In 1989, paleontologist Stephen Jay Gould proposed a thought experiment: What would the world look like if we turned back time and replayed the evolutionary tape? “I doubt that anything like Homo sapiens would ever evolve again,” he concluded. Maybe not. But crabs might.
Evolution just can’t stop creating crabs. Believe it or not, the flat-and-wide body plan has evolved at least five different times. The process is called carcinization, and it’s inspired comics, memes and entire subreddits.
Still, biologists don’t know why crabs keep evolving. Figuring it out would satisfy the online masses, sure, but it would also be a step toward solving other important scientific mysteries. For instance, why some species share evolutionary paths while others forge unique ones (looking at you, platypus).