13 ms·

How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so

by Imnimo 6y ago

How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years? The article seems to simply assume the former model ("We assume that once an evolutionary transition is possible (i.e., once the previous transition has occurred), it occurs at a constant average rate λi, so that each ti is exponentially distributed with an expected transition time of βi = 1/λi"), but that feels unjustified to me. Is it really the case that the transition from prokaryote to eukaryote was equally likely at any time, and things simply sat stagnant for a billion years until one day life got lucky?

enkid 6y ago
It also seems to assume that there is only one "path" to "observer" status. For example, could there be an alternative to Eukaryote cells that would allow equivalent cognition to our own? We don't know because we only have one instance of "observers" coming around.
- jjoonathan 6y ago
  Sure, all of this is speculative, but the eukaryotic jump is notorious for getting casually dismissed on account of being misunderstood. I think it's one of the better candidates for a filter, so let me advocate it for a second and make sure that if you still want to dismiss it's not due to oversight. The problem has nothing to do with having a nucleus. That's the solution. As you note, it's possible to imagine other solutions. The problem is dealing with gigabytes of genetic data instead of mere megabytes. Typically one would use units of base pairs, but in the context of talking about potential alternative forms of life I'd argue that units of information are more appropriate. In any case, the "easy" strategies suffer from a severe dead end that prevents them from going beyond a few megabytes. Lots of things go wrong at that limit, and while other forms of life would encounter those obstacles in slightly different places, the problem of "simple strategies that don't scale" is almost certainly universal. https://upload.wikimedia.org/wikipedia/commons/e/e4/Genome_size_vs_protein_count.svg https://upload.wikimedia.org/wikipedia/commons/e/e4/Genome_s... Eukaryotes, in contrast, scale. It's not an easy task. The strategies are highly elaborate and severely intrusive. They touch the most fundamental, highly conserved aspects of the genome, of cell functionality, and of reproduction. Genes have to be organized hierarchically, packed and unpacked, and everything that interacts with them has to be made compatible with that reality. Further, everything must be done in parallel. The entire architecture of the genome changes as a result. It's like a distributed system vs a monolith. It's a tough, deep-reaching transition to pull off, it's a tougher transition to justify, and that's if you're an engineer capable of things like planning, prediction, and delayed gratification! A greedy optimizer bumbling around in the dark can't rely on cognition (or even a hype cycle!) to propel itself from one mountain range of local optima to another mountain range. I'm sure there are plenty of strategies for scaling genomes, but if they're all difficult -- and the crazy elaborate mechanisms we see in Earth eukaryotes suggest that could be the case -- then they still constitute a filter. But yeah, this is all speculation. Nobody really knows.
  - enkid 6y ago
    Certainly everything you say is true for our genetic chemistry, but I don't see a reason why that is necessarily true for all genetic chemistry. For example, our data storage for computers scales from megabytes to gigabytes very well. There's no reason to think there aren't other solutions that scale just as well.
    - ClumsyPilot 6y ago
      If the solutions are trivial, we would see them emerge in the insane amount of time it took to eukariotes to apprear. The fact that they didn't suggest they either do not exist, or are equally difficult.
      - enkid 6y ago
        I'm clearly not articulating this well, so let me try to try another tactic. The evolution of eukaryotes is based on the specific path that Earth went down. The combination of RNA, DNA, proteins, and other cellular chemical building blocks are a way that a cell could be constructed, but not the only possible way a cell could be constructed. For an extreme example, we could have non-carbon based life. If that is true, then all of our assumptions about what is scalable and what is not, based on our biochemistry simple cannot be trusted. So, looking at how long it took for something to develop on Earth tells us basically nothing about how long it would take to do that with this other biochemistry.
        jjoonathan 6y ago
        I've made the "yes, we know this is speculative" rant in another post. Here I assume you're still interested in moving forward with the speculation. If not, please don't belabor the point. There is a substantial body of abiogenesis experimentation focused on reproducing DNA/RNA proto-life. They haven't managed to make anything that self-replicates, but they have managed to make nucleic acid polymers with catalytic activity, e.g. you zap the primordial soup with lightning, you get a bunch of short sequences, some of those sequences fold into RNA-zymes that catalytically produce long "AAAAAAAAA" sequences or long repeating "AUAUAUAU" sequences. The critical next step is to demonstrate the ability to do this from a template. In any case, are you aware of research that aims to do this with alternative polymer chemistries? Such results could inform our speculation about the likelihood of a fundamental 1000x difference.
