Extraterrestrial's body plan

[SkepticJ]

When you think about what intelligent aliens might really be like, what sorts of forms go through your head? Mine are often tripedal, hexapedal, octopedal or have an even greater number of limbs. Most have light and strong exoskeletons(made from silky or carbon composites), but some use muscular hydrostatic limbs with sticky pads, suckers or tongue-like growths on them to get around and manipulate objects. Endoskeletons are in my thoughts as well, but they're not made of the same material as our's are and they evolved from animals(or however the life would be classified, they could be fungus or plant-like as well) very unlike the fish we came from. Four or more eyes are the norm, two on the sides of their head, carapace, whatever they have, the other two are on the front, what we'd call the front anyway, for binocular vision. They're usually omnivores or carnivores.

[SolusLupus]

Geez, not quite sure how to answer this one.

The problem with playing the "guessing game" of alien life is not just that we don't know how alien life could evolve, and where, but also that our imagination, no matter how incredible it might seem sometimes, is also rather limited to what we have here on Earth. We imagine aliens as taking the form of insects, lizards, humans, etc. We imagine eyes and limbs and everything; all of those things (and more) that you see here on Terra Firma; or just a slight variation of what you see here.

For the most part, I think that if an alien being is "beyond imagination of all humans", then that's that; no matter what I do, I can't imagine it.

However, just for fun:

I imagine a starfish! Almost literally; a starfish that floats through space and can "crack open" shelled creatures (usually asteroids) for substance... but doesn't mind the odd spacecraft here and there. Oh, and they're gigantic. Why? Because I can!

[Ilya]

Puppeteers' home planet (before they exterminated everything remotely dangerous to themselves): All vertebrates are descended from an ancestor with Y-shaped notochord and Y-shaped digestive tract. All animals have two heads, two mouths, two eyes (one eye to a head), one stomach with two entrances and one brain in the base of the Y. Land forms have three legs, aquatic forms have three fins. Flying forms have two wings and one leg to sit on.

[jhwegener]

It may be a funny way of speculating intelligent creatures with a lot of limbs, and a generally very complicated "design"(You may find a better word ).
One can also think about what may be likely.
Is it just by chance that terrestrian lifeforms, especially all bigger and "higher" - as far as i know, in fact has a very simple overall bodyplan?
´Did that really happened by accident?
Perhaps one may think terrestrian lifeforms during 4-5 billion years evolved in a rather "erratic" way, escaping all the real good and effective sollutions. (like, say, 1000 heads, centipeds, facet eyes, like on flies, dosens of wings and legs and arms, not to speak of all the mouths, and sense organs, that surely would make us all work much better). Alternatively one could imagine for once, that there might be reasons that organisms are as they are- here -and that some economy "streamlinedness" might be the most effective and fitting (what about to versus say, 100 sexes?)

[SkepticJ]

Is it just by chance that terrestrian lifeforms, especially all bigger and "higher" - as far as i know, in fact has a very simple overall bodyplan?
´Did that really happened by accident?
Perhaps one may think terrestrian lifeforms during 4-5 billion years evolved in a rather "erratic" way, escaping all the real good and effective sollutions. (like, say, 1000 heads, centipeds, facet eyes, like on flies, dosens of wings and legs and arms, not to speak of all the mouths, and sense organs, that surely would make us all work much better). Alternatively one could imagine for once, that there might be reasons that organisms are as they are- here -and that some economy "streamlinedness" might be the most effective and fitting (what about to versus say, 100 sexes?)


To a certain extent, I think the answer is yes. The reason why animals like giant octopusses have taken over the land isn't because that many limbs doesn't work, when they plainly do. It also isn't because they're not smart, which they are. It's because they lack skeletons of the type that would let them do very well on land. They have a muscular hydrostatic form, but such things aren't strong enough using only normal biological muscles to get around well on land. Arthropods once did rule the world, before vertebrates existed. There were once centipede-like animals about two meters long. Relatives of scorpions about a meter long. You don't see truely giant arthropods on land anymore for several reasons. Vertebrates work better at the size range that arthropods once had, arthropods, at least of the forms that have evolved on earth, can't grow as large as vertebrates can due to the square cube law. Their legs can't keep being scaled up and still work. The limit for arthropods on land is about a meter in height, after that they're too heavy for their own legs. Yet another hold back for arthropods is how they breath. When those giant arthropods that I mentioned lived, Earth's atmosphere had much more oxygen than now. Such animals, if created artificially now, might very well die with our oxygen levels. The reason we have four limbs is because the fish we came from did. If on another world vertebrates evolved to have a different number of limbs than their ancestors could have more. Six limbs, maybe even eight, might evolve. If it had a vertabrate physiology then it could scale up like we reptiles, birds and mammals have.

[jhwegener]

So in this case I might actually be the more sceptic(!)
I once had a good time reading StevenJ. Gould, but find it hard to believe, that the dominaing bigger animals are so relatively simple buildt, just by chance. That there are not some principles of "economy" at work.
Perhaps, though this may sound far out (but it could be it is not), one could compare with engineering. Is it not so, that many machines, and other artifacts, once were had a much more "complex" appearance, and has "evolved" toward something more "streamlined". Like cars, like planes, and probably a lot of other things. Of course there may be some "accidental" or "historical" factors too, but I doubt they are the only ones (is there not only some basic chemistry in life? -amino acids and genetic material. If it not exactly the same chemistry other places, there may be some similar principles of simplicity? Cells and cell-division?)
And remember: The strongest argument that we are not alone is that it seems improbable, given the size of the universe, and if we accept the fact that life here has worked for so long. But I can hardly see that this argument can be extended to extremely different designs. We cannot rule out that they simply don´t work.

