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Note the recently discovered Winchcombe meteorite had equal amounts of L- and R- amino acids, suggesting that non-biological processes produce both at the same

Note the recently discovered Winchcombe meteorite had equal amounts of L- and R- amino acids, suggesting that non-biological processes produce both at the same rate, which is perhaps not what you'd expect if these cosmic ray or other physical processes were influencing L- vs R- handed molecule production/breakdown rates. https://news.ycombinator.com/item?id=33680493 https://news.ycombinator.com/item?id=33680493 https://www.science.org/doi/10.1126/sciadv.abq3925 https://www.science.org/doi/10.1126/sciadv.abq3925 It's likely life had to choose one or the other early on; imagine the mess it would be if you tried to build proteins or nucleic acids with a random assortment of left and right handed molecules, it'd be hard to get consistent structures. You'd have to have specific codons, the three-letter gene sequences that convert the 4-letter DNA code to the amino-acid code (22 for terrestrial life), for each handed version of the amino acids, so you'd need 44 different codons (out of 63 possible 3-letter combinations of ATCG) for the complete set, with no [little] overlap. [edit: it's 64, not 63! Today's life uses 61 for amino acids and 3 are reserved as stop signals. To get the full set in Python: set(list(itertools.permutations('AAATTTCCCGGG', 3))) ] I'd guess the early self-replicating systems (likely something like a RNA-protein ribosome complex capabale of self-replication using abiotically produced amino and nucleic acids) were only able to consistently replicate if they only used one enantiomer consistently, and it was just a roll of the die as to which one they settled on. There might even have been mixed populations of L-handed and R-handled life at the beginning, with only one branch surviving. Of course, that's the claim here, that of these two branches, one was more impacted by cosmic rays than the other. ???

idlewords 4y ago
This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. There's no reason in principle that a totally different biochemistry that made use of racemic mixtures couldn't work, but here we run into the wall of being unable to imagine forms of life substantially from our own. It's very easy to get into a loop of circular reasoning when answering questions like why life on Earth has a preferred handedness.
- lumost 4y ago
  Is this question substantially different from “why don’t animals have four legs and 2 hands?” It strikes me that there could have been dozens of “genesis” events early in earth’s history which evolution aligned into a few winning blueprints.
- Garlef 4y ago
  > This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. I don't think the argument hinges on a notion of 'naturality'. Instead it seems to be more of an statistical/occams razor kind of argument: Mixed chiralities would introduce a lot of incompatabilities among the building blocks, making the emergence of a stable form/process more unlikely. And also the argument (as far as I understand it) is in no contradiction to your caveat: Of course, a stable form/process might have emerged with mixed chirality. But it did not and was never very likely to begin with. [Note: This is not a statement about assigning truth values to these arguments but rather I hope it clearifies the argument itself.]
  - idlewords 4y ago
    What I'm saying is that the statistical argument already bakes in assumptions, since we don't know anything about the underlying distribution.
    - CyanBird 4y ago
      OP already stated that the initial distribution would ~seem to be ~50:50 per winchcombe meteorite
      - idlewords 4y ago
        I'm sorry; I meant the set of all possible biochemistries.
danuker 4y ago
> With a series of toy models, the researchers calculated that the biased cosmic ray particles were ever-so-slightly more likely to knock an electron loose from a “live” helix than from an “evil” one, an event that theoretically causes mutations. With a dataset of n=1 (a single example of abiogenesis), there is quite limited evidence for the claim. But you don't need much of an effect to influence something that could go either way.
b112 4y ago
Note the recently discovered Winchcombe meteorite had equal amounts of L- and R- amino acids, Everyone in the know, knows that rock is a chunk from trading station Alpha 7, which what was blown to bits by Algothrian terrorists. And of course, any trading station will have a mish-mash of life forms, and therefore, dna. Prove it is not so!

idlewords 4y ago

This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. There's no reason in principle that a totally different biochemistry that made use of racemic mixtures couldn't work, but here we run into the wall of being unable to imagine forms of life substantially from our own. It's very easy to get into a loop of circular reasoning when answering questions like why life on Earth has a preferred handedness.

lumost 4y ago
Is this question substantially different from “why don’t animals have four legs and 2 hands?” It strikes me that there could have been dozens of “genesis” events early in earth’s history which evolution aligned into a few winning blueprints.
Garlef 4y ago
> This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. I don't think the argument hinges on a notion of 'naturality'. Instead it seems to be more of an statistical/occams razor kind of argument: Mixed chiralities would introduce a lot of incompatabilities among the building blocks, making the emergence of a stable form/process more unlikely. And also the argument (as far as I understand it) is in no contradiction to your caveat: Of course, a stable form/process might have emerged with mixed chirality. But it did not and was never very likely to begin with. [Note: This is not a statement about assigning truth values to these arguments but rather I hope it clearifies the argument itself.]
- idlewords 4y ago
  What I'm saying is that the statistical argument already bakes in assumptions, since we don't know anything about the underlying distribution.
  - CyanBird 4y ago
    OP already stated that the initial distribution would ~seem to be ~50:50 per winchcombe meteorite
    - idlewords 4y ago
      I'm sorry; I meant the set of all possible biochemistries.

danuker 4y ago

> With a series of toy models, the researchers calculated that the biased cosmic ray particles were ever-so-slightly more likely to knock an electron loose from a “live” helix than from an “evil” one, an event that theoretically causes mutations. With a dataset of n=1 (a single example of abiogenesis), there is quite limited evidence for the claim. But you don't need much of an effect to influence something that could go either way.

b112 4y ago

Note the recently discovered Winchcombe meteorite had equal amounts of L- and R- amino acids, Everyone in the know, knows that rock is a chunk from trading station Alpha 7, which what was blown to bits by Algothrian terrorists. And of course, any trading station will have a mish-mash of life forms, and therefore, dna. Prove it is not so!