Twelve reasons we haven't found aliens

Discussion in 'Astronomy, Exobiology, & Cosmology' started by wegs, Feb 5, 2020.

  1. paddoboy Valued Senior Member

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    The reasons why we have not as yet contacted any Aliens can be summed up with time and distance. Distances are vast and civilisations mostly have a limited time.
    The important point to remember is that most scientists would agree that we are not alone and that life should exist somewhere, sometime, and at various stages of development, but mostly basic bacterial stuff.
    The thing is that despite those beliefs, as yet we have no evidence for any life existing off this fart arse little blue orb, let alone having visited us.
     
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  3. James R Just this guy, you know? Staff Member

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    DaveC:

    Are you sure the funnel is on the underside of the octopus? (It's not clear from the diagram.) That is, is it between the arms, or on the top of the body?

    Where does the octopus take in water to blow out its funnel?

    Pardon me if I'm not an expert in octopus anatomy. Just trying to learn something here. I find octopuses fascinating.

    Yes, it does. That's why so many different types of predator species have exactly that arrangement.

    To be fair, the anatomy of the octopus is somewhat remarkable. One might regard it as exceptional. One fascinating fact is that its brains are essentially distributed throughout its body and not centralised, even though it does possess a "middle" brain.

    But coming back to the point: the octopus is a bilaterally symmetrical top-of-the-food-chain predator. It is an example that supports what I said about bilateralism being a sensible body plan, rather than refuting it.

    Gravity tends to favour body plans that distinguish "up" from "down". Or, more precisely, evolution tends to produce body plans that distinguish up and down, at least for creatures larger than a certain size, to whom the effects of gravity are reasonably noticeable.

    Are you sure?

    The picture you provided does not actually answer the question I asked you. But perhaps you have a better one that does?

    Do you imagine that I didn't look at some pictures myself, before asking you?

    Well, you're right. I do think it makes evolutionary sense. I think that the proliferation of bilaterally symmetrical body plans among top-of-the-food-chain predators attests to that. I can immediately point you towards hundreds of existing and past species of bilaterally symmetrical predators. How many non-bilaterally-symmetrical predator species can you name?

    I get it that you think this is just an accident of evolution. I disagree with you, and you're not bringing anything to the table that makes me think I might be wrong, so far.

    Note that I have never claimed that a predator cannot be anything but bilaterally symmetrical. All I did was to comment that it's probably not an accident that so many are.

    Sure, but not so much for top-of-the-food-chain self-motivated predators that actively seek out their food, which are the ones I have been talking about.

    In general, I agree with you, but not in this case. Natural selection will favour beneficial body plans, along with all the other things that make an organism successful.

    You appear to think that bilateral symmetry is merely an evolutionary accident. I suggested some reasons why I don't think it's a mere accident. To be clear: initially, of course, it was an accident in the same way that every evolved trait is an accident. But natural selection has favoured that type of body plan, so that today it is rare to find a different body plan among top-of-the-food-chain predators. The evolutionary success of the body plan is not an accident.

    In the Cambrian explosion, lots of different body plans were "tried out" by evolution. Do you really think it's an accident that bilateral symmetry "won out" over the many alternatives (for top-of-the-food-chain predators)?

    I gave you some reasons. It only takes a sentence or two to set out the reasons, and that's what I did for you.

    Fine. I don't think you've refuted the case I made. I mean, I could be wrong. Maybe you have some better arguments you haven't put yet (?)

    Which counter-examples are you thinking of, in particular? Can you mention a few of them, please? The first one you mentioned was the octopus, which isn't a counter-example at all. So what else have you got?

    I don't know about strongly favoured. That seems to imply some kind of value judgment about what counts as "strong". I think that given gravity, a linear digestive system, sense organs, active locomotion, and predation, bilateralism would be favoured. You're welcome to tell me why I'm wrong.
     
    Last edited: Feb 10, 2020
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  5. DaveC426913 Valued Senior Member

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    Actually, those aren't contradictory.

    If triplets run a race and have identical finish times, no one is best, and yet no one is better.
     
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  7. DaveC426913 Valued Senior Member

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    We were talking about the anus, which is labeled.


    False. Correlation does not mean causation.


    And yet still well within the set of "Earthlike critters" when we add possible alien critters into the mix.