marshray 6y ago
Yeah. This looks to me like a hubristic level of extrapolation from a single data point.
- lopmotr 6y ago
  Why hubristic? Because he did it? What would a non-hubristic attempt to estimate the prevalence of life in the universe look like, short of actually finding aliens?
  - marshray 6y ago
    I said 'hubristic' because it seemed to me that the inability to draw conclusions about the cosmos from our own (single data point) limited perspective was a fundamental limitation of the human condition.
hnracer 6y ago
Precisely. Something taking astoundingly long to evolve isn't conclusive evidence that it's highly improbable (although it might suggest it). It could very well be highly probable. One reason is as you mention is prerequisites. Another reason could be that the solution is deep in the search tree, and while it takes ages to find it, the search algorithm will eventually do so. Consider a global optimizer running on a concave surface for a long period of time, all it needs is time.
- hnracer 6y ago
  Just realized that the eye is a counterexample to their assumption. Took three billion years to evolve but is easy to do so as we've seen it evolve independently many times.
sampo 6y ago
> an event that is inevitable, but requires many prerequisites, and so takes a billion years? In support of this idea, the Cambrian explosion of large (large relative to microbial life) multicellular organisms happened immediately after the 2 billion years of work by blue-green algae had produced enough oxygen into the atmosphere to make larger organisms possible. https://en.wikipedia.org/wiki/Great_Oxidation_Event https://en.wikipedia.org/wiki/Great_Oxidation_Event https://www.sciencedaily.com/releases/2010/12/101217145647.htm https://www.sciencedaily.com/releases/2010/12/101217145647.h...
- sideshowb 6y ago
  I guess it all depends on how you balance occam's razor against abusing the anthropic principle.
- AgentME 6y ago
  The article mentions that multicellular life is something that's known to have separately evolved at least 40 times, so it's probably not a useful evolutionary step to compare to ones that only happened once.
- arp242 6y ago
  While it made complex life possible, at the same time the introduction of oxygen also killed a lot of lifeforms and was a mass extinction. It's not inconceivable that with slightly different circumstances it could have just have wiped out all life. The development of (complex) life seems like a really fine balance.
deeeeplearning 6y ago
>How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years? Holy hell, this man trounced a team of Oxford scientists in a single line! Someone get this man a NObEl PRizE... So you, a random internet person caught such an obvious error and somehow no one at Oxford or the reviewers at Astrobiology noticed? That's really what you think?
- Twisol 6y ago
  Science is about testable, falsifiable hypotheses. It's important to question what we think we know, and how we know it. "Argument from authority" isn't scientific. We can simultaneously believe (a) that well-respected researchers from a well-respected institution are capable of carrying out well-grounded research and (b) that research is in principle understandable with sufficient interrogation. Authority supports (a) but does not render (b) unnecessary.
  - zebrafish 6y ago
    I think his point, though not well made, is that it’s likely parent is not the first to ask this question and that the researchers have likely already thought about that.
    - Twisol 6y ago
      Yeah, both this and the original question are good points. I wonder what the paper itself has to say. The early bits are pretty readable so far [0], but I doubt it calls the original question out quite as succinctly as it was asked. Lots to mull over though! [0] https://www.liebertpub.com/doi/full/10.1089/ast.2019.2149 https://www.liebertpub.com/doi/full/10.1089/ast.2019.2149
- Imnimo 6y ago
  Haha! I don't mean to imply that I've uncovered some fatal weakness (or even necessarily a weakness at all)! That's just the question that jumped to mind when I read their paper, and I figured someone else might know the answer.
joe_the_user 6y ago
How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years? I suspect that' gnawing for any research like this. But I could suggest that if we can show that a lot of fundamental changes have come from external shock rather than internal processes, then we might be closer. Further, if the theory of "puncture equilibrium" is true[1], that this would tend to be the case. If we can show that many evolutionary steps involved such external shocks, then we might be closer to this also. The question would be whether external shocks inevitably produce advances or whether such advances are indeed lucky. [1] https://en.wikipedia.org/wiki/Punctuated_equilibrium https://en.wikipedia.org/wiki/Punctuated_equilibrium
- AgentME 6y ago
  Punctuated equilibrium doesn't really change the calculations involved in the article. Either mutations happen randomly on their own, or random events cause bursts of mutations to happen. The burstiness doesn't matter much when you zoom out enough.
