We need to talk about crabs.

Specifically, why nature is seemingly so hell bent on ensuring that on a long enough timeline all creatures will, eventually, become crabs.

This is not a new phenomenon.

The process, which is called carcinisation (from the Greek karkinos, meaning both cancer and crab…a lovely thought) is a unsettling expression of the way animals can live in wildly different habitats, but end up evolving the same characteristics.

The term was coined by evolutionary biologist L. A. Borradaile, who described carcinisation as “one of the many attempts of Nature to evolve a crab”.

But this is where it starts to get weird.

You and I understand that animals that live in similar areas face challenges that can point them all toward the same evolutionary advantages. It’s obvious when we see it.

Birds and bats can both fly using mechanical wings. Birds and bats are both warmblooded, otters and ducks both have webbed toes, and so on. Seems totally normal and not at all horrifying. Right?

But not crabs. Oh no, not crabs.

Instead of being isolated like Darwin’s famous Galapagos inhabitants, they formed almost spontaneously instead of being geographically “imprisoned”.

Think about it: Different oceans. Different predators. Different eras. Nature sighs and gives us the same answer:

“You should really think about just like…being a crab, man…”

For those of us aware of the threat of crab people and/or space crabs, this is not good.

I can tell you’re surprised. Faced with different challenges, nature’s go to answer is to make you …a crab?

Yes. Five recorded times in fact.

And it’s not just the sometimes cute (but more likely horrifying) crab shape that unifies these five separately evolved crabs.

A 2017 paper that went viral details all the ways evolution is really just, like, obsessed with crabs: neurological development, circulatory systems, body shape, claws, mobility… it’s all crabs all the time.

Curiously, not only did the crab-like habitus evolve independently from the ‘true’ crabs (Brachyura), it also evolved three times independently within anomurans. […] Although enormous morphological disparity is observed in the internal anatomy of the crab-like taxa, reflecting the fact that the evolution of the crab-like habitus was indeed convergent, various corresponding dependences are found across the different lineages between the external characters of a crab-like habitus/morphotype and inner structures. In other words, as a result of carcinization certain structural coherences led to the specific internal anatomical patterns found in crab-like forms.

In fact so…many…things… have become crabs over time that it’s hard to tell where they originally came from. And it’s still happening now.

The paper dives into the fact that gigantic king crabs are the descendants of the tiny hermit crab, whose progenitor which may not have even BEEN CRABS AT ALL.

And this is not new: as far back as 1818 scientists have been trying to figure out even what exactly a crab is, because so many things are, well, crabs.

If all this crab talk has you unsettled about our evolutionary fate, you should be.

The authors of the paper end with this chilling note: “There is no reason to assume that ‘evolutionary tendencies’ or any such vague concept played a role.”

So it’s settled: no matter what happens, no matter where, nature is gonna make you a crab.

🦀

Photo by Tobias Tullius on Unsplash