The Man In A Suit - Alien Evolution

[Jodie]

I can see a race developing a hive mentality where you have one central control organism with a lot of little epsilons running around following directions.

 

[theprestige]

Alien life would still have to live with the same laws of physics and chemistry that we have, so evolution can be expected to follow some of the same tracks...

Sure, but which tracks, exactly? How can you tell?

Argument by assertion, argument by ignorance, snipped.

You seem to be asserting a lot of stuff, and you seem to be assuming a lot of stuff on the basis of not being able to imagine any alternatives. Do you have any actual science to support any of this?

Or is this just another evolutionary Just So Story, coasting along on the basic assumption that evolution is settled science, so any evolutionary narrative you dream up is also settled science?

 

[Roboramma]

You seem to be asserting a lot of stuff, and you seem to be assuming a lot of stuff on the basis of not being able to imagine any alternatives. Do you have any actual science to support any of this?

Or is this just another evolutionary Just So Story, coasting along on the basic assumption that evolution is settled science, so any evolutionary narrative you dream up is also settled science?

I found the bits about limb numbers in various animal taxa going down as they came onto land, with those most successful on land being those with the fewest limbs interesting, anyway

It don't see that it fully supports the ideas presented in the OP in any way, but it seems like a valid way of considering the issue: what has been the large scale trend of life on earth?

For instance, as organisms increase in size they develop systems for transporting nutrients through their bodies, that's a trend throughout all life on earth and one I'd expect to see in alien life as well

Rather than "snipping" the assertions, perhaps you could actually point out which bits of the post were "Argument by assertion" and which "argument by ignorance"?

 

[dlorde]

You seem to be asserting a lot of stuff, and you seem to be assuming a lot of stuff on the basis of not being able to imagine any alternatives. Do you have any actual science to support any of this?

Or is this just another evolutionary Just So Story, coasting along on the basic assumption that evolution is settled science, so any evolutionary narrative you dream up is also settled science?

I disagree - the arguments described for likely developments seemed quite reasonable. Some assumptions must be always be made, but we can look at the evolutionary paths of Earth creatures and gain some clues about how environmental conditions and changes affect phenotypes. There are common physical rules and limitations that apply in all environments, such as scaling, and the initial solutions to these physical problems need to be simple, which limits their diversity.

 

[GraculusTheGreenBird]

I disagree - the arguments described for likely developments seemed quite reasonable. Some assumptions must be always be made, but we can look at the evolutionary paths of Earth creatures and gain some clues about how environmental conditions and changes affect phenotypes. There are common physical rules and limitations that apply in all environments, such as scaling, and the initial solutions to these physical problems need to be simple, which limits their diversity.

Still too anthropomorphic.

Those evolutionary paths would only be taken specifically becase of that specific Earth environment. I think you can only extrapolate physical rules when they considering planetary environment which is broadly similar to Earth. Just take a difference in one simple variable, Gravity, and consider how it would affect development in many unknowable ways.

Then consider a planet with not only different gravity but wildly different temperature, composition to the atmosphere, ocean (if ocean exists at all), the planet structure itself, different elements in different proportions, completely different metabolic pathways to life.

Then add a completely different physical enviroment, not just maybe different looking trees in an alien jungle but something utterly unfathomable.

Think about a planet based around growth of a matrix of crystalline structures in a low g environment. Maybe a tube like body with sets of or more three limbs would be far more efficient for navigating such terrain, particular when there is less importance to up or down, which is after all, largely due to gravity. Or maybe not, it all depends on so many particular environmental factors at every stage of the evolution.

I just dont think you can generalise across all those possibilities.

 

[McHrozni]

Then consider a planet with not only different gravity but wildly different temperature, composition to the atmosphere, ocean (if ocean exists at all), the planet structure itself, different elements in different proportions, completely different metabolic pathways to life.

The last part in bold is problematic. Completely different metabolic pathways are probably unsuitable for support of complex life. I would expect them to be broadly similar to that found on Earth. I'd go as far as to say that complex and intelligent life will be based on carbon chains and water, have a metabolism similar to those found on Earth in that it will use a readily-available oxidant (most likely oxygen) to obtain energy. Complex life will also have structure similar to our cells, it will store hereditary information chemically and so on.

It's exact molecular markup may differ markedly, but the broad principles will likely be the quite similar, again for complex life. Simple life forms can be very exotic, but we're talking about complex life.

