What will real Aliens be like?

Alien Physiology

What will an alien look like? If you follow the viewpoint of most television sci-fi then all aliens will be men in rubber alien suits. The producers of Star Trek seem to think aliens are just like humans with little latex ridges on the noses or foreheads.

The reason for this anthropomorphism on TV is that it’s cheap. The alien in the Movie Alien was gross and ugly and we surly would never be able to discuss our new age feelings with such a creature. It cost the movie producers much more than a little latex on the bridge of an actors nose.

The truth is that we are much more likely to meet Sigourney Weavers’s alien than a Bajorran.

What kind of aliens will we meet in out wanderings in space? Will they be like us?
This can be answered in part by asking what kinds of animals have evolved intelligence here on earth?

The ratio of brain to body weight is a generalized way of looking at intelligence. It makes sense that a large brain will mean a higher intelligence. A large body needs a larger brain to control it so you have to allow that an elephant’s brain has more housekeeping to do than actual higher thought and might not be as smart as his large brain indicates.

Animals with the biggest brains are Whales, Elephants, Porpoises, Man, Chimpanzees, Baboons and Wolves. If you normalize the body weight, the order of size is Man, Baboon, Monkeys, Camels, Porpoises, Kangaroos and house cats. (I knew my cat was smart).

If you rank animals by human type intelligence tests, the large water mammals fall off the list and Horses, Pigs, Dogs, Ravens and Parrots move up the list. (Cats don’t sit still for tests.)

Some creatures have incredible memories. Surprising, the octopus has a large brain and in tests shows the ability to memorize things like the shapes and sizes of objects or the scent of another octopus. Octopus owners are amazed by the responsiveness of octopus.

Group creatures like swarms, flocks, schools and herds seem to have emergent properties which reflect communicated information that cause the group as a whole to display behavior which is smarter than any individual.

So what is the standard for earthly intelligence? Two legs don’t seem to be a requirement. Most smart animals walk on four legs. Birds and primates can walk upright. Birds do it because they have wings instead of arms. Man walks upright because he needs to carry things in his hands. Kangaroos hop upright because they are very strange creatures. Horses, pigs, wolves, dogs, camels and elephants walk on four legs because they need to be stable or need speed to survive.

The truth is that there is no body shape that easily connects to intelligence. On earth, multiple legs from 4 to 1000 was the standard until vertebrates started walking in the mud. After that, the four leg rule seems to have been cast in stone. We all descended from the first amphibious ancestors that learned to walk and inherited the 4 leg rule from them. This could have been six legs like insects or eight legs like spiders, or multiple legs like centipedes, but we started out with four legs and all our ancestors stuck with it. But insects and other polypod creatures are very successful. The two legged creatures are really four leggers with two of the legs adapted to other use.

Aliens will have just about any body configuration that we can conceive of if the earth is any guide. But what about physical attributes like eyes and noses and mouths and hands and thumbs?

An intelligent species will probably be able to manipulate the world with appendages. An intelligent species that can’t make tools won’t get to the stars. The hand is a good all purpose manipulator as is the octopus’s tentacles and the elephant’s trunk. Humans who lose the use of their hands get along fairly well with toes or lips. Who can forget the scene in the move “Freaks” where the armless and legless man rolls a cigarette and lights it using only his mouth? We can expect aliens to have hands or claws or tentacles or a trunk or a snaky body so that they can grasp things and make tools.

Will an alien have two eyes? Symmetry seems to be a standard of life on earth. Of all creatures that make our intelligence lists, only the octopus doesn’t display bilateral symmetry. He is symmetric, but has no obvious left and right sides. Octopus experts will probably correct me on this. (I have been corrected – they are indeed bilateral.)

Bilateral symmetry – having a left and right side seems to be the right amount of redundancy. Lose the left hand and you still have a right hand. Loose the left eye and you still have the right eye. Two eyes also give us binary depth perception. More than two eyes would not be especially beneficial. Two hands let us grasp with one and manipulate with the other. Three hands would get in the way. The examples in nature that we have of more than 2 eyes are for creatures that have very simple eyes and need multiple receptors in order to make out changes in dark and light or nearby motion. Two seems like a probable number for most things like hands, ears, testes and nostrils.