[SolusLupus]

I honestly think that evolution works on the terms of "If it works, why get rid of it?"

For instance, with the human body; if we did share the same ancestor as the chimp, then our evolution most likely was slight. Lost fur, gained straightness, etc. Baby steps, but after a while, even baby steps makes progress. However, at no point does "fifty heads" ever become a viable option in that case.

[Ara Pacis]

I like centaurs. They'd be a nice alien. And chances are that if we ever got into a war with them, we'd do better because we could take more acceleration. At least, I think so.

How about pneumatic life-forms, like intelligent airbags. I wonder if they might evolve on a planet with a dense, but habitable, atmosphere.

I also wonder if it might be possible to construct an alien that looks like an arthropod, but has managed to get around the limits of terrestrial types. Maybe it would only evolve on a low G planet. Or maybe it would be some sort of hybrid by combining elements of endoskeletons and better respiratory systems.

[SolusLupus]

I like centaurs. They'd be a nice alien. And chances are that if we ever got into a war with them, we'd do better because we could take more acceleration. At least, I think so.

Centaurs aren't that great, really. Too much of a bend required in the spine. Also, not much capability with turning the torso; you can barely turn it, if at all. So what's the point, really? If the only real advantage is the arms, then why bother with the top part? It just seems so... silly and unrealistic to me.

[Ilya]

Centaurs aren't that great, really. Too much of a bend required in the spine. Also, not much capability with turning the torso; you can barely turn it, if at all. So what's the point, really? If the only real advantage is the arms, then why bother with the top part? It just seems so... silly and unrealistic to me.
As a tool-user centaur may be inferior to a humanoid, but if it started out as an unintelligent hexapod, the only realistic tool-using end result would be a centaur. And there is nothing unrealistic about hexapod body plan -- most Earth animals are hexapods. They are called insects. Pure chance insects never evolved lungs -- if they had, they (well, their descendants) would be the dominant life form today.

[SolusLupus]

As a tool-user centaur may be inferior to a humanoid, but if it started out as an unintelligent hexapod, the only realistic tool-using end result would be a centaur. And there is nothing unrealistic about hexapod body plan -- most Earth animals are hexapods. They are called insects. Pure chance insects never evolved lungs -- if they had, they (well, their descendants) would be the dominant life form today.

Depends. When I see how "Centaurs" are drawn, they generally look very... encumbered by their own physiology.

I'm not sure on the whole insects thing. *Shrugs* But I'm pretty sure insects have a different physiology than how centaurs are depicted.

[Ara Pacis]

I remember someone once saying that nature never evolved the wheel, or more accurately, an axle. I actually devised a biological structure for making an axle-wheeled animal using a disconnected bone structure. I'm not sure what the point would be, not a lot of terrain for its use, but maybe a sea or airborn creature might make use of it.

[jhwegener]

And if there is it is likely some limits to our fertile imagination.
Another thing is: Can we say something about what´s realistic or likely?
Compare again with artifacts: There´s very, very many times more ways one might imagine them, than there is practical designs (and even a lot fewer of these will attrackt investors and become real products. I at least can imagine things done very different, as perhaps You too?)

[eburacum45]

Some features of our own design might be found to be common among alien intelligent creatures. Bilateral symmetry is common to most animals but not plants, so perhaps intelligent animal-like creatures will often be bilaterally symmetric. Such a creature will probably tend to have a front end and a rear end, with manipulatory appendages near the mouth, and sensors at the front end of some sort. But a radially symmetrical creature with a centrally placed mouth is not entirely impossible, perhaps only if the environmental conditions are very different to Earth. On a planet with a very thick atmosphere all movements will be slowed down, and a starfish-like bodyplan might compete well against a more streamlined bilaterally symmetrical quadruped plan.

But perhaps plant-like creatures or slime molds/fungi equivalents might sometimes also develop intelligence, in my opinion; exactly why such non motile organisms might require processing is another matter, but I think it is possible that some set of circumstances might allow this to happen.

Large brains or nervous systems capable of will be a necessity for complex thought, so larger animals will be able to support larger processing substrates. So a large animal will need sturdy means of locomotion; on an earth-like planet, strong legs with skeletal structures for support. Mostly this will be an internal skeleton of some sort- plausible external skeletons are too heavy for a large creature. This does not rule out a hybrid between an internal and an external skeleton; some armoured dinosaurs had extensive bony parts in their outermost layers, and such an outer shell could also perform support functions
. A large animal could be bipedal like a human, or bipedal like a dinosaur, using a cantilever like main support system. The development of an articulated spine, by the way, is a bonus, but need not be a universal feature. Even without a spine or backbone a creature large enough to carry a large brain could be tripedal, or quadripedal, with secondary limbs at the front end, or have even more legs; I suspect that more legs will be required on planets with gravity somewhat higher than Earth's. Similarly bipedal locomotion might be more advantageous on low gravity planets, although I have heard that the best form of locomotion on low grav worlds is hopping, so a skinny kangaroo-like bodyplan might be best.

It is possible that a head-like structure is a common feature of bilaterally symmetrical land animals; this will be more common in creatures with a backbone analogue.