Why is that? Because we know from biochemistry that carbon is by far best suited element to form long chains and other structures you need for complex life, and because water with it's dipole is indeed a special solvent. Some mechanisms can be mimicked using widely different approaches involving fairly exotic metals (which may be more abundant elsewhere) or molecules, but reproducing all of them together just seems impossible at this time. Chemistry and biochemistry just aren't that nebolus

It would be very exciting to be proved wrong at this.

Think about a planet based around growth of a matrix of crystalline structures in a low g environment.

Here is where the definition of life comes in. That aside, crystals are an interesting option, though a crystal-based life form would resemble our plants better than animals. Intelligence has little to offer for a sessile lifeform.

McHrozni

 

[GraculusTheGreenBird]

Interesting, thanks. Perhaps I cant take that metabolism argument too far then.

Re: The crystalline structure, I was considering that more as an environment through which such tubular creatures might move and feed, rather than that the creatures would be made of crystals themselves. And that was a argument as to why we wouldnt necessary expect 4 limbs and bilateral symmetry to be the norm everywhere.

 

[McHrozni]

Interesting, thanks. Perhaps I cant take that metabolism argument too far then.

Not without good evidence, no. I must be very careful here as not to make an argument from ignorance but from what we know, there are no good alternatives that could replace the trio of carbon structures, water and oxygen for complex life.

Re: The crystalline structure, I was considering that more as an environment through which such tubular creatures might move and feed, rather than that the creatures would be made of crystals themselves. And that was a argument as to why we wouldnt necessary expect 4 limbs and bilateral symmetry to be the norm everywhere.

Yes, it's an interesting thought, but why would 3 limbs be prefferable to 2 or 4 in such enviroment? At the very least 4 limbs give you passive stability even if 1 limb is moving, and temporarily even if 2 are moving. On the other hand, 3 limbs require you to use active stability all the time. Then it comes to the next issue, why would 3 limbs be prefferable to 2? It's a lot cheaper to grow one limb less for the same purpose, as you need the fairly expensive stability mechanisms anyway (composed from inner ear for detection, small brain for calculations and all skeletal muscles for compensation in humans).
That doesn't mean 3 limbs couldn't occur in an alien life form due to coincidence, just that there is no reason to expect a 3-limb system to be favored over either 4 or 2.
A crystaline forest seems fairly similar to our jungles in some aspects, and I'd sooner expect an equivalent of a snake, moving without limbs at all.

McHrozni

 

[PixyMisa]

Well, actually, we're locked into two pairs of limbs because that's what the first land vertebrates had, evolved from the pectoral and pelvic fins of lobe-finned fishes.

But this limitation only applies to vertebrates on this planet. There's no convincing reason that land animals on another planet would have had to evolve from a vertebrate ancestor with four limbs.

If you're developing from a large(ish) aquatic vertebrate, four fins is the optimum for mechanical efficiency, though eight works fairly well too. It's not arbitrary, the way the number of fingers and toes is.

And if you're not developing from a large(ish) aquatic vertebrate, you should prepare to be eaten by something that did.

 

[GraculusTheGreenBird]

Not without good evidence, no. I must be very careful here as not to make an argument from ignorance but from what we know, there are no good alternatives that could replace the trio of carbon structures, water and oxygen for complex life.



Yes, it's an interesting thought, but why would 3 limbs be prefferable to 2 or 4 in such enviroment? At the very least 4 limbs give you passive stability even if 1 limb is moving, and temporarily even if 2 are moving. On the other hand, 3 limbs require you to use active stability all the time. Then it comes to the next issue, why would 3 limbs be prefferable to 2? It's a lot cheaper to grow one limb less for the same purpose, as you need the fairly expensive stability mechanisms anyway (composed from inner ear for detection, small brain for calculations and all skeletal muscles for compensation in humans).
That doesn't mean 3 limbs couldn't occur in an alien life form due to coincidence, just that there is no reason to expect a 3-limb system to be favored over either 4 or 2.
A crystaline forest seems fairly similar to our jungles in some aspects, and I'd sooner expect an equivalent of a snake, moving without limbs at all.

McHrozni

I was thinking of a very low gravity environment. Where there would be less sense of up and down. So dont think of a tripod, but a tube with arms sticking out at maybe 0, 120, 240 degrees around the body, which would be used to anchor/propel oneself at any convenient point which might be in any direction. Here 3 would be better than 2 as it would have better range of accessible directions, but I wonder if 4 be necessarily be any better, precisely because of the extra cost of evolving the extra one. And if so, they could well be one set of limbs at 0,90, 120, 270, rather than two sets in the conventional way we think of arms and legs.

