[asymptosis]

> Because primates are a universal deterministic outcome of evolution on all worlds

In all fairness, if you think of the constraints required for a species to become space-faring, you're going to be hard-pressed to make it work with an organism which isn't at least a bit like us.

1. You can't be a marine organism, because developing advanced technology requires combustion, and water isn't something you want to be carting into space with you.

2. You need a musculoskeletal system which can support a large brain. For non-marine organisms, this implies something with a big head on top of an upright stance.

3. Having a surplus of limbs is contraindicated for large organisms. Large limbs are expensive to build, and larger organisms are more constrained by gravity than surface tension, which makes multiple limbs less useful.

4. You need appendages for manipulating tools, and voices to debate and share ideas.

5. To develop non-trivial intelligence, you need to be multicellular, and multicellular organisms need to be able to reproduce. So, there is probably going to be sex involved, along with all the complexity that goes along with that, such as sexual competition and selection, caring for the young, and all the politics that arise from these kinds of interactions.

Putting these constraints together, you don't have too many options for aliens which are both realistic and interesting enough to build a story around. Your aliens are either:

* Bipedal politickers.

* Robots.

* Not capable of building something we would recognize as technology or civilization.

[eesmith]

> Having a surplus of limbs is contraindicated for large organisms

Having a large brain is also expensive to build. It's always a questions of trade-offs.

I can easily imagine how a hexapod like a centaur (four legs and two arms) can combine the speed of a horse and dexterity of a human and make up for the metabolic overhead.

> 4. You need appendages for manipulating tools, and voices to debate and share ideas.

You don't need sound. Sign language exists even in humans.

That wouldn't even require large appendages. The "talking" could be done by photophores, or 1cm long flexible vermiform appendages, or controlling the pattern of fur movement.

[aeneasmackenzie]

A comment there mentioned “human panspermia” such as Niven’a Protectors, but I’ve also seen “humans evolved independently on every planet in the universe exactly the same.” I hunk this was the justification in Dickson’s Wolfling for example. I really like the absolute lack of concern for this entire list and the mindset behind it that drives a decision like that.

[p_l]

Or you can have a design like Liir from Sword if the Stars. Space Dolphins where everything fits regarding how they got to space, but full details are a big spoiler

[fouc]

technology or civilization doesn't require our recognition, it exists or not regardless.

Our combustion-based technology is rather a fluke of having a huge amount of one-time crude oil reserves. Other planets won't necessarily have that.

[asymptosis]

We're talking about fiction. If you can't recognize it as technology or civilization, how do you plan to write about it?

As for combustion, indeed, other planets may not have it. So how do you propose that they would start to develop a technology which would lead to building spaceships?

[uncletaco]

This was not a problem in Solaris, Annihilation, or Story of Your Life.

Some stories very much are about aliens who use tech or have civilizations that are very very alien to us.

[filoeleven]

Children of Ruin does this quite well also.

[kragen]

I don't think that's right, though I deplore the ignorant subhumans who were downvoting you like some kind of fucking spammer.

> 1. You can't be a marine organism, because developing advanced technology requires combustion, and water isn't something you want to be carting into space with you.

Humans cart water into space with them; an 80kg human contains about 50kg of water. It hardly matters whether that water is all inside your skin or partly outside your skin but inside your spacesuit.

The combustion question is more interesting: can you develop advanced technology without being able to burn things in your native environment? I think there are three reasons that the answer is "yes":

A. There are lots of other ways to manipulate material properties other than changing the material's temperature. The humans use fire because it's easy, but that doesn't mean it's the only way. Electrolysis can be rather surprisingly effective, and there's also manipulation of pressure rather than temperature, which is how the humans finally produced a room-temperature superconductor a couple of years ago, and of course crucial to the Haber-Bosch process. Manipulating pressure is very hard in a gaseous environment; being underwater makes it a lot easier, especially if, like a sperm whale, you can dive from 1 atmosphere down to 2 km of depth (200 atmospheres), or if, like a mantis shrimp, you can create cavitation bubbles that create plasma hotter than the surface of the sun when they collapse. Organisms like electric eels might be able to do electrolysis intrinsically, without tools, if they were intelligent, but you can also pound native copper into wires to make windings for electrical machines like generators.