  - joe_the_user 6y ago
    Punctured equilibrium can matter if fundamentally new adaptation happen only or primarily with external disruptions. Mammals replaced reptiles after a mass extinction event cause by a meteor - another world might not regular meteors or might have too many. The question is how non-earth world might fail, right.
    - AgentME 6y ago
      It doesn't matter to the equations whether you're modeling the chance that a mutation happens on its own, or the chance that an event happens that causes the mutation. You would use the same equation to model either of those.
monkeycantype 6y ago
This doesn't contradict the conclusion of the paper, it makes no difference as to whether we're going to find anybody we can have a conversation with, ("hey, how annoying is light speed?") but I think our definition for simple and complex life is off. eg "more likely to find simple life on Mars." That ape and octopus exist, says that earth didn't win the intelligence lottery, we are watching the long slow grind of compound interest. When you look at our world we see that the lipid bilayer is preserved, that rna is preserved in every living thing, but eyes have evolved independently many times. That the last common ancestor of octopus and human was a little wriggly thing, leads me to believe that forming a boundary between self and non self is hard (the bilayer), that forming a system of heredity is hard (first rna then dna). That the accumulation of processes that use energy, resources and information from the environment in new ways is a long relentless grind. The basic body form, multicellularity and a gut were, big difficult changes, but maybe intelligence is just paint on a hard won foundation.
- joe_the_user 6y ago
  Yeah, in the discussion of "where is the intelligent life", you seldom see the argument that it really does takes 11+ billion years to produce that intelligence life. With a universe "only" 13 billion years old and possibly chaotic, this factor, rather than any specific "filter", might why we're not seeing any other intelligent life.
  - CryptoPunk 6y ago
    Consistent with that, evidence suggests that it may have taken billions of years for the precursor molecules of the first Earth-based life to emerge/evolve: https://www.technologyreview.com/2013/04/15/113741/moores-law-and-the-origin-of-life/ https://www.technologyreview.com/2013/04/15/113741/moores-la...
    - joe_the_user 6y ago
      Thanks, I remembered the article but couldn't find the link. This is a really neat argument.
ClumsyPilot 6y ago
That does not actually matter - most planets cannot be habitable for very long and stars change in brightness - eath will become uninhabbitable in a billion tlyears. So most life would die before evolving intelligence.
- cgriswald 6y ago
  I don’t think we can really make this claim. Life which forms around less stable stars may adapt if there is enough time for them to do so. It’s also important to note the sun is not the mean star. The vast majority of stars are red dwarves which, while more variable, are much longer lived.
  - ClumsyPilot 6y ago
    On Earth all water will boil away, I don't see any plausible way for complex life to adapt. Likewise if Mars was habitable, you can't adapt to survive there now un less you are a subterranian microbe. Habitability of planets around red drawfs would of-course change the game, but it's not clear at present.
    - ben_w 6y ago
      “On Earth” is the problem with the argument. If any alien life exists, the one place it isn’t is Earth. A super-Earth in a Goldilocks orbit around a K1V star would keep atmosphere and water for longer. Eventually they too will become uninhabitable, but the relevant question about alien life is not “eventually” but rather “now”.
  - mcswell 6y ago
    The article addresses red dwarves, you should read it.
    - cgriswald 6y ago
      I read the paper. Did you read this thread? Context matters.
AgentME 6y ago
If the transitions were inevitable given the time they took here, then we would expect to see the transitions happen concurrently throughout the planet in many separate instances. But we see a number of important transitions that happened exactly once on Earth.
- galgalesh 6y ago
  Not necessarily. A number of stages in the evolution of life require a planet devoid of more complex life forms. Spontaneous generation of cells, for example, requires very high doses of molecules that more complex life forms eat.
  - fotdutah 6y ago
    Also worth pointing out that this applies to some potential 'Great Filter' events that we haven't yet encountered. If intelligent cultures don't explore the universe because they destroy their own planets in destructive wars as soon as they have that level of technology, then conditional on our existing, we should expect to be the first such culture to evolve on our planet. If on the other hand, most intelligent cultures neglect to explore the universe because they are busy with art, contemplation or hedonism, we might expect to exist in a world where hyperintelligent dinosaurs, frogs and cephalopods are already sitting around enjoying these things. The fact that they aren't means that maybe our current stage of evolution was hard to reach.

