4 ms·

> Specifically, unless the probability for evolving a civilization on a habitable-zone planet is less than one in 10 billion trillion, then we are not the first

by jawns 10y ago

> Specifically, unless the probability for evolving a civilization on a habitable-zone planet is less than one in 10 billion trillion, then we are not the first. 1 in 10 billion trillion at first seems like such an incomprehensibly low probability that our first gut reaction is, "Well then of course there's no way it could be the case." But then we must bear in mind that abiogenesis (the creation of life from non-life) might consist of a series of independent events, each of which is improbable. And guess how you figure out the probability of all of those events occurring: P(A and B) = P(A) * P(B) So, what's 1 in 10 billion trillion? 10^-22? Well, if you have a mere eight improbable things that must all occur, and each has a probability of 1 in 1,000, the total probability is now at 10^-24. Hmm, 10^-22 doesn't seem quite as incomprehensibly low anymore, does it? Aside from that, we really have to think hard about what probability means in the context of the snippet quoted above. As statistician to the stars William M. Briggs points out, "There just is no such thing as unconditional probability, or probability without respect to any evidence." Because we have insufficient evidence to establish what the frequency of abiogenesis is, the quoted snippet basically could be rephrased: For all we know, the probability of evolving a civilization on a habitable-zone planet could be 10^-22 or 10^-222 or 10^-2222, and if it's less than 10^-22 then we are not the first. Isn't it strange that in a certain sense, the probability of each of those probabilities being correct is essentially the same, given our current insufficient level of evidence?

neaden 10y ago
One good example is that as far as we can tell multi-cellular life only evolved on Earth once. And while life started up on Earth pretty quickly it took about 600 million years for that life to become multicelluar. It's possible that we'll someday discover life is relatively common but never meet anything but amoebas.
- cmrdporcupine 10y ago
  Totally. Not only did multicellular life only evolve once, but eukaryotes themselves seem to have evolved only once. And they are 1000x more complex than their prokaryote predecessors. [edit: without any real evidence of anything convincingly between prokaryote and eukaryote] It's one thing to say there might have been abiogenesis elsewhere that created something like the simple self-reproducing energy machines that bacteria and archaea are. It's another to claim that there is some inevitable progression from that to complex multicellular life. In my opinion this is a very teleological, very 'progressivist' notion of evolution that implies that one inevitably follows from another, and it is not borne out in the reality of what we know so far about happened on earth and what follows from first principles. There may be a lot of complex, self-reproducing systems in the universe. It's arrogant to assume that any of them have to look anything like what we call "life" unless by life we mean the simplest single cell organisms. [edit: In fact it looks like simple prokaryotes evolved _twice_ on earth a "short" distance in time apart].
  - Retric 10y ago
    Multi cellular life has evolved several times. There are several distinct cases of single called organisms promoting conditions which aid others of it's species. Causing a colony to form, and then spawn new colonies. Now, highly complex multicellular life seems to share common descent. But that likely has more to do with predation than anything else. Further single called organisms preform horizontal gene transfer to both other single called life and multicellular life, making things impossible to trace back.
- Retric 10y ago
  That's not really known. Of note life showed up very close to as soon as possible on early earth. So, similar events may have happend 30+ times. However, the first time life shows up it can spread easily, the second time it's likely food.
marcosdumay 10y ago
Another take at it is that life here very likely started with RNA chains. That number sounds very low, but 10^-22 < 4^37. That is, if only one chromosome among all of the ones 37 basis long could self reproduce, it would already fit the probabilities cited on the article. Now, 36 basis is extremely short. I don't think anybody believes there's anything that size that able to reproduce. Last time I checked, the smallest known self-reproducing chromosome had around 160 basis. That is, it had a probability of ~10^-96 of appearing between all 160 basis chromosomes. (And remember, there are ~10^80 atoms on the observable Universe...)
- Retric 10y ago
  At a minimum there are several right vs left handed molecules which doubles the ways you can get our current ecosystem. So, really the question is how many possible ways can you get self replication not how complex is the first example.
  - marcosdumay 10y ago
    Still, the only think we know is that the odds are bigger than 10^-96. You will need a huge amount of self-replicating chromosomes between 180 and 160 basis to make up for the increased size - it's known that self replication is not common, but I don't think we know that to a 10^-22 certainty either, so all that can still be wrong. Anyway, there isn't a lot to argue about self-replicating on that context. It means that this chromosome is able to create copies of itself in a RNA-rich ocean. It can require light for that, or a big thermal gradient, but not both. The exact conditions of the ocean are, AFAIK, unknown, but things like your example do not fit.
    - deleted 10y ago
      [deleted]
    - Retric 10y ago
      I don't think we can define a lower bound as we don't know the size of the universe, or if there is a cycle of previous universes without life. However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan. Without other information to go on earth is probably topical and life generally shows up within the first 500 million years watter shows up.

