Aside from humanoid, what shape would otherworldly sentient life likely have?

In My Humble Opinion
41

Earth has already seen the evolution of massive insect-like creatures that are large enough to support a complicated brain. Let’s start with the 8-foot-long Arthropleura, which even meets your criteria by existing on land.

These guys were ultimately limited by their lack of lungs, not their preponderance of legs. Call it an evolutionary accident, if you will. Give an alien Arthropleura a pair of lungs, and I see no reason to assume they’d have gone extinct, and no reason they’d have settled down with 4 legs.

42

Personally, I suspect that most intelligent tool users will have more than our four limbs. Having 4 limbs makes it harder to specialize a pair for something like manipulation or flight; if vertebrates had evolved with 6 or more limbs I think that there’d be a lot more of them with one pair specialized for something besides walking on. There’d be no need for bipedalism to free up a pair. IMHO, this would make intelligence and tool use more likely to evolve on that planet; it would have fewer hurdles.

If they can regenerate like many Earth life forms can, then that becomes much less of a concern; losing an eye is less catastrophic when it can grow back.

Yes, they exist. Xenophyophores and Valonia ventricosa, for example. IIRC, they suffer from structural weakness due to the lack of cell walls, however.

Unlikely; without a boundary, they’d dissolve into their surroundings.

43

I was hoping for some sort of gaseous creature, myself. Why do they have to be filthy monoforms?

44

Just in case anyone thinks I’m not being productive, here’s what I think an intelligent species either needs or is likely to have:

A front and a back, and a top and a bottom. Not necessarily symmetrical, but I’d consider that likely.

Sensory organs at the front/top because that’s all the better to see you with. Sensory organs will always include chemical sensors. Some combination of organs will allow distance visualization (whether that be by sight, echolocation, etc.)

An input orifice (call it a mouth) near at least some of the sensory organs, so you make sure you’re eating the right thing.

At least one complex appendage for manipulating the environment/tools. Whether it’s a hand, mouth, tentacle, pseudopod, etc. is up for grabs. I place no bets on the number or type of total appendages except to say that tails seem remarkably common.

I’m assuming the creature will weigh at least a few ounces, but that’s about the only bet I’d make on size. There’s a pretty poor correlation between smarts and size even with animals that are closely related.

Intelligence seems closely linked to coping with group living. While I wouldn’t rule out solitary sentient life, a truly intelligent species would reason out the various advantages to cooperative/group living anyway.

I have no bets on aquatic vs. land when it comes to sentience, but I do think aquatic creatures are going to have trouble with technology. Fire, chemistry, metallurgy and electricity, are all difficult under water.

45

Then you are not asking about sentience or consciousness or intelligence or even cognitive capability. You are asking what sort of creatures would evolve and implement the ability to produce human-like modern technology. So sure, something human-like in whatever ways drive technological development. Limit the question to being like us and the answer is of course limited to being somewhat like us as well.

So critical features of a technology capable creature that could get to a point of building skyscrapers and such - tool-users with culture and both cognitive and communication skills sophisticated enough to reach a level of designing tools to better make tools, to plan ahead, to work in concert with a group, and to pass skills and knowledge learned across generations.

So something that serves the function of hands - an agile trunk, pincers, tentacles, something that can do fine motor skills. A social structure that allows for collaboration and with some pressure to develop better technology - such as competition with another group, or a changing environment that requires adaptive change by way of tools for continued survival. Perceptual organs appropriate for the environment, which may not be visual ones (imagine an environment that is always so murky that vision is useless … sonar, sensing magnetic or electric fields, smell, who knows?) Located according to the need of the environment and the input.

Still leaves many forms open without specifying the environment. High gravity? Low gravity with little level ground? Evolved mainly living primarily in narrow tunnels underground? What sort of competition, predators and prey did it evolve to deal with? Each would put different constraints.

46

This is why I find it very hard to imagine a purely aquatic species ever developing advanced technology like space travel or fire.

47

Any shape is conceivable, I guess, but I’m partial to octopusoids.

Those we have on earth can manipulate stuff and have been shown experimentally to be quite bright. I can easily imagine sentient octopuses.

48

I don’t think we have to look farther than our own planet. After humans, the dominant life forms are plants, insects, fish, birds, reptiles and mammals. We can eliminate plant life, as they aren’t likely to ever evolve sentience, a nervous system, mobility, etc… Fish and insects barely evolve brains past brain stems. Birds and reptiles have a poor brain to body mass ratio. Among mammals, dolphins are able to communicate with a healthy brain to body ratio, and primates have thumbs, a huge plus in using tools and controlling their surroundings. I think the ability to communicate, thumbs and brains would be an important prerequisite for technological evolution.

Then, we could compare humans with the other groups. What singular characteristics do the other things have that humans don’t, yet humans were able to develop better and faster? Plants, for example, breathe carbon. Most mammals are covered in body hair. Spiders and insects have multiple legs. Wolves, gators, dogs, etc. have a huge amount of jaw pressure, prominent teeth, and a sharp sense of smell. So, we can logically say that none of those were necessary for humans to make the leap to technology.

Basically, we were strong enough make, build and use tools, but weak enough that we had to use them. Without body hair, we had to make clothes and build houses. Without strong jaws and senses for hunting, we made weapons.

Therefore, the key human features that allowed us to create technology were almost random luck that they all occurred in one organism at the same time, yet we were missing key physical characteristics that would have allowed us to avoid technology altogether. If humans had gills and webbed feet, for example, what technology would not exist today? If humans didn’t have eyes, what new technology would we have made? Could we have made anything without eyes?

