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Nov 09 2013

The curiously limited argument from convergent evolution raises an ugly tentacle/fin again

I am not a fan of the convergent evolution argument for humanoid aliens. I can well believe that it’s likely that intelligent aliens exist out there in the universe, but I’m not even going to try to predict what they look like: there are too many alternative paths that are possible. But for some reason, many people like to insist that it’s reasonably likely that they’d resemble us in general, if not in detail, and they’ll then go on to extrapolate that behaviorally and culturally they’ll share many properties with us. Usually, as with Simon Conway Morris and now George Dvorsky, this argument relies entirely on the premise of convergent evolution.

It annoys the hell out of me, because it requires waving away or consciously ignoring basic principles of evolution. Here’s how Dvorsky illustrates the concept:

Convergent evolution between ichthyosaurs and dolphins

I’ve seen versions of this illustration a thousand times. Gosh, look, dolphins and ichthyosaurs all have paddle-shaped fins and streamlined bodies! Therefore, this is evidence that aquatic forms all converge on similar morphologies. And therefore, intelligent, terrestrial organisms will also converge on an ideal form for their niche, which is ours also, therefore we represent a morphological ideal.

I hate the argument because it isn’t applicable to alien species. In both cases shown above, the organisms involved belong to the same subphylum, the Vertebrata, and the same superclass, the Tetrapoda. They share a common ancestor, and the same starting point. When you start with a terrestrial creature that looks like this, with four limbs and a suite of similar traits…

Eryops, a kind of amphibian from which other tetrapods evolved

…and then let it re-adapt to a marine life as a free-swimming, active predator after long detours into mammalian and reptilian forms, is it any surprise that they converge on similar structures? They are both constrained by their ancestry! The four-finned torpedo does not necessarily represent an ideal form that will be recreated on every planet we ever someday visit, but is instead a compromise, a form that can be generated from a four-limbed vertebrate with a minimum of fuss.

But what if we look at organisms with more remote ancestry? A whole different phylum, perhaps? If we start down the evolutionary road with a conchiferan sort of creature, a mollusc…

Limpet

…which later evolves into a free-swimming, active predator, you get this:

Lovely torpedo-shaped squid

That’s something that looks completely different from a fish-like ichthysaur or dolphin; it’s got a completely different shape, a completely different set of feeding behaviors, a completely different internal organization.

We could ask the same question of other phyla. Where are the sleek torpedo shaped crustaceans sporting a nice dorsal fin and quartet of paddles? Show me a marine annelid that has followed this same path.

Now keep in mind that life on another planet will share no ancestry with anything on Earth. If our history is any example, they will be the product of a few billion years of single-celled tinkering, with a riotous adaptive radiation of multicellular forms that will explore a small fraction of morphospace…and every step will be contingent on prior states.

You can only make this ludicrous convergence argument if you think 1) contingency is relatively unimportant, that 2) adaptation is extremely powerful and will always drive a species towards an optimum, and that 3) the shape of a relatively tiny subset of species on this planet represent that optimum. There is a fourth requirement as well: you must be oblivious to the fact that (2) and (3) contradict each other.

77 comments

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  1. 1
    Nick Gotts

    But, but, but there are so many stunning examples of convergence! I mean, look at grazers! Who but an expert can tell a cow from a kangaroo?

  2. 2
    d.c.wilson

    But I’ve seen aliens on Star Trek. They all look like people with bumpy faces!

  3. 3
    ChasCPeterson

    They share a common ancestor, and the same starting point….is it any surprise that they converge on similar structures? They are both constrained by their ancestry!

    prezackly. We need a more rigorous way to distinguish between convergent and parallel evolution.

    On the other hand, true convergence certainly does happen, at some levels of analysis. For example, I would argue that the squid is not “a completely different shape” than a dolphin or ichthyosaur. or sea lion. or tuna or shark. or, for that matter, submarine.

    and then there’s this:
    exhibit A
    exhibit B
    I rest my case.

  4. 4
    ChasCPeterson

    oh, and one science-fiction author who concocted truly alien aliens was James White. He got it.

  5. 5
    F [i'm not here, i'm gone]

    And dolphins and ichthyosaurs certainly have the same kinds of eyes, and digestive tracts and brain and method of sexual reproduction and behaviors, right? Just like all primates walk upright and hunt deer.

  6. 6
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    Chas, I have looked at your exhibits and am confused as to the point those pictures are supposed to be making.

    Care to clarify for someone having a rough time intuiting your point?

  7. 7
    Nathaniel Frein

    Stanislaw Lem did some really “different” aliens when he did his serious sci-fi.

  8. 8
    Nathaniel Frein

    Crip Dyke, I think it’s a joke. The first picture is a type of sea cucumber called the “sea pig”.

    Wiki page here

  9. 9
    vernonbalbert

    Two movies that got aliens right were The Blob and The Monolith Monsters.

  10. 10
    mudpuddles

    Thanks for this post PZ! This is something that has bothered me for years, and watching some of the first series of Star Trek on TV today I couldn’t help thinking how a series often credited with “before its time” concepts that had some good science behind them failed utterly on this front, and seeing the same humanoid forms repeated throughout science fiction is a shame. (Yes, I am a complete nerd).

    IF there are intelligent life forms on other planets, about the only things we might be certain that they have in common with us are (1) they can reproduce, (2) they grow, and eventually die, (3) they need to eat or otherwise absorb nutrients to survive or complete their life cycles, (4) they excrete wastes, (5) they can see, and / or hear, and / or have a sense of touch, and / or can detect the presence of chemicals in heir environment (taste, smell, or other biochemical mechanisms), (6) they can respond to stimuli and probably move around. So they plausibly could look like humans, IF they evolved from a similar ancestor, with similar selection pressures and similar biogeochemical environments throughout the various stages of evolution and development. Which is pretty unlikely.

  11. 11
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    There was a fake documentary called, IIRC, “Alien Planet”. Of course it’s all speculative, but they talked about what choices they were making to decide aliens might look like this or that. Convergent evolution played only a very limited role.

    I was actually more interested in the speculation on the technology we would send to another world and how that tech would work than in the speculation on the alien ecosystem itself. That speculation seemed well grounded and reasonable to me, but I’m not a techie myself.