But perhaps a large neural network could be built up between many smaller creatures, using temporary (or perhaps permanent) information-carrying connections between individual members of a colony or swarm. Such a hive mind is a staple of science fiction, but it might occur somewhere. Colonial sponges with shared nervous systems, hives of insects or flocks of birds or dinosaurs communicating by chemicals, sound or electromagnetic signals spring to mind.
I recommend reading 'Starmaker' by Olaf Stapleton, where he deals with hive mind creatures in some detail; he also suggested bipedal creatures which have evolved from five pointed starfish-like creatures, or from centaurs (where the rear legs have merged with the front), and interestingly, intelligent ships that sail the seas using wind power.

[novaderrik]

i think they will look like us, but with bumps on their foreheads.
we will know they are friendly if they wear loose fittng, earth-tone colored clothes and are generally calm and cool about things.
we will know they are unfriendly if they wear darkly colored, tightly fitting or angular clothing, and get really worked up over little things.


everything i know about aliens, i learned from Star Trek.

[Relmuis]

The bend in the centauroid's spine would be awkward, but so is our upright stance. In fact, if I hadn't seen two-legged animals (and if I were not two-legged myself), I would not think it possible for such an animal to walk without falling over.

The centauroid would have emerged from an entire class of six-legged animals, just like we emerged from an entire class of four-legged animals, by freeing the front pair of legs, turning them into arms. In both cases, there is a price to be paid.

If I had to guess, I think that among intelligent species the humanoid form will be quite common with the centauroid form coming in a close second. Centauroids will tend to live on slightly more massive worlds than humanoids.
And on some massive worlds with dense atmospheres the angeloid form will be found (two legs, two arms, two wings).

I also expect (intelligent or non-intelligent) beings to exist, whose bodies are in effect giant wheels, rolling over vast plains. Whether wheel-like appendages can evolve seems more doubtful; much could go wrong with them, which might mean that they would always be selected against.

[Ara Pacis]

I'm not sure that a centauroid form would develop in heavier gravity fields. I would think that the awkward bend in the spine would be detrimental with a heavier load and that the four legs would not necessarily counter it.

On the other hand, there may be an increased likelihood of large winged animals (angeloid?) on higher gravity worlds for two reasons. Denser atmospheres would increase lift coefficients. Denser oxygen atmospheres would allow for higher metabolism for the larger creatures for flight. Although it may be debateable if they are actually flying or just gliding/soaring. Who wouldn't like to own a Pegasus? an Angeloid might evolve as needing 4 legs to climb to the top of a tall tree and jump off, instead of flapping up against gravity. I'd also be interested a large sentient sixlegged and winged creature like a flying centaur (hexangeloid?) Maybe in the future we could GM such creatures for our own amusment.

As for large arthropoids, I wonder if we replaced the moltable chitin-based exoskeleton (http://en.wikipedia.org/wiki/Exoskeleton) with a continuously growing bone-based exoskeleton, like a tortoise but articulable. It might not be an actual exoskeleton since it might be covered with a skin or dermis of some sort.

[Vaelroth]

I like to imagine a methane sack with an internal skeleton and thick leathery skin. Some of the skin on its fore side is sensitive to light and heat radiation, but can't distinguish color very well. The organism has six tentacles and end with a tough nail like spine that can spear prey and enemies. The spines also have a slight hole in them for ingestion and excretion, and finger like objects can extend to interact with technology.

Then there are other possible hominid species with six appendages, an evolution from prehistoric fish that required four fins and a powerful flipper to maneuver through heavy gravity environments.

[eburacum45]

The centaur is not the only possible bodyplan for a non-biped with manipulatory appendages. Elephants have a trunk which extends forward from the head region. I can imagine a tetrapod or hexapod with multiple appendages extending forward level with, or even below, the shoulder.
Here is a similar species I drew for Stephen Inniss;
http://www.orionsarm.com/xenos/Jade_Chime_Singers.html
apologies, but pencil artwork is not my best medium...

[ryanmercer]

To me, Aliens look like Mila Jovovich... they ALL look exactly like her... *drools*

No...I see everything for tribble-like fuzzballs to arachnid-like creatures to humanoid to super-advance machine...

[SkepticJ]

If I had to guess, I think that among intelligent species the humanoid form will be quite common...


That's just silly. Now I'm not saying that bipedal aliens won't exist, but to say they'd be humanoid is über-chauvinistic.

[Ilya]

SkepticJ --

Do you really look like your avatar?

And before you ask, no I am not Creature From The Black Lagoon. Even if I do spend as much time as I can underwater.

[ryanmercer]

SkepticJ --

Do you really look like your avatar?

And before you ask, no I am not Creature From The Black Lagoon. Even if I do spend as much time as I can underwater.

If SkepticJ looks like Mila Jovovich as Lelu Dallas... man... I'm so finding them!

[SolusLupus]

That's just silly. Now I'm not saying that bipedal aliens won't exist, but to say they'd be humanoid is über-chauvinistic.

Very true. Of course, without something like telepathy or Fine Manipulators, the opposable thumb seems most likely for tool-using aliens. Without tools, there's somewhat of a damper on what you can, potentially, do.

But, of course, you could easily have hands to use with a different body type. Plus, you could always get an alien species that can "mold" itself into any shape it really needs to accomplish a goal.

[SkepticJ]

SkepticJ --

Do you really look like your avatar?