Will aliens ever look like us? The answer is Probably not but there is a theory that there are only a few basic body types possible. The example that is always given is Dolphin, Shark and Ichthyosaurus. These are three animals with the same body types which are totally different kinds of creatures. One is a fish, the other a mammal and the last is a reptile. They look so much alike that a layman would not be able to tell them apart without years of watching the discovery channel under his belt.

Could it be that man is a basic type and that there would be a tendency for evolution to create intelligent beings with two arms and two legs and a head? Bipeds are rare on earth. Man walks upright because he probably had the need for speed while bringing food home to the family. He would pick up food in his arms and sprint on his hind legs to get home. A woman could pick up her infant child and run fast enough to save the both of them. This would also allow him to eventually use tools and would help in the development of useful hands. Thumbs would help him to climb trees and coincidentally to pick up large bones for use as clubs. Creatures that lived on plains on the edge of forests that previously lived in trees might develop as humans did.

It is much more likely that four legged animals with trunk like manipulators or extended lips or mouth parts would be the tool makers on any planet. Evolution wouldn’t make two legged creatures from scratch and they’d have to evolve from four leggers. It’s hard to think of that many scenarios where the four leggers would gain anything by going upright on two legs. The birds did it because they needed their wings. The Kangaroos did it for some unknown reason – but probably, like man, they needed speed while holding their young or food. It’s not impossible that we’ll meet bipeds, but not real likely.

How will aliens solve the problem of sex? Sex is a requirement for fast evolution. Traits are passed down from parent to child, but when there are two parents, the child can inherit from both of them. This spreads mutations around in a species far faster than can be done without sexual reproduction. It seems two sexes are sufficient and more would be redundant. Sex is a real requirement for the evolution of alien life. Whether there will be male-female type differentiation or another solution is up to your imagination.

One thing that I know will be different is alien sexuality. Humans have lips and breasts because they are mammals. The lips are used for sucking and the breasts are used to provide milk. This is a rather specific solution to the general problem of feeding young. The obvious solutions are for the parent to pre-chew food or even partially digest food and regurgitate it. Birds do this. Bees have complicate variations on this. The breast solution seems a little strange (although I personally like it).

Very few aliens will have breasts and lips and of those that do, the breasts might be located in armpits or in pouches on the stomach and they will not need large alien bras.

The male and female genitalia seem to be hard to explain away as being the obvious solution. All that is needed is a good way to get germinating material from here to there. On earth there are lots of complicated ways to do this. Pollen and bees springs to mind. Fish lay external eggs which are fertilized externally. There is often some kind of tool for placing sperm and some kind of receiving place for taking it in, but these are in no way similar to the human solution. The placement of our reproductive organs was set in stone for us millions of years ago and proved successful enough that there was little variation afterwards. An alien may have evolved differently and accidents of evolution could have placed the sexual organs at many interesting places.

Even if an alien walks erect and superficially looks like a humanoid, it will be very unlikely that your characters could have sex with such a creature.

The only time that you should use humanoid characters in your science fiction stories is if they are for TV or the movies. Sci-Fi (as opposed to SF which is the literature of Science Fiction) deals with unsophisticated audiences. The story line is usually a western or a war story with space or alien elements. The time it takes to develop explanations about alternative aliens is not available in the short format so it’s either evil beast-like alien or man-in-a-rubber-suit aliens. Sci-Fi likes female aliens with big breasts — by far the least likely alien we will ever meet – but at least it provides the men in the audience with something to watch when the space ships aren’t shooting at each other.


  • I dislike the reptile-as-alien bias, but, then again, therapods were bipedal too. If it weren’t for a cosmic collision 65mya, perhaps there’d still be non-avian dinosaurs, smaller versions, probably, that had plenty of time to develop intelligence.

    So, assuming a similar course of evolution elsewhere, it doesn’t seem a stretch to me that there’d be a bipedal reptilian humanoid, probably with a prehensile tail (that third, in-the-way limb).