    Yes. Almost all Earthlike critters are doomed to have bilateral symmetry - because that's the line that happened to survive the great extinction.

    But you can see that - even when starting from a bilateral plan - Earth predators are doing a very successful job of predation and intelligence with a central head and organs - with the rest of the body spanning out from there. Evolution is producing a radial design even from a bilateral start.

    What does that to do with bilateral symmetry?

    An umbrella has a distinguishable top and bottom too.

    You are the one who first made the claim that bilats are "more likely" and "makes sense". It may or may not be true, but you have drawn a hasty conclusion.


    I don't really understand why this is up to me.

    Well, this is all kind of funny. I think you're playing some sort of game here.
    You ask me for pictures. You ask me if I've "actually looked" at pictures. You don't like my pictures to prove your point. And now you want me to find better ones for you.
    What's going on here James?


    One argue in the same fashion that "DNA makes evolutionary sense - the fact that every creature on Earth attests to the that."
    Can you see how that's flawed? Earth critters lost any evolutionary option of an alternate to DNA.
    Likewise, they lost any evolutionary option of an alternate body plan.

    And yet- even though that door is pretty much close to complex Earth life, it is finding a successful alternate.


    James, this is beneath you.
    It's not like every body plan was dealt the same cards. One plan of a dozen got a break.


    You are drawing a hasty conclusion. That's a logical flaw.


    "...probably..."

    Probability cannot be applied meaning fully to a dataset of one point.

    OK. Your goalposts are getting more and more narrow.


    Natural selection is not the only factor in determining the course of successful species. Accidents steer it too. The most perfectly adapted critter will not survive a meteor strike, volcanic super-eruption or tsunami.

    That's self-contradictory.

    If you acknowledge that is was initially due to an accident, then you've got to acknowledge that natural selection cannot favour a type of body plan that goes extinct because of that accident.

    It would be like saying 'My cat ''Epsilon is "obviously" the best of its litter. Since the accident that killed Alpha, Beta, Gamma and Delta - clearly Epsilon has fared the best in the intervening ten years.'
    The first four are dead.



    Yes. As did Stephen J. Gould, who wrote several books on the subject, and is widely regarded as the authority on the Burgess Shale and the Cambrian Explosion.
     
  8. wegs Matter and Pixie Dust Valued Senior Member

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    Hmm, I don't know. This idea isn't widely accepted though, and somewhat falls into pseudo-science, don't you think? I can't help but wonder if those who are ''pushing'' it, already have a bias towards believing in alien life. Not saying it's impossible, but why do some scientists feel it necessary to ''call on'' extraterrestrial life to explain the complexities of our origin?
     
  9. DaveC426913 Valued Senior Member

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    Wait. What? OK, if by "extraterrestrial life" you mean nothing more than microbes at best.

    The reason it's appealing is because of the following logic:
    1] Life did arise at least once in the universe. So, whether or not it is unlikely is moot.

    2] Where it got it's start is kind of an arbitrary - what's the diff between organic soup on that planet and organic soup on this planet?

    3] We know for a fact that bits of other planets - and bits of other solar systems - did and do end up as part of our Solar System.

    4] If it started on Earth, it got started damned fast.

    Evidence of life has been found as early as about a half-billion years after the Earth has even cooled enough to have a crust. That is ... implausibly fast. It suggests that life ought to be very, very common - erupting on every surface in the solar system that isn't molten or as cold as liquid nitrogen.

    5] If the products were formed on some other, much older planet - and got blasted here on a comet - then that pushes life's origins back another 8 billion years or so.

    That gives it much more time (at least 10x more) - for something that appears to be very rare - to form.




    To recap: Essentially you've got a paradox.

    If life is so virulent that it took over a whole nasty planet in the blink of an eye, why isn't it everywhere on every planet?

    If life is so fragile or picky that it needs juuuust the right circumstances (otherwise it would be everywhere in the solar system), how is that it managed to find the perfect soil and flourish in the blink of an eye?


    Bring on the extended timeline ... if the time life has to get started were much muuuuuuuch longer than the blink of an eye - that solves both problems. To-wit:

    It is both rare and has sufficient time to develop such a rarity.
     
    Last edited: Feb 10, 2020
  10. billvon Valued Senior Member

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    Legless annelids do great with perfect radial symmetry.
    ?? Both are true. Bilateral symmetry is not the best plan; there are different best plans for every environment and every ecological niche.
     