And before you ask, no I am not Creature From The Black Lagoon. Even if I do spend as much time as I can underwater.

Nope, not even the same gender, or age. I just think it's a fun photo, so I use it. Someday I'll switch it.

You SCUBA dive, eh?

[SkepticJ]

Very true. Of course, without something like telepathy or Fine Manipulators, the opposable thumb seems most likely for tool-using aliens. Without tools, there's somewhat of a damper on what you can, potentially, do.

But, of course, you could easily have hands to use with a different body type. Plus, you could always get an alien species that can "mold" itself into any shape it really needs to accomplish a goal.

And nothing says their hands need be like ours. I mentioned the tentacle-like arms with tongue-like growths all over them. They'd make our hands seem like oven mitts in comparison. Also, even if their hands are somewhat like ours, why not multiple opposable thumbs? Say they have seven fingers on each hand, two of them are thumbs. Perhaps their fingers are covered in small, tongue-like, muscular hydrostatic growths? Perhaps their hands are covered in tube-feet that have sticky tips. Picking up individual sand grains, or whatever, and moving them where they want them wouldn't be a problem. I really should design out on paper, computer, wherever, some alien appendages.

[SolusLupus]

And nothing says their hands need be like ours. I mentioned the tentacle-like arms with tongue-like growths all over them. They'd make our hands seem like oven mitts in comparison. Also, even if their hands are somewhat like ours, why not multiple opposable thumbs? Say they have seven fingers on each hand, two of them are thumbs. Perhaps their fingers are covered in small, tongue-like, muscular hydrostatic growths? Perhaps their hands are covered in tube-feet that have sticky tips. Picking up individual sand grains, or whatever, and moving them where they want them wouldn't be a problem. I really should design out on paper, computer, wherever, some alien appendages.

Sounds cool. These all would fall under Fine Manipulators. So would Thumbs. Hence, my statement was mis-stated. Oh well.

There are a lot of possibilities for "Fine Manipulators" that are physical. But that's relatively easy to come up with. Try for some theories on having Fine Manipulators that are NOT physical! There's a fun challenge.

BTW, Psionics will fall under Magic for this one, and will be deemed "cheating". Psionics are mostly "theoretical", if even that.

[pmcolt]

What do you mean by nonphysical fine manipulators? If it exists, isn't it physical by definition?

Hmm. A collection of vacuum/blower tubules that allows the creature to move objects through air pressure changes? Electromagnetic manipulators on a world rich in iron and ferromagnetic materials? Creatures with giant, adjustable biological speaker-horns that they can use to vibrate objects around sonically?

[SolusLupus]

What do you mean by nonphysical fine manipulators? If it exists, isn't it physical by definition?

In that case, then, something that's not solid, I.E., a hand, a tentacle, any appendage, your mouth, your rear end, toes, teeth, tongue, etc.


Hmm. A collection of vacuum/blower tubules that allows the creature to move objects through air pressure changes? Electromagnetic manipulators on a world rich in iron and ferromagnetic materials? Creatures with giant, adjustable biological speaker-horns that they can use to vibrate objects around sonically?

Those sound pretty cool, though the last one seems hard to really "condense" in predictable ways... and might have very very bad side effects...

[octoman]

The number of environments on earth is quite astounding. I think when we find life elsewhere it will remind us of something we've had here. Imagine if Trilobites became the sentients?

The OP question was about intelligent aliens, right? (scrolls up to make sure...)
So let's think about the things that we have. Upright posture frees up half our limbs from locomotion. Forward facing vision allows for detailed view of things within our grasp. Prolonged dependence on parental care gives time for language and culture transfer.

On earth we have rats and kangaroos that meet some of those criteria. Perhaps the neighbors, when we meet them, will look like kangaroos.

I doubt intelligent lifeforms could develop that look like some of the weird things on startrek and stuff. Saw an episode last night with the "horta," a "silicon based life form." Looked like a humanoid under a packing blanket.


Part of what we have available is a "generalist" body plan, rather than being highly tuned for specific environments. That seems like a pretty powerful tool that any potentially sentient species is going to need to make the step from "animal" to "person."

I could see a vertebrate species developing more than two limb girdles. Nothing on earth meets the plan, but I don't see why it couldn't happen during skeletal evolution on another world. That would make a forward pair of limbs available as manipulators leaving a centauroid hindlimb system.

The manipulator thinking is interesting, but again I think we could look around at things on earth for answers. The entire vertebrate line has fingers and toes to start with, and evolved specialized structures for feeding and locomotion like whales and cats. Non-vertebrates that have non-mouthpart manipulators are fewer and less adaptable. Crab claws are pretty good, octopus tentacles are good, feathers and beaks and cilia are rather limited.

[Ara Pacis]

How about an appendage made from hairs that grow into a flexible horn with a central tube where strong hairs attached to muscles flex the horn in different directions for fine manipulation? Several of these could be formed along a limb. However, they could be easily soiled and broken.

[Relmuis]

If I had to guess, I think that among intelligent species the humanoid form will be quite common...

That's just silly. Now I'm not saying that bipedal aliens won't exist, but to say they'd be humanoid is über-chauvinistic.

I used humanoid as a technical term, denoting a bilateral body plan with a trunk, two legs, two arms and a head. Most humanoid species would not look anything like human beings. Tyrannosaurus Rex was a humanoid species (and has even the same number of eyes, mouths, and so on, which I did not even specify).