by Imnimo 6y ago

enkid 6y ago

It also seems to assume that there is only one "path" to "observer" status. For example, could there be an alternative to Eukaryote cells that would allow equivalent cognition to our own? We don't know because we only have one instance of "observers" coming around.

jjoonathan 6y ago
Sure, all of this is speculative, but the eukaryotic jump is notorious for getting casually dismissed on account of being misunderstood. I think it's one of the better candidates for a filter, so let me advocate it for a second and make sure that if you still want to dismiss it's not due to oversight. The problem has nothing to do with having a nucleus. That's the solution. As you note, it's possible to imagine other solutions. The problem is dealing with gigabytes of genetic data instead of mere megabytes. Typically one would use units of base pairs, but in the context of talking about potential alternative forms of life I'd argue that units of information are more appropriate. In any case, the "easy" strategies suffer from a severe dead end that prevents them from going beyond a few megabytes. Lots of things go wrong at that limit, and while other forms of life would encounter those obstacles in slightly different places, the problem of "simple strategies that don't scale" is almost certainly universal. https://upload.wikimedia.org/wikipedia/commons/e/e4/Genome_size_vs_protein_count.svg https://upload.wikimedia.org/wikipedia/commons/e/e4/Genome_s... Eukaryotes, in contrast, scale. It's not an easy task. The strategies are highly elaborate and severely intrusive. They touch the most fundamental, highly conserved aspects of the genome, of cell functionality, and of reproduction. Genes have to be organized hierarchically, packed and unpacked, and everything that interacts with them has to be made compatible with that reality. Further, everything must be done in parallel. The entire architecture of the genome changes as a result. It's like a distributed system vs a monolith. It's a tough, deep-reaching transition to pull off, it's a tougher transition to justify, and that's if you're an engineer capable of things like planning, prediction, and delayed gratification! A greedy optimizer bumbling around in the dark can't rely on cognition (or even a hype cycle!) to propel itself from one mountain range of local optima to another mountain range. I'm sure there are plenty of strategies for scaling genomes, but if they're all difficult -- and the crazy elaborate mechanisms we see in Earth eukaryotes suggest that could be the case -- then they still constitute a filter. But yeah, this is all speculation. Nobody really knows.
- enkid 6y ago
  Certainly everything you say is true for our genetic chemistry, but I don't see a reason why that is necessarily true for all genetic chemistry. For example, our data storage for computers scales from megabytes to gigabytes very well. There's no reason to think there aren't other solutions that scale just as well.
  - ClumsyPilot 6y ago
    If the solutions are trivial, we would see them emerge in the insane amount of time it took to eukariotes to apprear. The fact that they didn't suggest they either do not exist, or are equally difficult.
    - enkid 6y ago
      I'm clearly not articulating this well, so let me try to try another tactic. The evolution of eukaryotes is based on the specific path that Earth went down. The combination of RNA, DNA, proteins, and other cellular chemical building blocks are a way that a cell could be constructed, but not the only possible way a cell could be constructed. For an extreme example, we could have non-carbon based life. If that is true, then all of our assumptions about what is scalable and what is not, based on our biochemistry simple cannot be trusted. So, looking at how long it took for something to develop on Earth tells us basically nothing about how long it would take to do that with this other biochemistry.
      - jjoonathan 6y ago
        I've made the "yes, we know this is speculative" rant in another post. Here I assume you're still interested in moving forward with the speculation. If not, please don't belabor the point. There is a substantial body of abiogenesis experimentation focused on reproducing DNA/RNA proto-life. They haven't managed to make anything that self-replicates, but they have managed to make nucleic acid polymers with catalytic activity, e.g. you zap the primordial soup with lightning, you get a bunch of short sequences, some of those sequences fold into RNA-zymes that catalytically produce long "AAAAAAAAA" sequences or long repeating "AUAUAUAU" sequences. The critical next step is to demonstrate the ability to do this from a template. In any case, are you aware of research that aims to do this with alternative polymer chemistries? Such results could inform our speculation about the likelihood of a fundamental 1000x difference.

marshray 6y ago

Yeah. This looks to me like a hubristic level of extrapolation from a single data point.

