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> perhaps only the DNA-based life survived some early period in Earth's history. My thoughts exactly. Also, the emergence of an intelligent, technologically c

> perhaps only the DNA-based life survived some early period in Earth's history. My thoughts exactly. Also, the emergence of an intelligent, technologically capable species (i.e. humans) is a relatively very recent occurrence in Earth's history. It's as if it just suddenly happened, even though there was a long history of dynamic evolution for many hundreds of millions of years. But the sudden emergence of humans doesn't mean there had to have been an external cause.

dvfjsdhgfv 7y ago
> the emergence of an intelligent, technologically capable species (i.e. humans) is a relatively very recent occurrence in Earth's history. Citaton needed.
- H8crilA 7y ago
  "History of Earth" https://en.m.wikipedia.org/wiki/History_of_Earth https://en.m.wikipedia.org/wiki/History_of_Earth
  - dvfjsdhgfv 7y ago
    That's what we currently know based on what we discovered so far. You can't really rule out the existence of a relatively advanced civilization - although it might advance in a completely different way than ours - whose remains lie buried somewhere under the Mariana Trench for example.
    - throwaway2048 7y ago
      https://en.wikipedia.org/wiki/Russell's_teapot https://en.wikipedia.org/wiki/Russell's_teapot
      - andai 7y ago
        Sure, but we aren't trying to prove or disprove anything here, we're speculating for enjoyment.
    - mellosouls 7y ago
      Yes, this has been investigated before - e.g. https://arxiv.org/abs/1804.03748 https://arxiv.org/abs/1804.03748 https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e... But the evidence we have (as per prior comments) is that a human-level intelligence civilisation has arisen only once on Earth.
    - mikekchar 7y ago
      There are actually an infinite number of possible things that could have happened which we can't rule out. Let me preface what I'm going to say with I don't mind what anyone believes. If it makes you happy to believe one thing over another thing, then I think that's great. With that out of the way, when we're having these kinds of discussions, it's not really productive to bring up an infinite number of possibilities that we can't rule out. Which one should we choose to support? Without some criteria, we will just talk about it forever -- which might be fun, but it's not productive. This is where science comes in. I'm going to say something a bit controversial. Science doesn't really talk about absolute truth. We can't know what that is -- because there are an infinite number of possibilities that we can't rule out. Instead it talks about things that are "productive" (my term). In a very hand-wavy way, science is about making observations and building a model that explains those observation. There are a couple of other important things. The model should also make predictions about thing we haven't observed that we can test. We try it and if it also fulfills those predictions, we thing it's a "productive" model (again, my term). Why is it productive? Because it allows us to reason about things and make conclusions that are likely to work out for us. However, we shouldn't mistake that for the absolute truth. There really is a possibility that things appear one way to us, but are very different in ways that we can't see. The key is that from the perspective of science that's fine -- as long as we can keep making predictions and they keep working out for use, we can use our model. But what if we have 2 models that are both equivalent? For example, let's say they both explain the observations we see and they make predictions that work out. Which should we pick? By convention, we pick the simplest one. In truth, the simplest one might not be correct, but it's always easier to work with a simpler model... because it's simpler ;-) So while there may truly be advanced civilizations out there -- we can't rule it out, there is no test we can currently do that would show that advanced civilizations exist. Our models without advanced civilizations (except our own) explain everything we can currently observe and everything we can currently test. So we choose the model with no other advanced civilizations. You really don't have to believe that, but when discussing with others we have to set some rules. If we keep in mind other advanced civilizations, it's just as reasonable to keep in mind an infinite number of other possibilities -- some of which would be truly bizarre. In order to keep the conversation on track, we have to choose somehow and the scientific method is a good, proven way to narrow the discussion down to something that is productive. However, if you find people who want to talk about the kinds of things you want to talk about, I think there is nothing at all wrong with that. You should do what makes you happy. I hope that makes things a bit clearer. I often meet people who make comments like you did and I think it's really mystifying to those people why science oriented people act this way.
- kitd 7y ago
  I think the emphasis was, tongue-in-cheekily, on "intelligent".
H8crilA 7y ago
What is surprising to me is not just that it's always DNA, but that it's always translated in the same way (codons to aminoacids, and the mapping function is fixed). Is there any simple reason for that?
- dtech 7y ago
  Changing it makes the organism non-viable, so a change there never enters a population. In contract DNA/RNA-mutations can be viable so happen all the time.
  - gomijacogeo 7y ago
    There's a tiny bit of variation across the tree-of-life, see https://en.wikipedia.org/wiki/Genetic_code#Alternative_genetic_codes https://en.wikipedia.org/wiki/Genetic_code#Alternative_genet... But the variation is in the one place you could possibly have it - by changing the interpretation of one or two of the three available STOP codons.
- gomijacogeo 7y ago
  The simplest reason is that the ribosome evolved very early on (and is probably the best preserved remnant of whatever the earlier "RNA world" looked like) and it was always easier to leverage that machinery than to evolve another whole system from scratch. Once you have a world populated by any form of proto-life that can self-reproduce, even with crappy fidelity, it's basically game-over for any of the other semi-closed metabolic pathways that might have been competitors up until that point - they're now just food. There's no opportunity for another system to arise because all the raw materials are being scooped up by the new superpredator on the scene - the ribosome & whatever associated machinery it drags along. The competition now heats up between different ribosome-equipped complexes - improve metabolism, increase independence, increase reproduction rate, improve reproductive fidelity, etc.

dvfjsdhgfv 7y ago

> the emergence of an intelligent, technologically capable species (i.e. humans) is a relatively very recent occurrence in Earth's history. Citaton needed.

