[yourenotsmart]

The example of convergence between fish and dolphins, birds and insects, the infamous "why does everything evolve into crabs" study and so on should tell us that while we should be open for radically different forms of life, the most likely outcomes will look like something we've seen here on Earth.

I'm personally expecting something like 80% humanoids and 20% exotic forms. Maybe I'm primed incorrectly by cheesy soap operas and sci-fi TV shows, but I think they're not far off (even if for unrelated reasons like SFX/VFX budget and character empathy).

[spywaregorilla]

Given how rare humanoid shape is on Earth, it doesn't seem especially sure that humanoids will be dominant among even intelligent life.

[godelski]

What are we referring to as humanoids though? And what are we about as intelligent? Crows? Crows aren't going to build spaceships and don't really have the means to because a beak isn't a great manipulator, even though they use tools. I don't think the person above is saying that quadrupeds would be out of the realm of possibility (maybe they are. IDK I'm a computer scientist, not a biologist. I could totally see body size, caloric intake ratios, and brain mass being related in a way that would make these unlikely), but rather things like fractaling appendages would be expected because intelligent life would need to have fine motor control. (Is a centaur humanoid?) There are just more efficient ways to do things than other ways. Yeah, maybe alien life will have a beak. Maybe their pupils will look different but I'd still expect them to have eyes with squishy lenses because that's pretty much required to be able to focus and intelligent creatures need to be able to sense things both near and far (without technological enhancements). Light sensing isn't enough if you want to build things, you need depth perception. I think if you follow this line of reasoning you'll find that a lot of attributes humans have would be pretty likely for intelligent alien life as well.

[imbnwa]

Can echo location be used for depth perception?

[godelski]

Yes but it is very expensive. Here's some more on bats[0] (mentions expensive echolocation around 5:45 and moving from sonic location to echolocation evolution). Eyes do also convey more information. You can get colors in addition to depth and shape and that's a good reason and easy path for eyes to develop since light sensing is a pretty easy thing to develop. Also, bats aren't blind, despite common belief.

[0] https://www.youtube.com/watch?v=zWeYCULC0UQ

[ncmncm]

It can. One eye and echolocation gives you everything you get with two eyes except redundancy.

Cyclops got by with one eye and throwing rocks.

[dtech]

Arms+hands and a head with a similar face though.

A head is pretty universal because eyes are so important and a feeding hole near your sensory organs is a massive advantage.

Having hands seems almost a pre-requisite to become truly intelligent and tool-using.

[titzer]

Octopi have all the things you mentioned (except hands). Their eyes are even better than human eyes. No one would describe them as "humanoid".

[godelski]

Also consider an octopi's environment. That environment is not well suited for being able to build lots of things. How do you get to the bronze age underwater? How about even earlier. Land based creatures have pretty similar forms. Snake like, bipedal, quadru/multiped, and flying/winged creatures. Snakes don't have arms and so aren't going to have fine motor control. Winged creatures are going to have a hard time dealing with heavy objects (they have hollow bones to fly and wings are incredibly fragile and I don't see nature creating super materials, plastics, or metal structural systems for animals). Quadrupeds probably aren't going to develop arms like centaurs (more likely legs become arms). So if we want a creature that can have fine motor control, live in an environment that can easily create metals, not be extremely fragile, and is able to devote a significant amount of its energy intake to its brain, you're probably going to come up with something ape like (bipedal). There are other forms here, but we can see that there are some pretty good hints that we learn just from mechanics and aren't so much dependent on specifics of Earth or humans.

[Alan_Dillman]

"Also consider a human's environment. That environment is not well suited for being able to build lots of things. How do you get to the <untranslatable> age on earth?"

Earlier, you mentioned that beaks can't make spaceships. Well, maybe neither can hands. What we call a spaceship might be laughable nonviable. In fact, we know it is.

We're struggling at limits that some other lifeform might not have. We're hill climbing for tools that will let us do things we really want to do. Quite likely a lot of our progress is orthogonal or even oppositional to what we need to do to get off the planet.

We have no idea if some of our progress might be backsliding or entirely halting our future progress. Due to our natures. Due to our beaks.

[godelski]

> Earlier, you mentioned that beaks can't make spaceships. Well, maybe neither can hands.

Except hands did create spaceships...

The "beaks can't make spaceships" is a comment about crows not having hands. Crows use their beaks to manipulate objects. This does not imbue cows with great motor control. The use of tools is very different than the ability to finely manipulate tools. Aliens could have beaks, but these would not be their way to build spaceships. Similarly they wouldn't have pincers. Such grasping mechanisms just are extremely inefficient and don't allow for certain tasks.This excludes a lot of classes of tools from crows. This isn't biology, this is physics.

[ClumsyPilot]

"Quadrupeds probably aren't going to develop arms like centaurs (more likely legs become arms)"

They already have, it's called praying mantis.

May insect forms are very non-humanoid and are very viable.

[godelski]

But this form is also extremely rare. You're also ignoring the main component of the argument, which is where calories are going, not that arms can come out of a body.

[d110af5ccf]

I largely agree with the general idea here.

> metal structural systems for animals

Something resembling this has actually been observed in a species of deep sea snails. Iron sulfide is incorporated into the hard bits (shell, foot armor). (https://en.wikipedia.org/wiki/Scaly-foot_gastropod)

[JoeAltmaier]

Hm. We have what, a dozen or more on Earth? Apes, monkeys, homo etc. Plus dozens of dinosaurs that stood on 2 legs. It seems pretty common.

[ivoras]

That's a wrong way to think about it, since all modern "humanoids" are descended from the same ancestor not that long ago.

And if you consider dinosaurs humanoid, then so is that meme cat that can walk on its two back legs.