So, through deduction, we can say:

  1. Key features of humans allowed us to become what we are today.
  2. Characteristics of other organisms that humans don’t have aren’t necessary, and may actually hinder technological advancement.
  3. Aliens that have similar tech as us would have a similar situation as 1 and 2.

So, we can say:
2 eyes: important. More than 2 eyes is unnecessary.
2 arms: possibly important, as there aren’t any species with only one arm, but several with more arms that weren’t as successful.
Thumbs: vital.
2 legs: I don’t think anyone would disagree that 0 or 1 leg isn’t that great, but would 4 or more legs be better or worse? With more than 2 legs, would we have cars?
Large brains: vital.

So, I would say that in terms of thumbs, arms, legs, eyes, and brains, an alien species would need similar structures, but maybe not placed in the same way. To maximize brain size, a crab-style body might be better, with most of the torso being used for the brain. An external skeletal system would bump up against #2 above, so probably an internal skeleton would be better. Internal organs, vocal chords, lungs, etc could also be contained in the torso. To maximize brain size, I think combining the mass of the head and torso with some of the arm/leg mass would be better. The total mass would be equivalent to humans today, but a shorter, wider, deeper and thicker torso, no head, and shorter arms/legs.

49

Insects seems to be doing quite well with 6 limbs, and aren’t outcompeted due to “wasted energy” or anything like that.

So, I don’t see why a specific condition or need at some early point couldn’t have led to land vertebrates having 6 legs.

50

I agree with clairobscur.
There is at least one species of cephalopod that is amphibian.
Surely you have all heard of the Pacific Northwest tree octopus.

51

Certainly. Why not? Assuming we wouldn’t have eyes (because, for instance, we evolved as a subterranean specie) we would use other senses. Maybe echolocation, wiskers, extremely sensible touch, electric fields detection…

After all, we’re using magnetism in our tools, even though we can’t detect magnetic fields (contrarily to some other animals).

52

Nope. But something that strange must be living in Australia.
Upon checking, it doesn’t and lives in the Americas. Surely they were intented for Australia, though, and god or Noah made a mistake and misplaced them.

53

Just wanted to say this made my day. Thanks!

54

It would be interesting to find even a lower life form on another planet. I would like to see it in my life time,I know the odd are small!

55

You’re going to dismiss birds so easily? When ravens and African Gray parrots frequently make it into top 10 lists of most intelligent animals? Ravens even use tools!

56

They also have brains that scale up better than mammal brains. Mammal brains do their high level processing on the surface; which is of course why a human brain is covered in convolutions. Bird brains do their high level processing in nodes spread throughout the brain, and aren’t dependent on having lots of brain surface for being smarter. Their biggest limitation is not having a free unspecialized set of limbs to evolve into good manipulators, not potential brainpower.

57

Because all of the “higher” lifeforms on earth are that way.

58

When they notice they are observed by another bird while hiding food, ravens also wait for the bird to leave, then pick up the food again and hide it in another place, which is pretty smart (since it seems to require anticipation of another being actions). They also pass the “mirror test” (consisting of putting a mark on an animal or even a toddler, and putting it in front of a mirror to see if the creature figures out that the mark is actually on itself. Few animals pass this test)

59

Sure, but as it has already been mentioned, sentience doesn’t require the ability to make tools. It’s for sure a nice side-effect, but sentience would be useful in its own right, for instance by allowing social animals to communicate or organize hunts.

60

I’ve often pondered this question.

How about the following possibilities?

  1. Body shape basically a cylinder, no neck. “Eyes” that are wraparound like the prostheses used by Data in Star Trek, probably multiple lenses like an insect. Six limbs. Various lower species have different adaptations, but for the dominant sentient being, the upper two are strong gripping limbs, the middle two are better for fine motor skills, and the lower two are for locomotion. Other species on the planet have evolved to use the limbs differently, for flight, for climbing, etc. Perhaps one or more of the upper limbs is positioned so that it can reach pretty far toward the rear.

  2. Perhaps breathing doesn’t have to be in and out of the lungs. Perhaps it could be a continuous flow, like the circulation of the blood except in at one end, out at the other like a vacuum cleaner. The input is through a long tube like an elephant’s trunk, except it’s at the top of the cylinder. Output is toward the front so it can be used for making sounds.

  3. Food input is through an opening front and center, sort of like an enlarged stomata.

  4. Reproduction: The possibilities are of course endless. What if everything is born male and develops into a female at a certain stage of maturity? The young adults carry out the tasks requiring strength, and the older adults carry out the child-bearing and nurturing tasks. Or perhaps no sexes at all, but reproduction requires two for mutual fertilization? Offspring are borne as eggs. After hatching, any adult can feed them through their long childhood with predigested food (like penguins and some other birds).

  5. Perhaps a six-limbed centaur-like body shape; four limbs for locomotion, two for other tasks.

  6. Why not a circular being with radial symmetry and an array of legs at the bottom that lets it move in any direction? Multi-lensed eye on top that can look in any direction? Brain safely ensconsed in the center.

  7. How about a non-mobile sentient life form, anchored in the ground like a tree, with the brain as a special underground well-protected “bulb?” It grows a large stem-like projection above ground that contains as many eyes as it needs as well as structures for collecting energy from its sun. Underground it projects various filaments that perform other functions. Some could extract nutrients from other life forms both above and below ground. Others gather water. Some connect to others of the same species and use electrical impulses to communicate. Finally, some connect to others of the same species for gene-swapping prior to reproduction. Reproduction is by means of budding. Or perhaps individuals do move, but extremely slowly, but growing in one direction and atrophying in another to make room for newly budding offspring.