B. The humans do a lot of material manipulations in environments they can't live in: the hard vacuum of an electron microscope, the interior of a furnace itself, the freezer in your house, the sulfuric acid of a car battery, the violently water-reactive environment of a Grignard reaction, the boiling airless interior of a soup pot, even the room-temperature airless interior of a water bath. Intelligent marine organisms could do their hot material processing in a trapped bubble of air as easily as the humans do their solvated material processing in a trapped flask of water.

C. A fish is a far more complex, delicately balanced, and robust system than an Audi, and yet genes are able to construct a fish entirely underwater, without using any fire. If genes can do it, obviously it can be done, even if the humans haven't had to figure out how to do it themselves.

I do think doing without fire in your native environment on Earth would be a lot more difficult, though.

But what about environments that are radically different from Earth? Venus's atmosphere at the surface consists of mostly supercritical carbon dioxide, where the familiar solid/liquid distinction ceases to make sense, and it's warm enough for phosphoric acid to polymerize into polyphosphates that are soft and yielding like carbon chains are on Earth. On Venus's surface, carbon chains are unstable because the temperature is 500 degrees, much as many compounds that are stable in dry ice are unstable at Earth's surface temperature. So think about Titan's atmosphere, which is mostly nitrogen with methane in liquid, solid, and gaseous forms at the surface, at a temperature of 94 K. Think about what it's like inside the sulfur volcanoes of Io, or the water ocean under Enceladus's shell of ice, or the catastrophically periodic environment on Halley's Comet, with ice exposed to vacuum most of the time.

> 2. You need a musculoskeletal system which can support a large brain. For non-marine organisms, this implies something with a big head on top of an upright stance.

You might not need a large brain at all; Alex the African grey parrot had a brain the size of a walnut and was capable of answering questions like "Which color bigger?" or "How many green cubes?" --- up to three or four, anyway. Corvids, about the same size, construct and use tools. If you do need a large brain, you could still be aquatic, or the brain could be located in the middle of your body instead of at one end as it is for octopodes (who can walk around on land without a skeletal system at all, just not breathe there the way some other mollusks like land snails do), or distributed in smaller brains around your body as it is for corporations or anthills.

Where does the "upright stance" thing come from? I don't see that you've made an argument for that at all.

Organisms floating around the atmosphere of a gas giant don't have to worry about supporting anything, just like marine organisms. And there are many other strange places self-reproducing patterns could arise and become intelligent: the magnetic fields and convection cells of a star, the nuclear reactions in a neutron star, the plasma winds of a nebula, the deep subsurface which on Earth is largely populated by ferric-ion-reducing archaea.

> 3. Having a surplus of limbs is contraindicated for large organisms. Large limbs are expensive to build, and larger organisms are more constrained by gravity than surface tension, which makes multiple limbs less useful.

Yet humans have four limbs and only need two or three, and giant squids reach 12 meters in length and hundreds of kilograms in weight while having ten tentacles and arms. (The colossal squid weighs more but is a bit shorter.) Pando is a much larger organism than any human, and has thousands of "arms"; they're just called "trunks". Coconut crabs, who can live their entire life on land (as adults they lose their gills and can no longer survive underwater), weigh 4 kg, about ten times bigger than an African grey parrot or crow (300-600 g); their ten legs (including their claws) span over 90 cm.

> 4. You need appendages for manipulating tools, and voices to debate and share ideas.

You probably need some kind of way to manipulate tools, but you could use the sucker-covered arm of an octopus or starfish, the beak of a crow (obviously enough), the claw of a crab, the trunk of an elephant, the ephemeral pseudopod of a slime mold, or the tails dolphins use to send one toroidal vortex bubble through the middle of another. There's no reason the appendages have to look much like human hands; even if they do, they could be attached somewhere else, like the hind feet of chimpanzees or the trunks of elephants. If you can reflect or refract light, you might be able to manipulate tools by focusing light. You probably need some way to communicate, but it doesn't have to be a voice; octopuses can create moving patterns on their skin that other octopuses can see by expanding and contracting their chromophores, and Deaf humans constantly debate and share ideas without using voices. Most fish can sense electrical fields in the water, and some fish like the electric eels mentioned above can generate them as well.

And of course if you have manipulating appendages of any kind, you can manipulate things in the world into symbols that others can observe, as I am doing now with my manipulating appendages.

> 5. To develop non-trivial intelligence, you need to be multicellular, and multicellular organisms need to be able to reproduce. So, there is probably going to be sex involved, along with all the complexity that goes along with that, such as sexual competition and selection, caring for the young, and all the politics that arise from these kinds of interactions.