A snake like tube could work up to a point, but snakes only work because they have gravity to hold them down to a surface which they can act upon. If they didnt have that, they would need to maintain contact and propulsion maybe a different way. Not sure.

After all, why does the octopus not have at 5 or 7? (Don't say because then it wouldnt be an octopus! ) Dont know enough about the record of how that evolved, but its clear that they give it some particular advantage for its particular environment, or at least no obvious disadvantage.

It all depends on that particular environment, but its pretty easy to see there might be optimum configurations that wouldn't depend on exactly 4 limbs.

 

[Hellbound]

I was thinking of a very low gravity environment. Where there would be less sense of up and down. So dont think of a tripod, but a tube with arms sticking out at maybe 0, 120, 240 degrees around the body, which would be used to anchor/propel oneself at any convenient point which might be in any direction. Here 3 would be better than 2 as it would have better range of accessible directions, but I wonder if 4 be necessarily be any better, precisely because of the extra cost of evolving the extra one. And if so, they could well be one set of limbs at 0,90, 120, 270, rather than two sets in the conventional way we think of arms and legs.

A snake like tube could work up to a point, but snakes only work because they have gravity to hold them down to a surface which they can act upon. If they didnt have that, they would need to maintain contact and propulsion maybe a different way. Not sure.

After all, why does the octopus not have at 5 or 7? (Don't say because then it wouldnt be an octopus! ) Dont know enough about the record of how that evolved, but its clear that they give it some particular advantage for its particular environment, or at least no obvious disadvantage.

It all depends on that particular environment, but its pretty easy to see there might be optimum configurations that wouldn't depend on exactly 4 limbs.

The only issue there is that if the gravity is so low that up and down lose meaning, then the planet is unlikely to maintain it's atmosphere long enough for life to develop.

 

[luchog]

Well, except the assumption is that oxygen is needed for life underwater, which is pretty specific to metabolism of life on earth, and not even all earth life. Other planets could have completely different forms of life, completely different biology underwater, and plenty of materials available for tool making.

Except that there is very little chance that life could exist without the Carbon/Oxygen combination. Silicon develops bonds highly reactive an unstable, far more than Carbon, and is not capable of the same chemical diversity as Carbon, precluding much of organic chemistry. Phosphorous has similar problems. Boron appears to be a good choice, capable of similar or greater diversity, but is still someone unstable outside of a narrow range of conditions. It's also far less prevalent than Carbon, so would require an anomalous concentration in order to become the basis for a life form.

Ammonia is a possibility, possessing similar characteristics to water, and being highly abundant throughout the universe; but requires extremely low temperatures and higher pressures to remain liquid and stable. This results in an environment with much less free energy, and therefore far less likelihood of any life, let alone more complex higher life forms, evolving.

It's highly unlikely that anything other than Carbon/Oxygen would form the basis for complex life; or any life outside a very narrow range of conditions.

We also still have an anthropomorphic assumption that lighter fluids like gas is somehow necessary for life, which I dont think is true. It makes just as much sense for example, to think of an alien spacecraft filled with a dense liquid as it does with air, they are both self contained environments needed to protect the life from vacuum when travelling through space.

No, it's actually far less likely. Oxygen exchange with water takes more energy than it does with air. Further, oxygen concentration is more variable in water than air, and it's easier for a region to become oxygen starved, or to reach toxic levels. Further, compounds and reactions necessary to power a spacecraft cannot be produced in a water environment, a gaseous atmosphere is necessary. Water has a lot less free energy available than a gaseous atmosphere, and solar energy is attenuated rapidly. As complex life requires a great deal of free energy, it is far less likely to reach a level of sentience in an aquatic environment.

And regarding the earlier comment that animals will larger number of legs tend to be smaller, as their extra legs help them navigate more bumpy terrain, I don't really buy that. My understanding was that arthropods seem to have reached a size limit due to their respiration method, rather than anything else. There have been plenty of huge insects in the past, and we have large spiders and centipedes now.

You're misunderstanding. Their size is limited by their respiration. Their multiple extra leg pairs are adaptations arising from their small size, not the other way around. At larger sizes, the extra leg pairs have far less benefit, and are therefore too energy-intensive to be a useful adaptation.