  12. 12
    NateHevens, resident SOOPER-GENIUS... apparently...

    I think the only thing we might have in common with an ET visiting us is some sort of mechanism for grasping/manipulation… because, if they’ve come to Earth to visit us, they have to be controlling the ship somehow…

    On the other hand, though, I’m not entirely convinced there wouldn’t be at least one other intelligent species with two arms and two legs that walks upright and such, if only because of numbers; this is a HUGE universe with HOLYCRAPTOOMANYTOCOUNT planets.

    Full disclosure: while I do not believe we’ve ever been visited, I do actually think there has to be more life out there, and even more intelligent life, based on the size of the universe and the potential 1,000,000,000,000,000,000,000,000 planets (that’s a lower limit) in our universe. Based on the numbers alone, I’m not sure how it’s possible that we’re alone in the universe. I could accept that we’re alone in the Milky Way, perhaps… but the universe?

    Plus there could be other universes as well, and some of those other universes might even have humans! Our doppelgangers!

    Again, that’s pure speculation based on numbers alone (so it doesn’t even rise to the level of hypothesis… it’s my imagination, mostly :D), but I wouldn’t be especially surprised by such, anyway…

  13. 13
    aziraphale

    It seems to me that the cephalopod body plan would be a very good starting point for an intelligent, tool-making species. If only they weren’t so short-lived!

  14. 14
    Naked Bunny with a Whip

    But I’ve seen aliens on Star Trek. They all look like people with bumpy faces!

    Yeah, but the aliens who evolved into pure energy are just faking it.

  15. 15
    Bronze Dog

    I’m reminded of a brief scene from Stroker and Hoop. A largely human-like green alien woman has crashed on Earth and Stroker (I think. Only seen a few episodes and not likely to watch more.) has decided to help her fix up her ship. At one time, they decide to try some interspecies fun. They both drop their clothes. She has a screaming mouth-like orifice with flailing tendrils. He has his human equipment pixelated out. They simultaneously react to each other with shock and horror and then awkwardly put their clothes back on.

    Anyway, yeah, I don’t expect humanoid aliens. If we’re talking about sapient technology users, about all I’d expect is the large brain and some kind of appendage for fine manipulation. I wouldn’t be too surprised if I’m wrong about the latter and there’s some species that outsourced it to symbiotic “hand pets” or something.

  16. 16
    Scott de Brestian

    That’s far too unkind. First of all, I’d like you to produce a believable non-human alien, in a week’s time, on a $1000 budget, with no CGI.

    Second, TOS actually had a number of non-humanoid aliens. Among them the Horta, Korob and Sylvia, the Medusans, the Companion, the life form on Argus X, the neural parasites on the Deneva colony, Redjac, among many others.

  17. 17
    Scott de Brestian

    Crap, that was a response to #10. Apparently quoting is broken.

  18. 18
    khms

    Convergent evolution … I’d point to mollusk eyes as a nice example what it does and doesn’t do. Star Trek bumpy-head aliens … not so much. All arguments I’ve seen why aliens ought to have two legs two arms, two eyes and so on, have been so much bovine droppings.

    A while ago, I came up with a different thesis. That is, I certainly won’t expect aliens to look like us – I can’t see a good reason for that – but IF they share a few important properties with us, THEN I’d expect their cultures to not be completely alien to us.

    A list of those properties:

    1. They’re true individuals. No group mind, queen bee, brainwave connection, anything like that.

    2. They’re not divided into clearly different kinds except possibly for some kind of sexual reproduction. Individuals otherwise are very similar, especially their minds. Nothing like, say, worker bees, or extreme sexual dimorphism. Especially not of the mind.

    2. They managed to build a technological civilization.

    I don’t recall right now if there was more, but at least not a lot more. In other words, given these conditions, I’d expect a sort of cultural convergence. They’d need to solve too many of the same problems. I should add that convergence doesn’t mean exactly the same; we’ve developed quite a list of cultural ideas over time, so I’d expect they’d do the same, and the actual overlap with us might be in the more obscure corners. But given that both sides managed to develop those obscure corners, mutual understandability doesn’t then seem very far fetched … to me, at least.

    But if they DON’T share those properties with us, all bets are off. (And I won’t bet on how much more likely the former option is than the latter, if at all.)

  19. 19
    khms

    @15 Bronze Dog:

    I wouldn’t be too surprised if I’m wrong about the latter and there’s some species that outsourced it to symbiotic “hand pets” or something.

    Well, if our cetaceans ever come up with a technological civilization, that’s pretty much how I’d expect them to do it … starting from fish farming.

  20. 20
    michaelbusch

    ChasCPeterson:
    oh, and one science-fiction author who concocted truly alien aliens was James White. He got it.

    White did come up with many alien aliens; but also too many that were furry humans or indistinguishable from us except under close examination (three species across the Sector General series).

    Also: White did have good peace-making ethics, but he was very sexist – to the point of claiming that women were “mentally unsuited” to being senior medical personnel.

  21. 21
    markd555

    Something I have always wondered:
    Could a non-predatory species have a technological society?
    Would there actually be direct and immediate benefit strong enough to favor tool usage and ridiculously sized calorie consuming brains for a species that did not hunt?

    And sorry folks, Star Trek is intelligent design with seeded genetics for bipedal humanoids as per TNG 6-20 “The Chase”. The series prioritizes moral and social issue stories, not accuracy in speculative science – even if it has given us much in both regards.

  22. 22
    mudpuddles

    Hi Scott de Brestian (#16 & #17),

    First of all, I’d like you to produce a believable non-human alien, in a week’s time, on a $1000 budget, with no CGI.

    You’re suggesting that imagination is limited by resources…? I tend to think that’s a load of pants. And to be fair, its also contradicted by your second point:

    …TOS actually had a number of non-humanoid aliens.

    Yes, it did have quite a lot and some were really cool for their time, which shows that money or time were not major obstacles at all. And, for science fiction, it still doesn’t excuse the most human of the humanoid aliens that were included. (And yes, I know its only make believe! But its a shame its crappy humanoid concepts seem to have been taken as a standard that later, better funded series and movies have rarely challenged.)