[Vaelroth]

How about an appendage made from hairs that grow into a flexible horn with a central tube where strong hairs attached to muscles flex the horn in different directions for fine manipulation? Several of these could be formed along a limb. However, they could be easily soiled and broken.

Thats actually a pretty neat idea, but you could take it one step further and figure that the flexible horn would be like a chitin substance that would easily regrow, much like fingernails. Flexible, yet still tough enough for very fine manipulation.

[Ara Pacis]

Thats actually a pretty neat idea, but you could take it one step further and figure that the flexible horn would be like a chitin substance that would easily regrow, much like fingernails. Flexible, yet still tough enough for very fine manipulation.
Basically the biological equivalent of a bicycle cable.

[nizmo_man]

i hope there aren't any Wraith-like ETs hanging around

[eburacum45]

Basically the biological equivalent of a bicycle cable
You could bundle a few together and control a single appendage with great precision. Hmm; not too different to the way a bird's foot works, now I come to think of it.
Different evolutionary pathway, though.

[publiusr]

I had a horrific 'dream of finding an ET out in the field with an elder thing body but the head/thorax that looked like it was attached to a ghost crab--with the tall black eyestalks. It was scuttling sideways. Eew!

[Ara Pacis]

I had a horrific 'dream of finding an ET out in the field with an elder thing body but the head/thorax that looked like it was attached to a ghost crab--with the tall black eyestalks. It was scuttling sideways. Eew!
It wasn't a dream...

[Relmuis]

A possible subdivision of body plans:

Symmetry:
A: No discernable symmetry (a bush, an amoeba)
B1: Spiral symmetry (certain snails)
B2: Helical symmetry (other snails)
C2: Bilateral symmetry (most vertebrates)
C3: Threefold cylindrical symmetry
C4: Fourfold cylindrical symmetry
C5: Fivefold cylindrical symmetry (like a starfish)
CN: N-fold cylindrical symmetry
Coo: Complete cylindrical symmetry (like a jellyfish or a wheel)
D: Rectangular symmetry (like a two-headed snake or amphisbaena)
E1: Tetrahedral symmetry
E2: Cubical/octahedral symmetry
E3: Dodecahedral/icosahedral symmetry
Eoo: Spherical symmetry

C2: Bilateral symmetry
C2.0: No appendages (like a snake)
C2.1: One pair of appendages
C2.2: Two pairs of appendages (like most mammals)
C2.3: Three pairs of appendages (like a centaur)
C2.4: Four pairs of appendages (like a spider)
C2.5: Five pairs of appendages (like a butterfly)
C2.N: N pairs of appendages
C2.V: Variable (large) number of pairs of appendages

B2.2: Bilateral symmetry; two pairs of appendages
B2.2.H: With a head on one end
B2.2.T: With a tail on one end
B2.2.B: With a head on one end and a tail on the other end
(absence of both head and tail would make the symmetry rectangular)

Kind of appendage:
T1: Tentacle
T2(1,1): Tentacle, which divides into two sub-tentacles
T3(2(1,1)1,1): Tentacle which divides into three sub-tentacles, one of which divides into two sub-sub-tentacles, none of which divide any further
A: One rigid part
B: Two rigid parts
B2(A2(A1,T1),B1) Two rigid parts, the last one sprouting two sub-appendages, the first of which has one rigid part, sprouting yet another rigid part and a tentacle, the second of which has two rigid parts, sprouting nothing further.
C: Three rigid parts
C5(B1,C1,C1,C1,C1) Three rigid parts, the last one sprouting five sub-appendages, one of which has two rigid parts, the other four having three, none of these subdividing any further.

Description of the human body plan:
C2.2.H ; 2B2(C1,A4(C1,C1,C1,C1)) ; 2C5(B1,C1,C1,C1,C1)

Description of the equine body plan:
C2.2.B ; 2D1 ; 2D1 ; 1T1 (the tail is not made of rigid parts, therefore a tentacle)

If the bilateral symmetry must be manifest in the appendages, the 2 in 2C is of course redundant.

Placement of sensory apparatus and orifices is not indicated in this scheme.

Any scheme starting with C2.2.H or C2.2.B would be considered humanoid, unless one or both pairs of appendages are wings or fins.

My expectation is that of all intelligent species a large part (perhaps even more than 50 percent) will have body schemes starting with C2, and of these the majority will be C2.2 (and these mostly humanoid) or C2.3 (and these mostly centauroid or angeloid).

[ToSeek]

C2.3: Three pairs of appendages (like a centaur)

Or an ant, if you'd prefer not to use a mythical creature.

[eburacum45]

Plant like mobile organisms might not be bilaterally symetrical, but they might have specific growth habits, like the plants on our own world.
The structure of such an organism might be whorled, alternate, basal or opposite, with pinnate type subdivisions on the extremities.
http://www.borealforest.org/picgloss.htm

No advanced plant-like organism on our planet has anything more than limited mobility, but I can see the potential for mobile plant-like organisms developing on other worlds, perhaps as a stage in the reproductive cycle. If they did evolve from organisms with branching growth habits, then they might retain similar forms.

Now I come to think of it, some sessile animals on our world have branching growth habits so these creatures need not have plant-like ancestors.

[Ara Pacis]

Now I come to think of it, some sessile animals on our world have branching growth habits so these creatures need not have plant-like ancestors.
Thinking of a hydra?

