, and more.
8. Crab Diversity: From Fiddler to Coconut
[25:41–27:13]
- Crabs range from fiddler crabs (famous for their asymmetrical, display-ready claws) to giants:
- Largest by leg span: Japanese Giant Spider Crab (can exceed an adult human’s arm span).
- Heaviest: Coconut Crab (a land-dwelling, terrestrial “hermit crab” the size of a small dog).
- “The heaviest arthropod ever known is alive with us now. And it's the coconut crab, which is not truly a crab, it's a hermit crab.” (Joanna Wolfe, 26:12)
9. What Makes a Crab, Biologically and Philosophically?
[13:11–14:29, 23:17]
- The crab “plan” is effective because it subdivides walking and manipulating limbs; most crabs have differently specialized claws.
- Left- or right-handedness in crabs develops depending on usage!
- Crabs, like language, are hard to define by hard boundaries—more philosophy than taxonomy, sometimes.
10. Memorable Moments & Banter
- Dara jokes about feeling betrayed that hermit crabs aren’t “real” crabs, launching into comedic mock outrage:
- “You are not a crab! You're a crab of lies. You are False. I abjure thee, false crab.” (Dara Ó Briain, 30:27)
- Hannah explores the meme of “everything becomes crabs,” referencing Monterey Bay Aquarium’s social media:
- “This is, you know, one of the most respected institutions in the entire world just posting a crab content meme with zero context.” (Hannah Fry, 06:36)
Notable Quotes
- On Evolution and Popularity:
- “Crabs are weird and funny looking… so why wouldn't you hinge a whole discourse about evolution on a crab?” (Ned Sysat Williams, 08:37)
- On Convergent Evolution:
- “A lot of them looked like paramecium… The only really recognizable thing was a crab.” (Dara Ó Briain, 05:01)
- On True vs. False Crabs:
- “There's two groups… they're the true crabs and the false crabs. That's not a value judgment, it's just based on taxonomy.” (Joanna Wolfe, 09:40)
- On Crab Functions:
- “Lots of different appendages doing different jobs… even the pincers—they have a crushing claw and a cutting claw.” (Matthew Wills, 27:16)
- On Symbiosis:
- “Some crabs will live inside the bums of sea urchins. Other crabs will wear jellyfish on their heads upside down, like, as kind of hats.” (Ned Sysat Williams, 23:45)
- On Crabs in the Food Chain:
- “People will eat a lot of things.” (Dara Ó Briain, 18:24)
Timestamps for Important Segments
- Introduction & Crossover Context: 01:08–05:01
- “Everything Becomes a Crab” Meme: 05:01–07:19
- Intro to Guests & Carcinization: 07:19–09:06
- True vs. False Crabs: 09:06–13:11
- Evolutionary Explanation (Crab Biology & Fossils): 13:11–19:13
- Crab Body Plan & Adaptations: 19:13–21:29
- Convergence & Evolutionary Trees: 21:29–22:48
- Crab Coolness & Ecological Importance: 23:38–25:12
- Giant Crabs & Diversity: 25:41–27:13
- Wrap-Up & Final Thoughts: 29:20–30:51
- Notable Banter: 30:27–30:51
Tone & Style
The episode is highly conversational, witty, and full of good-natured teasing between Hannah and Dara, as well as their expert guests. Despite the humor, the discussion remains rigorous, delving into the nuances—and the mysteries—of evolutionary biology. Running jokes about fake crabs, internet memes, and crab “PR” combine with lively explanations to make a scientific topic genuinely engaging for all listeners.
Conclusion
This episode both uncovers the science behind one of nature’s quirkiest evolutionary trends and celebrates the oddball appeal of crabs. With guest experts weighing in on taxonomy, evolution, and just why crabs capture the human imagination, listeners come away appreciating that the answer to “Why do things keep becoming crabs?” is as much about our perceptions—and internet memes—as it is about the power of convergent evolution. As always, the hosts make learning hilarious and accessible.
“I think this program has been absolutely excellent PR for crabs.” (Hannah Fry, 29:33)
For more odd natural questions and answers with wit and science, subscribe to Curious Cases on BBC Sounds.