  11. James R Just this guy, you know? Staff Member

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    DaveC:

    It's almost as if you're arguing for the sake of arguing. I don't think that what I said is particularly controversial.

    It is my understanding that the octopus anus expels its waste into the funnel of the octopus. Is that wrong? If it is correct, then you'll see that my interest in the location of the funnel is relevant.

    You think the correlation is accidental, there?

    That was a side comment of mine that has no bearing on what you're arguing about with reference to bilateral symmetry.

    Why did that line survive, while so many others went extinct? Accident?

    Examples, other than the octopus?

    It's what I explained in my first post in this sequence - the one you got all upset about in the first place. Gravity forces a distinction between top and bottom. The digestive system and sensory organs lead to a very likely distinction between a "front" and a "back". The environment does not, in general, favour particular lateral directions. Hence bilateralism.

    Umbrellas are not top-of-the-food-chain predators, or any of those other things I talked about.

    Not hasty at all. A conclusion based both on our understanding of the terrestrial environment and on our experience of successful top-of-the-food-chain predators.

    You put forward the example of the octopus in order to try to refute my position. It's not my fault you didn't do the necessary leg work before you jumped in to suggest that example. If you couldn't bring the relevant information to back up your claim, why use that example at all?

    What's going on is that the pictures all support the view that the octopus is a bilaterally symmetrical animal, which makes it irrelevant as a refutation of my claim about bilaterally symmetrical predators from the start. Your claim, added on by you, was that octopuses break the "rule" of having their anus on the opposite side of their body to their mouth and sensory organs, but you have so far been unable to show that this is, in fact, the case with octopuses, using pictures or any other kind of evidence.

    My initial impression was that you assumed the octopus was an example of a radially-symmetrical animal, which it clearly is not. Now it seems like you're just being contrary for the hell of it.

    Look, if it's too much trouble for you, let's just agree that you're not any more of an expert in octopus anatomy than I am, and move on to something else. Okay?

    It's not flawed. DNA does make evolutionary sense, otherwise we wouldn't have a 3 billion year history of DNA-based life on Earth. If there was something fatally wrong with DNA, life couldn't have lasted that long.

    I take it your answer is "none", or at least none that come readily to mind, then? Why the attempt at distraction? Why make it personal?

    Dig deeper. Why was that plan so successful? Just accident, or something else?

    No. I'm not doing that. And hasty conclusions have nothing to do with logical flaws, by the way. I can hastily conclude that Socrates is a man, and that doesn't mean the logic is flawed.

    Right! Probably. I've already said - many times - that I could be wrong. If you can show me why I'm wrong, I'll thank you and go away having learned something new.

    There are literally millions of data points in the relevant set, that being the set of species of bilaterally symmetrical predators.

    Not at all. I was very specific right from the start.

    Remember, all of this back and forth is springing from a single paragraph I wrote.

    Sure, but the comment you quoted talked only about natural selection, so the rest of what you wrote in response is irrelevant.

    I don't see the relevance of your cat example. The only measure of "success" in evolutionary terms is a creature surviving long enough to pass on its genes to a new generation. Clearly, bilaterally symmetrical animals have survived over millions of generations, faithfully passing on their genes. How can you say anything other than that this is an impressive record of evolutionary success of the bilaterally-symmetrical body plan?

    Ah, something interesting at last!

    Quote, please!
     
  12. wegs Matter and Pixie Dust Valued Senior Member

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    @ Dave (in reference to post #46):

    But, finding evidence of life on other planets, won't technically answer the ultimate question of where it started or if it has the capability (?) to start in even more diverse conditions. That said, it's an intriguing concept to me because if we can prove that life started somewhere other than Earth, there is hope for colonization.

    To your point: It suggests that life ought to be very, very common - erupting on every surface in the solar system that isn't molten or as cold as liquid nitrogen.

    Is that like saying -- if life can make it here on Earth...it can make it anywhere? (I disagree) But, the onus is on you to try to convince me.

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  13. James R Just this guy, you know? Staff Member

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    More diverse conditions surely include entirely different planets (or moons, as the case may be)?

    If we discover life on Mars or on Europa or on Titan, then at the very least it will show us that life can exist in other places than on Earth. The kind of life will also be very interesting. Will it use the same chemistry as Earth life? Will it have DNA or something similar?

