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The paper claims LUCA doesn't count as life because it still depended on its environment to metabolize. It's kind of interesting that there's parasites that ar

The paper claims LUCA doesn't count as life because it still depended on its environment to metabolize. It's kind of interesting that there's parasites that arguably don't meet this definition either. Looking it up: Chlamydia can't reproduce independently; relies on its host's metabolism. Microsporidia can't make ATP on its own. Are these "life"?

randomImmigrant 2mo ago
The difference is more on survival. A closed loop metabolism is indeed a good boundary marker. Viruses would fail this. But many have “closed but for a few critical dependencies”, and the argument here is that when life depended on metals like this, it’s more critical dependencies than closed loop. Somewhere in there is a transition. But it’s poorly defined, and so the argument can be there was a bifurcation of sorts.
- snovv_crash 2mo ago
  People love to put things into neat boxes so that we can somehow reduce them to a single concept. Unfortunately the real world is usually a bit more messy than that. This is one example that makes it pretty obvious that our model is a little bit overly reductive, and at least to me the "Is this life?" question seems to have an answer that is on a spectrum rather than binary.
  - Y_Y 2mo ago
    [flagged]
- scotty79 2mo ago
  > A closed loop metabolism is indeed a good boundary marker. Presence of metallic catalysts is just an environmental factor. Not counting the organisms that can't live without them as life would be as not counting as life something that can't do metabolism without liquid water. Life at time of LUCA just had a bit stricter environment requirements, but it should still be counted as life. So I wouldn't read this as discovering that life evolved twice. Life just evolved a hack for dealing with environments without metallic catalysts twice.
  - randomImmigrant 2mo ago
    Presence of metallic catalysts is just an environmental factor. No, it isn’t quite that. For it to count as “environment” the organism must be able to survive for at least a time without it. The issue here is, the metal wasn’t a nutrient. That would be fine and exactly like it is for all life now. Instead the metal was the anchor. If an organism needed to grow on it to enable half its metabolism, it is at the least very distinct from current life. The only issue with the “two origins” claim is both lineages, bacteria and archea, come from this, and even with an open metabolic chain, you already had the nucleic acid function etc all sorted out, and common between both kingdoms. So it’s a stretch to say there were two origins to life, but not that this proto life is distinct from modern life. That we need things from our environment is not the same as what they found about proto life in the vents.
    - scotty79 2mo ago
      > For it to count as “environment” the organism must be able to survive for at least a time without it. How long can a cell survive without liquid water? It literally enables almost all of the chemistry inside the cell. Cell requiring a specific metal to be present is not very different from cell requiring for liquid water to be present. Initially life started in favorable conditions, then spread to less favorable ones. Lack of metal catalyst around was the initial less favorable condition. At some point lack of liquid water was one. But eventually life spread to various very dry or cold places because it found workarounds for environment infeasibilities. Maybe in 5 billion years life that can't survive without liquid water around and can't substitute it with self-made polar solvents and thus is stuck to surfaces of very few, very particular planets is going to be considered proto-life.
      - randomImmigrant 2mo ago
        >How long can a cell survive without liquid water? Depends on the cell, but it’s not instant death. By definition, a cell is a membrane with some water inside it. Sure, move that cell to totally dry conditions and most will die. But not all, by any means. Bacterial endospores last millenia without water. Tardigrades can do years. This isn’t quite the gotcha you think it is. The metal use for multiple catalytic steps is distinct. The paper isn’t wrong about that at all. Trying to prove the closed loop metabolism of modern life is secretly open loop isn’t going to work because it isn’t open like that. An organism can survive without constant contact with any of its components. Sometimes not for very long, but nothing alive today is as dependent on something external as these proto cells were on reduced metal.
applicative 2mo ago
Where there is chlamydia or microsporidia, there is undisputed life. How much of it one assigns to chlamydia or microsporidia is moot from the point of view above

randomImmigrant 2mo ago

The difference is more on survival. A closed loop metabolism is indeed a good boundary marker. Viruses would fail this. But many have “closed but for a few critical dependencies”, and the argument here is that when life depended on metals like this, it’s more critical dependencies than closed loop. Somewhere in there is a transition. But it’s poorly defined, and so the argument can be there was a bifurcation of sorts.

snovv_crash 2mo ago
People love to put things into neat boxes so that we can somehow reduce them to a single concept. Unfortunately the real world is usually a bit more messy than that. This is one example that makes it pretty obvious that our model is a little bit overly reductive, and at least to me the "Is this life?" question seems to have an answer that is on a spectrum rather than binary.
- Y_Y 2mo ago
  [flagged]
scotty79 2mo ago
> A closed loop metabolism is indeed a good boundary marker. Presence of metallic catalysts is just an environmental factor. Not counting the organisms that can't live without them as life would be as not counting as life something that can't do metabolism without liquid water. Life at time of LUCA just had a bit stricter environment requirements, but it should still be counted as life. So I wouldn't read this as discovering that life evolved twice. Life just evolved a hack for dealing with environments without metallic catalysts twice.
- randomImmigrant 2mo ago
  Presence of metallic catalysts is just an environmental factor. No, it isn’t quite that. For it to count as “environment” the organism must be able to survive for at least a time without it. The issue here is, the metal wasn’t a nutrient. That would be fine and exactly like it is for all life now. Instead the metal was the anchor. If an organism needed to grow on it to enable half its metabolism, it is at the least very distinct from current life. The only issue with the “two origins” claim is both lineages, bacteria and archea, come from this, and even with an open metabolic chain, you already had the nucleic acid function etc all sorted out, and common between both kingdoms. So it’s a stretch to say there were two origins to life, but not that this proto life is distinct from modern life. That we need things from our environment is not the same as what they found about proto life in the vents.
  - scotty79 2mo ago
    > For it to count as “environment” the organism must be able to survive for at least a time without it. How long can a cell survive without liquid water? It literally enables almost all of the chemistry inside the cell. Cell requiring a specific metal to be present is not very different from cell requiring for liquid water to be present. Initially life started in favorable conditions, then spread to less favorable ones. Lack of metal catalyst around was the initial less favorable condition. At some point lack of liquid water was one. But eventually life spread to various very dry or cold places because it found workarounds for environment infeasibilities. Maybe in 5 billion years life that can't survive without liquid water around and can't substitute it with self-made polar solvents and thus is stuck to surfaces of very few, very particular planets is going to be considered proto-life.
    - randomImmigrant 2mo ago
      >How long can a cell survive without liquid water? Depends on the cell, but it’s not instant death. By definition, a cell is a membrane with some water inside it. Sure, move that cell to totally dry conditions and most will die. But not all, by any means. Bacterial endospores last millenia without water. Tardigrades can do years. This isn’t quite the gotcha you think it is. The metal use for multiple catalytic steps is distinct. The paper isn’t wrong about that at all. Trying to prove the closed loop metabolism of modern life is secretly open loop isn’t going to work because it isn’t open like that. An organism can survive without constant contact with any of its components. Sometimes not for very long, but nothing alive today is as dependent on something external as these proto cells were on reduced metal.

applicative 2mo ago

Where there is chlamydia or microsporidia, there is undisputed life. How much of it one assigns to chlamydia or microsporidia is moot from the point of view above