A meme consisting of text is not a meme.
You need a picture too.
No, a picture of text doesn't count.
I doubt crabs could make it as an intelligent interplanetary species. I mean claws are cool and all, but really tough to use tools with.
Sure, but have you ever tried to disarm a crab and lived to tell the tale?
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Neal Asher's Praedor Moon is a fun read if you want to see what advanced humans would do against space faring crabs.
Rumors say that the upcoming new Children of time book will also involve crabs
Life can have infinite forms and can exist and evolve in the most inhospit environments. But an advanced tecnologig species only can exist in certain environments and with reduced posibility in their appearence. Aquatic beeings can be intelligent, but never can create advanced tecnologies. The basic condicion of advanced tecnology is the domination of fire and electricity, not possible in the water, it need Oxign in the atmosphere.
They must have limbs skilled enough to handle and construct this technology, a complex communication system, and a binocular vision system (for this reason the most used in all species) to perceive their environment. The humanoid shape is one that best fits these maxims and therefore it is quite possible that an advanced species would also have a more or less similar shape.
It is known as convergent evolution, when unrelated species have a very similar physique to each other by living with the same challenges in similar environments. Evolution always use similar solutions for similar tasks. A good example is the genet, which looks and behaves very similar to cats, even with retractil claws), but they are a completely different species (Viverridae)
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Genets are bad example, because Viverridae are the closest relatives to Felidae. Convergent evolution would be better illustrated by fish and dolphins.
Well, viverridae are called feliforme for obvious reasons, bit their genealogic tree is way far from felidae. Yes, there are certainly a lot of other examples of convergent evolution.
I can't help but notice that you didn't list a whole lot of traits that would be considered vital to having a fairly human sillhouette. There's nothing here about obligate bipedalism, for example, or having just two legs in the lower part of the body at all. There's nothing here about how the forelimbs are articulated, and whether it would look meaningfully like hands or an array of dexterous tendrils or something. And all this gritty realist speculative biology seems out of place when most sci-fi is basically a particular sub-genre of fantasy anyway. Even being generous to the sci-fi writers, supposing the universe works in a fundamentally different way from how ours does (breaking laws of relativity and entropy, commonly), why can't some ecosystems work out to stretch your imagination of what could be an advanced species? It all seems very narrowly prescriptivist, even beyond the fact that this is fiction to the point of taking negative liberties with the bounds of what is truly realistic.
Edit: idk, it just seems obtuse. Like, "Advanced life can only be carbon-based because being that way affords these benefits" without considering that other models could provide other benefits (I'm sure you know better than I about the use of silicon-based life in speculative biology). And that's if the subject is addressed at all.
Yes, you can have 4 or more legs, but it isn't an advantage because energy efficience, same as more than two eyes ith an mobile head don't make much sense. Nature evolution don't waste energy. Humans a very efficient runners, which can beat several animals in a hunt. In the past they made a test between an horse and an trial champion, the horse lose it. Yes it was faster as the human, but not on long distance. There are championships like Ironman and others, where are races of 500 km, a horse can't even 42 km without a break. Efficience of two legs.
Dr Angela Collier has done a video essay on why aliens won't be silicon-based. She's not a biologist but an astrophysicist but the focus of her video is mostly about how carbon chemistry and cosmic abundance is better suited to producing life.
Maybe there's a rock out there made, by complete chance, in such huge proportion of silicon that it becomes more viable, I don't give a shit. It was just an aside anyway, pick another based on the same principle if you like. Why an obligate biped? Why this size? Why not a flying creature? Why not a rotationally-symetrical monstrosity? Why not an intelligent species that physically couldn't really be engineers but happen to live on the same planet as creatures who can? Or who just get contacted by outside life that can? I'm a dipshit who mostly prefers pulp and cosmic horror (read: fantasy) science fiction, so I'm sure someone who knows more could come up with more and better prompts.
