Life in Universe: Is Intelligent Life Inevitable?

[Chronos]

Life started on Earth almost immediately after it became possible. It nearly got wiped out several times, but, still survives - which asserts life is a resilient parasite and threat to any habitable planet in the universe.

 

[twofish-quant]

Life started on Earth almost immediately after it became possible. It nearly got wiped out several times, but, still survives - which asserts life is a resilient parasite and threat to any habitable planet in the universe.

Or else, it may be that we are just damned lucky.

This is something that looking at other planets will resolve.

 

[Eric333]

Life started on Earth almost immediately after it became possible. It nearly got wiped out several times, but, still survives - which asserts life is a resilient parasite and threat to any habitable planet in the universe.

Is life a "threat"? ANd when you say "life" do you mean sentient or any life at all? Take an apple tree for instance, all its apples would fall right beside it if it weren't for animals eating them and excreting the seeds elsewhere to make more trees...

 

[Ryan_m_b]

Is life a "threat"? ANd when you say "life" do you mean sentient or any life at all? Take an apple tree for instance, all its apples would fall right beside it if it weren't for animals eating them and excreting the seeds elsewhere to make more trees...

"Life" isn't a tricky thing to talk about in this context. A primordial Earth would have been a world of small molecules, see the RNA or Protein world hypotheses. Current thinking in abiogenesis is that natural selection would have worked on early configurations of various molecules selecting for those that were stable enough to self replicate e.g. single RNA strands that are stable long enough for free nucleotides to bind and form a second strand before the two separate.

Over time molecules with catalytic activity arose and slowly different molecules began to be able to aid each other. Lipid membranes worked into this mix allowing for protective environments.

There is no objective way to point to any stage and say "that is where life started" because we don't have an objective definition of life.

Final point but cellular life arrives much later in this story, let alone trees and birds!

 

[cepheid]

Ryan_m_b,

I don't claim to know what abiogenesis is, but regarding your point that maybe Earth was "extremely lucky". Okay, let's quantify that. How much of a statistical fluke was the development of life? Are we talking 1 in a million? One in a billion? Given that probability, but given also the vastness of the cosmos, how many instances of life arising does that lead to? I cannot help but think that the answer is always going to be: "a lot."

Regarding, I think it was Nabeshin who mentioned that all the parameters of the Drake equation are well-defined, we just don't know their values. Aren't actually being a little too restrictive in our thinking here? I'm no biologist, but if there's one thing that life on Earth has taught me, it's that it is resilient and that it can thrive even in what we think of as the most extreme of conditions. Who says that extraterrestrial life will need liquid water, or will need to live in a habitable zone where it is not too hot or cold, or that it will find somewhat high levels of radiation to be detrimental? What seems unlikely to me is that life arising elsewhere independently would have a similar biochemistry to our own, as opposed to something truly alien

 

[Travis_King]

My $0.02 for the current discussion:

1. The Drake equation is interesting in that it describes parameters for determining the probability of other life, but it is useless whether or not the parameters are well defined. If you are missing even one of the values, the equation becomes meaningless. So the fact that really most of the parameters have values which are unknown or unknowable really just makes it a fun thought experiment.

2.

Who says that extraterrestrial life will need liquid water, or will need to live in a habitable zone where...

Good point, but then we have no business discussing the probability of such life, as we have no experience with what it could be, the likelihood of it being true, etc. It's a nice thing to speculate on, but there are far too many unknowns to make any reasonable judgements on the matter, let alone conclusions.

 

[cepheid]

I think your first point illustrates that your second point applies equally well to "familiar" life as it does to weird life. Even if we set defined criteria for the existence of life -- criteria that have a known geocentric bias, we *still* can't say anything meaningful (ie quantitative) about the abundance of such life in the galaxy or the universe as a whole. It was not my intention to. My only point was to say that there seems to be a good logical argument for being optimistic that life in some form exists elsewhere, and that it is plentiful.

