Instant Crabification: Why Evolution Keeps Coming Up Crustacean

By Helen LinLast Updated May 27, 2021 6:44:54 PM ET
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Photo Courtesy: q phia/Getty Images

Plenty of interesting things took place during the pandemic lockdown of 2020. With everyone stuck at home, attention wandering aimlessly, it was only natural that many of us would revert to scrolling around online. It was during this mass instance of random swiping when a Twitter post gained steam and the internet collectively discovered an evolutionary process called carcinization.

According to Know Your Meme, it was around October of 2020 that carcinization memes began appearing in full force as a common search result. And the memes that a quick Google search delivers depict the strange scientific process that describes how various creatures seemingly turn into crabs over time. But is carcinization real, or is it just meme fodder? Let's take a closer look into the process and its biological implications.

What Is Carcinization?

So what exactly is carcinization, and why did it become the focus of so many internet users in 2020? If memes are to be believed, it’s the idea that everything, from internet routers to other memes, eventually evolves into a crab. But memes often come with a hefty dose of hyperbole, and the idea that every creature on Earth is destined to eventually resemble a Dungeness from the depths is a pretty hefty exaggeration.

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Photo Courtesy: One of many carcinization memes that began appearing online during the second half of 2020. Credit: Wikimedia Commons

Carcinization is an actual evolutionary process, however, and it involves crustaceans specifically. Scientists have documented ample instances in which previously un-crab-like crustaceans have evolved into far more crab-like forms, and their process of doing so is called carcinization. ("Carcin" comes from the Greek "karkinos," which means "crab" and is also the origin of the zodiac sign Cancer.) This isn’t a recent development in the scientific community, either; the term "carcinization" was first coined by zoologist Lancelot Alexander Borradaile in 1916. Researchers have been observing carcinization taking place for over a century.

In 2017, several academics performed a scientific study on the subject and published their findings in the Biological Journal of the Linnean Society. The study discussed five documented instances in which creatures that started out as something else all managed to evolve to display much more crab-like forms. A 2020 tweet from a user who’d just discovered this research ended up going viral. The internet latched on and began creating jokes, and the rest is meme history — much like the creatures that gradually turned into crabs.


Not All Crabs Are Created Equal

Before we go any further, it's important to define exactly what "crab" means, at least in scientific terms. The answer sounds like it should be obvious, right? Well, not exactly. As it turns out, science is far pickier about naming conventions and descriptions than many of us might imagine.

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Photo Courtesy: Theo KRUSE/Wikimedia Commons

There are actually two branches of the crab family: true crabs (brachyurans) and false crabs (anomurans). Generally, true crabs are distinguished by their four pairs of legs, while their false counterparts only sport two or three pairs. Additionally, true crabs have short abdomens that are curled up under their bodies for protection, while false crabs have longer, less protected abdomens. Their exposed abdomens were actually what prompted hermit crabs to use borrowed shells — they needed additional protection.


While true crabs are believed to have come from rather crab-like ancestors, the false crab crowd may have only developed its crabbiness more recently.

So, What Creatures Have Achieved Crab-Like Status?

What exactly does carcinization entail? According to the original study published in 1916, "carcinization...consists essentially in a reduction of the abdomen of a macrurous crustacean, together with a depression and broadening of its cephalothorax, so that the animal assumes the general habit of body of a crab." In today's English, this means that a creature that used to have a longer, leaner body — perhaps something like a lobster — evolved to assume the rounder, more squatty shape of a crab.

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Photo Courtesy: Humberto Ramirez/Moment/Getty Images

Several creatures are believed to have undergone this crab-like makeover, including:

  • King Crabs: Scientists believe that these crabs, which are now rather intimidating in appearance, actually evolved from the humble hermit crab.
  • Porcelain Crabs: Though they now look distinctly crab-like, porcelain crabs may have originally begun as squat lobsters. Squat lobsters themselves may actually be partially carcinized lobsters.
  • Hairy Stone Crabs: They actually do look quite hairy and may have also evolved from the hermit crab/king crab family.
  • Coconut Crabs: Also known as "robber crabs" due to their predilection for stealing human garbage — they’ve evolved to live on land — these creatures may have begun their ancient evolution as hermit crabs looking to level up.
  • Cyclida: This prehistoric crustacean is believed to have been the pioneer of carcinization, and cyclida that failed to evolve into crabs were eventually pushed to extinction by those that had carcinized.

What's Behind This Crab-Like Sorcery?

Now that humans have discovered the reality that some creatures undergo carcinization, the scientific community’s next step is figuring out how and why it happens. These are two questions for which science has not yet managed to find definitive answers.

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Photo Courtesy: Rickard Zerpe/Wikipedia

That said, there have been a number of studies digging deeper into this phenomenon — some of them even fairly recent. A 2021 study published in the peer-reviewed journal BioEssays posed a hypothesis based around something called phenotypic integration, which studies the development of different evolutionary traits in a species and the ways those traits work together to provide overall benefits.


The researchers concluded that multiple features of a crab’s body — the flat, hexagonal shape; the short abdomen; and the hard shell, among others — confer physical advantages that make creatures with those features more likely to thrive. The more crab-like a crustacean can become, the more likely it is to survive in its environment. In essence, it pays, biologically speaking, to pass on these crabbier traits to offspring.

But this is just the beginning. There's still a lot we don't know about carcinization, except that it makes sense in terms of offering crustaceans a better protective advantage.


Evolution in Other Species

As mind-blowing as carcinization may initially seem, it's more or less just another form of evolution that's hardly unique to crabs. Evolution is simply the sum of changing traits a species or population inherits over time.

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Photo Courtesy: Shahzaib Damn Cruze/Wikipedia

For instance, camels probably weren't always as perfectly suited for the desert as they are today. But, over time, they developed third eyelids and long eyelashes to keep sand out of their eyes and humps that store fat and water that can sustain them when nourishment is inaccessible. Their fur is even thinner in some places to allow heat to escape and thicker in others to shield their skin from the sun.


Just don’t expect them to start sprouting pincer claws and turning red anytime soon — leave that to the crustaceans.