    I’ve always figured that if man’s shape is basic (and I do, hey, I’m biased), so are the following:
    * Light sensitive organs would be on top
    * Olfactory/chemical sensory organs should be on top AND elsewhere (near the ground)
    * Pressure/vibration sensory organs should be on top AND near the ground
    * Nutrition intake should be on the upper half (let gravity do its magic)
    * Excretory organs would be lower
    * Communication organs would most likely be on the upper half
    * I’ve always thought that the brain is in a weird spot. It’d make more sense to put it in an armored case in the middle of the body.

    I figured a “body” with most of the digestive and nervous systems would make the core, supported by two limbs, and maybe a tail, with three appendages: “arms” and a “head” (or maybe combined into two limbs). The “head” would carry mostly sensory organs – two of them would be best! Reproductive organs on the limbs makes sense too, or maybe one or two more limbs for those.

  • The one problem with a trunk-like appendage leading to tool use and sapience is there would be, most likely, only one gripping appendage. This gives the advantage to a pair of arms with hands featuring opposable thumbs: two hands are better than one. Think of swinging a stick, a hammer, a sword, a baseball bat with one hand (or trunk) instead of two: major disadvantage. Now maybe an animal would evolve two trunk-like appendages to add stability to its tool use but that seems less likely to happen to me than a four legged animal rearing on its hind legs to free its forelimbs if only to reach for food high up in a tree like Sloths, Chalicotheres, Therizinosaurs, Giant Pandas, etc. have done; or a tree dwelling, four limbed animal returning to the ground with ready made hands built to explore the world that surrounds.

    • Good point. Two Trunks? I am on shaky ground here as far as saying the bipeds might not be common. As I think about it, two legs or four matters little. Two arms absolutely give an advantage as monkeys and apes have proved. I’ve seen raccoons do amazing things with their hands without thumbs and walking on four legs.

      I would guess that aliens could easily have four legs. Thumbs would be helpful, but there are probably other gripping solutions that would work well. Trunks may or may not be a solution – not impossible, but probable?

      I can hardly wait until the first alien shows up so we can see how right or wrong everyone is.

  • Though I enjoy coming up with funky aliens for my stories I am leaning towards convergent evolution for interstellar aliens in the real world, but as you said: ‘I can hardly wait until the first alien shows up so we can see how right or wrong everyone is.’ -So who knows. I could never have imagined a creature with the abilities of a pistol shrimp evolving, so maybe there is something really funky out there!

  • read Nivan’s Footfall for a wonderful description of a four legged two trunked alien, they had four digits each

    • No that such things would actually exist outside of Niven and Pournelle’s imagination. When I read it I felt that vegetarian herd animals would never evolve to the point where they would explore outer space, in the story, they did not. As far as I remember, they were engineered and did not create their own technology. Even Niven and Pournelle though these to be unlikely aliens, and they had to create a convoluted excuse for them.

  • I actually think that intelligent/sentient life will be humanoid/anthropoid.

    I think these factors are important

    Endo-Skeleton, which also indicates an upper size limitation – not too big, or the musculature will not support it. Can’t see an exo skelton working for a large life form.

    Bipedal, with 2 (maybe 4) limbs adapted for manipulation – maybe a prehensile tail.

    Lung-Type resperatory system needed for Oxygen/C02 interchange

    Forward facing eyes, featuring stereoscopic vision – but maybe with other bat-senses, also

    Diploid reproduction

    Warm-blooded – definitely an advantage, but not necessary.

    I thought the book “Lucy” carried a very informative explanation on the way all these things work together.

    • You are probably correct, but this does not eliminate any alternatives.

      Endo-Skeleton – correct for land animals, perhaps not for sea based life forms. Also “Mission of Gravity” type creatures, essentially lobsters, may require more complicated exoskeletons to operate in very high gravity and pressure.

      Bipedal – Sea based fins, earth digger based? Airborne? Manipulaters should also include trunks as in elephants and tongues (think frog?). Insects have a variety of interesting claw and antenna configurations and lastly one might consider prehensile sex organs that do double duty as general manipulators (R. Crumb?).