  23. 23
    cbarf

    For me the most interesting thing about an alien species is whether they are built on the same basic cellular chemistry. What does their DNA equivalent look like? Do they use all the same amino acids, mostly the same or completely different ones? Are their sugars like ours? And no I’m not just wondering if we can eat them.

  24. 24
    Menyambal

    Yeah, the dolphin shape is good for rear-drive vertebrates, but there are seals and sea lions who did things much differently. The tail-wagging guys did converge, but notice that one has horizontal flukes, one has vertical. The ichthy also has an extra set of belly fins, as do sharks.

    Whoever wrote that the dorsal fin was there to cut through the water was full of shit. Why would a thing stick out just so it could cause drag? It’s there to aid in turning, to counter the torque of the pectorals. Maybe the idiot thought it was supposed to slice through the surface like a shark fin in a bad movie.

    PZ, on the other hand, you did good.

  25. 25
    transenigma32

    One approach I’ve always taken when designing aliens for either my fiction or RPG settings is to not think of some biological organism, but think of some inanimate object. Imagine a basic shape or series of shapes – there are only so many shapes – and then figure a symmetry. Go from there; human speech is based on metaphors, so no matter how alien your alien is, you’ll still need something to relate it, and that’ll happen in real life, too (aliens that look only vaguely like millipedes will be called “millipedes” or “centipedes” or, vulgarly, “bugs”; never mind their body segments are cubes, they’re endothermic, give birth to live young, and are a size of a semi trailer). My favorite settings (both to read and write about) are ones where the critter typically considered “alien” in most other works of science fiction are actually some form of modified human.

    “Yeah, they guy over there with the four arms, sonar, blue skin, black hair and pointed ears? He’s a human, and he’s not a guy, they’re a true hermaphrodite; best of both worlds, you know. The thing over there that looks like a bacterophage mixed with a dodecahedron of Jell-o mounted on telescoping stilts? The thing that sounds sort of like a dolphin? That’s an alien.”

    I’ve seen some people above say that aliens will live and die like us. Is that necessarily true? We die because of biomechanical and biological reasons; evolution lead to death here on Earth. But does that mean the same thing is true somewhere else? Isn’t it possible that there’s a species that evolved to be biologically immortal, and only dies because of accidents or violent means (I’ve heard some people speculate that lobsters are biologically immortal here on Earth; I’m not sure how accurate that is).

  26. 26
    Amphiox

    The post-anal tail is a contingently inherited part of the chordate and vertebrate body plans. Without that, you can’t evolve the tail-powered fish/ichthyosaur/dolphin shape at all.

  27. 27
    Becca Stareyes

    I wonder how much of the humanoid aliens is partially due to the ability of the human face to convey emotional states very quickly to a human audience in a visual medium (TV, movies, comics). It seems like the farther from human it is, the less understandable or empathetic the aliens are expected to be: the writers knew that the audience would be likely to see the Horta as a monster and, say, the Klingons as intelligent antagonists. So they could spend an entire episode establishing that the Horta was pissed off that aliens were killing her family, and was killing people in defense, while a humanoid alien, even one that couldn’t use the Universal Translator, might get the benefit of the doubt that they had a good reason for feeling threatened, and there would be immediate attempts to negotiate.

    In the unlikely event we meet aliens, this does not look good for humanity.

  28. 28
    EnlightenmentLiberal

    I am much more partial to the idea of a somewhat shared morality and culture. I’d argue that space flight requires technology. I’d argue that technology requires communication and culture. I’d argue that culture can only happen with a species that has a somewhat similar morality from genetics (or whatever passes for genetics for the aliens). IMO, it’s a pretty weak argument, but I don’t feel like I’m pulling it all out of my ass when I make it.

    Still, even given all of that, we can look at history and what happens when different human groups meet each other. It’s invariably very bad for the technologically inferior group. And even if they has something of a morality similar to ours, we in our own recent history have done massive wars, slavery, genocide, and so on. In-group vs out-group is a bitch.

  29. 29
    michaelbusch

    transenigma32:

    I’ve seen some people above say that aliens will live and die like us. Is that necessarily true? We die because of biomechanical and biological reasons; evolution lead to death here on Earth. But does that mean the same thing is true somewhere else?

    I believe you are looking for the Red Queen hypothesis: http://en.wikipedia.org/wiki/Red_Queen_hypothesis

  30. 30
    adamk

    “And sorry folks, Star Trek is intelligent design with seeded genetics for bipedal humanoids as per TNG 6-20 “The Chase”. The series prioritizes moral and social issue stories, not accuracy in speculative science – even if it has given us much in both regards.”

    Definitely simpler to prioritize moral and social issues in a universe in which gay people don’t exist.

  31. 31
    cactusren

    In addition to the different shapes arrived at through cephalopod and vertebrate evolution, I think it’s important to point out the variety of shapes of aquatic predators within Tetrapoda. While dolphins and ichthyosaurs do have similar shapes, plesiosaurs, mosasaurs, seals and sea lions, baleen whales, sea snakes, and sea turtles are all quite different from each other. So even knowing something is a marine tetrapod isn’t nearly enough information to determine what it looks like. Hell, the existence of sea snakes means you can’t even predict with certainty the presence of paired fins! That anyone thinks we can predict what aliens might look like truly boggles my mind.

  32. 32
    lpetrich

    However, within PZ’s example of vertebrates vs. cephalopods, there’s a well-known case of convergence: lens-camera eyes. The closest relatives of each don’t have eyes nearly as fancy, and their eyes differ in lots of little details.

    I don’t know if anyone’s tried to estimate how good the resolution one can get with various types of eyes. But insects’ compound eyes don’t get very good resolution. Each simple eye in them makes only one pixel, and their direction separations are at least about 1 degree of arc. That’s bigger than the angular size of the Sun and the Moon. We can do much better, at a few minutes of arc.

    Color vision evolved at least twice, in arthropods and vertebrates.

    Many squid have side fins, and fins also evolved in vertebrates and more-or-less in arthropods.

    So there’s something to be said for convergence.

  33. 33
    lpetrich

    This reminds me that there is something weird that I once discovered. Animallike multicellularity evolved only once, but plantlike, funguslike and slimemoldlike multicellularity several times. So there may be planets with abundant multicellular biotas and no multicellular animals.

