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Thread: What do you think is the most likely explanation for the Fermi paradox?

  1. #871
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    Quote Originally Posted by Colin Robinson View Post
    Have you heard of the planula hypothesis? It's the theory that all animals with bilateral symmetry, including tree-climbers, are descended from a cnidarian (jellyfish family) larva that failed to grow up.
    That's certainly an interesting hypothesis, and I had never heard of it. That's one cool thing about this forum, that you get exposed to interesting things, whether they turn out to be true or not.
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  2. #872
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    Quote Originally Posted by Colin Robinson View Post
    So, when you said



    You actually meant: "Nothing that isn't related to a jellyfish is going to climb a tree." ?
    An organism evolved to climb a tree is no longer in any way recognizable as a jellyfish, any more than a primate is a lungfish. It would require adding far too many genetic and selective differences. But that was arguing with your specific example, not with my main premise; which is that common ancestry will not be shared with alien life, and so the very specific factors that led to cephalization in one very specific line of development in Earth life will not be shared.
    Last edited by Noclevername; 2020-Jun-30 at 05:01 PM.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  3. #873
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    Quote Originally Posted by Noclevername View Post
    An organism evolved to climb a tree is no longer in any way recognizable as a jellyfish, any more than a primate is a lungfish. It would require adding far too many genetic and selective differences. But that was arguing with your specific example, not with my main premise; which is that common ancestry will not be shared with alien life, and so the very specific factors that led to cephalization in one very specific line of development in Earth life will not be shared.
    So when you wrote, "If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree," you didn't mean that a jellyfish would never evolve to climb a tree, but rather that if it did evolve, we would no longer call it a jellyfish? That seems like a pretty obvious point to me. I can't imagine why anyone would argue the opposite, that if one organism evolves into another, we would still use the same name...
    As above, so below

  4. #874
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    Quote Originally Posted by Jens View Post
    So when you wrote, "If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree," you didn't mean that a jellyfish would never evolve to climb a tree, but rather that if it did evolve, we would no longer call it a jellyfish? That seems like a pretty obvious point to me. I can't imagine why anyone would argue the opposite, that if one organism evolves into another, we would still use the same name...
    The context was, I was responding to what Colin Robinson said about ecological niches. Why do people keep fixating on the jellyfish part of that post?

    Quote Originally Posted by Colin Robinson View Post
    In an organism which occupied a comparable ecological niche, wouldn't you expect comparable adaptions?
    Quote Originally Posted by Noclevername View Post
    If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree.
    The niche is not simple. It is a complex interaction of many species and environmental factors in a complex ecosystem. So a non-terrestrial biosphere would not contain the same niches as the present lines of evolution on Earth. It would comparing apples to fnordsperk*.

    The substrate that parallel evolution is built on is the organism's genetic structure; a dolphin and a large shark are both similar in niche and general body plan, but no shark has lungs and no dolphin has gills. ET life might plausibly evolve large, complex mobile life forms, but they will not be Animalia. There would be no reason to expect Nature to find the same solutions to survival (including cephalization) every time. Natural selection of random mutations is not deterministic. It is a Rube Goldberg device of mistakes that sometimes work out well enough.


    * Know what a fnordsperk is? Nope, because we've never seen one. It's alien.
    Last edited by Noclevername; 2020-Jul-01 at 06:39 AM.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  5. #875
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    Quote Originally Posted by Noclevername View Post
    The context was, I was responding to what Colin Robinson said about ecological niches. Why do people keep fixating on the jellyfish part of that post?
    Perhaps because the jellyfish (with its kinship to other Animalia) is a relevant and fascinating case of how evolution actually works.

    The niche is not simple. It is a complex interaction of many species and environmental factors in a complex ecosystem. So a non-terrestrial biosphere would not contain the same niches as the present lines of evolution on Earth. It would comparing apples to fnordsperk*.

    The substrate that parallel evolution is built on is the organism's genetic structure; a dolphin and a large shark are both similar in niche and general body plan, but no shark has lungs and no dolphin has gills. ET life might plausibly evolve large, complex mobile life forms, but they will not be Animalia. There would be no reason to expect Nature to find the same solutions to survival (including cephalization) every time.
    If they are large, complex and mobile, that's 3 important characteristics they have in common with many of Earth's Animalia. If that much is plausible, why isn't it plausible that they'd have other features in common with Animalia as well?

  6. #876
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    Quote Originally Posted by Colin Robinson View Post
    If they are large, complex and mobile, that's 3 important characteristics they have in common with many of Earth's Animalia. If that much is plausible, why isn't it plausible that they'd have other features in common with Animalia as well?
    I'm not saying it's not plausible that they do. I'm saying there are also an indefinite but very large number of other ways they could go.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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