 

[Ryan_m_b]

I don't claim to know what abiogenesis is

It is the study of how life originates. As I said we don't yet have a comprehensive theory of abiogenesis but there are some very interesting areas of research.

but regarding your point that maybe Earth was "extremely lucky". Okay, let's quantify that. How much of a statistical fluke was the development of life? Are we talking 1 in a million? One in a billion? Given that probability, but given also the vastness of the cosmos, how many instances of life arising does that lead to? I cannot help but think that the answer is always going to be: "a lot."

You seem to have missed the point, that and you seem to think I can't do basic maths. Of course if the chances of a star having a planet with life were 1 in 1 million or 1 in 1 billion the universe would be teeming with life. But we have no idea what that probability really is, without a good understanding of how life evolves and under what circumstances it is (un)likely to and the distribution of conditions that would lead to a planet of that nature forming it's all just guess work.

Yes it could be 1 in 1 million, it could also be 1 in 10²³. We just don't know.

 

[Travis_King]

My only point was to say that there seems to be a good logical argument for being optimistic that life in some form exists elsewhere,

Agreed.

and that it is plentiful

This, however, I disagree with. It does not follow from what we've said that life is plentiful. There is a good argument that there is other "living" stuff out there, but we can't make any meaningful statements about the likelihood, let alone the abundance, of it.

 

[DaveC426913]

My bet is that the evolution curve between no life and primitive life is shallower than the evolutionary curve between primitive life and complex life.

i.e. I think that the basic replication of life happens "relatively" frequent in the galaxy where conditions are right, but that the vast bulk of them never evolved past the unicellular level.

Depending on how you interpret the timeline, life began relatively quickly (only a few 100My) after the crust cooled enough to allow it. By comparison, the the step from unicellular life to multi-cellular life took as much as a Gy.

I suspect that life forms but that systems aren't stable enough over huge expanses of time to allow more complex life.

Furthermore, I suspect that, when we go looking over the next millenia, we will encounter thousands of planets with microbial life before we come across one with anything as complex as a plant. And hundreds of those until we come across something as complex as a mammal. and so on...

Kind of depressing when you look at intelligent life as being at the end of a very long tail.

 

[Ryan_m_b]

Depending on how you interpret the timeline, life began relatively quickly (only a few 100My) after the crust cooled enough to allow it. By comparison, the the step from unicellular life to multi-cellular life took as much as a Gy.

IIRC this is because it took billions of years to do alter the environment (e.g free oxygen) to a level where more complex life was possible. Not that I disagree with anything else you say, it's certainly a possibility.

 

[Chronos]

Even a planet identical to Earth in every respect would be an unlikely host for beings such as ourselves [sentient intelligence]. The development of intelligent life is precariously dependent on an unlikely sequence of events and blind luck. In my estimation, dinosaurs would still be the dominant life form on many such planets. I would hazard to guess intelligent life is exceedingly rare in the universe at any particular point in the history of the universe. I would not at all be surprised if we are one of the few, if not sole example of sentient intelligence in this galaxy at this particular time.

 

[Eric333]

I would not at all be surprised if we are one of the few, if not sole example of sentient intelligence in this galaxy at this particular time.

Just to clarify, are you saying "galaxy" or Universe? I think you make a good argument either way mind you.

 

[cepheid]

Even a planet identical to Earth in every respect would be an unlikely host for beings such as ourselves [sentient intelligence]. The development of intelligent life is precariously dependent on an unlikely sequence of events and blind luck. In my estimation, dinosaurs would still be the dominant life form on many such planets. I would hazard to guess intelligent life is exceedingly rare in the universe at any particular point in the history of the universe. I would not at all be surprised if we are one of the few, if not sole example of sentient intelligence in this galaxy at this particular time.

I don't understand this, because it seems like you are just making a whole series of assertions that you think are obvious, but what you say is not at all obvious to me, and there is nothing to back any of them up. Could you maybe elaborate on what you think the unlikely sequence of events and blind luck was that led to the development of Homo sapiens, and why it is, in your estimation, so improbable, even given nearly identical conditions on some other planet?

