askchapo

I think Maoo is right in the sense that it is much more likely that aliens would look like giant shrimps and not like hot blue women. But sure you most likley need something to manipulate your environmnet with but that could be a tentacle and doesnt need to be a hand with 5 fingers.

A given hypothetical alien may have an entirely different chemical base or not be chemical at all in the sense we'd understand it. Their senses for, say, light, could be made from entirely different strategies.

To your point, look at octopus eyes vs. mammalian (or even fish) eyes. Both evolved independently with likely little more than light-sensitive patches of cells but ended up with similar "solutions" of an enclosed orb with a lens and light sensitive array of cells at the back.

But we should remember that our common ancestor was already highly constrained. Incredibly similar biochemistry. Bilaterals. Same strategy for being multicellular at all. General developmental patterns and mechanisms.

Aliens would share none of that with us. Look at the myriad precambrian body forms and then think about how every single one of them would've shared like 80%+ of the DNA we have. Aliens would share none of it.

So much of all of that is contingent on historical "accidents", just like hiccups are a behavior resulting from our fish ancestry that no longer applies or how mammals' urethra + penis is moved around during development makes penis-havers' lower abdomens more prone to hernias or how we're basically a big connected tube from mouth to anus going back to our ancestry as worms.

If you went back and replayed Earth's own life history and jostled some of the "accidents" it would go wildly differently. Different body plans winning out, different mass extinctions creating different opportunities for radiations of minority clades. Birds and mammals only exist in their currently recognizable forms and diversity because the most recent global mass extinction killed off the dinosaurs and a similar story applies to every global mass extinction. Imagine the conditions going in a different order.

Now look to aliens. Imagine they come from an environment where oxygen could be available because the chemistry of Earth's photosynthesis was not favorable. No mass extinction due to the rise of oxygen in the atmosphere, no oxygen-breathing animals. Who knows what they'd look like or how they'd form multicellularity or if they'd even be cells. We have no base of reference: our planet's life is the only example we know of. In fact, we might even be alone.