      Lung types – perhaps for earth type O2 based life, but water based need gills. Life on planets with higher partial pressure of oxygen would not require lungs, but could absorb through skin or gills. If life form gets energy from other than Krebs cycle, there might be need to gather sulfates, Nitrates or phosphates for energy, as in anaerobic bacteria. Think of Hal Clement’s Nitrogen Fix.

      Forward facing eyes – probably unless bat like sonar is used, even then, binary sonar would be better. Underground creatures or ones on the bottom of the sea or in caves do not need to see at all.

      Warm blooded would be an advantage in climates that vary in temperature, but may not be needed on planets where the axis was perpendicular to the sun and the orbits did not vary. Then there would be no seasons.

      I think that humanoid will be very common, but there will be some odd cases out there. The exceptions might not be uncommon, depending on how common Earth type planets are.

  • Can’t believe how many typos I get in there.

    It’s probably my humanoid thinking, but I struggle to believe that animals with exo-skeletons, or marine-based, or, to be honest those without “strong” dextrous manipulation skills would be able to develop.

    Not sure about the Oxygen breathing. It just seems to me that the respiration equation, seems so fundamental and important to all this.

    C6 H12 O6 + 6O2 = 6H2O + 6CO2

  • “Man walks upright because he needs to carry things in his hands”

    Well, no, Man can carry things in his hands because he walks upright. Wrong end of telescope, I think

    I suspect ETIs capable of technological civilisation will be essentially humanoid. You need a body plan which provides binocular vision, grasping & manipulating appendages and, crucially, with none of the advantages that other plans give – why bother evolving intelligence if you can simply outrun any predator or run down any prey? Intelligent creatures have evolved intelligence as an alternative to high speed, massive strength, etc., so they’re pretty likely to be slow, upright creatures.

    Intelligence needs to manipulate tools, but also fire. Therefore, big shaggy creatures with lots of fat and fur in a cold climate are unlikely to evolve expensive intelligence because they don’t need it to survive. Skinny naked creatures, on the other hand, will need fire.

    • One thing to be careful about is that you response is very earth-centric. It is quite possible that life could develop on warm planets or very cold planets or planets where a flame will not be possible. Fire might not be a requirement. If there were life forms that developed on methane planets and used a different metabolism, then fire, as we know it, would not be an option. Smelting of metals might be accomplished in volcanoes or using solar mirrors. Not all planets, and perhaps few, with intelligent life, will be like our Earth. I expect that intelligent life might arise for many reasons on many different types of worlds.

  • “It is quite possible that life could develop on warm planets or very cold planets or planets where a flame will not be possible”

    Indeed, but probably not intelligent life and certainly not technological intelligence.

    “Fire might not be a requirement”

    It is, at least for technology. Ore smelting, alloying, combustion etc., are essentials for that and all require manipulation of fire. You can’t get from jungle to spaceship without fire.

    “Smelting of metals might be accomplished in volcanoes or using solar mirrors”

    Only if you first know how to smelt, which means somehow you have to figure out that concentrated heat applied with control can smelt ores. Since solar mirrors don’t occur in nature and since volcanoes cannot be controlled by bronze age technology, you beg the question here – how can you get to building solar concentrators without first working out the effects of concentrated, controlled heat energy? You cannot.

    “Not all planets, and perhaps few, with intelligent life, will be like our Earth”

    Intelligent life is one thing. Intelligent, tool-using, technological life which can build, say, steam engines or spacecraft, is quite another.

    The planet may not be entirely like ours, but I doubt if there is a feasible biochemistry for highly complex life other than the carbon-hydrogen-oxygen system, so the gross environment, IMO, is not going to be radically different. You can talk of silicon life, for example, but the environmental conditions which support that may prohibit the development of other precursors of technological civilisation.

    Convergent evolution – the Tu144 didn’t look like Concorde because the Soviets stole the plans, but because that’s pretty much what a supersonic airliner needs to look like. Intelligent tool-using technological civilisations are likely, from what we know, to be made up of generally humanoid creatures because such a body plan forces the development of abstract thought, planning, cooperation, etc., simply because speed of flight or ferocity of might are not viable options. You will not get, for example, a race of intelligent technological creatures which are capable of flying unaided, because the ability to fly negates the need to develop technology. Basic tool use, yes, and we see that here, but not technology – simply no need.

