[psadri]

Hydrogen, carbon and oxygen are amongst the most common elements in the universe. So probabilistically life will be carbon based. And it will probably be first formed in water. But it would develop tools on land once opposing thumbs are formed (from climbing trees). So I think there is a high chance aliens with technology will look a lot like us.

[albertsondev]

That logic follows... right up until the leap to arboreal lifeforms with opposable thumbs being an inevitability (or even a prerequisite to tool use!).

Opposable thumbs are not a guarantee. Nor are tree-dwelling lifeforms, nor trees, nor thumbs, nor digits, nor four limbs. For all we know, intelligent life elsewhere might better resemble intelligent octopi using alkaline metals as their first rudimentary energy source as we did with fire.

[cmrdporcupine]

Why even assume multicelluarity as some kind of inevitability?

Hell, it took 2 billion years to get to single celled eukaryotes on earth. But the earth was teaming with prokaryotes the whole time, two entire separate branches of them, too, and they seem to have sprung into existence almost as soon as the earth cooled enough.

There's still a lot more of them in terms of total weight than animals and protists. A lot.

[psadri]

It’s not inevitable. I was simply stating the most probable form for the life that DID get that far.

[psadri]

I was describing the most probable path, not the only path.

I do think that developing more sophisticated tools under water is difficult. Once you have plants on land, taller “trees” are very probable, because they are competing for light. Once you have trees, it’s likely that animals will climb then for safety or food. Once they climb, they will likely develop better gripping, etc…

I guess another way to look at this is that life on Earth is not special (although it is still an insanely amazing occurrence).

[cocoa19]

Abundant carbon is not the most compelling reason for aliens to be carbon based.

Carbon is one of a few elements to be able to easily bind to other elements including itself and able to form long and complex chains. Silicon is another that can form long, complex chains.

[bluGill]

Both are needed. If it isn't abundant, then odds are against those long chains forming.

[anigbrowl]

https://www.usatoday.com/story/life/animalkind/2023/12/13/th...

[jvanderbot]

Snakes climb trees.

[nomel]

Not nearly as well as monkeys, or any other legged thing you can find in a tree.

[jvanderbot]

I'd say leopards are probably the best tree climbers. Or squirrels.

Not a thumb between them.

[nomel]

Leopards can't begin to approach what a monkey can do [1], since they can't hang safely, since they don't have thumbs. Leopards rely on penetration of their claws, or being on top of the branches, like squirrels. It works for the squirrel because they're small, and the tension forces applied to the bark are negligible, so they can just crawl upside down. You won't see a leopard hanging from anything, in a non-comical way. A leopard does have an advantage of clawing up thick trunks, which is one of the reasons they hunt monkeys that are first on the ground, rather already in the trees.

[1] https://youtu.be/9rdn26Hpdwo?feature=shared&t=118

[jvanderbot]

Speaking of hanging, you know who really climbs trees well though? Sloths. Great at hanging. Practically live up there.

No thumbs.

[nomel]

Yes great at hanging, like a coat hanger. You can only easily pull with a hook. With a thumb, you can push, pull, and easily grip, with much less risk of "unhooking". That's the same risk for a leopard: unhooking. Sloth can't climb a thinner vertical rope, or hang from a thinner branch, because their grip strength is relatively weak, due to the leverage. And, good luck using any sort of tool, like a stick to get terminates, with giant hooked claws!

[wolverine876]

Why do we assume land and trees, and everything required for them?

[andrewflnr]

Trees, for one, have evolved convergently several times. You could arguably include those giant early fungus, too. Given land, trees will follow.

Land mostly requires that your planet doesn't have too much water. Plate tectonics helps, but I'm not sure it's required.

[wolverine876]

> Trees, for one, have evolved convergently several times.

They evolved here. The whole question is how much their existence depends on Earth's specific environment, genetics, etc.

[psadri]

I think there are lots of worlds that don’t have dry land. I doubt they would develop advance technology - hard to build fire to melt metals. But perhaps nature will find another way?

[deafpolygon]

At one point, this planet was covered in mushrooms!