5 ms·

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

dtech 5y ago
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 5y ago
  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 5y ago
    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.
    - ClumsyPilot 5y ago
      "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 5y ago
        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.
        ClumsyPilot 5y ago
        Insects are all not quadrapods, they are not rare, their combined biomass is much greater than mamals I am not clear on calories - are insects inefficient?
        godelski 5y ago
        The calorie part is about where you're spending calories. Brain or body? This gets complex real fast though. One easy part to understand is surface area and volume (but there's also things like metabolic rate and many others that go in here). But consider that brains are pretty resource intensive. In a human it's 2% of the mass but 20% of the energy. There's a linear relationship between neurons and calories but humans are an outlier in percent of energy that goes to brains. Additionally, it is the third most resource intensive system (for humans), behind skeletal muscle and the liver[0]. Which those last two parts matter a lot. Skeletal muscle scales with volume. So if you're bigger you have to eat more. The more you have to eat the more time you have to spend eating and your metabolism is probably going to slow. So it gets really complicated here really fast (and I'm admitting to my naivety to the subject matter) but basically it's not hard to see here that if you're pretty big you're probably not going to have the resources (or metabolism) to spend time thinking, which means a downward selection pressure on brain and thinking. There's going to be a Goldilocks zone here (like most things). So basically if you can get food and don't have to spend significant time thinking to do so, there isn't going to be a selective pressure to encourage brain growth. And if you have a selective pressure to devote energy to the brain you're also probably going to have a selective pressure to reduce energy from elsewhere. Additionally, I'll add that humans both lost fur and stood up because it is better for thermal regulation (there are other pressures too, there's never _one_ reason). So this also helps with the surface area-volume issue. Basically what I'm saying is that there's these locally optimal conditions that need to exist at the same time to produce intelligent, tool using, civilization making creatures. (I mentioned in another comment that environment matters too. Can't get a bronze age underwater. But I also didn't mention you can't get a bronze age if you don't have a social structure, something, for example, octopi lack). Basically what astrobiologists are looking for are the combination of these optima necessary to produce certain traits. What many commenters here are missing is the combination part, mostly thinking that only intelligence matters to create a space fairing civilization, but you can't get to space if you can't create advanced composites, explosives, and many other things. Or in other words, the astrobiologists aren't idiots and probably know what they are talking about despite what it looks like. It only looks like they are dumb because people are overly simplifying the problem. [0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046985/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046985/
JoeAltmaier 5y ago
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.
- ajuc 5y ago
  a dozen out of millions of species is not "pretty common"
  - JoeAltmaier 5y ago
    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 5y ago
      100.0% of spacefaring earth creatures are bipedal /s
      - excitom 5y ago
        Dogs have been send into space
        asah 5y ago
        They were sent, not by choice = not spacefaring! /s
- ivoras 5y ago
  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).
godelski 5y ago
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 5y ago
  Can echo location be used for depth perception?
  - godelski 5y ago
    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 https://www.youtube.com/watch?v=zWeYCULC0UQ
  - ncmncm 5y ago
    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 5y ago

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 5y ago
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 5y ago
  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.
  - ClumsyPilot 5y ago
    "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 5y ago
      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.
      - ClumsyPilot 5y ago
        Insects are all not quadrapods, they are not rare, their combined biomass is much greater than mamals I am not clear on calories - are insects inefficient?
        godelski 5y ago
        The calorie part is about where you're spending calories. Brain or body? This gets complex real fast though. One easy part to understand is surface area and volume (but there's also things like metabolic rate and many others that go in here). But consider that brains are pretty resource intensive. In a human it's 2% of the mass but 20% of the energy. There's a linear relationship between neurons and calories but humans are an outlier in percent of energy that goes to brains. Additionally, it is the third most resource intensive system (for humans), behind skeletal muscle and the liver[0]. Which those last two parts matter a lot. Skeletal muscle scales with volume. So if you're bigger you have to eat more. The more you have to eat the more time you have to spend eating and your metabolism is probably going to slow. So it gets really complicated here really fast (and I'm admitting to my naivety to the subject matter) but basically it's not hard to see here that if you're pretty big you're probably not going to have the resources (or metabolism) to spend time thinking, which means a downward selection pressure on brain and thinking. There's going to be a Goldilocks zone here (like most things). So basically if you can get food and don't have to spend significant time thinking to do so, there isn't going to be a selective pressure to encourage brain growth. And if you have a selective pressure to devote energy to the brain you're also probably going to have a selective pressure to reduce energy from elsewhere. Additionally, I'll add that humans both lost fur and stood up because it is better for thermal regulation (there are other pressures too, there's never _one_ reason). So this also helps with the surface area-volume issue. Basically what I'm saying is that there's these locally optimal conditions that need to exist at the same time to produce intelligent, tool using, civilization making creatures. (I mentioned in another comment that environment matters too. Can't get a bronze age underwater. But I also didn't mention you can't get a bronze age if you don't have a social structure, something, for example, octopi lack). Basically what astrobiologists are looking for are the combination of these optima necessary to produce certain traits. What many commenters here are missing is the combination part, mostly thinking that only intelligence matters to create a space fairing civilization, but you can't get to space if you can't create advanced composites, explosives, and many other things. Or in other words, the astrobiologists aren't idiots and probably know what they are talking about despite what it looks like. It only looks like they are dumb because people are overly simplifying the problem. [0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046985/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046985/

JoeAltmaier 5y ago

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.

ajuc 5y ago
a dozen out of millions of species is not "pretty common"
- JoeAltmaier 5y ago
  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 5y ago
    100.0% of spacefaring earth creatures are bipedal /s
    - excitom 5y ago
      Dogs have been send into space
      - asah 5y ago
        They were sent, not by choice = not spacefaring! /s
ivoras 5y ago
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).

godelski 5y ago

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 5y ago
Can echo location be used for depth perception?
- godelski 5y ago
  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 https://www.youtube.com/watch?v=zWeYCULC0UQ
- ncmncm 5y ago
  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.