    Technological intelligence is more than the ability to hold a tool. It requires the NEED to hold and, crucially, develop tools because the unaided creature finds it hard to manage.

  • Rule of thumb: It it looks like an actor in a rubber suit, it is not a real alien.

  • Y’see the thing here is that we are all firstly assuming that tools and discoveries would be made based on the senses we ourselves and many lifeforms on earth posses.

    But technology is as much a result of how we experience the world as it is a result of ‘solution to problem’

    It is IMO entirely consistent with technological development for a species to perceive MORE than we do with different sense and still not even be aware they are living on a spheroid in a solar system with an actual star until they accidentally come across this information..

    Consider the senses of a creature which evolves on the dark side of a tidally locked planet…. or the senses of one on the light side.

    for sure they might have light reception as a sense… but are we sure they would see light… they might hear it? or small it? or perceive it totally differently using a sensory organ and mental model we simply don’t have. They might be able to feel how hard the ground id three feet in front of them without touching it because this is what their (eyes?) which really aren’t eyes tell them.

    So their progression is absolutely not solely linked to their physiology, because regardless of how they see the world it will still be there acting on them… I accept that… but it is unlikely to be hindered by it…and their invention’ should they reach that stage will be solutions to ‘their’ problems. If they don’t see a star in the sky called a sun… or if they don’t have day and night, or winter summer etc. then they don’t have any of the accompanying problems to resolve.

    their evolution might follow this pattern too… what use of arms in a world where manipulation of tools is a lot easier and not contained by the same gravity. What use of computers if one evolved to be able to network with other members of the same species. What us is there of hearing if the atmosphere is less dense….

    I feel we are anthropomorphisizing the issues too… not just the physiology.

    Heres a fast example… we are multi celled creatures… we derive intelligence by being essentially a super-swarm… a very well advanced super-swarm.

    Now what if that swarm was less dense that communicated from cell to cell using light…or chemical messages…or sound… or electromagnetism… and individual who needs no appendages and can manipulate whatever they like with no arms or legs because they are essentially a ball of gas consisting of billions of celles which just happen to be further apart than ours will a looser infrastructure.

  • There are five basic body types for an intellegent species capable of manipulating fire on a terrestrial planet that is 80 to 120% the mass of Earth with an oxygen/nitrogen content between 18/82% to 23/77%, orbiting in the habitable zone of a G type star.

    These are:

    Humanoid – morphology like human, head, trunk, two arms and two legs.
    Vishnuoid – morphology like vishnu, head, trunk, four arms and two legs.
    Centauriod – morphology like centaur, head, trunk, two arms and four legs.
    Elephantiod – morphology like elephant, head, trunk, four legs, and extended nose appendage like an elephant’s trunk with two manipulating appendages at the end.

    The body would maximize the flow of motion and minimize energy expenditure
    as consistent with biomechanics and the theory of motion flow for the physical structure of fauna. The height of the being would be proportional to the size of the planet, this being for an earth-like planet, to be between 1.65 to 2.25 metres (depending on the planet’s mass, density, and gravity).

    The most likely morphology is humanoid.

    See “Evolution of Movement Design is Deterministic”, researchers at Duke University’s Pratt School of Engineering and Pennsylvania State University
    have found that all animals bear the same stamp of physics in their design.

    Also see “Nature’s Destiny, How the Laws of Biology Reveal Purpose in the Universe” by Dr. Michael J Denton. You can check his website at http://www.michaeljdenton.com

    • G types within about 20% of Earth normal is a very small minority of planets. Fire as a prerequisite of intelligent life is an interesting twist, but I am not convinced it means much. Your list of animal types seem like they are all like mammals. What about fish, insects, plants, and other life forms? All that you say might be true, but I when we do encounter intelligent life out there, I wonder if their morphology will fit the types you listed?

  • There is life, there is intelligent life, and there is technological intelligent life.

    The first can be of any form from bacteria to human, may or may not be vertebrate, may or may not be air breathing.

    The second can be one of several forms, but has a lower limit on size due to the necessity for a reasonable brain capacity.