lopmotr 6y ago
Why hubristic? Because he did it? What would a non-hubristic attempt to estimate the prevalence of life in the universe look like, short of actually finding aliens?
- marshray 6y ago
  I said 'hubristic' because it seemed to me that the inability to draw conclusions about the cosmos from our own (single data point) limited perspective was a fundamental limitation of the human condition.

hnracer 6y ago

Precisely. Something taking astoundingly long to evolve isn't conclusive evidence that it's highly improbable (although it might suggest it). It could very well be highly probable. One reason is as you mention is prerequisites. Another reason could be that the solution is deep in the search tree, and while it takes ages to find it, the search algorithm will eventually do so. Consider a global optimizer running on a concave surface for a long period of time, all it needs is time.

hnracer 6y ago
Just realized that the eye is a counterexample to their assumption. Took three billion years to evolve but is easy to do so as we've seen it evolve independently many times.

sampo 6y ago

> an event that is inevitable, but requires many prerequisites, and so takes a billion years? In support of this idea, the Cambrian explosion of large (large relative to microbial life) multicellular organisms happened immediately after the 2 billion years of work by blue-green algae had produced enough oxygen into the atmosphere to make larger organisms possible. https://en.wikipedia.org/wiki/Great_Oxidation_Event https://en.wikipedia.org/wiki/Great_Oxidation_Event https://www.sciencedaily.com/releases/2010/12/101217145647.htm https://www.sciencedaily.com/releases/2010/12/101217145647.h...

sideshowb 6y ago
I guess it all depends on how you balance occam's razor against abusing the anthropic principle.
AgentME 6y ago
The article mentions that multicellular life is something that's known to have separately evolved at least 40 times, so it's probably not a useful evolutionary step to compare to ones that only happened once.
arp242 6y ago
While it made complex life possible, at the same time the introduction of oxygen also killed a lot of lifeforms and was a mass extinction. It's not inconceivable that with slightly different circumstances it could have just have wiped out all life. The development of (complex) life seems like a really fine balance.

deeeeplearning 6y ago

>How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years? Holy hell, this man trounced a team of Oxford scientists in a single line! Someone get this man a NObEl PRizE... So you, a random internet person caught such an obvious error and somehow no one at Oxford or the reviewers at Astrobiology noticed? That's really what you think?

Twisol 6y ago
Science is about testable, falsifiable hypotheses. It's important to question what we think we know, and how we know it. "Argument from authority" isn't scientific. We can simultaneously believe (a) that well-respected researchers from a well-respected institution are capable of carrying out well-grounded research and (b) that research is in principle understandable with sufficient interrogation. Authority supports (a) but does not render (b) unnecessary.
- zebrafish 6y ago
  I think his point, though not well made, is that it’s likely parent is not the first to ask this question and that the researchers have likely already thought about that.
  - Twisol 6y ago
    Yeah, both this and the original question are good points. I wonder what the paper itself has to say. The early bits are pretty readable so far [0], but I doubt it calls the original question out quite as succinctly as it was asked. Lots to mull over though! [0] https://www.liebertpub.com/doi/full/10.1089/ast.2019.2149 https://www.liebertpub.com/doi/full/10.1089/ast.2019.2149
Imnimo 6y ago
Haha! I don't mean to imply that I've uncovered some fatal weakness (or even necessarily a weakness at all)! That's just the question that jumped to mind when I read their paper, and I figured someone else might know the answer.

joe_the_user 6y ago

How do you differentiate an event that is very improbable and so takes a billion years from an event that is inevitable, but requires many prerequisites, and so takes a billion years? I suspect that' gnawing for any research like this. But I could suggest that if we can show that a lot of fundamental changes have come from external shock rather than internal processes, then we might be closer. Further, if the theory of "puncture equilibrium" is true[1], that this would tend to be the case. If we can show that many evolutionary steps involved such external shocks, then we might be closer to this also. The question would be whether external shocks inevitably produce advances or whether such advances are indeed lucky. [1] https://en.wikipedia.org/wiki/Punctuated_equilibrium https://en.wikipedia.org/wiki/Punctuated_equilibrium