  34. 34
    michaelbusch

    @lpetrich:
    There are basically three ways of having eyes with angular resolution: small lenses with single detectors at the focus, pinhole cameras, and larger lenses with focal plane arrays. That’s set by optics.

    But, as you said, notice how the cephalopod and vertebrate eyes are still very different from one another: our eyes are wired with the photoreceptors in back of the nerves; the cephalopods have the photoreceptors in front. Cephalopods can’t see color*, but can see polarization. We can see color, but not polarization. There are the limits to convergent evolution.

    *Although some other molluscs have independently evolved color vision.

  35. 35
    jakc

    I for one believe that convergent evolution has produced two sets of aliens who are fighting for control of the Earth. One, a race of giant space ants who are preparing us for the coming conquest through the spread of the famous Simpson meme (“I for one welcome our new insect overlords”) and the other, a squid-like race which is probably using mind rays to encourage biologists like PZ to make people love squids (what reader of this blog hasn’t learned to love the cephalopods?)

  36. 36
    Stardrake

    The real reason for lots of humanoid aliens in film/TV SF actually has a name. It’s called Central Casting Syndrome™. Basically, if you’re casting humans to play the aliens, it’s a lot easier if they aliens are shaped like humans! (There aren’t many air-breathing cephalopods with agents…..)

    BTW, a novel with an intriguing alien race based on a decidedly non-biped base is MOTHER OF DEMONS by Eric Flint. The people of the world they call The Meat of the Clam evolved from mollusks. The story is how a small group of stranded humans manage to work into their society. A good read.

  37. 37
    jakc

    obviously the budget constraints on the original Star Trek caused a lot of convergent evolution, including several planets that were just like Earth, but the convergent evolution on ST also caused lots of aliens to speak English, a truly amazing phenomena. I’m just glad that when I saw the original Planet of the Apes I wasn’t old enough to wonder why Charlton Heston didn’t know he was on Earth from almost the beginning as the apes spoke English

  38. 38
    lochaber

    I’ve thought about this every now and then (frequently when drunk, bored, or having recently heard the mention of the topic…).

    I’m guessing that at the very least, alien life would have plenty of vermiform type critters, just cause it’s a rather basic body design, and seems to work pretty well.

    I also imagine there would be light-gatherering analogs of trees and grasses (probably more plant types, but those seem to be some fairly basic strategies that are pretty common.

    For a species to achieve inter-stellar travel, I’m sorta assuming it will need some sort of culture, problem-solving ability, and ability to manipulate objects.
    I’ve heard people claim they would have to be terrestrial, to build fires and work metal. Sounds likely, but I’m wondering if an aquatic species couldn’t find alternatives until they could build atmospheric environments for metal work and such, or do metal work via precipitation/crystalization/biological secretion or whatever, or maybe just find some other way to get stuff done, do we really need metal?

    I want to say tetrapod is a likely configuration, as it’s about the minimum a bilaterally symmetrical (and how important is that? how about radial?) critter would need to not fall over, barring active balancing and stuff. Once you are a tetrapod, it sorta makes sense to free up an extra set of limbs for other stuff (flying, carrying, punching, lookingsillylikeaTrex, whatevs), so I could see an argument for a bidped w/ two manipulators. maybe.

    Also wondering about the bio-chem aspects. I thought I heard someplace that humans had made/discovered other potential nucleotides, but no idea how stable/reliable/etc. they are. would having 6 nucleotides, (vs. 4), change anything significantly? allow for more variance? shorter DNA? more/less prone to mutations/errors?

    For that matter, would alien life necessarily be cellular? I’m sorta assuming so, figuring they would start at something very similar to our bacteria and get more complex from there, but is that necessarily so?

    Anyways, for all the alien talk, I rather liked Turtledove’s short: ‘The Road Not Taken’ (I think I even heard about it in the comments on this blog/blognet, but not certain).

  39. 39
    unclefrogy

    when thinking of aliens and and pacifically ones that might come for a visit I have to try and think about some of the things that made them evolve into an intelligent creature.
    They would not be very fast movers but may have been fast enough to survive. They would not have been really strong or real big either. They would have no big break your neck jaws or rip you face off claws in fact no real effective weapons at all. they would not have much of anything exceptional physically at all but this intelligence all of course in comparison with others.
    They would have to have had the ability and need to make tools and the ability to teach others how to make and use tools and it might be the more important ability is the one about teaching others how to use and make tools. They would have to be highly social and enjoy cooperative behavior.
    they would have at least 2 manipulative appendages binocular vision with good depth perception but not eyes like an eagle Most likely be air breathing where tools would be easier to make and use. would need to wear clothes. None of their senses would be extremely sensitive. The thing we would share would be our insatiable curiosity.
    Any remarkable characteristics like extreme long life or esp or things we find in the fictional invader monster aliens would be most likely bio-engineered by the aliens for there own reasons. as their scientific understanding progressed. Otherwise the look of them would be the result of their intelligence on their evolution.
    the most remarkable alien species I have ever come across is the Pierson’s Puppeteers who appear in Ring World by Larry Niven
    uncle frogy

  40. 40
    monad

    lochaber:

    I want to say tetrapod is a likely configuration, as it’s about the minimum a bilaterally symmetrical (and how important is that? how about radial?) critter would need to not fall over, barring active balancing and stuff.

    Radial is maybe a little difficult because if conditions are anything like on earth, it doesn’t go as easily with cephalization and its consequences. But why is the minimum number of limbs important? Most known species on earth have six, and there are more that have a higher number than lower.

  41. 41
    brett

    Star Trek had an explanation for the humanoids everywhere bit, albeit a stupid one (the whole “seeded DNA with predisposition for developing humanoids).

    This is a universe with god-like beings like the Q. It would have been more interesting if the whole “humanoids everywhere” bit was some type of Q experiment to seed the galaxy with tons of small population groups of humans taken off of prehistoric Earth, and then see how they would interact and develop. That might also explain why so many of them seem to be at the same technological level plus or minus a couple thousand years.

    As for real-life aliens, the only thing I’m comfortable assuming about an alien society is that they will be social creatures (hence “society”), and that they’ll have some way of sensing and manipulating their environment. I’m not even convinced that being aquatic would be an impossible hoop for them to jump, provided they live in the pelagic zone of their world’s seas.