    The third is highly likely to be broadly humanoid because there is a biological penalty for evolving intelligence, which means advanced intelligence is only likely to evolve where other, biologically cheaper answers to the perennial “fight or flight” question – it is unlikely that alien rocket scientists will simultaneously possess incredible intelligence, wings, half-metre long dagger-like teeth and legs that can propel them faster than an antelope. Advanced intelligence evolves where such physical solutions to the problem do not exist or are not feasible.

    Humanoid body plans *cannot* fly or run like the wind for simple reasons of physics. Advanced intelligence is therefore a reasonable answer to the problem.

    Fire is not a necessary precondition for intelligence, but it is necessary for technological intelligence.

  • > Lower limit on size.

    You cite no evidence that size is related to intelligence. You assume cells like ours and a nervous system made of neurons. You cannot assume that life will be like living things on earth. Cells, Neurons, brains even, might be earth-centric assumptions which could be wrong.

    > likely to be broadly humanoid…
    Nothing you said indicates that this will be true. All of your examples are mammals. You cannot assume that only the humanoid is a reasonable solution. Humanoid is ONE solution and I would say that you could come up with dozens of other solutions without trying hard.

    >Fire is necessary for technological intelligence.
    high intelligence does not need to be technological. There are other ways to create objects as strong as metal. Fire is a byproduct of intelligence, not a source, or reason for it.

    It seems that you clearly want all aliens to be humanoid. I would say that some aliens might be humanoid, but mostly they will not look like humans in any way. They will not be mammals, will not have lips and the females (if they have two sexes) will not have breasts.

  • I thank you for your comments, in a couple of days I will explain in further detail why these morphologies are the most likely for intelligent life. I will explain this from the point of astrobiology which is multidisiplinary approach to the question of life in the universe. It will involve giving a brief explaination of such things as what is intelligence, two main types of evolutionary theory, darwinian and directed evolution, there underlying implicatios, types of life and there likely hood, the type of stars most suitable for the development of life, the size of planets best suitable for life, the significance of fire in the development of intellegent life, the significance of mammals and primates in particular. There are specific scientific reasons why these aspects are significant and necessary for the development of multicellurar life in the form of flora and fauna capable of developing intelligent life. This is provided as a means of improving the scientific basis of your discussions. There are several sourses available on the internet on astrobiology and related bodies of knowledge as well as books on the topic from a variety of view points. We are only now a few months away from finding a true earth analogue. One even better than Kepler 22b.

    The morphologies provided previously were those suggested over 30 years ago by an exobiologist as the most likely for alien races and mounting scientific enquiry is moving towards humanoid.

  • Size Limit:

    A minimum degree of brain organisation and capacity is required. Whilst a more efficient organisation might give brains markedly smaller than ours for a similar level of intelligence, this isn’t certain and even then there does have to be a lower bound to the brain mass. That brain mass has to be carried around by a body, and so there is a lower bound to body size.

    Brain mass is broadly related to intelligence, although from what we know it is related to a useful combination of brain absolute mass and brain to body mass ratio. Blue whales have enormous brains, but also vast bodies – they’re probably as smart as goats, because their brain to body mass ratio isn’t favourable. There are primates with much higher brain to body mass ratios than humans, but their absolute brain mass is too low to support a sufficient intelligence.

    Note, though, that it is technological intelligence that is of interest here. Life generally is interesting, but life capable of building spacecraft is rather more interesting.

    Broadly Humanoid:

    We can only argue from what we know. However, all vertebrates share a common gross body plan, likely for no better reason than it is a good combination of simplicity and flexibility. More limbs bring problems, but when very small a simpler invertebrate structure may be better and can more readily support additional limbs.

    Technological intelligence is unlikely to arise in a species which can easily survive without it. Humans cannot run fast, cannot climb or swim well, cannot fly, do not have powerful jaws with dangerous teeth. We cannot rely on physical ability to escape predation or to hunt. We therefore exploit intelligence, and then as a last resort because large brains and intelligence have substantial evolutionary and practical penalties.


    No, intelligence doesn’t need to be technological, but frankly that’s the kind that’s of most interest, especially to SF writers. It is difficult to create a compelling drama around the life of an octopus, however smart they may be.

