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]

Originally Posted by Delvo

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?

Quote:

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]

Originally Posted by theprestige

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]

Originally Posted by theprestige

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]

Originally Posted by dlorde

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]

Originally Posted by GraculusTheGreenBird

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.

Quote:

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]

Originally Posted by GraculusTheGreenBird

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.

Quote:

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]

Originally Posted by Mojo

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]

Originally Posted by McHrozni

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]

Originally Posted by GraculusTheGreenBird

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]

Originally Posted by GraculusTheGreenBird

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.

Quote:

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.

Quote:

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.

Quote:

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]

Originally Posted by GraculusTheGreenBird

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.

Quote:

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

Good thing I didn't.

[gumboot]

Originally Posted by GraculusTheGreenBird

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]

Originally Posted by GraculusTheGreenBird

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]

Originally Posted by GraculusTheGreenBird

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.

Originally Posted by GraculusTheGreenBird

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.

Originally Posted by GraculusTheGreenBird

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.

Originally Posted by GraculusTheGreenBird

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.

Originally Posted by GraculusTheGreenBird

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.)

Originally Posted by GraculusTheGreenBird

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.

Originally Posted by theprestige

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.

Originally Posted by theprestige

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]

Originally Posted by gumboot

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]

Originally Posted by gumboot

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....

[GraculusTheGreenBird]

I've learned a lot on this thread, really interesting, thanks.

[quadraginta]

Originally Posted by I Ratant

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

Because ...

[McHrozni]

Quote:

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.

Though we generally agree, I would say that the low amounts of Boron in the Solar system shouldn't be a limitation here. Boron could be more common in other star systems or galaxies.

McHrozni

[McHrozni]

Originally Posted by GraculusTheGreenBird

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.

As mentioned by others, such low gravity makes atmosphere problematic. That said, I don't see any reason why a 3-limbed animal couldn't evolve, but I also don't see many reasons that would favor it. In your particular example you would actually favor more limbs, not less. Four forming a tetrahedron seems notably better, imho.

Quote:

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.

Considering what we see on Earth it's sensible to conclude that an even number of limbs is favorable to an odd number. I suspect Delvo could explain better why, I'd say that body formation is less complex if you're doing two very similar halves.

McHrozni

[Ladewig]

Furthermore, any species that has mastered interstellar flight probably has mastered genetic engineering as well. Maybe the "human" looking aliens created a centaur-like animal which eventually took over the planet. Or these "human" looking aliens might have decided that bones might be more of a hindrance in zero-G and they created from scratch an intelligent life form without bones.


ETA: Perhaps someone more knowledgeable than I can explain if it is possible for an alien species to not have its birth canal located between its legs. If so, then it might be easier to accommodate the large heads.

[I Ratant]

Originally Posted by quadraginta

Because ...

http://forums.randi.org/imagehosting...db53d1f6b0.jpg

.
Grrrrrrrrrrrrrrrrrr888888888888888!

[SezMe]

Originally Posted by Ladewig

ETA: Perhaps someone more knowledgeable than I can explain if it is possible for an alien species to not have its birth canal located between its legs. If so, then it might be easier to accommodate the large heads.

On Earth, all species that don't have legs. What limits the brain size of a whale?

[RecoveringYuppy]

Originally Posted by SezMe

On Earth, all species that don't have legs. What limits the brain size of a whale?

Or something born from eggs.

[Delvo]

Originally Posted by McHrozni

Considering what we see on Earth it's sensible to conclude that an even number of limbs is favorable to an odd number.

With bilateral symmetry, it not only makes sense to balance forces to make "forward" the most natural, easy, neutral direction of travel and make both right and left turns equally easy instead of favoring turns in one direction over the other, but it's also practically biologically impossible to avoid. A bilaterally symmetrical body doesn't really know how to grow just one of something instead of a pair. It might work for structures right down the middle of the body (like the organs of your digestive system, before they get pushed around), where there can be just one of something and it's still symmetrical, but limbs on the midline wouldn't work very well for reasons I expect we can all visualize without explanation, and anything that isn't along the midline is out in "everything in pairs" territory.

Without bilateral symmetry, it's a different story. The next symmetrical pattern to consider would be meridional, which is an easy word to remember if you remember that the Earth's lines of longitude can also be called "meridians". Pentaradial symmetry is one version, best known in starfish. But meridional symmetry could come in other numbers of meridians instead of always five. Jellyfish and their relatives are tetraradial, although it can be hard to see in some species; it's easiest to see in box jellyfish, with their rounded square bodies, four groups of tentacles at the corners, and four groups of eyes. I can't say whether octopus tentacles follow the bilateral symmetry that the rest of the body has (four tentacles on each side) or break bilateral symmetry and got the way they are by octoradial symmetry around the mouth. Flowers can be radially divided into three, five, or six meridians, although some species such as roses hide that by having more than one petal per slice (just as some starfish have 10 or 15 arms instead of 5). Don't get me started on stems & twigs. There could be radially symmetrical bodies, not divided into any number of meridians, but those wouldn't have limbs; as soon as there are limbs on a radial body, there's some particular number of them, which turns it meridional (or not symmetrical at all, in theory, but I don't believe there are examples of that).

