I’m not aware of an argument that there was only on abiogenesis event on Earth, just the observation that all known surviving lineages come from a universal common ancestor fairly early on. In principle that would be compatible with any number of initial events. It’s just that once a given lineage evolved enough adaptions/improvements, it would spread and take over, and then no new lineage would be able to compete/get started.
Also, your scale for probability seems to be starting from assuming a single long self-replicating genome, but that isn’t strictly necessary to bootstrap the evolution of a basic self-replicating metabolism. There are much shorter RNA strands (<200 base pairs) that have some catalytic activity including synthesizing additional RNA (though not copying themselves, AFAIK). Something like that could locally generate large numbers of shorter RNA strands, many with some form of catalytic activity of their own, collectively comprising some form of catalytic cycle that includes making more of all of them. Such a system would also be better able to cope with low copying fidelity b/c the individual strands that need to be copied correctly are shorter.
As far as going from bare RNA to a bacterium, I admit I don’t know how this happen(ed? happens?). My naive initial thought is some RNA arising in this environment that could produce fatty acids, which could form a lipid layer around a cluster of RNA molecules spontaneously. Repeat and replicate enough times, and add in some endosymbiosis events and you’re not too far off?
I’m not aware of an argument that there was only on abiogenesis event on Earth, just the observation that all known surviving lineages come from a universal common ancestor fairly early on. In principle that would be compatible with any number of initial events. It’s just that once a given lineage evolved enough adaptions/improvements, it would spread and take over, and then no new lineage would be able to compete/get started.
Your observation is an argument for only one abiogenesis event, and your claim that one would spread and take over and no new lineages would be able to compete is a counterargument. I think mentally using this wording is helpful for properly probabilistic thinking.
I didn’t mean for the opening comments of my question to be interpreted as justification for the structure of my vague estimate. Said estimate (although plausibly off by several hundred orders of magnitude) says abiogenesis events are cosmically unlikely, and this notion was used in the presentation of the question.
That’s fair, and I genuinely wasn’t trying to nitpick, it is a very good question. If I try to answer that question as written, I’d say that any time I see a probability estimate with on-the-order-of-hundreds of zeroes, when I know that event actually happened (at least) once in Earth’s past light cone, I’m going to assume there is an error in the model that generated the estimate, whether I know what it is or not. So what I way trying to point to is that if a catalytic cycle of many (much smaller) RNA strands was sufficient for an abiogenesis event, that could lower the probability estimate enough to make such events more likely by enough that there could have been multiple even just on Earth without straining credulity, and the world today would likely look basically the same either way since the more-competitive biochemistry would have long since reach fixation (and/or the lineages could have merged in some analog of later endosymbiosis events).
If I try to answer that question as written, I’d say that any time I see a probability estimate with on-the-order-of-hundreds of zeroes, when I know that event actually happened (at least) once in Earth’s past light cone, I’m going to assume there is an error in the model that generated the estimate, whether I know what it is or not.
I would agree for pretty much any other topic. This is an event required for people to be around to observe it. Imagine a universe in which abiogenesis events really were absurdly rare- unlikely to ever occur in a given observable universe sized area. Every observer in this universe would still look back and see an abiogenesis event occurring in their past! Having observed exactly one event is completely required and provides no evidence. This is essentially the weak anthropic principle.
The fact that we observe only exactly one event is thus bayesian evidence in the direction of rare abiogenesis. You bring up the point that the fact we observe only exactly one event in earth’s history isn’t that strong of evidence because e.g. events being concealed by significantly more advanced competitors. I certainly don’t disagree- that was just unfortunate overemphasis on my part.
So what I way trying to point to is that if a catalytic cycle of many (much smaller) RNA strands was sufficient for an abiogenesis event, that could lower the probability estimate enough to make such events more likely by enough that there could have been multiple even just on Earth without straining credulity, and the world today would likely look basically the same either way since the more-competitive biochemistry would have long since reach fixation (and/or the lineages could have merged in some analog of later endosymbiosis events).