  42. 42
    unclefrogy

    what ever other characteristics a creature my have that gives advantage to survival and reproduction intelligence must be the most important one.
    I think minimum would suggest that that would be the smallest number of limbs (4) that would be likely it would need at least 2 to stand while it uses the other 2 to manipulate the tool more might be OK like 6 or 8 or 10 even but maybe unlikely. Many of the earth creatures who have more than 4 have had some of their limbs evolved into tools themselves there by eliminating the need to make any
    uncle frogy

  43. 43
    lochaber

    monad>

    gahh… I meant to put in some sort of aside about beetles or something, but lost it in that mess of a post.

    Yeah, I don’t have a lot to back that. I could make up all sorts of just-so explanations (multiple limbs via arthropods would enable specialization that would preclude tool use, 6-legged deer analog would only really need 4, and one pair would get weaker/become vestigial/disappear…), but that doesn’t really mean anything.

    thanks for pointing it out though

  44. 44
    lochaber

    and unclefroggy>

    if I ever meet you (unlikely, I’m not social…), I’ll gladly buy you a beer (or whatever drink of your choice, provided it’s not prohibitively expensive…).

    We’re posting similar stuff almost simultaneously, and what I was thinking but neglected, you covered (in addition to covering all kinds of stuff I wasn’t thinking about, etc.)

  45. 45
    Nick Gotts

    what reader of this blog hasn’t learned to love the cephalopods? – jakc@35

    I must admit I’m one: I find them fascinating but repulsive.

    It would have been more interesting if the whole “humanoids everywhere” bit was some type of Q experiment to seed the galaxy with tons of small population groups of humans taken off of prehistoric Earth, and then see how they would interact and develop. That might also explain why so many of them seem to be at the same technological level plus or minus a couple thousand years. – brett@41

    I’ve thought much the same about Iain M. Banks’ Culture universe, where the prevalence of humanoids (IIRC, they are definitely said to be independently evolved) goes unexplained except for one throwaway joke that it’s the galaxy’s way of mopping up all the excess alcohol! In that universe, the galaxy is teeming with technological species, and “mentor” relationships between more and less technically advanced species are common, so seeding such as you suggest would fit into the scenario easily.

  46. 46
    NelC

    Beca Stareyes @27, plus the Horta had the wonderful Leonard Nimoy emoting for her, via the unlikely-but-incredibly-useful Vulcan mind-meld.

    Back in the days before CGI, Wayne Barlowe did a wonderful job of depicting humanoid but not especially human aliens in his Barlowe’s Guide to Extra-Terrestrials, as well as distinctly non-humanoid aliens, all drawn from written SF. Well worth checking out.

  47. 47
    hyperdeath

    Do the females of intelligent species convergently evolve to like the colour pink?

  48. 48
    lochaber

    hyperdeath>

    only if most of the edible berries were blue/black colored.

    or maybe it had to do with internal organs being pinkish?

  49. 49
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    @Hyperdeath, #47:

    Interesting that you ask. In fact, while the Hooloovoo were once thought to be a species, it later became clear that this was simply a gendered subset of the species “Loovoo”. The Shooloovoo actually are a hyperintelligent shade of the color pink. Ongoing gender wars within the Loovoo have led to each side visiting as many planets as possible and trying to get the dominant gender (generally interpreted by a Loovoo as being of their own gender, as members of each Loovoo gender consider themselves dominant, and because whatever sexual apparatus a physical being might have is certainly so different from that of a Loovoo it makes the comparison…difficult) convinced that color is hierarchical, with shade close to that of the Shooloovoo (or Hooloovoo, depending on the case) being more valuable and dominant, thus preferred by the dominant gender of the new species.

    So, no, not convergent evolution at all: the terrible collateral damage of an ongoing war. Curiously enough, there is quite a lot of evidence that earth itself has been visited by the Loovoo – though only by two of their genders so far Isloovoo, Gqloovoo, and Trooloovoo have yet to impose their color preference regimes, though exochromologists believe it is inevitable that one or more will attempt to do so in the future.

    BTW: if you’re one of those Loovoo deniers, I’d like to see your evidence that gendered color preferences arose through the action of some entirely earth-based set of forces!

  50. 50
    What a Maroon, el papa ateo

    jakc, 37,

    but the convergent evolution on ST also caused lots of aliens to speak English, a truly amazing phenomena.

    Well, they did have the universal translator, which must have been a chip implanted in everyone’s mind because it seems to have always worked. Except occasionally when the Klingons broke out into song or insult.

    What’s truly odd is that the translator apparently had the effect of making the aliens’ lips appear to move as if the aliens were speaking English.

  51. 51
    Amphiox

    I want to say tetrapod is a likely configuration

    Terrestrial tetrapods on earth were contingent on the fact that the lobe-fin fish happened to have four fleshy fins that could be adapted into limbs. There’s really no a priori reason four such limbs on a swimming animal should be favored over 2, or 6, or 8.

    Humanoid bipedalism is further continent upon primates losing their tail. If tails had been retained then bipedalism could very easily have gone the route of a kangaroo, or a theropod dinosaur. There is also no good adaptive reason for a tree-living primate to lose its tail. That too is an accidental contingency.

  52. 52
    Amphiox

    Another consideration when it comes to advanced alien civilizations:

    These may also be contingent on other organisms in the biosphere, ie species suitable for domestication and exploitation for resources.

    Where would human civilization be if the plants of earth’s biosphere had not evolved lignin, and there was therefore no wood?

    Where would human civilization be if there were no horses? No cattle?

    And suitability for easy domestication is a very rare trait.

  53. 53
    jd142

    Two quick thoughts:

    Wouldn’t there be some sort of convergence depending on medium and role? For example, IF an organism evolved in water or something like it, and IF the gravity was right, and IF it was a chase and catch (as opposed to sit and wait or filter) predator, then would it be more true to say that it would probably end up with the same general outline as a dolphin? It might have a duck’s bill and 20 flippers and be covered in feathers, but there’s a shape that is good for moving through a liquid approximately the viscosity of water and if you are something that has to move fast to catch prey or run away from a predator, you are probably going to get close to that.