    If life is possible on other planets in our own solar system, that would make it highly likely that it can exist on other planets in other solar systems, too.

    Finding life on other planets is not likely to ever answer the "ultimate" question of where the first life started, although it might well turn out that life has got started separately in many different places.

    Colonisation only requires that the conditions to support life be present, which is a much lower bar to clear, I think, than having the conditions for life to start from scratch.

    But that's the thing. As things stand, we don't know if it's difficult or easy to start life going on a planet. Finding life on another planet will at least tell us that the starting of life is not a unique, one-off occurrence that has happened here and nowhere else in the galaxy.
     
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  14. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    That's the option / scenario I would favour

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  15. Seattle Valued Senior Member

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    I've spent a fair amount of time diving with both Red and Giant Pacific Octopuses. I also volunteered for a while with the Seattle Aquarium. I haven't read every post in this thread carefully but I've seen a few questions that I can answer.

    The mantle is behind the head. It takes in water through its gills (located inside the mantle) and forces it through the funnel when it needs to get away in a hurry.

    It doesn't do this often and even though it can move quite fast this way, it can't go all that far. It's kind of anemic from what I recall. It has blue blood. It's quite tiring to do this. The mantle also encloses the organs. That's not their "head".

    I also wouldn't call the octopus at the top of the food chain. They camouflage themselves to hunt of course (quite effectively) but they camouflage just as often to prevent themselves from being eaten (or losing arms) from harbor seals and sea lions.

    The only hard part of their body (the largest part) is their beak. If they find a crack in a rock that has an opening as big as their beak, that's all they need to squeeze though it as the rest of them is mainly water.

    When they are really trying to get away it can look like a puff of smoke and then they are gone even though you have been looking at them the whole time. They just disappear though the tiny hole.

    If you are looking at them and then they spread out on a rock and camouflage themselves (instantly) you can't see them unless you already know they are there and even though you have to look for the eyes. If they aren't feeling threatened they don't bother to camouflage themselves and they can just look like a lump on a log or boulder while they "sleep". They mainly hunt at night. Most of my dives or many anyway were at night.

    The red octo is more prone to biting even though it is small (a few pounds). The Giant Pacific Octopus (which I'm even more familiar with) can stretch out several feet or even yards long and a typical adult would be 60 lbs to 120 lbs but they actually can get as large as their food supply allows. They only live about 3 or 4 years. The males die soon after mating and the females die after their long (6 months) gestation period and they don't leave their den during the entire period and therefore don't eat. They have to stay there to aerate the eggs (1,000s) or they won't survive and they have to protect the eggs from crabs who will eat them.

    Sometimes the females die before the eggs hatch and then the whole thing was a waste.

    The picture that I posted on the whole octo wasn't a big one. The one with the eggs was. The largest of the suckers were silver dollar sized.
     
    Last edited: Feb 10, 2020
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  16. Seattle Valued Senior Member

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  17. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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  18. wegs Matter and Pixie Dust Valued Senior Member

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  19. DaveC426913 Valued Senior Member

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    That wasn't my intention. My experience with discussions about exolife are filled with people assuming that what we've got here on Earth is darned good plan. The arguments are terribly Earth-centric, in my view.
    I'm surprised to hear this coming from a scientific literate.

    (Sorry, there's no way for that not to sound condescending. I intend no sleight or disrespect. For all I know, my surprise is due to my being too surrounded by my own knowledge of the issue.)

    The problem is we have no way of knowing whether all these body plans got the same chance. But once one dominated, it will have shouldered the others aside.
    I think it is hasty to assume that bilats flourished because they were superior in the first place. There were a great die-offs that they think occurred from accidents. There's no reason to assume one got a break because it was superior. Yes. Chance is a factor in evolution.


    Yes.

    Sure. It's not going to force bilaterality in particular.
    It's going to affect all body forms.

    Once bilateralism was baked in to every modern creature, it loses the ability to find other paths - even if those other paths are as good as or better than the path taken.

    Or radialism.

    Do you grant he point that gravity (and sunlight) can bias a creature to have a top and bottom whether or not it has a bilateral plan?
    Is there some reason you think other plans would not develop such a distinction?
    If not, then top/bottomness is not an argument in favour of bilateralism.