    Technological intelligence DOES need fire. You mentioned earlier exploiting the thermal energy of solar radiation or volcanoes, but don’t seem to have considered that one cannot make solar concentrators without smelting ores, and that volcanoes are somewhat hard to control.

    You cannot build complex machines without smelting ore. You cannot do that without mastering and controlling fire. If you already know about fire, metals, smelting, and so on, then yes, you could use solar concentrators or exploit the energy of volcanoes, BUT you would need to (a) build machines to do it and (b) have somehow figured out what to do in the first place.

    Technical Limitations Generally:

    Chemistry and the relative cosmic abundance of the elements suggests the most viable life chemistry will be based around the Krebs cycle. It is highly unlikely that anything else is capable of providing sufficiently energetic reactions to sustain advanced life.

    Physics dictates upper and lower bounds of size and capability, whether you want it to or not.

    Overall, it is very hard to see how the various factors all pushing in one direction – reaction energy, mechanical limits, convergent evolution, elemental abundance, and so forth – can mean that technological (i.e. interesting) intelligence is likely to be physically much different than something recognisably humanoid.

  • You make quite a few claims without any real argument as far as proof. This is speculation, but you just can’t throw something out.

    1) “there does have to be a lower bound to the brain mass”. Perhaps. Off the top of my head, the lower bound is probably about a gram, but I could think of ways where functional brains could be microscopic.

    2)”Brain mass is broadly related to intelligence” If that were the case then Elephants would be smarter than humans. Brain mass on Earth is related to Body size. Intelligence does not have a linear relationship to brain size. Birds, for instance, have very small brains, but have much more “I.Q.” per ounce than humans.

    3) “all vertebrates share a common gross body plan” There are, however, complex higher intelligence life forms ON EARTH that are not vertebrates. Vertebrates are a unique adaptation to the conditions on Earth, and are by no means the only successful format for life.

    4)”Technological intelligence is unlikely to arise in a species which can easily survive without it.” This makes no sense. There is no evidence that this is true. Of course, we only have evidence of one technological species. Primitive human species were very strong, very agile, and very smart. Primitive species of humans created fire, speech, and tools before they evolved higher intelligence. Modern humans only lost their superior strength after they began to develop higher intelligence.

    5)”large brains and intelligence have substantial evolutionary and practical penalties” No basis in fact. Large brains seem to favor species that develop them. Pack animals, especially use their brains for hunting and depend on them much more than sharp teeth. Successful species are either very prolific breeders or very successful in finding food and protecting their young. Breeding requires little brains whereas finding food and protecting young require intelligence.

    6) “It is difficult to create a compelling drama around the life of an octopus” Read Andre Norton, Sea Siege – about smart octopi.

    7)”Technological intelligence DOES need fire” Technology may eventually need fire, but technology is building tools. Man existed for 99% of his history without using fire for anything other than cooking mastodon meat. Man created tools, maps, pictographic writing, art, probably math, astronomy, chemistry, and pharmacology and other sciences, long before smelting of ore.

    8) “You cannot build complex machines without smelting ore”. I can build a clock out of wood, as well as a sextant or a slide rule. I can use plant material to make almost anything. I can grow crystals without fire. The presence of metal ores on earth did not create intelligence. If there were no metals in Earth’s crust, don’t you think that men would have created work-arounds. Trying to equate fire with intelligence is a waste of time. Man was intelligent and technological long before fire.

    9)”Chemistry and the relative cosmic abundance of the elements suggests the most viable life chemistry will be based around the Krebs cycle.” Only on earth, and not even here at first. Life came first and then Krebs cycle followed. There is some evidence that there are versions of Krebs that use Arsenic. I may be possible that silicon, at higher temperatures, might replace carbon. Methane planets might have different food energy cycles. Krebs won’t work on non-earth type planets so they will, of necessity (remember they have billions of years to experiment on billions of non-earth-like planets) come up with alternatives.

    10)”Physics dictates upper and lower bounds of size and capability, whether you want it to or not.” No, only in your world view. You are a homo-centrist. God did not create man’s body in his own image, so much as create man’s soul in his own image. The shape of the body is an accidental side effect of living on Earth, pushed along by a few large asteroids shuffling the deck.