However, none of those meridionally symmetrical critters are known for moving around on their own power, and as soon as there is much of a call for that, there's clear physical incentive to move toward bilateral symmetry. This has already happened in two groups of echinoderms (relatives of starfish) independently. They're pentaradially symmetrical as adults. You can see this even without the starfish arms in sand dollars (sea cookies) because of their pentagonal bodies, and in sea urchins and sea cucumbers because of the 5 lines running from one end to the other; think of starfish and sand dollars as what happens when you squash a sea cucumber/urchin end-to-end until it splats out to the sides.

• But sea cucumbers, instead of being oriented with the mouth down like other echinoderms, lie on the side, and move with the mouth in front. Now, out of those five meridional lines running between mouth and anus, three touch the ground and two don't, which is like a starfish or sand dollar going up on edge with three arms/corners touching the ground and two above... but in sea cucumbers, the three lines on the ground are where you'll find tube feet, like the bottom of all five arms on a starfish, and the two lines above are where you'll find thickened, hardened, or spikey skin, like the top of all five arms on a starfish. That gives sea cucmbers a primitive version of bilateral symmetry from a pentaradial starting point, with different front & back, different top & bottom, and reflected right & left.
• Sand dollars, meanwhile, tend to move with one corner in front all of the time, even while the body stays flattened in starfish-like orientation with the mouth in the middle of the bottom surface. Now the other four corners aren't evenly distributed around the body anymore; they've migrated around toward the front, with the anus migrating down into the widened space this creates between the two in the back. That gives them a primitive version of bilateral symmetry from a pentaradial starting point, with different front & back, different top & bottom, and reflected right & left, just in a completely different way from how sea cucumbers got there.

Originally Posted by Ladewig

Perhaps someone more knowledgeable than I can explain if it is possible for an alien species to not have its birth canal located between its legs. If so, then it might be easier to accommodate the large heads.

Birth canals aren't something we can make comparisons with on Earth because not enough lineages have internal gestation and birth canals at all. But if we expand it to egg-laying organs, of which birth canals are just a derivative anyway, then we can. And egg-laying organs nowhere near the legs are pretty common. Some insect species are known for pretty long ovipositors sticking out in back, and their legs don't come from anywhere near the back end of the body. For an example more closely related to us, some fish also have ovipositors on the bottom surface up closer to the pectoral fins than the pelvic fins, which is like you having an external reproductive organ somewhere between your navel and the bottom of your breastbone, but it's where it really is in some relatives of yours. That may even be the ancestral condition for humans, since your reproductive glands started up higher in your torso and then had to migrate down before you were born to get where they are now (a longer trip if you're male than if you're female). So where it ends up in one lineage or another seems to be not particularly constrained, but just incidental to that lineage's past.

What happened to the human vagina is incidental to a history that might sound strange but isn't hard to see by comparison with other living tetrapods. The ones that aren't mammals, along with monotreme mammals, have a cloaca, which just means an anus which is used not only for solid wastes but also for liquid wastes and reproduction; the kidneys and reproductive openings simply empty into the area right before the anus's opening to the outside, instead directly to the outside themselves. (Remember what I said in a previous post in here about the predictability of using the mouth for both eating and breathing because there's a tendency to use one hole for multiple uses instead of multiple separate holes? This is another example.)

In mammals other than monotremes, the urethral opening and egg-laying opening have migrated out of the anus. But they didn't get far because by that time there was a pubic bone in the way. That's the part of the pelvic girdle which sticks up and forward from near the sockets for the femurs, ending just barely under the skin right above the external reproductive organs. Whoever put it there when there was a cloaca just wasn't planning ahead for having the cloaca's three functions move away from each other later. Babies wouldn't need to escape through the space under that bone if we either hadn't ever had a stage in our history with a cloaca, or hadn't gotten a circle of bones fused around it. Some other lineages either don't have a cloaca or have one that isn't surrounded by fused bones, so the particular arrangement we've got there didn't need to happen.

[McHrozni]

Originally Posted by Delvo

With bilateral symmetry, it not only makes sense to balance forces to make "forward" the most natural, easy, neutral direction of travel and make both right and left turns equally easy instead of favoring turns in one direction over the other, but it's also practically biologically impossible to avoid. ... (etc)

Thanks

McHrozni

[Ladewig]

Originally Posted by SezMe

On Earth, all species that don't have legs. What limits the brain size of a whale?

The question was about species smart enough to develop interstellar travel.

Originally Posted by Delvo

Birth canals aren't something we can make comparisons with on Earth because not enough lineages have internal gestation and birth canals at all. But if we expand it to egg-laying organs, of which birth canals are just a derivative anyway, then we can. And egg-laying organs nowhere near the legs are pretty common. Some insect species are known for pretty long ovipositors sticking out in back, and their legs don't come from anywhere near the back end of the body. For an example more closely related to us, some fish also have ovipositors on the bottom surface up closer to the pectoral fins than the pelvic fins, which is like you having an external reproductive organ somewhere between your navel and the bottom of your breastbone, but it's where it really is in some relatives of yours. That may even be the ancestral condition for humans, since your reproductive glands started up higher in your torso and then had to migrate down before you were born to get where they are now (a longer trip if you're male than if you're female). So where it ends up in one lineage or another seems to be not particularly constrained, but just incidental to that lineage's past.