 

[DaveC426913]

In my estimation, dinosaurs would still be the dominant life form on many such planets.

Perhaps so but that doesn't mean they wouldn't be intelligent.

http://www.daviddarling.info/encyclopedia/D/dinosaurintell.html

 

[Chronos]

Yes, galaxy. 1 such planet per 100 billion or so star systems may seem optimistic, but, appears reasonable. Of course that implies there may be 100 billion or so intelligent civilizations scattered throughout the universe.

 

[Chronos]

I don't understand this, because it seems like you are just making a whole series of assertions that you think are obvious, but what you say is not at all obvious to me, and there is nothing to back any of them up. Could you maybe elaborate on what you think the unlikely sequence of events and blind luck was that led to the development of Homo sapiens, and why it is, in your estimation, so improbable, even given nearly identical conditions on some other planet?

Like the drake equation, this is merely an unsubstantiated guess. The unlikely sequence of events would be the evolutionary chain leading to homo sapiens. Blind luck was the series of catastrophic events that enabled the process without causing extinction of a link in our ancestral chain. As I recall the Toba supervolcano nearly wiped out the human race a mere 75,000 years ago.

 

[ImaLooser]

I think you are completely right. I don't see how there is anything terrifically special about our Solar System. I don't see why there can't be jillions of earth-like planets.

I also don't see why there can't be forms of life very different from ours that have nothing to do with atoms. In fact since atoms are quite rare in this Universe I would think non-atomic life would be much more common.

 

[DaveC426913]

As I recall the Toba supervolcano nearly wiped out the human race a mere 75,000 years ago.

I am astonished to discover my ignorance. I have never heard of this Toba eruption or the bottleneck in the human race.

 

[ImaLooser]

I am astonished to discover my ignorance. I have never heard of this Toba eruption or the bottleneck in the human race.

I have been to Lake Toba. Very big.

 

[Chronos]

I have way too much free time since I retired.

 

[Whovian]

I also don't see why there can't be forms of life very different from ours that have nothing to do with atoms. In fact since atoms are quite rare in this Universe I would think non-atomic life would be much more common.

Then what would they be formed out of? Fundamental bosons have almost no capability to combine into bodies. Perhaps dark matter life, but that would have no basis yet other than "there's this dark matter stuff and we don't know exactly what it is so life could be made out of it."

I have way too much free time since I retired.

Studying history? Yep, you do.

 

[Ryan_m_b]

I don't understand this, because it seems like you are just making a whole series of assertions that you think are obvious, but what you say is not at all obvious to me, and there is nothing to back any of them up. Could you maybe elaborate on what you think the unlikely sequence of events and blind luck was that led to the development of Homo sapiens, and why it is, in your estimation, so improbable, even given nearly identical conditions on some other planet?

Most mutations are inherently random, natural selection then works in a non-random way on the products of these mutations. Because of this if you start out with two identical populations in two identical environments or hypothetically rewound Earth back to a former state it is extremely unlikely that you will get the same evolutionary processes.

 

[mfb]

Depending on how you interpret the timeline, life began relatively quickly (only a few 100My) after the crust cooled enough to allow it. By comparison, the the step from unicellular life to multi-cellular life took as much as a Gy.

IIRC this is because it took billions of years to do alter the environment (e.g free oxygen) to a level where more complex life was possible. Not that I disagree with anything else you say, it's certainly a possibility.

Both steps were not the result of single, unlikely events, therefore the involved time-scale cannot be used to compare their probability.
There is nice toy model to show this: Assume that the evolution from "cellular life in some way" to "multicellular life" needs 10^3 major evolution steps in some way. Assume that each step happens randomly at a single time, with an expected time of 1 million years. This is horribly wrong, of course, as there are multiple ways to multicellular life - but it shows the general idea. Using this model, the expected time for the evolution is 1Gy. However, the probability for the process taking less than 0.9Gy or more than 1.1Gy is close to 0. Therefore, you would expect this process on all planets with the same initial conditions and enough time.

