If there is one thing that’s clear from 250 million years of evolution, it’s that the world can’t stop generating crabs. Over and over, creatures that looked nothing like the crab have turned into crab-like beings. Some die out. New forms are born, looking nothing like the crab. Then some of them turn into crabs too.

It’s a phenomenon that was first described in 1916, by British evolutionary biologist LA Borradaile. He used the term “carcinisation” to describe the process by which a crustacean evolves into a crab-like form. Crabs often keep evolving (this creature does not have the most evolutionarily sound design). They sometimes shed the characteristics that made them crabs (the pincers, broad shell, flattened abdomen, staggering gait, lack of a real tail, and relative lack of defences), and live on as something else. This process has been named decarcinisation.

A series of recent studies, including one led by Harvard phylogeneticist Joanna Wolfe, published in the journal BioEssays in 2021, suggests that the evolution into crab-like form has occurred at least five times, and the process of shedding the crab form has occurred at least seven times, over the past 250 million years.

Why would this be? “There has to be some kind of evolutionary advantage to being this crab-like shape,” Heather Bracken-Grissom, an evolutionary biologist, associate professor at Florida International University and co-author of the 2021 study, said in an interview with the platform Popular Science.

Researchers believe it may have something to do with gaining an edge in new habitats. The fact that there are more than 7,000 unique crab species scattered around the world is cited to support this argument.

Wolfe might soon have a clearer picture. In her next study, she plans to assess the evolutionary success of the species that carcinised and decarcinised, against samples of those that did not. Could being crabby simply help you survive?

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