    Free yourself up. Aliens will be alien to us. The world of Star Trek is fantasy. We will not recognize the aliens when they choose to show up.

    I would say more, but it is time to knock off for the day.


  • Concerning the minimum size of the brain:
    Neurons are as small as 5 Micrometers and are usually larger up to 100 Micrometers. There are however, living bacterium such as Mycoplasma genitalium which are as small as 200 Nanometers. I don’t know the average Neuron size, so I will guess that it is 50 micrometers. This makes one 250 times larger than the smallest single celled organism. If there were a life form composed entirely of very small cells, it would need a brain about 1/250th in diameter of a human’s or more than 15 million times smaller in volume and weight.

    A human brain composed of these small cells would weigh 8.7×10-5 grams.

    Could a neuron be that small? I don’t know, but I don’t see why not. There would be a great advantage in these small cells, in that communication to other cells would be faster and they would require less energy to operate. There must be some kind of evolutionary reason why cells in larger animals are larger than the small bacterium, but without a clear reason, I can’t see why a small cell is unreasonable. Half, one tenth, seems not unreasonable, and might even be common on other worlds.

    When cell size is small, body mass might be smaller by a factor or 100 or even 1,000, and mechanical differences may predominate resulting in truly alien physiognomy.

    Going in the opposite direction, very large single cell creatures are common, and they work well enough. Perhaps on a world which favored higher animals with larger cell size, an intelligent creature would be a giant, with corresponding alien solutions to the mechanics of motility.

  • It doesn’t seem reasonable to me that we can more or less infinitely extend reasoning about such things.

    I’m not a biologist, but it seems to me from an engineering point of view that such things as necessary complexity of organisation, sufficient volume for energy storage and fuel reaction, the need for cooling, and so forth would likely limit the smallest size certain structures can be. I’m not sure it’s valid to say that just because some cells (or unicellular organisms) can be very small, so cells of any type can be very small. I therefore suspect – admittedly on the basis of nothing but engineering prudence – that the brains of technological intelligences are likely to be of not less than a given volume, which is likely somewhere in the region of a third to a half litre.

    Brain organisation is another question. As I suggested above, size alone is not enough, but size in relation to body size matters (to some degree) and organisation certainly matters. The more intelligent the being, the more complex the internal wiring of the brain is bound to be, and this wiring requires volume of its own. The connections between neurons does, AFAIK, take up more volume than the neurons themselves.

    I would not insist that technological intelligences must have human sized brains, but I doubt very much if they would have tiny brains.

    Going the other way, there are mechanical limits to how large a structure such as an organism can be. One could have a very large creature indeed, and we can see evidence of such things as Blue whales and the larger dinosaurs. Whether intelligence would evolve in them to any worthwhile degree is another question, not least since enormity is itself a useful defence mechanism and so might reduce the need to outsmart predators.

    I’m particularly interested in ET life that is technological. Life in general I suspect is very common throughout the universe and is not really anything special. The kind of life that can look up at the stars, wonder what they are and then build a spaceship to go and find out is interesting – all else is nothing more than complex chemistry.

    Yes, this is speculation, but I don’t think we can speculate infinitely in any direction. I think it reasonable to suppose there are limits, not simply because we see them here but because there are only so many ways some things can be done. Just because aliens will be alien does not mean they must be utterly different.

    Culturally, I suspect they would be like us too, possibly closer in culture than in exact physical appearance – or at least any of them that manage to get into space. Any species prepared to take the immense risks and costs of space travel is going to be a collection of hard b*stards, probably not very nice to know & very unpleasant to oppose, and almost certainly completely unlike the nice sensitive liberal aliens one sees in the Hollywood view of things.

    You know, like us.

  • Its bilateral, not binary symmetry, and, yes, octopods do have it!


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I started reading Science Fiction in the 1950s. I started Writing SF in the 1960s. Then, I had a life. Now I am retired, raising chickens and keeping bees. I am still an avid reader and I have sold about 70 stories in the last 20 years.
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