H8crilA 7y ago
"History of Earth" https://en.m.wikipedia.org/wiki/History_of_Earth https://en.m.wikipedia.org/wiki/History_of_Earth
- dvfjsdhgfv 7y ago
  That's what we currently know based on what we discovered so far. You can't really rule out the existence of a relatively advanced civilization - although it might advance in a completely different way than ours - whose remains lie buried somewhere under the Mariana Trench for example.
  - throwaway2048 7y ago
    https://en.wikipedia.org/wiki/Russell's_teapot https://en.wikipedia.org/wiki/Russell's_teapot
    - andai 7y ago
      Sure, but we aren't trying to prove or disprove anything here, we're speculating for enjoyment.
  - mellosouls 7y ago
    Yes, this has been investigated before - e.g. https://arxiv.org/abs/1804.03748 https://arxiv.org/abs/1804.03748 https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e... But the evidence we have (as per prior comments) is that a human-level intelligence civilisation has arisen only once on Earth.
  - mikekchar 7y ago
    There are actually an infinite number of possible things that could have happened which we can't rule out. Let me preface what I'm going to say with I don't mind what anyone believes. If it makes you happy to believe one thing over another thing, then I think that's great. With that out of the way, when we're having these kinds of discussions, it's not really productive to bring up an infinite number of possibilities that we can't rule out. Which one should we choose to support? Without some criteria, we will just talk about it forever -- which might be fun, but it's not productive. This is where science comes in. I'm going to say something a bit controversial. Science doesn't really talk about absolute truth. We can't know what that is -- because there are an infinite number of possibilities that we can't rule out. Instead it talks about things that are "productive" (my term). In a very hand-wavy way, science is about making observations and building a model that explains those observation. There are a couple of other important things. The model should also make predictions about thing we haven't observed that we can test. We try it and if it also fulfills those predictions, we thing it's a "productive" model (again, my term). Why is it productive? Because it allows us to reason about things and make conclusions that are likely to work out for us. However, we shouldn't mistake that for the absolute truth. There really is a possibility that things appear one way to us, but are very different in ways that we can't see. The key is that from the perspective of science that's fine -- as long as we can keep making predictions and they keep working out for use, we can use our model. But what if we have 2 models that are both equivalent? For example, let's say they both explain the observations we see and they make predictions that work out. Which should we pick? By convention, we pick the simplest one. In truth, the simplest one might not be correct, but it's always easier to work with a simpler model... because it's simpler ;-) So while there may truly be advanced civilizations out there -- we can't rule it out, there is no test we can currently do that would show that advanced civilizations exist. Our models without advanced civilizations (except our own) explain everything we can currently observe and everything we can currently test. So we choose the model with no other advanced civilizations. You really don't have to believe that, but when discussing with others we have to set some rules. If we keep in mind other advanced civilizations, it's just as reasonable to keep in mind an infinite number of other possibilities -- some of which would be truly bizarre. In order to keep the conversation on track, we have to choose somehow and the scientific method is a good, proven way to narrow the discussion down to something that is productive. However, if you find people who want to talk about the kinds of things you want to talk about, I think there is nothing at all wrong with that. You should do what makes you happy. I hope that makes things a bit clearer. I often meet people who make comments like you did and I think it's really mystifying to those people why science oriented people act this way.
kitd 7y ago
I think the emphasis was, tongue-in-cheekily, on "intelligent".

H8crilA 7y ago

What is surprising to me is not just that it's always DNA, but that it's always translated in the same way (codons to aminoacids, and the mapping function is fixed). Is there any simple reason for that?

dtech 7y ago
Changing it makes the organism non-viable, so a change there never enters a population. In contract DNA/RNA-mutations can be viable so happen all the time.
- gomijacogeo 7y ago
  There's a tiny bit of variation across the tree-of-life, see https://en.wikipedia.org/wiki/Genetic_code#Alternative_genetic_codes https://en.wikipedia.org/wiki/Genetic_code#Alternative_genet... But the variation is in the one place you could possibly have it - by changing the interpretation of one or two of the three available STOP codons.
gomijacogeo 7y ago
The simplest reason is that the ribosome evolved very early on (and is probably the best preserved remnant of whatever the earlier "RNA world" looked like) and it was always easier to leverage that machinery than to evolve another whole system from scratch. Once you have a world populated by any form of proto-life that can self-reproduce, even with crappy fidelity, it's basically game-over for any of the other semi-closed metabolic pathways that might have been competitors up until that point - they're now just food. There's no opportunity for another system to arise because all the raw materials are being scooped up by the new superpredator on the scene - the ribosome & whatever associated machinery it drags along. The competition now heats up between different ribosome-equipped complexes - improve metabolism, increase independence, increase reproduction rate, improve reproductive fidelity, etc.