What happened to the human vagina is incidental to a history that might sound strange but isn't hard to see by comparison with other living tetrapods. The ones that aren't mammals, along with monotreme mammals, have a cloaca, which just means an anus which is used not only for solid wastes but also for liquid wastes and reproduction; the kidneys and reproductive openings simply empty into the area right before the anus's opening to the outside, instead directly to the outside themselves. (Remember what I said in a previous post in here about the predictability of using the mouth for both eating and breathing because there's a tendency to use one hole for multiple uses instead of multiple separate holes? This is another example.)

In mammals other than monotremes, the urethral opening and egg-laying opening have migrated out of the anus. But they didn't get far because by that time there was a pubic bone in the way. That's the part of the pelvic girdle which sticks up and forward from near the sockets for the femurs, ending just barely under the skin right above the external reproductive organs. Whoever put it there when there was a cloaca just wasn't planning ahead for having the cloaca's three functions move away from each other later. Babies wouldn't need to escape through the space under that bone if we either hadn't ever had a stage in our history with a cloaca, or hadn't gotten a circle of bones fused around it. Some other lineages either don't have a cloaca or have one that isn't surrounded by fused bones, so the particular arrangement we've got there didn't need to happen.

Thank you.

[RecoveringYuppy]

These discussions that focus on whether aliens will have bilateral symetry, be vertebrate/invertebrate, have hands, have birth canals between their legs, etc always seem so extremely parochial to me. We don't even know if something as basic as the plant/animal dychotomy will be apparent in aliens. And even that trait of Earth life was decided billions of years beyond other traits that might merely be frozen accidents that only happen on Earth.

[I Ratant]

Originally Posted by SezMe

On Earth, all species that don't have legs. What limits the brain size of a whale?

.
The container.
http://www.skullsite.co.uk/Whale/whale.htm

[SezMe]

Originally Posted by Ladewig

The question was about species smart enough to develop interstellar travel.

No, the question was "... if it is possible for an alien species to not have its birth canal located between its legs." It's a straightforward question and I gave a straightforward answer. Your post contained nothing about intelligence nor space travel.

[RecoveringYuppy]

Originally Posted by SezMe

No, the question was "... if it is possible for an alien species to not have its birth canal located between its legs." It's a straightforward question and I gave a straightforward answer. Your post contained nothing about intelligence nor space travel.

I'm confused as to why ladewig thinks it would matter to your answer, but just for clarity in the conversation, his original post was about aliens who've mastered interstellar travel and genetic engineering.

[SezMe]

I'm apparently not adding to the conversation so I'll drop out.

[RecoveringYuppy]

Originally Posted by SezMe

I'm apparently not adding to the conversation so I'll drop out.

Just to be doubly clear, your original answer was useful and I'm not sure why ladewig chose to act as if forgetting that his post was about interstellar aliens matters.

[Ladewig]

Originally Posted by SezMe

No, the question was "... if it is possible for an alien species to not have its birth canal located between its legs." It's a straightforward question and I gave a straightforward answer. Your post contained nothing about intelligence nor space travel.

ETA: I have deleted much of this post.

Here is the point I was trying to make. I can see how the error was mine because I did not lay out the reason for my question.

I was under the (possibly false) impression that the size of human babies' head was a great factor in both the development of advanced intelligence and the shape of modern humans. IF it were possible to give birth to offspring with gigantic heads and have a birth canal in a completely different place, then such advanced aliens might look very much less like humans.

In the end, I agree with RecoveringYuppy. If someone shows up, his/her/its shape is very, very, very unlikely to be similar enough to humans that adding a suit would make it indistinguishable from modern humans.

[gumboot]

Originally Posted by luchog

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.

This is certainly very true. "Humanoid in basic difference" is of course a far cry from "biologically the same", and once you get into cultural considerations the range of variety within human cultures tells a pretty clear tale.

I think, however, you could establish the very first common frames of reference by using principals found throughout the galaxy. In a similar way, when early explorers first encountered native peoples around the world there was often little or no frame of reference from a cultural point of view, but we still had the basics in common; land, water, sky, etc.

By that same principal, we and any advanced lifeform have things in common; elemental particles, orbital patterns, stars, pulsars, etc.

[gumboot]

Originally Posted by RecoveringYuppy

These discussions that focus on whether aliens will have bilateral symetry, be vertebrate/invertebrate, have hands, have birth canals between their legs, etc always seem so extremely parochial to me. We don't even know if something as basic as the plant/animal dychotomy will be apparent in aliens.

These things all build on each other. At the very basis of these discussions is our current understanding of scientific principals as basic as gravity, energy, and the behaviour of atomic particles. Ultimately, everything we are is dictated by the fundamental behaviour of matter and energy.

Never mind our understanding of anatomy or evolution, life forms that varied dramatically from those we know (to the degree that we may not even recognise them as life) would quite likely force us to reassess basic physics and chemistry.