[eburacum45]

Yep; and these
http://www.priweb.org/ed/earthtrips/Kashong/images/crinoid_diagram.gif

[SkepticJ]

Here's some fun musings: http://www.eponaproject.com/

[TheBlackCat]

There are a couple issues. The most serious limitation for any intelligent life form is the nervous system or equivalent thereof. All life-forms on earth use ionic gradients as a signalling mechanism. This is the basis of the animal nervous system, but is also critical to all other life-forms on earth. I will assume that animals on another world use ionic gradients as the primary signalling mechanism as well. Chemical tranport is far too slow for a mobile organism. The only other alternatives we are aware of is electrical conduction through fluid or solid conductor (like a computer) or some sort of fiber-optic system. An electrical conduction system is complicated due to needing seperate systems to drive the electrical current, transport it, and process it. There is also much more loss in an electrical system over long distances when dealing with low power levels like you would see in a life-form (too high of power levels gets into capacitance issues). Fiber-optics are possible, but are probably not as efficient over very small distances and for doing complex mathematical calculations in a very small space. I would say for organic life-forms that an ionic signalling system is a very likely choice.

That being said, ionic signalling is slow. Not as slow as fluid transport, but still on the millisecond order. This poses a serious limitation. In order to maximize the response rate, it is wise to put your central processing system in a single confied space, and to put the senses that are most likely to detect food or threats first as close to this central processing system as possible. This is called cephalization (i.e. a head). Most advanced animals have heads, including vertebrates, arthropods, many worms, and cephalopods. This guarantees that your brain gets information quickly. No matter what the life form we are dealing with, if it has a signalling system based on ionic signalling then you can expect a haed of some sort. Naturally, it would have to feed. Any animal based wholly on internal food sources, such as symbiotic photosynethetic bacteria, would not need to develop extremely sophistacted intelligence simply to keep itself in the sunlight (or get to the nearest sulfur vent or whatever the autotrophic bacteria feed on).

All the smartest animals on earth are either carnivors or omnivores, since it is a lot more difficult for something that eats things that can run away to survive than something that simply needs to run away. This is because a given level in the food chain must have 1/10th the biomass of the previous level. The chances for a herbivore are a lot better than those of a carnivore. Similarly, pure scavangers probably would not need that high of intelligence.

As people have said, any intelligent organism would need manipulators of some sort.

I would not say that bilateral symmetry is necessary, since the most intelligent invertebrate is an octopus, which does not have bilateral symmetry. Squids are also rather intelligent but lack bilateral symmetry. However, they do have heads. So a jellyfish design would be unlikely because it lacks any central processing center or cephalization. The problem with non-bilateral symmetry is although it is effective underwater where up and down do not pose as serious a limitation, on land there is a definitive up and down that seriously limits possible modes of movement. The animal would have to move in some direction. The advantage of bilateral symmetry is that there is a definitive front and back, this allows the organism to focus its limited senses in a certain direction defined as "front". If you look at squid and octopi, they actually technically are bilaterally symmetrical. They have two eyes, an ink gland, a beak, a water jet intake and outlet, and in the case of squid a pair of feeding tentacles. Despite their eight radially symmetrical tentacles these paired or singular structures give a definitive bilateralness to their structure. Reall the only truly radially symmetrical animals are the sponges, cnidarians, and some echinoderms. These are all rather limited organisms (by contrast we appear to have evolved from bilaterally symmetrical echinoderms). So bilateral symmetry, if only for the senses, would be useful and possibly necessary.

They would also need some sort of ranged communication system, but this could be smell, sound, low-frequency pressure waves, vision, electrical or magnetic activty, or some non-optical electromagnetic radition. This is not really a serious limitation.

Beyond requiring a head, manipulators, likely having some degree of bilateral symmetry, and possibly eating meat, I am not sure there are really any other serious limitations. An internal skeleton is based on limitations in Earth structural biomolecules, it is conceivable that other organisms might get around this somehow when Earth animals cannot because of evolutionary baggage.

[parallaxicality]

The idea of a hand with hydrostatic growths may make sense from a motor standpoint, but don't forget that motor function isn't the only issue in evolving a hand. The hand has to have a certain amount of force behind it, the better to punch and scratch your enemies with when peeved. Also, there would need to be less "fleshy bits" then around the rest of the body, because hands tend to get worn and cut, and so would need to heal fast. Imagine a "tongue-handed" creature getting a nasty cut. It would bleed and bleed and bleed, and take ages to heal, especially if the cut took out a large chunk of fleshiness with it. The fact that our hands are mostly bone and sinew is an advantage; they're durable and hard to break.

Personally, I think Simon Conway Morris is right; we simply don't yet grasp the full power of evolutionary covergence. So many bodyplans, (the "fishform" in icthiosaurs and cetaceans) chemical compounds (hemoglobin in legumes), organs (the camera eye) and survival strategies (such as eusociality) have evolved multiple times in our own biosphere, and I see no reason why we won't see the same phenomenon on other worlds. Although it is impossible to test on our world, as we currently only have a sample of one, it's likely that evolution, much like any other physical process, is governed by a set of repeatable laws that find the best solution over time to similar circumstances. Given that when we speak of extraterrestrial beings, we are not just talking about a emergent, elusive property (like intelligence) but of a series of unstated physical capabilities (such as the ability to build cities, radio transmitters and spacecraft) it is likely that evolution would have chosen the most efficient physical form to enable them to do this. Hence it really isn't much of a stretch to assume that extraterrestrial intelligent beings would be (at least vaguely) humanoid, and probably share concordances with ourselves we never expected.