    Doctor Who tried to do some of its aliens right, and given the budget and the lack of cgi, they did not always come off the best. There were the Rutans from the Horror of Fang Rock (http://cdn3.whatculture.com/wp-content/uploads/2013/04/horroroffangrock2.jpg was the best I could find). The Daleks, while starting out humanoid were just little blobby things in a shell. The Nestine Consciousness is essentially a gas. Alpha Centauri, http://en.wikipedia.org/wiki/File:Alpha_Centauri.jpg, is a good example of a good idea and a bad budget. Even when they had humanoid aliens, they were at least trying, like the Zygons at http://en.wikipedia.org/wiki/File:Zygon_%28Doctor_Who_monster%29.jpg or the Sontarans. There were a couple of insect based life forms, like Wirrn from the Ark in Space and the Zarbi from the Web Planet. The Menoptorans from the Web Planet were humanoid insects, and possible drugs were involved in their creation.

    Even though I prefer Who to Star Trek, don’t be a hater. If you are ok with FTL, matter transmission, phasers, and universal translators, don’t nitpick on the aliens being humanoid. When you get some non-humanoid actors, you can have non-humanoid aliens.

  54. 54
    Menyambal

    jd142, your first full paragraph is pretty much spot on. But the mode must include, in this case, tail propulsion. Ichthy, dolphin and shark all look alike, if of a certain size and lifestyle. Penguins and seals (and sea lions) propel themselves with front limbs and feet.

    Looking at the picture above, I’d say the dolphin travels faster, while the ichthy swings its head side-to-side when feeding a little more. I’ll give that to the dolphin’s sonar, which makes for a different hunting style. But the back fin shows they both turned to the side, fast at times, so they didn’t need a flexible neck.

    The blue whale, at least, uses its front fins for propulsion more than a dolphin does. The large whales don’t do hunting turns, so they don’t have back fins of any size.

    (I am sick abed and writing on a tablet, so even less coherent than usual.)

  55. 55
    Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden

    @menyambal, whom I estimate to be esteemable:

    You come across perfectly coherent to this reader.

  56. 56
    ChasCPeterson

    Penguins and seals (and sea lions) propel themselves with front limbs and feet.

    True for penguins (and sea turtles) and mostly true for sea lions, but much less true for seals (phocids)–their locomotion is highly undulatory, they just use thair webbed hindlimbs instead of a flattened tail for force production.

  57. 57
    timgueguen

    The language question is actually a lot simpler. It’s simply the case that most advanced humanoid civilisations eventually develop a language that’s identical to English. Or Japanese, or whatever it is that they actually speak in the Star Trek universe. Other than the English on Federation starship hulls I don’t think there’s ever a mention in the original series that they are in fact speaking English.

    Original Trek did have an alien race that transported Earth humans to other planets, the Preservers. They were responsible for the Native American colony seen in the episode “The Paradise Syndrome.” Like a lot of stuff from the original series they were ignored in subsequent TV series, although they did turn up in spin off novels and other materials, all of which are not canon for the various TV series.

  58. 58
    jakc

    @What a maroon

    The universal translator on ST is kinda like the shuttle craft and artificial gravity. They didn’t seem to know they had it at first and discovered later (2nd season for shuttle craft and movies for artificial gravity). What a shame though they couldn’t add a communicator to that implanted chip – would have saved a lot of hassle when their communicators got taken

  59. 59
    sugarfrosted

    @37. No, in canon that was because of a device called a universal translator. They were in fact speaking different languages. (Now, it still seems that the languages would have to be similar enough in quite a few aspects, but that’s a different issue. So maybe you would have to have some convergent aspects for such a device to be possible, but not as much as “all the aliens know english”)

  60. 60
    RickR

    I thought the movie “Alien” answered the “why does the adult alien have the same basic body shape of a humanoid?” question rather elegantly.
    In the first movie, the host is a man, so the alien is bipedal.
    In the third movie, the host is a dog (or cow, depending on which cut you’re watching) so the alien is a quadriped.
    It takes a portion of its body plan from the host organism, while still retaining all of its super nasty aspects like acid-for-blood, heavy body plating/ exoskeleton etc.

  61. 61
    Kagehi

    Perhaps the real issue is… well, convergence will happen if the “form” is already pretty much the same, and conditions arise which promote similar adaptations, but not in cases where the conditions differ sufficiently that either a) the same adaptation isn’t actually effective, or b) the prior divergence was sufficient to not leave enough similarity to produce such a convergence in the first place?

    Because, otherwise.. I don’t see a huge problem with the idea. The opposite idea is.. imho, less sensible, in that it proposed that there are an infinitely number of solutions to physical problems, and we cannot, somehow, expect something at least analogous to those we already see, from nearly identical sets of conditions, on say, another planet. That we might not see the exact ones that represent the majority of them on this planet, is a given, but that there would be “no” analogous forms, at all, between forms on two different worlds.. just seems.. ridiculous.

  62. 62
    Vicki, duly vaccinated tool of the feminist conspiracy

    Kagehi @61 wrote:

    Perhaps the real issue is… well, convergence will happen if the “form” is already pretty much the same, and conditions arise which promote similar adaptations, but not in cases where the conditions differ sufficiently that either a) the same adaptation isn’t actually effective, or b) the prior divergence was sufficient to not leave enough similarity to produce such a convergence in the first place?

    What you’re missing here is that even quite similar conditions—Earth’s oceans, with the same gravity, about the same temperature range, and an oxygen atmosphere—have produced several very different organisms. As PZ explains: a squid doesn’t look much like a penguin, and the penguin isn’t that much like a dolphin (even though the latter two are both tetrapods).

    Because, otherwise.. I don’t see a huge problem with the idea. The opposite idea is.. imho, less sensible, in that it proposed that there are an infinitely number of solutions to physical problems, and we cannot, somehow, expect something at least analogous to those we already see, from nearly identical sets of conditions, on say, another planet. That we might not see the exact ones that represent the majority of them on this planet, is a given, but that there would be “no” analogous forms, at all, between forms on two different worlds.. just seems.. ridiculous.

    It doesn’t require an infinite number of solutions, just a large enough number that the first few intelligent species we meet are using different ones. If we first met, oh, something vaguely cephalopod-shaped, but bearing live young; and then got a “get out of our corner of the galaxy or else” from colonies of single-celled extremophiles (as in some of Ken MacLeod’s science fiction novels); and, fleeing from that, met something vaguely trilobite-shaped except that it had evolved flight, would the bilateral symmetry of the not-trilobites be enough to get people to say “see, convergent evolution”?

