If the form of a crab works because it makes it easier to scurry away into rocks and such, then some kind of rocky geography could also help a planet's chances of carcinization. But largely, it seems that water or some kind of liquid on a planet would increase the odds of crabs being there. There are also terrestrial false crabs, such as the terrifying coconut crab. On Earth, there are terrestrial crabs, which evolved from their marine kin. And a converse is also true: planets different from Earth are less likely to have crabs.įor example, a planet like Naboo in Star Wars-which has land, bodies of water, rock, etc.-could be home to crabs, Wolfe said. Wolfe noted that any creatures on these theoretical planets would still need to have the right genetic building blocks to be capable of evolving into crab-like forms. With the right environment, however, crab-like aliens could hypothetically evolve elsewhere. Even if we found aliens that looked like crabs, they obviously wouldn't be crabs as we've defined them. Right now, there's no evidence that there is any life, much less crab life, on other planets. So, for example, both shrimp and crabs have a genetic toolkit that lets them produce many limbs and exoskeletons, while humans do not-meaning, most likely, there are no human-relative crabs on the horizon. The genetic makeup of a species that evolved a crab-like body plan would need to have the right building blocks for the process. Wolfe also suggested that there are probably genetic limits to carcinization. Some crabs don't even use their claws for predation a male fiddler crab, for instance, uses his one massive claw for sexual display. (Even though, again, having claws doesn't make a species a crab-lobsters have huge claws but aren't crabs.) But defending that argument is made harder by the fact that claws have multiple functions. AdvertisementĬlaws might be a boon as well, Wolfe said. This could make them smaller targets for predators and could allow the crabs the ability to run and hide in smaller crevasses. Crab bodies tend to be compact and quite flat, with their abdomens folded up below. Wolfe said that the similar body plans may evolve because the body shape of a crab could have some advantages. Though they evolved to have crab-like features, they are not true crabs, which are in the infraorder Brachyura. For instance, a hermit crab is a decapod crustacean and part of a group called Anomura. Yet crab-like forms are common enough that a number of the things we call crabs aren't all that closely related to crabs. “There is no clear-cut reason why being a crab is better than not being a crab,” she told Ars. However, Wolfe-who penned a paper on the topic last March-also noted that there are still no definitive answers. According to Jo Wolfe, a researcher at Harvard University's Department of Organismic and Evolutionary Biology, carcinization could be a mixture of genes and the environment. The reasons creatures evolved crabby features are still unknown, though there are numerous hypotheses. The answer: it's highly speculative, given that we haven't found life-crab-like or otherwise-anywhere else, but it's not wholly impossible. But if there are benefits to having a crab-like shape on Earth, should we view that as a general rule of life? Could it hold true on other planets? If the process of carcinization operates here, it's not unreasonable to expect that it might happen elsewhere.īecause we take these things far too seriously, Ars spoke to experts on crabs, evolution, and alien life to find out. "Everything" is clear hyperbole-the overwhelming majority of things on Earth are not crabs and seemingly have no plans to become them. Headlines like “ Why everything eventually becomes a crab” and “ Why Does Evolution Keep Turning Everything Into Crabs” popped up. Hermit crabs are not alone over the history of life on Earth, there have been five separate cases in which decapod crustaceans have evolved this way, a process common enough that it has picked up a formal term: carcinization.Īround a year ago, this evolutionary process captured the imagination of the Internet. For example, a hermit crab has a distinctly crab-like appearance but is not technically a real crab. But a surprising number of creatures either are crabs or look a lot like them. Science also suggests that humans are not, in fact, crabs. Many organisms on planet Earth aren't crabs. David Kirkland / Design Pics reader comments 161 with
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