AgentME 6y ago
Punctuated equilibrium doesn't really change the calculations involved in the article. Either mutations happen randomly on their own, or random events cause bursts of mutations to happen. The burstiness doesn't matter much when you zoom out enough.
- joe_the_user 6y ago
  Punctured equilibrium can matter if fundamentally new adaptation happen only or primarily with external disruptions. Mammals replaced reptiles after a mass extinction event cause by a meteor - another world might not regular meteors or might have too many. The question is how non-earth world might fail, right.
  - AgentME 6y ago
    It doesn't matter to the equations whether you're modeling the chance that a mutation happens on its own, or the chance that an event happens that causes the mutation. You would use the same equation to model either of those.

monkeycantype 6y ago

This doesn't contradict the conclusion of the paper, it makes no difference as to whether we're going to find anybody we can have a conversation with, ("hey, how annoying is light speed?") but I think our definition for simple and complex life is off. eg "more likely to find simple life on Mars." That ape and octopus exist, says that earth didn't win the intelligence lottery, we are watching the long slow grind of compound interest. When you look at our world we see that the lipid bilayer is preserved, that rna is preserved in every living thing, but eyes have evolved independently many times. That the last common ancestor of octopus and human was a little wriggly thing, leads me to believe that forming a boundary between self and non self is hard (the bilayer), that forming a system of heredity is hard (first rna then dna). That the accumulation of processes that use energy, resources and information from the environment in new ways is a long relentless grind. The basic body form, multicellularity and a gut were, big difficult changes, but maybe intelligence is just paint on a hard won foundation.

joe_the_user 6y ago
Yeah, in the discussion of "where is the intelligent life", you seldom see the argument that it really does takes 11+ billion years to produce that intelligence life. With a universe "only" 13 billion years old and possibly chaotic, this factor, rather than any specific "filter", might why we're not seeing any other intelligent life.
- CryptoPunk 6y ago
  Consistent with that, evidence suggests that it may have taken billions of years for the precursor molecules of the first Earth-based life to emerge/evolve: https://www.technologyreview.com/2013/04/15/113741/moores-law-and-the-origin-of-life/ https://www.technologyreview.com/2013/04/15/113741/moores-la...
  - joe_the_user 6y ago
    Thanks, I remembered the article but couldn't find the link. This is a really neat argument.

ClumsyPilot 6y ago

That does not actually matter - most planets cannot be habitable for very long and stars change in brightness - eath will become uninhabbitable in a billion tlyears. So most life would die before evolving intelligence.

cgriswald 6y ago
I don’t think we can really make this claim. Life which forms around less stable stars may adapt if there is enough time for them to do so. It’s also important to note the sun is not the mean star. The vast majority of stars are red dwarves which, while more variable, are much longer lived.
- ClumsyPilot 6y ago
  On Earth all water will boil away, I don't see any plausible way for complex life to adapt. Likewise if Mars was habitable, you can't adapt to survive there now un less you are a subterranian microbe. Habitability of planets around red drawfs would of-course change the game, but it's not clear at present.
  - ben_w 6y ago
    “On Earth” is the problem with the argument. If any alien life exists, the one place it isn’t is Earth. A super-Earth in a Goldilocks orbit around a K1V star would keep atmosphere and water for longer. Eventually they too will become uninhabitable, but the relevant question about alien life is not “eventually” but rather “now”.
- mcswell 6y ago
  The article addresses red dwarves, you should read it.
  - cgriswald 6y ago
    I read the paper. Did you read this thread? Context matters.

AgentME 6y ago

If the transitions were inevitable given the time they took here, then we would expect to see the transitions happen concurrently throughout the planet in many separate instances. But we see a number of important transitions that happened exactly once on Earth.

galgalesh 6y ago
Not necessarily. A number of stages in the evolution of life require a planet devoid of more complex life forms. Spontaneous generation of cells, for example, requires very high doses of molecules that more complex life forms eat.
- fotdutah 6y ago
  Also worth pointing out that this applies to some potential 'Great Filter' events that we haven't yet encountered. If intelligent cultures don't explore the universe because they destroy their own planets in destructive wars as soon as they have that level of technology, then conditional on our existing, we should expect to be the first such culture to evolve on our planet. If on the other hand, most intelligent cultures neglect to explore the universe because they are busy with art, contemplation or hedonism, we might expect to exist in a world where hyperintelligent dinosaurs, frogs and cephalopods are already sitting around enjoying these things. The fact that they aren't means that maybe our current stage of evolution was hard to reach.