    I did. I even provided pictures to refute your claim. Octopi do not have their mouths and one end and their anus at the other end.
    If you want to disprove it that's not really my responsibility.

    No. While it is true that octopi stemmed from the same bilateral plan, the doesn't mean it's superior. In fact, even starting with the bilateral plan octopi are doing a darned good job of having a functional radial plan even if it had to start with bilateralism.

    OK,
    1] it's not a rule.
    2] You didn't say "opposite", you said at one end and the other end. Octopi do not have their eyes or their anus on the ends. They are both mid-body.

    My only onus is to how counter examples to your claims.

    I'm sorry you feel that way.

    It is developmentally bilateral, but it is functionally radial.

    It is taking what it was given and (evolutionarily) making a radial arrangement to suit its survival needs.

    I never claimed to be anything.

    You claim to know what "makes sense" for exo-life. I don't think you've made that case.

    Nobody said "fatally wrong".

    Just because it's the only thing available doesn't mean it's the best of all possible things for the job.

    Heck, for all we know, a "better" body plan might have evolved intelligence in only a hundred million years years, instead of a half billion. How do you judge what's "best" when you only have one planet as an example?

    It wasn't my intention. It was more of a point-of-order, or a sanity check on the discussion. I am flabbergasted that this issue of alien body plans is even in contention between us. Anyway, I'll avoid that in the future.


    Sorry, it's formally called a hasty generalization - and it is a logical fallacy.

    You could certainly say Socrates is a man, but you cannot then build upon that in the form of "And since he's a man, he must... etc."

    Your conclusion is only true if Socrates is demonstrated to be a man. And that's what is on contention here.


    No. The dataset is Earth's complex animals. That's one datapoint.

    Bilateralism was baked in at the start for whatever reason. It can't be changed without an huge extinction.

    Given another shot at it, radial body plan might get baked in.


    It is as impressive as cat Epsilon. Cat Epsilon is not successful because it is superior; it is successful only because it didn't get killed in a freak accident that had nothing to do with its fitness.

    For all that could be said, it could have been the runt of the litter and its kin were strapping examples of felinity. We will never know because they were killed.

    As with body plans. It is a hasty conclusion that bilats got the edge because they're more fit. There's a lot of bad luck in the deep history of evolution.



    "Wind back the tape of life to the early days of the Burgess Shale; let it play again from an identical starting point, and the chance becomes vanishingly small that anything like human intelligence would grace the replay."
    https://quotefancy.com/quote/121302...fe-to-the-early-days-of-the-Burgess-Shale-let

    Now, he talks about humans specifically in this quote, because that makes a better sound bite, but his thesis is that the entire lineage of what is alive today is greatly dependent on some good luck and bad luck way back before the body plan was baked-in.

    It's not a coincidence that this is in the context of the Burgess Shale. It's one the world's best sites for examples of the Cambrian Explosion 500 million years ago.
     
    Last edited: Feb 11, 2020
  20. wegs Matter and Pixie Dust Valued Senior Member

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    So, suppose scientists discovered non-DNA based life forms on other planets, would that rule out the Panspermia theory? Did this idea take shape mainly because it's hard to fathom that life couldn't have ''appeared'' that quickly on Earth (without it coming from another planet)? I can't find who hinted to this, maybe Dave, but I guess that makes sense. At least why the idea came into focus, anyway.

    But, why would it be difficult to imagine life establishing itself rapidly, once the conditions became ...hospitable?
     
  21. DaveC426913 Valued Senior Member

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    OK, having thought upon some the things you've said about octopi, I concede that I do not actually know that its anus is on the inside as opposed to the outside of its bell shape. I will retract that portion.

    But I stand by the primary fact that it does not have its mouth and sensory organs "at one end" and its anus at "the other end". They are mid-body.
     
  22. DaveC426913 Valued Senior Member

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    Because that immediately raises the question of why it didn't establish itself - in some form or another - rapidly everywhere that conditions became hospitable.
    Venus, Mars, Jovian and Saturnian moons, etc.
     
  23. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    Perhaps life did, but only at microbe level since none of those appear suitable for life above the level of a microbe

    As for design I would contend physics has a large part to play

    Walking for locomotion is far simpler than wheels for life forms which need to cover various terrains

    Very doubtful we will find any animal life form using wheels

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