If there was an apex predator in every tree of life, in the "humanoid" shape, and I'm talking "humanoid ants" here, then it would be reasonable to assume that there's something beneficial in the "humanoid" shape that helps long-term survival.

And that's not even taking the majority of lifeforms into account - those in the seas, and greatly discounts birds. We still can't agree on if dolphins and crows are intelligent.

So, no, chances that the "humanoid" shape is somehow special out there are basically 0, since it's not even special here on Earth. We're an accident. Insects, mushrooms, plants - all those life forms are better adapted for mere survival than us (judging by cumulative mass of live organisms).

[JoeAltmaier]

That's the wrong way to think about it. Nothing is 'better adapted' than anything else. Each is adapted to its own niche. And no accidents really - convergent evolution shows that similar ecological pressures very very often result in similar forms. Witness fish ("there's no such thing as a fish") or trees ("there's no such thing as a tree").

And that dinosaur comment - I don't know what to do with that. Dinosaurs only walked on two legs in internet memes? That's so far wrong I can't comment.

[ajuc]

a dozen out of millions of species is not "pretty common"

[JoeAltmaier]

Many convergent evolution paths led to the same similar form, in time. That was the point. If the environmental pressures are similar, the forms may be similar.

[asah]

100.0% of spacefaring earth creatures are bipedal /s

[excitom]

Dogs have been send into space

[dogorman]

> convergence between fish and dolphins

The convergence between dolphins and ichthyosaurs is even more remarkable. Ichthyosaurs were marine reptiles; air breathing tetrapods that, like dolphins, had ancestors that walked on land but eventually returned to the sea to kick fish ass.

https://en.wikipedia.org/wiki/Ichthyosaur#/media/File:Ichthy...

[ncmncm]

Bony fish evolved in rivers, and eventually returned to the sea to kick... what? Analogies fail.

Those fish are overwhelmingly more closely related to horses than to sharks.

[mike_hock]

Sure, organisms that already share a massive amount of commonalities can diverge and then converge again.

What about the branches that happened early on? We essentially have only two lineages of macroscopic organisms that are actually fundamentally different: Plants and animals.

I would expect any kind of macroscopic extraterrestrial life to be at least as distinct from Terran plant and animal life as they are from each other.

[depressedpanda]

> We essentially have only two lineages of macroscopic organisms that are actually fundamentally different: Plants and animals.

That's not true, we also have fungi as a macroscopic lineage.

Or maybe you put them in the plant group? If so, that's a mistake, as they are more closely related to animals than they are to plants.

[uh_uh]

I think it's fine to lump fungi together with plants for the spirit of this discussion. The distinction between plants and fungi are made on the basis of metabolism but in this thread people are clearly talking about external behaviours observable with the naked eye.

[godelski]

Metabolism influences external attributes (I think behavior isn't the right word you're looking for). A larger creature requires higher caloric intake than a smaller creature (and this process isn't linear). A larger creature has different thermal regulations than smaller creatures because surface doesn't scale with volume linearly. The bigger the creature the more it calories it has to expend on the body vs the mind. There are equilibriums here that are physics based.

And then consider the selective pressures from plants vs fungi. A fungi gets its environment. Plants do some, but also need to perform photosynthesis. These have very different selective pressures for these lifeforms.

[hoseja]

If you're talking about lineages you should actually lump Fungi with animals. Also, how are fungi behaviours comparable to plants?

[uh_uh]

If their behaviours are not comparable, then why were fungi lumped together with plants up until the 1960s?

[yourenotsmart]

DNA is extremely flexible, there's no macroscopic form or shape it can't take, as various insects camouflaging themselves as sticks and leaves and what not shows.

So the idea we'll see some vastly different concepts with different starting blocks is possibly unfounded.

Alien life might be very different at low level depending on their environment, but in terms of macroshapes, things like the formation of a head with eyes and mouth, upper and lower limbs, bilateral symmetry and so on will repeat over and over.

We'll see (in another life probably).

[mike_hock]

Yeah, but so what? The geometric shape isn't very interesting. The insect camouflaging itself as a leaf still functions as an insect. It doesn't perform photosynthesis.

Considering that we have a whole class of lifeforms that have nothing like a head with eyes and mouth or limbs, the idea that this would evolve independently more likely than something completely different, is also possibly unfounded.

[harperlee]

Having two eyes, as a simple example, is arguably the cheapest way to perceive 3d at things-may-want-to-eat-me distance: just two points that enable triangulation. Similar constraints reduce the configuration space a lot. It still remains huge, but I don’t think someone that believes about certain convergence to be necessarily naive.

[ClumsyPilot]

Having three eyes, as a simple example, is arguably the cheapest way to percieve 360-degree view of things-may-want-to-eat-me.

Plenty of animals that have 2 eyes and no 3d vision, they try to get as close to 360 coverage as possible.

[spywaregorilla]

> DNA is extremely flexible, there's no macroscopic form or shape it can't take, as various insects camouflaging themselves as sticks and leaves and what not shows.

That feels like a really bold claim given the evidence.

[ncmncm]

Let me know when you spot an animal that drives around on wheels.

[dtech]

Physically you could have wheeled animals, but wheels just won't evolve. They are perfect for somewhat smooth surfaces where you want to travel in a somewhat straight line. Organisms just cannot confine themselves to that and survive.

Unless we find a planet composed entirely of solid smooth rock we won't find wheeled animals.

[jhgb]

How would wheels get fed with nutrition? Would they have tiny mouths?

[mod]

Gears have evolved, though, which is equally cool IMO.

[pvaldes]

rotifers

[ncmncm]

Rotifers do not, in fact, have wheels.

[rendall]

... on planets. That have a precise similarity to Earth. Sure, I can provisionally accept that.