by jawns 10y ago

neaden 10y ago

One good example is that as far as we can tell multi-cellular life only evolved on Earth once. And while life started up on Earth pretty quickly it took about 600 million years for that life to become multicelluar. It's possible that we'll someday discover life is relatively common but never meet anything but amoebas.

cmrdporcupine 10y ago
Totally. Not only did multicellular life only evolve once, but eukaryotes themselves seem to have evolved only once. And they are 1000x more complex than their prokaryote predecessors. [edit: without any real evidence of anything convincingly between prokaryote and eukaryote] It's one thing to say there might have been abiogenesis elsewhere that created something like the simple self-reproducing energy machines that bacteria and archaea are. It's another to claim that there is some inevitable progression from that to complex multicellular life. In my opinion this is a very teleological, very 'progressivist' notion of evolution that implies that one inevitably follows from another, and it is not borne out in the reality of what we know so far about happened on earth and what follows from first principles. There may be a lot of complex, self-reproducing systems in the universe. It's arrogant to assume that any of them have to look anything like what we call "life" unless by life we mean the simplest single cell organisms. [edit: In fact it looks like simple prokaryotes evolved _twice_ on earth a "short" distance in time apart].
- Retric 10y ago
  Multi cellular life has evolved several times. There are several distinct cases of single called organisms promoting conditions which aid others of it's species. Causing a colony to form, and then spawn new colonies. Now, highly complex multicellular life seems to share common descent. But that likely has more to do with predation than anything else. Further single called organisms preform horizontal gene transfer to both other single called life and multicellular life, making things impossible to trace back.
Retric 10y ago
That's not really known. Of note life showed up very close to as soon as possible on early earth. So, similar events may have happend 30+ times. However, the first time life shows up it can spread easily, the second time it's likely food.

marcosdumay 10y ago

Another take at it is that life here very likely started with RNA chains. That number sounds very low, but 10^-22 < 4^37. That is, if only one chromosome among all of the ones 37 basis long could self reproduce, it would already fit the probabilities cited on the article. Now, 36 basis is extremely short. I don't think anybody believes there's anything that size that able to reproduce. Last time I checked, the smallest known self-reproducing chromosome had around 160 basis. That is, it had a probability of ~10^-96 of appearing between all 160 basis chromosomes. (And remember, there are ~10^80 atoms on the observable Universe...)

Retric 10y ago
At a minimum there are several right vs left handed molecules which doubles the ways you can get our current ecosystem. So, really the question is how many possible ways can you get self replication not how complex is the first example.
- marcosdumay 10y ago
  Still, the only think we know is that the odds are bigger than 10^-96. You will need a huge amount of self-replicating chromosomes between 180 and 160 basis to make up for the increased size - it's known that self replication is not common, but I don't think we know that to a 10^-22 certainty either, so all that can still be wrong. Anyway, there isn't a lot to argue about self-replicating on that context. It means that this chromosome is able to create copies of itself in a RNA-rich ocean. It can require light for that, or a big thermal gradient, but not both. The exact conditions of the ocean are, AFAIK, unknown, but things like your example do not fit.
  - deleted 10y ago
    [deleted]
  - Retric 10y ago
    I don't think we can define a lower bound as we don't know the size of the universe, or if there is a cycle of previous universes without life. However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan. Without other information to go on earth is probably topical and life generally shows up within the first 500 million years watter shows up.