Slime molds aren't multicellular, but they can learn to run mazes, but the whole multicellular thing is a red herring; organisms are defined in part by being able to reproduce, and slime molds, as well as many other single-celled organisms including the remarkable foraminifera, have sex. (Slime molds have many more than two sexes.) Moreover, many organisms reproduce without sex, and many organisms that have sex don't care for the young. So I think your argument in this point is so weak as to be incoherent.

Overall, I think you've entirely failed to make the argument for bipedalism.

[asymptosis]

Hey, thanks for replying, your answer is excellent :)

Regarding the upright stance things, how do you see Alex the African Grey Parrot evolving towards becoming a spacefaring species without going towards an upright stance? He's smart, but he'll need to get smarter.

Regarding the upright stance thing, if you read again you'll notice that I qualified my assertion with "non-marine". Once we already ruled out the idea of marine organisms becoming spacefaring, there's no point arguing about things like whether giant squids can be spacefaring.

Naturally, I haven't answered your every point, because you made some valid points.

[kragen]

Thanks! It's a pleasure!

How would an upright stance help him get smarter?

My comment about the squids was just meant to rebut the claim that large organisms will invariably have four limbs. Yes, they'll probably have fewer limbs than a centipede or isopod, because the square-cube ratio makes limbs thicker, but maybe not as few as four. Now that I think about this, though, this only applies to land organisms like the coconut crab, the goliath bird-eating spider, or Pando (who has many more limbs than any centipede!), so the squid wasn't really relevant. A lion's mane jellyfish might be 30 meters in length and have 1200 tentacles, because there's no issue of them buckling under compressive stress; they're floating in the water.

Alex was already bipedal, as it happens, being a bird; I was just saying that evidently hundreds of grams of brain mass aren't necessary to be able to count, use symbols, and draw comparisons between objects. African greys also use tools to scratch the backs of their heads, pass down oral culture from generation to generation, live long enough to remember it for decades, live in large flocks, and drive around in tiny cars with joysticks. If I were somehow revived from suspended animation two million years in the future and humans were extinct but African greys were a spacefaring species, and I had to guess how it happened, I might guess:

1. They became pack hunters, feeding on birds such as pigeons, creating stronger evolutionary pressures to outwit their prey and to coordinate for hunting, as well as to learn to make weapons and traps. This enabled them to increase their nutrient intake.

2. They started living in smaller flocks, perhaps due to the necessity to escape from humans trying to capture them as pets, or perhaps because they adopted a less herbivorous mode of life which couldn't support such high population densities. This enabled their culture to innovate more rapidly.

3. They started making tools rather than just using them. Some stone-age equivalent of Lawn Darts would be totally adequate for hunting non-avian prey, perhaps incrementally developed from a practice of just dropping rocks on its heads; a wattle-and-daub birdhouse with a door would greatly diminish the threat from somewhat larger but dumber nocturnal predators; twine enables snares for smaller prey; nalbinding sweaters might enable the colonization of cooler areas;

4. They grew a little larger, perhaps after the humans went extinct and the forests grew back. Grey parrots don't normally get bigger than 600 g, but female harpy eagles can reach 9 kg, and eat prey in the 2.5-9 kg range, mostly sloths, while remaining entirely capable of flight. Being larger might give the parrots a little more body-weight budget for a brain, though it doesn't seem to have helped the poor eagles that much, but also a little more body-weight budget for clothing (like a hermit crab's shell) and tools. It's totally plausible that some populations of grey parrots might have evolved into formidable 2.5-kg pack apex predators, then started engaging in territorial warfare.

5. Pastoralism and agriculture developed, since once you have a territory you can securely hunt within, you can muster more warrior parrots to defend it if the territory is full of productive, easily edible animals like sheep, allowing you to feed more warriors; and this goes double if you can supplement your meat with lots of calories from things like grains.

6. Fire use developed for warfare purposes before being redirected to other purposes such as cooking and smelting. Fire is incredibly dangerous to birds, not only because of their easily-burned feathers but also because of their delicate respiratory systems; which means that whichever flock can somehow work out a way to drop hotshots on their enemies without dying in the process can become the parrot equivalent of Mongols (or Bantus, Conquistadores, or Indo-Aryans).

Honestly, though, the humans have no idea what is or isn't necessary for the development of intelligence. They've only seen it happen once, and they forgot what that was like.