On Earth, things evolve into crabs -- could the same be true in space?

[C C]

https://arstechnica.com/science/2021/07/...-in-space/

INTRO: Many organisms on planet Earth aren't crabs. Dogs, for instance—definitely not crabs. Science also suggests that humans are not, in fact, crabs. But a surprising number of creatures either are crabs or look a lot like them. For example, a hermit crab has a distinctly crab-like appearance but is not technically a real crab. 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.

Around a year ago, this evolutionary process captured the imagination of the Internet. Headlines like “Why everything eventually becomes a crab” and “Why Does Evolution Keep Turning Everything Into Crabs” popped up. PBS even made a video.

"Everything" is clear hyperbole—the overwhelming majority of things on Earth are not crabs and seemingly have no plans to become them. 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.

Because we take these things far too seriously, Ars spoke to experts on crabs, evolution, and alien life to find out. 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... (MORE)

[Yazata]

https://arstechnica.com/science/2021/07/...-in-space/

INTRO: Many organisms on planet Earth aren't crabs. Dogs, for instance—definitely not crabs. Science also suggests that humans are not, in fact, crabs.

I hope not.

But a surprising number of creatures either are crabs or look a lot like them. For example, a hermit crab has a distinctly crab-like appearance but is not technically a real crab. 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.

Around a year ago, this evolutionary process captured the imagination of the Internet. Headlines like “Why everything eventually becomes a crab” and “Why Does Evolution Keep Turning Everything Into Crabs” popped up.

"Everything" is clear hyperbole—the overwhelming majority of things on Earth are not crabs and seemingly have no plans to become them. But if there are benefits to having a crab-like shape on Earth, should we view that as a general rule of life?

I don't think so. It isn't every animal where this happens, only some of the arthropods. So I'd say that it's a function of the genetic potentialities associated with the basic arthropod body plan. Something that they inherited from their ancestors.

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.

Again, that sounds far fetched. It would require not only that alien life have Earth like metazoa, it would require that those alien metazoa have the same repertoire of inherited developmental processes as our arthropods.

Given the size of the potential possibility-space that life might evolve to fill, I think that would be very unlikely. I don't anticipate that even if future space explorers find alien life (or something suitably like life) that they will encounter any reproductions of Earth life. That's probably as true for crabs as for humanoid mammalian bipeds.