I was thinking of systems more complex than the random coalescence of nucleotides when I wrote my post, but I didn’t know how to productively model that. Someone else had a similar argument and I responded that I slightly shifted away from rare-abiogenesis because I wasn’t thinking of complicated groups of cross-catalyzing RNA in particular, which are dumb enough to have no modern analogues but not so dumb as to not be competitive against single-strand solutions which require the random coalescence of another 100 base pairs, or whatever it is. It’s unclear to what degree this should affect my model, given a lack of understanding of how such systems work.
I’m not aware of an argument that there was only on abiogenesis event on Earth, just the observation that all known surviving lineages come from a universal common ancestor fairly early on. In principle that would be compatible with any number of initial events. It’s just that once a given lineage evolved enough adaptions/improvements, it would spread and take over, and then no new lineage would be able to compete/get started.
Also, your scale for probability seems to be starting from assuming a single long self-replicating genome, but that isn’t strictly necessary to bootstrap the evolution of a basic self-replicating metabolism. There are much shorter RNA strands (<200 base pairs) that have some catalytic activity including synthesizing additional RNA (though not copying themselves, AFAIK). Something like that could locally generate large numbers of shorter RNA strands, many with some form of catalytic activity of their own, collectively comprising some form of catalytic cycle that includes making more of all of them. Such a system would also be better able to cope with low copying fidelity b/c the individual strands that need to be copied correctly are shorter.
As far as going from bare RNA to a bacterium, I admit I don’t know how this happen(ed? happens?). My naive initial thought is some RNA arising in this environment that could produce fatty acids, which could form a lipid layer around a cluster of RNA molecules spontaneously. Repeat and replicate enough times, and add in some endosymbiosis events and you’re not too far off?
Your observation is an argument for only one abiogenesis event, and your claim that one would spread and take over and no new lineages would be able to compete is a counterargument. I think mentally using this wording is helpful for properly probabilistic thinking.
I didn’t mean for the opening comments of my question to be interpreted as justification for the structure of my vague estimate. Said estimate (although plausibly off by several hundred orders of magnitude) says abiogenesis events are cosmically unlikely, and this notion was used in the presentation of the question.
That’s fair, and I genuinely wasn’t trying to nitpick, it is a very good question. If I try to answer that question as written, I’d say that any time I see a probability estimate with on-the-order-of-hundreds of zeroes, when I know that event actually happened (at least) once in Earth’s past light cone, I’m going to assume there is an error in the model that generated the estimate, whether I know what it is or not. So what I way trying to point to is that if a catalytic cycle of many (much smaller) RNA strands was sufficient for an abiogenesis event, that could lower the probability estimate enough to make such events more likely by enough that there could have been multiple even just on Earth without straining credulity, and the world today would likely look basically the same either way since the more-competitive biochemistry would have long since reach fixation (and/or the lineages could have merged in some analog of later endosymbiosis events).
I would agree for pretty much any other topic. This is an event required for people to be around to observe it. Imagine a universe in which abiogenesis events really were absurdly rare- unlikely to ever occur in a given observable universe sized area. Every observer in this universe would still look back and see an abiogenesis event occurring in their past! Having observed exactly one event is completely required and provides no evidence. This is essentially the weak anthropic principle.
The fact that we observe only exactly one event is thus bayesian evidence in the direction of rare abiogenesis. You bring up the point that the fact we observe only exactly one event in earth’s history isn’t that strong of evidence because e.g. events being concealed by significantly more advanced competitors. I certainly don’t disagree- that was just unfortunate overemphasis on my part.
I was thinking of systems more complex than the random coalescence of nucleotides when I wrote my post, but I didn’t know how to productively model that. Someone else had a similar argument and I responded that I slightly shifted away from rare-abiogenesis because I wasn’t thinking of complicated groups of cross-catalyzing RNA in particular, which are dumb enough to have no modern analogues but not so dumb as to not be competitive against single-strand solutions which require the random coalescence of another 100 base pairs, or whatever it is. It’s unclear to what degree this should affect my model, given a lack of understanding of how such systems work.