[Ilya]

So many bodyplans, (the "fishform" in icthiosaurs and cetaceans) chemical compounds (hemoglobin in legumes), organs (the camera eye) and survival strategies (such as eusociality) have evolved multiple times in our own biosphere, and I see no reason why we won't see the same phenomenon on other worlds.
True, but...
Hence it really isn't much of a stretch to assume that extraterrestrial intelligent beings would be (at least vaguely) humanoid, and probably share concordances with ourselves we never expected.
...humanoid stance depends on having four limbs, and quadrupedal body plan evolved on Earth only once.

I think that things that evolved many times independently, such as those Parallaxicality listed, also wings, poison, camouflage, etc. are "universals" and we can expect to find them elsewhere in the Universe. Whereas those that evolved only once (no matter how many descendants inherited it), such as quadrupedal body plan, Hymenoptra tail stinger, or vertebrate jaw are "parochials" and are probably rare if not unique.

[SkepticJ]

The idea of a hand with hydrostatic growths may make sense from a motor standpoint, but don't forget that motor function isn't the only issue in evolving a hand. The hand has to have a certain amount of force behind it, the better to punch and scratch your enemies with when peeved.

Also, there would need to be less "fleshy bits" then around the rest of the body, because hands tend to get worn and cut, and so would need to heal fast. Imagine a "tongue-handed" creature getting a nasty cut. It would bleed and bleed and bleed, and take ages to heal, especially if the cut took out a large chunk of fleshiness with it. The fact that our hands are mostly bone and sinew is an advantage; they're durable and hard to break.


This assumes the animal, whatever, in question doesn't use other means of self defence or attack. Perhaps they spit poison like a cobra does? Perhaps they have nematocyst covered skin? Spine covered skin?
Perhaps they can fire a needle-like dart tipped in a highly lethal poison from their body? Perhaps they have a symbiotic relationship with tiny flying animals that live on them and fly out and sting, bite, whatever, a potential predator or prey creature?

One wonders how octopusses ever managed to evolve, what with all the sharp coral everywhere that should be cutting them to shreds? Or an elephant trunk? A tapir's nose? They seem to do fine. Perhaps the creature in question doesn't have just two hands? They have many others to take it's place until it heals. It'd also make sense that the creature would evolve blood that clots better than ours does if they get cut so much.
You also assume they don't have tougher skin than we do. Look at sharks, they have skin covered in dermal denticles: http://en.wikipedia.org/wiki/Dermal_denticle , they don't get cut even when scraping along and banging violently into coral(Which is sharp rock.)

[SkepticJ]

Ooops, didn't mean to sound like such a *bleeping bleeper* in the above post. Sorry. I just type bluntly sometimes without even thinking how it's coming across. My talking isn't a problem that way though, since a voice carries a tone of what emotions are involved, but text can't do that.

[umop ap!sdn]

To be fair, scorpions and stingrays also have tail stingers, even if they're of a very different construction than those of bees et al. :)

Centaur like forms might not be all that uncommon, since that's basically what the praying mantis has evolved into. Other animals such as decapod and stomatopod crustaceans have started with an even greater number of paired limbs and similarly adapted the most forward appendages for non-walking uses.

[Ara Pacis]

BTW, Coral isn't rock.

I have designed a creature for a SF story that is like a blob. Instead of specialized structures like bones and organs, it has semi-autonomous subdivisions I call organicles. These can semi-differentiate, but are not much different.

[eburacum45]

True, but...

...humanoid stance depends on having four limbs, and quadrupedal body plan evolved on Earth only once.


Strangely enough, some butterflies have only four walking legs; a tetrapod order of creatures descended from butterflies is unlikely, but not impossible.

[Ilya]

Strangely enough, some butterflies have only four walking legs; a tetrapod order of creatures descended from butterflies is unlikely, but not impossible.
And on related note, a cockroach running flat out actually rises up on its hind legs and runs semi-upright, with front and middle legs waving in the air. A centaur is not the only tool-using path for a hexapod -- a four-armed "humanoid" is also possible.

[SkepticJ]

BTW, Coral isn't rock.

It is when it's dead. Coral's mostly dead, even when it's not: only the outer layer is alive. Everything else is just calcium carbonate. Or, if not a rock, what would you call it?

[Lance]

Or, if not a rock, what would you call it?
Skeletal remains.

[SkepticJ]

Skeletal remains.

Uh, yeah, but so is diatomaceous earth, that's called a rock. Whatever though, my point was coral is hard and sharp, and otherwise very rock-like, if not a rock, and it doesn't even hurt a shark. If you banged into coral like they can do you'd have awful cuts and chunks of flesh missing.

[TheBlackCat]

Uh, yeah, but so is diatomaceous earth, that's called a rock.
Diatomaceous earth is a fossil. An existing reef still has living parts to it. "Coral rock" which is found on land in Florida is considered a rock because there is no living coral and it was buried underground. Current coral reefs still have living components. It is the same reason fossile seashells are rock but living seashells aren't.

Whatever though, my point was coral is hard and sharp, and otherwise very rock-like, if not a rock, and it doesn't even hurt a shark. If you banged into coral like they can do you'd have awful cuts and chunks of flesh missing.
Sharks have very thick and leathery skin compared to humans, not to mention covered in tiny teeth. In fact, shark leather is a commercial product and shark skin has been used as sand paper in the past. However, tough, thick skin limits the sensetivity of touch receptors on the skin, which is a key component of manipulative appendages in an intelligent species.