Also, why do we assume that intelligence has to be embodied in a physically large form, or a size similar to ours? It seems that primates brains needed to reach a particular size to enable our intelligence to flourish, but under a different planetary biology, that size might be completely different.

So why not a hand size intelligent insect or fish equivalent, or organisms based around sets of three limbs? Seems just as likely to me.

Tri-lateral symmetry is a possibility, but smaller brains are simply not. In order for cognition to occur, a minimum complexity is necessary. Brains much smaller than ours are simply not capable of the required level of complexity. Biochemistry has absolutely nothing to do with it (aside from the requisite energy usage), it's the number of neurons and neuronal connections that are the critical factor.

 

[dlorde]

Still too anthropomorphic.

Not anthropomorphic at all. I said nothing about humans. Physical laws are universal, and will limit the developmental options of lifeforms everywhere.

On a broadly Earth-like planet, as I presumed the post I was responding to was describing, the extrapolations seem quite reasonable to me.

I just dont think you can generalise across all those possibilities.

Good thing I didn't.

 

[gumboot]

Still too anthropomorphic.

Those evolutionary paths would only be taken specifically becase of that specific Earth environment. I think you can only extrapolate physical rules when they considering planetary environment which is broadly similar to Earth. Just take a difference in one simple variable, Gravity, and consider how it would affect development in many unknowable ways.

Then consider a planet with not only different gravity but wildly different temperature, composition to the atmosphere, ocean (if ocean exists at all), the planet structure itself, different elements in different proportions, completely different metabolic pathways to life.

Then add a completely different physical enviroment, not just maybe different looking trees in an alien jungle but something utterly unfathomable.

Think about a planet based around growth of a matrix of crystalline structures in a low g environment. Maybe a tube like body with sets of or more three limbs would be far more efficient for navigating such terrain, particular when there is less importance to up or down, which is after all, largely due to gravity. Or maybe not, it all depends on so many particular environmental factors at every stage of the evolution.

I just dont think you can generalise across all those possibilities.

I think this is probably at the heart of the issue, at least in my head. Current understanding of life proposes a relatively narrow range of planetary characteristics for habitability. This narrow range necessitates an earth-like environment, which I argue will inevitably produce similar animals to what we see on earth.

However if it turns out scientists are wrong, and habitability encompasses a far broader range of planetary characteristics than first thought, this would be a major rewrite of our understanding of life.

In that instance, I would propose that, for example, life could develop in the atmosphere of a gas giant, the resulting life would probably be so fundamentally different to here on earth that it's possible we'd never even recognise it as life. Even if such a type of life could achieve sentience (and even interplanetary travel), it would be likely we'd be incapable of even recognising them as alien lifeforms, let alone communicating with them or establishing the sort of complex inter-gallactic relationships seen in science fiction.

 

[gumboot]

I was thinking of a very low gravity environment.

A planet with such low mass wouldn't be capable of retaining an atmosphere, which is essential for protecting life from cosmic radiation, trapping solar energy, and many other functions considered vital to support life.

 

[Delvo]

Well, except the assumption is that oxygen is needed for life underwater, which is pretty specific to metabolism of life on earth, and not even all earth life.

Oxidation releases more energy than other common chemical reactions, so it makes a more effective and practical energy source for life to use. And intelligence takes more energy than life without it. For that matter, intelligence is ultimately a development of the abilities to move and react quickly to surroundings, which also takes more energy than life without it.

Other planets could have completely different forms of life, completely different biology underwater, and plenty of materials available for tool making.

It might be useful to separate chemical arguments from physical/geometric arguments here. Even if we find life forms made from different chemicals and using different chemicals and different chemical reactions, they'll still be shaped by their physical requirements. Macroscopic size will call for specialization of different parts of the body for different functions because of a handful of implications of the scaling effect of square and cubic functions (surface areas and volumes). The more movement is called for, the more bilateral symmetry is favored as the most effective shape to be in to do it. Consumption & digestion of food and disposal of waste can run both more efficiently and at a higher rate in a one-way system with separate openings for "in" and "out". If the environment generally allows any particular range of electromagnetic rays to pass mostly unaltered, sensors responsive to that range of frequencies will be very useful. Support and propulsion on a solid surface instead of by buoyancy in a fluid medium calls for feet, which will be in pairs if there's bilateral symmetry. A wider variety of potential body shapes exist with relatively few large limbs in contact with the ground than with numerous small limbs, but the tripod effect makes 1 pair a difficult number to use, thus unlikely to be the original number.