    I suspect that bilateral symmetry will turn up moderately often; the tetrapod thing, probably less so. But that’s just on the basis that “bilateral symmetry” is a much simpler concept, and includes a lot more. It’s not quite up there with “photosynthetic,” which again I think is likely to be common but take on even more shapes that we’re familiar with.

    lochaber said they expected grasses, but those are a fairly recent development, and I suspect are contingent. “Trees” in the broadest sense of “photosynthesizing organisms with some sort of support so they can reach up for sunlight” I think are more likely, but they might not look much like trees to an Earth-dweller (and especially not someone whose idea of trees is northern hemisphere, mostly temperate with a few palm trees lurking in the background).

  63. 63
    Kagehi

    Perhaps the real issue is… well, convergence will happen if the “form” is already pretty much the same, and conditions arise which promote similar adaptations, but not in cases where the conditions differ sufficiently that either a) the same adaptation isn’t actually effective, or b) the prior divergence was sufficient to not leave enough similarity to produce such a convergence in the first place?

    What you’re missing here is that even quite similar conditions—Earth’s oceans, with the same gravity, about the same temperature range, and an oxygen atmosphere—have produced several very different organisms. As PZ explains: a squid doesn’t look much like a penguin, and the penguin isn’t that much like a dolphin (even though the latter two are both tetrapods).

    And, of course, there couldn’t have been niches, and/or sufficiently different conditions, specific to those species, to allow for the adaptation of radically different solutions, like.. I don’t know.. one of them not needing to spend any time, at all, on land, unlike the ones that obviously adapted “to” land, then from it…

    I don’t think I missed anything. You, on the other hand, are making assumptions about what I meant.

    Also… when it comes to “meeting species from other worlds”… well, there you have another issue, which is that, well, its kind of hard to imagine squid finding themselves in a position to learn metallurgy, or develop plastics, or propulsion of the sort that might initially get them “into” space, etc. Is it impossible? Maybe not, but.. in certain respects, their environment, and the limitation of being trapped in it, even more so than we are, kind of.. adds additional constraints to what could be “invented”, including the means to explore land masses, or study things that tend to only work “outside of water”. It a bit different to build a tank, fill it with water, then use “land based” technology, to make a suit, to work in that tank, versus.. trying to make “sea based” suits, that let you work “out of the water”.

    Imho, it presents a bit of a different enough engineering problem as to make it.. unlikely you could even develop it, at all, from that position. I could be wrong, of course, but.. the assumption being made, again, is that, “all conditions present equal opportunity”, somehow. I am, personally, not so sure that is actually the case for some things, like advanced technologies.

  64. 64
    Amphiox

    well, its kind of hard to imagine squid finding themselves in a position to learn metallurgy, or develop plastics, or propulsion of the sort that might initially get them “into” space, etc.

    All that would be required for that is some amount of land on their planet, and their original habitat being shallow waters close enough to shore that they have an opportunity to develop amphibious habits. Having an amphibious domesticate earlier in their technological development would probably help too.

  65. 65
    monad

    @ Kagehi:
    The problem is that you’re taking squid as-is except making them smarter, not thinking what they could become, or what could develop from creatures with a similar body plan. It would be hard to guess the shape of a human from a minnow.

    And on that, I’ve seen lots of aquaria that have both fish and crustaceans in them. If I might imagine them as representative of what the two lineages were like back in the Silurian, then if some alien had looked at them and tried to guess which was more likely to develop tool use and metallurgy some day…I’m sure they would have picked the crustaceans.

  66. 66
    jakc

    @sugarfrosted

    Your point about the UT being canon made me curious so I went over to Memory Alpha. The UT actually shows up in the same episode as the shuttlecraft. Saying that it was always in use strikes me as abit of a retrocon – you don’t see the device in early episodes. Roddenbery thought about having the crew wear a UT on the wrist to solve the English problem, but to quote from Memory Alpha: “Jerry Sohl, the writer of “The Corbomite Maneuver”, later explained, “We were originally going to have [each crew member] carry a language translator, which would fit on the wrist like a beeper, and no matter what area of the universe they were in, the thoughts that the people were thinking would automatically be translated into English as they spoke. We got rid of that idea, and assumed that everybody did speak English.”

  67. 67
    brett

    @Kagehi

    Also… when it comes to “meeting species from other worlds”… well, there you have another issue, which is that, well, its kind of hard to imagine squid finding themselves in a position to learn metallurgy, or develop plastics, or propulsion of the sort that might initially get them “into” space, etc. Is it impossible? Maybe not, but.. in certain respects, their environment, and the limitation of being trapped in it, even more so than we are, kind of.. adds additional constraints to what could be “invented”, including the means to explore land masses, or study things that tend to only work “outside of water”. It a bit different to build a tank, fill it with water, then use “land based” technology, to make a suit, to work in that tank, versus.. trying to make “sea based” suits, that let you work “out of the water”.

    You don’t necessarily have to do the whole “full tank of water” thing for an aquatic life form to spend some time out of the water. We don’t know how they would breath, for example – air-breathing life forms might be able to stay out of the water as long as they can keep themselves damp and avoid being crushed by gravity, and even water-breathers might be able to pull it off if they keep their equivalents to gills wet (like with crabs).

    I could easily see an aquatic civilization eventually figuring out how to build dry platforms/floating ships/structures that they can go on to in order to do dryland work. It might take them a while to figure out stuff that we take for granted (like fire – although some types of combustion can happen in water), but they’ve had plenty of time.

  68. 68
    petrander

    Hear, hear! Tired of people thinking alien intelligence will look human-like. That so-called dinosauroid humanoid dinosaur has also always annoyed the hell out of me.

    When people talk about the dolphin-ichthyosaur similarities, they really should think about how much of it is caused by parallel rather than convergent evolution, as PZ rightly points out. This goes also when dragging in fish/sharks and talking about the general shape. Well, yeah! Aquatic streamlining generates some pretty similar shapes. But the human shape is in no way the result of some streamlining. What happened there is that there was an ape body plan available, of which the different bits and pieces got new roles.

