Sciency Words: Carcinization

Hello, friends!  Welcome back to Sciency Words, a regular series here on Planet Pailly where we talk about the definitions and etymologies of scientific terms.  Today, we’re talking about:


In time, we will all evolve into crabs.  Crabs are the ultimate life form, evolutionarily speaking.  At least that’s what certain Internet memes would have you believe.  But like most Internet memes, this whole “we will all become crabs” idea is an oversimplification of the truth.  Carcinization is a surprisingly common evolutionary process, but it doesn’t happen to all animals in all situations.

Definition of Carcinization: In evolutionary biology, carcinization is the process of evolving a crab-like body structure, especially a crab-like carapace (shell) with the pleon (tail) folded underneath the belly.  A surprising number of animals have evolved to have this body structure independently of one another.

Etymology of Carcinization: The term was coined in 1916 by English zoologist Lancelot Alexander Barradaile.  It uses a Greek root word meaning “crab.”  Although the term carcinization was coined in 1916, scientists had noticed the unusual prevalence of crab-like animals well before that.  Research on this phenomenon can be traced back to the mid-to-late 1800’s.

Carcinization seems to happen a lot in nature, but it does not happen to all animals equally.  It is far, far, far more likely to happen to an animal that already has a few crab-like characteristics.  For example, if you’re a lobster, a shrimp, or a prawn—in other words, if you’ve already got a bunch of legs and a pair of claws, and if you’re already living on the ocean floor—then there may be some real benefits to evolving even more crab-like characteristics.

It’s hypothesized that the compact body shape of a crab (compared to the more elongated shape of a lobster, for example) may make it easier to defend yourself against predators.  A lobster’s pleon (tail) is very exposed; crabs have their pleons neatly tucked beneath their bellies.  The compact body shape of a crab may also make it easier to scuttle about on the ocean floor, which could help crabs evade predators, and crabs may find it easier to fit into tight spaces as a way to hide from predators.

As a science fiction writer, I’ve long wanted to include some crab-like extraterrestrials in my Sci-Fi stories.  All those memes about crabs being the “ultimate life form” led me to believe this would be a good idea.  The actual science behind carcinization makes me think otherwise.  Carcinization certainly happens a lot with certain animals (i.e., crustaceans) living in certain environments (i.e., the ocean floor).  But it’s not a universal principle of evolution.

All that being said, I’m going to put some crab-like extraterrestrials in a story anyway, because I still think it’s still a fun idea.


Here are the research papers I have read or am in the process of reading on the topic of carcinization.  I will have more to say about carcinization later this week.

6 thoughts on “Sciency Words: Carcinization

  1. Every time I see the word “carcinization” I think cigarettes. (I know “carcinization” is not “carcinogen”. Just my brain over associating.)

    This crab convergence is similar to another convergence that’s been coming up lately, that trees are not a specific species or even clade of species, but a growth strategy that many plants evolutionarily converge on. It also reminds me of the proliferation of beetle species, although I think beetles are a real taxonomic order.

    You’ve probably seen me mention Neal Asher’s fascination with alien crabs. He has a crab like species as the chief competitor to humans in his Polity universe. He gets into what the psychology would be for intelligent crabs. Pretty disturbing.

    Liked by 1 person

    1. I hadn’t heard that about trees. Maybe all those alien planets in Sci-Fi that are covered in suspiciously Earth-like trees make sense after all.

      I haven’t read much of Asher. I think I know the aliens you’re talking about, though in my head I pictured them as more bee-like than crab-like. Disturbing either way, of course.

      Liked by 1 person

    2. Oh, and carcinogen and carcinization come from the same Greek root word meaning crab. The ancient Greeks looked at cancerous tumors and thought the swollen blood vessels around them looked kind of like crab legs. That’s the connection between cancer and all these crab-related words. I learned that fun fact while looking up the etymology for this post.

      Liked by 1 person

      1. Yeah, Asher’s not for everyone. (He isn’t always for me either. I sometimes have trouble finding sympathy for his characters.)

        That’s really interesting on the etymology of carcinogen. Funny how many of the technical sounding words we use came about.

        Liked by 1 person

    1. Thanks! I’ve found that it’s a lot easier to understand science if you learn the vocabulary first. That’s been true for me, at least, and the theory behind this series is that it may be true for others as well.


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