1. The Drake equation is interesting in that it describes parameters for determining the probability of other life, but it is useless whether or not the parameters are well defined. If you are missing even one of the values, the equation becomes meaningless. So the fact that really most of the parameters have values which are unknown or unknowable really just makes it a fun thought experiment.

Even if you do not have precise values with well-defined uncertainties, you can try to estimate the numbers. The uncertainty just becomes large.

 

[Ryan_m_b]

Both steps were not the result of single, unlikely events, therefore the involved time-scale cannot be used to compare their probability.
There is nice toy model to show this: Assume that the evolution from "cellular life in some way" to "multicellular life" needs 10^3 major evolution steps in some way. Assume that each step happens randomly at a single time, with an expected time of 1 million years. This is horribly wrong, of course, as there are multiple ways to multicellular life - but it shows the general idea. Using this model, the expected time for the evolution is 1Gy. However, the probability for the process taking less than 0.9Gy or more than 1.1Gy is close to 0. Therefore, you would expect this process on all planets with the same initial conditions and enough time.

That's not how evolution works at all. You acknowledge that there are multiple paths to evolution but have not taken into account how significantly this affects your working out. There are many scenarios where mutations would be positively beneficial but would force an organism up a peak on a fitness landscape that is not conducive to evolution towards multicellularity. This in turn means that future mutations would have a deleterious effect and would not be selected for. In addition you haven't taken into account the changing environmental conditions that would be both biotic and abiotic in origin changing the context for selection.

Lastly you're post has the tone of teleological evolution, this is fallacious. There is no set path in evolution, merely a diverse fitness landscape created by the environmental factors working on the frequency of alleles in a population.

 

[mfb]

As I said, the model is horribly wrong. There is no point in describing all the details how. The main message stays: If an evolution has to consist of many steps (and I am sure that you agree here for the discussed step), the required time is not a good measure for its probability.
Multicellular organisms probably just could not form within 100 million years (with reasonable probability), regardless of the probability of their evolution later.

 

[Ryan_m_b]

As I said, the model is horribly wrong. There is no point in describing all the details how. The main message stays: If an evolution has to consist of many steps (and I am sure that you agree here for the discussed step), the required time is not a good measure for its probability.
Multicellular organisms probably just could not form within 100 million years (with reasonable probability), regardless of the probability of their evolution later.

Possibly but we can't really know for sure (at the moment that is). There may have been perfectly achievable routes that never evolved.

 

[thorium1010]

Multicellular organisms probably just could not form within 100 million years (with reasonable probability), regardless of the probability of their evolution later.

For the majority of geological time of our planet, favored unicellular organisms . Multicellularity is relatively late in this game. It is still not very clear how multicellularity came about. Planets outside our system maynot be so lucky to have similar conditions that favor multicellurarity. It is reasonable to think most planets that can harbor life would contain unicellular organisms. Multicellularity would be much more rare i.e. taking what we have learn t so far from our planet.

 

[mfb]

Sorry, but we are talking about different things.
The point of my posts is: You cannot use the time-scales involved on Earth to estimate the probability of such an evolution.

Do you disagree with that? If yes, why? If not, we have the same opinion in that respect.


As an unrelated topic, I think that the evolution from single cells to multicellular organism needs a lot of time. I do not try to estimate any numbers for that (apart from "<=1Gy is possible" of course). But the difference between simple cells and the task sharing in complex multicellular organism is quite large.

 

[thorium1010]

Sorry, but we are talking about different things.
The point of my posts is: You cannot use the time-scales involved on Earth to estimate the probability of such an evolution.

Do you disagree with that? If yes, why? If not, we have the same opinion in that respect.

My point is we do not know exactly how multicellularity arose on Earth. Timescales or evolution is pretty insignificant in answering this question.