None of those general principles depends on what substance the objects are made of or how they're powered. In fact, we use them in our own inventions regardless of what materials we're building with.

It makes just as much sense for example, to think of an alien spacecraft filled with a dense liquid as it does with air, they are both self contained environments needed to protect the life from vacuum when travelling through space.

Aliens native to liquid environments might not have a choice about it, but a heavier ship is harder to move around.

My understanding was that arthropods seem to have reached a size limit due to their respiration method, rather than anything else.

That is among the possible influences, but not the only one, particularly when you consider what vertebrate respiration was like when we first came out of the water and what it's still like in the most comparable modern tetrapods, which are also the smallest class of tetrapods. And there are other possibilities too, from digestion to skeleton strength & growth to the different effective ranges of the different types of eyes. I believe the size difference between vertebrates is caused by a combination of factors, of which limb count was one, but I just deleted a few paragraphs of blather about why, including some on the implications of lineages that don't use all of their limbs the same way (such as frogs & orthopterans, or mantises), to control this post's size.

There have been plenty of huge insects in the past, and we have large spiders and centipedes now.

When the atmosphere was different and there was less vertebrate competition (which themselves hadn't gotten as advanced in the respiration or locomotion departments yet.)

Also, why do we assume that intelligence has to be embodied in a physically large form, or a size similar to ours? It seems that primates brains needed to reach a particular size to enable our intelligence to flourish, but under a different planetary biology, that size might be completely different.

Have you ever seen diagrams of the simplest possible arrangements of parts to be able to take input and produce different kinds of output depending on what the input was, like truth tables, decision trees, and logic gates? You almost certainly have seen flow charts, which are a somewhat less formal implementation of the same idea. You can think of every item in something like that as corresponding to a single nerve cell, connection between two nerve cells, or signal passing to or from a nerve cell. Invariably, because each component has only a limited and very simple function, doing anything more complex with that kind of setup requires adding more parts to it.

Sure, but which tracks, exactly? How can you tell?

The ones that either can definitively be attributed to an established law of physics, or are known to be the way things already actually have worked in more than one real lineage of life independently.

coasting along on the basic assumption that evolution is settled science

That isn't an assumption. It's a fact. If you want to dispute that fact, this is not the thread for it. Start a Creationism thread and I might go over how this is known to be a fact in that thread, but not here, where it's barely even related enough to the subject to qualify as a tangent. This thread is for people who have already acknowledged and accepted that part of reality and moved beyond it to a conversation about some of the finer details of its implications and examples and results. Bringing Creationism into this is like barging into a conversation about the similarities and differences between two types of jet engine to lecture the jet enthusiasts about "coasting along on the basic assumption that {combustion} is settled science".

 

[Delvo]

A planet with such low mass wouldn't be capable of retaining an atmosphere, which is essential for protecting life from cosmic radiation, trapping solar energy, and many other functions considered vital to support life.

Making up/down irrelevant would require so little gravity that there wouldn't even be a planet.

 

[Skeptic Ginger]

Without other planet's life we have no way of knowing the range of components but if it is similar to what evolved on Earth you can expect a brain, locomotion, hands, complex sensory organs to perceive the surrounding environment and of course a respiratory, circulatory, skeletal, nervous and muscular systems.

You start with that and see how incredibly diverse life is on Earth. Octopi and some bird species offer intriguing means of intelligence that we don't fully understand.

That's all I have at the moment.

 

[luchog]

In that instance, I would propose that, for example, life could develop in the atmosphere of a gas giant, the resulting life would probably be so fundamentally different to here on earth that it's possible we'd never even recognise it as life. Even if such a type of life could achieve sentience (and even interplanetary travel), it would be likely we'd be incapable of even recognising them as alien lifeforms, let alone communicating with them or establishing the sort of complex inter-gallactic relationships seen in science fiction.

Speaking of science fiction, this pretty much describes about half of Stanislaw Lem's oeuvre. Particularly Solaris and His Master's Voice.

Even if the lifeforms were substantially human-like, chances are there would be so few mutual points of reference that communication would be extremely difficult, particularly since there's no guarantee that the environment that produces such a lifeform would generate the sort of evolutionary pathways and divisions we see in Earth animals. Finding a common frame of reference may end up being an insurmountable barrier.

 

[I Ratant]

I wondered why this lizard-skinned guy would be interested in the very desirable mammal....