Evolution keeps making crabs.
In fact, it's happened so often that there's a scientific term for it: carcinization.
If you close your eyes and think of a crab, you might picture a round, flat body. Big front claws and multiple sets of scuttling small legs. A hard outer shell. That's the form that seems to be favored by evolution. And scientists have known about it for a long time.
In 1916, English zoologist Lancelot Alexander Borradaile coined the term to describe what he called "the many attempts of Nature to evolve a crab."
"He knew already that some animals, like hermit crabs, may evolve a crab-looking form from a non-crab ancestor," says Javier Luque, a senior research associate and curator of crustaceans at their museum of zoology at the University of Cambridge in the United Kingdom.
But it wasn't until more recently that Luque and his colleagues started diving deeper into the multiple evolutions of crab-like forms.
Thanks to that research, they now know that carcinization – the evolutionary process during which non-crab crustaceans take on a crab-like form – has happened at least five times in the past 180 million years.
"We have evidence that decarcinization, which is the secondary loss, or the dramatic departure from a crab looking ancestor, has occurred at least seven times," added Luque.
With all of this talk of turning into or away from a crab-like life, some social media users have wondered: Could humans ever turn into crabs? For Luque, the answer is a simple no. "I don't think crabs will be the answer to all forms."
Instead, he says, all of this change is a reminder about the wonder and joy to be found in life's many forms. "You can divide and conquer. So that is the beauty of evolution, these splits in the branches of the tree of life, allow different branches to try different combinations and have a fail, an error like trial and error.
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This episode was produced by Hannah Chinn and edited by Rebecca Ramirez. Tyler Jones checked the facts. The audio engineer was James Willetts.
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