  69. 69
    unclefrogy

    as smart animals we think about the advantages of being smart and how we developed and how we use our smarts it is all we have any alien that develops into a smart animal will need to have nothing else going for it any better.
    our smarts need to only get more food and make more babies, that is the least it needs to be preserved and develop through the generations until today.
    I think that the question is will the forms resemble each other regardless of the line of development given similar roles, will form follow function?
    If we look broadly and disregard the way they are propelled through the water some animals that live in the sea tend to be streamlined and the faster they go the more streamlined. squid that go fast are very streamlined.
    will any intelligent animals that are on par with us appear similar? In those ways that follows function probably but they probably wont be 5’5″ and blond with big tits.
    uncle frogy

  70. 70
    Thumper: Who Presents Boxes Which Are Not Opened

    Interesting. I’ve always been aware of, and frustrated by, the idea, most obviously expressed in sci-fi, that any sentient alien species is going to be “humanoid”; but I’ve never come across any attempt to rationalise it before. As far as I can see, the only morphological trait we can be certain a sentient, civilised alien is going to possess is some dextrous appendage with which it can manipulate tools. And even that still leaves us with a very wide selection of possibilities; there’s no reason to suppose it would be opposable thumbs.

    I remember a similar conversation at school, where a friend of mine was very insistant that an alien would have to have a large head relative to it’s body, like humans, in order to accomodate the large brain-to-body weight ratio which is presumably required for sentience. Everyone was very impressed by this argument until I asked why we were assuming that said alien would keep it’s brain in it’s head. Or even have a head.

  71. 71
    Menyambal

    So all the aliens in the Trek ‘verse convergently evolved English? Yet somehow they all have different biosigns that can be picked out in a bustling space station.

    Wikipedia’s page on ichthyosaurs starts with a picture of all the different shapes of them. Ichthyosaurs didn’t even converge on the ichthyosaur shape.

    ——-

    Most of our environment for the last million years or so has been us. Our culture, each other, human-made things, have been more influential than the outside world and natural environment. I’m lying on a bed in a house, and if I go outside, I’m wearing clothes and driving a truck. When I eat, it’s prepared food from domesticated plants and animals. The only wild thing in my life is the virus that is kicking my colon, and even that seems to be humanized enough that the dogs aren’t catching it.

    So any intelligent alien species is not going to be shaped by anything like its natural world, or our culture, it’s going to shape itself. Suppose they didn’t start on cooked food, but went with swallowing live termites and chewing the twigs they’d caught them with–they’d have big jaws and bulging bellies, and regard them as desirable. They would build houses and vehicles for their body shapes, and be shaped by them in turn. Their manipulative members would influence their tools.

    Or perhaps they would gradually change from being pack hunters to being herders of animals, and never bother with tools at all. Or develop agriculture from scratching soil and pecking seeds, and just be inteligent birds.

    To discuss what intelligent aliens might look like, we need to consider what we mean by intelligence, and what we would call civilized and tool-using. If we define them as space-faring, say, we have to define space-faring. We would probably find all shapes and kinds of aliens, at all levels of what might be called intelligence, some of which we might like more than others.

    I favor the Star Wars universe for that representation of what might be out there. And for the seeming lack of inter-species ugly-bumping.

  72. 72
    Menyambal

    Arrr. What I was trying to say is that intelligence and culture is apt to be wildly divergent.

  73. 73
    Kagehi

    The problem is that you’re taking squid as-is except making them smarter, not thinking what they could become, or what could develop from creatures with a similar body plan. It would be hard to guess the shape of a human from a minnow.

    No.. The problem is that you “solution” ends up being, “Well, what if they develop amphibious adaptations?”, at which point you have to ask, “What sort of adaptations would that require?”, and the effective answer is, “There are no known animals, or any kind, which rely entirely on muscle mass to move on land, with the possible exception of things like slugs and snails, which, again, have a whole set of issues with maintaining moister, etc., in order for that body type to function on land at all.” The argument amount to, “Well, if you start with squid, then at some point their stop really being squid any more….” Sure, none of us are likely to be entirely successful at imagining the result, but.. what ever that result is, it has to be constrained by the realities of the physics, and that means that you “will” end up with something that works “under those new conditions”, and it won’t end up looking like a squid any more, save very superficially. Whether than means bones, bipedal locomotion, etc., is probably not the case, but its going to end up looking more like a land animal, as we understand it. Form follows function, whether you are building a something as simple as a spoon, or something as complex as an animal, right?

  74. 74
    Crimson Clupeidae

    Although a lot of his writing is rubbish for other reasons, this is something I think Piers Anthony might have done well. In his Kirlian Quest series, the aliens are all quite alien, and not even vaguely humanoid. Some of them are really quite interesting and rather fanciful, but at least they aren’t humans with bumpy faces….

  75. 75
    John Horstman

    The writers of Star Trek: TNG realized this decades ago and explained the prevalence of intelligent humanoid species in the galaxy as the result of ancient aliens seeding thousands of planets with life in their own image, in a clever postmodern allusion to what the Star Trek writers themselves are literally doing – filling countless alien worlds with beings in their own images. This is noted above, but I thought I’d point out that it is in fact a self-reflexive commentary on writing and the constraints of producing a sci-fi TV show with only human (and a couple feline) actors and really basic CGI animation in addition to a way to hand-wave the evolutionary issues.

  76. 76
    David Marjanović

    ^ It’s also creationist frontloading.

  77. 77
    David Marjanović

    If we’re talking about sapient technology users, about all I’d expect is the large brain

    For some value of “brain”. :-)

    I’ve heard some people speculate that lobsters are biologically immortal here on Earth; I’m not sure how accurate that is

    It’s also being wondered about turtles. Understandably, the study is still ongoing.

    The post-anal tail is a contingently inherited part of the chordate and vertebrate body plans. Without that, you can’t evolve the tail-powered fish/ichthyosaur/dolphin shape at all.

    Why? The chaetognaths have done it. They’re tiny, tiny, tiny killer whale lookalikes. :-) And their embryonic development is deeply bizarre.

    There is also no good adaptive reason for a tree-living primate to lose its tail.

    Unless you get too big for a non-prehensile tail to be of any use. That’s what we did.

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