[SkepticJ]

Sharks have very thick and leathery skin compared to humans, not to mention covered in tiny teeth. In fact, shark leather is a commercial product and shark skin has been used as sand paper in the past. However, tough, thick skin limits the sensetivity of touch receptors on the skin, which is a key component of manipulative appendages in an intelligent species.

There's a way around this too, and it's already been evolved: hairs. Hairs in a ball-and-socket joint to be more precise. Scorpions have such on their feet, and scorpions feel the world *very* well. The hairs could grow from follicles that are inside the dermal teeth. The nerves that sense the hairs moving around are protected inside the dermal teeth. So, you have a highly tough but *highly* tactilely sensitive appendage. I smell an alien species I can fully flesh out here...

[epenguin]

I remember someone once saying that nature never evolved the wheel, or more accurately, an axle. I actually devised a biological structure for making an axle-wheeled animal using a disconnected bone structure. I'm not sure what the point would be, not a lot of terrain for its use, but maybe a sea or airborn creature might make use of it.

Something like that has been famously fancied before.
2022

[Halcyon Dayz]

It's an Escher. :D

[SkepticJ]

Something like that has been famously fancied before.
2022

I have that picture too, but mine's less compressed, and therefor less ugly. I think it's a neat idea, but the legs seem dubious: how are they supposed to bend around into the wheel propelling mode? They better have a hip joint as flexible as an owl's neck.

[Ara Pacis]

Something like that has been famously fancied before.
2022
It's a wheel, but not similar to my design.

[TheBlackCat]

How, exactly, would your concept of a wheel get nutrients? The cells in that part of the body would have to be fed somehow. There is no way to get nutrients to any freely-spinning organ, any blood would leak around the seams and would give a perfect place for injury or infection.

[SkepticJ]

There is no way to get nutrients to any freely-spinning organ, any blood would leak around the seams and would give a perfect place for injury or infection.

I think wheels on the ends of biological legs, or wherever, are pretty silly, but I have thought of a way that would work. The wheels get their blood when they're not spinning. Little tubes would poke into valves on the wheel when it's not spinning and the blood would flow. Then the tubes would pull out and the valves would close right behind them. There wouldn't be many living cells in the wheel part, just enough to grow the outer coating of keratin, chitin(or whatever) that would wear down during the wheels rolling action.

[TheBlackCat]

I think wheels on the ends of biological legs, or wherever, are pretty silly, but I have thought of a way that would work. The wheels get their blood when they're not spinning. Little tubes would poke into valves on the wheel when it's not spinning and the blood would flow. Then the tubes would pull out and the valves would close right behind them. There wouldn't be many living cells in the wheel part, just enough to grow the outer coating of keratin, chitin(or whatever) that would wear down during the wheels rolling action.

What about if the wheel is injured? The human skeletal system is extremely metabolically active, and actually has a very powerful repair system in the evenet of injury. But it needs a lot of blood to do this sort of repair. It also needs cells that can grow around the injury and then transform themselves into new bone cells. This is not a minor affair.

[SkepticJ]

What about if the wheel is injured? The human skeletal system is extremely metabolically active, and actually has a very powerful repair system in the evenet of injury. But it needs a lot of blood to do this sort of repair. It also needs cells that can grow around the injury and then transform themselves into new bone cells. This is not a minor affair.

Well, the animal could cut the offending end of their leg off, by cellular means. Think rotting off, but the animal is doing it to itself. Then a growth forms on the end of the leg. The new wheel and axle arrangement forms inside the growth, and when they're fully developed the husk-like growth falls off, leaving the new wheel to go about it's job. The animal would just have to limp and roll around on its other legs while one of them can't roll. The husk need not be undurable though, so that opens up the possibility of the husk being the foot until the wheel is done.
I'm just tossing these out as possibilities, I think an evolved wheeled organism is very, very, very unlikely. Where would the wheels be useful? What places in nature would be smooth and flat enough? Dry lake beds, and that's about it.

Now the whole organism rolling on the other hand, that's evolved several times already. There's a spider that lives in the Namib desert that rolls down dunes to get away from its predator. There's a lizard, or maybe it's a salamander, whatever, I've seen it, it rolls and twists its body into a tire-like shape and rolls down hills. And some kind of insect larva grabs its back end with its front, forming what looks like a green Cherrio and rolls down hills.

[Relmuis]

The screw of a seagoing ship must have the same leakage problem as an organic wheel. The organism can't afford to have blood leaking out, the ship can't afford to have water leaking in. Somehow the problem has been solved.

If the wheels were to function essentially as separate organisms, having their own, mouth, digestive system, lungs, etcetera, no blood would need to be passed to and from the wheels. They still would gain an advantage by remaining attached, if essential parts of the sensory apparatus (eyes and ears) and information processing (brain) were to reside in the main body. The only things that would have to be passed back and forth would be mechanical forces and information. Ball bearings can pass mechanical forces. Pairs of luminescent and photosensitive cells (passing each other every second or so) can pass information.

[TheBlackCat]

The screw of a seagoing ship must have the same leakage problem as an organic wheel. The organism can't afford to have blood leaking out, the ship can't afford to have water leaking in. Somehow the problem has been solved.
The problem is the ship won't get septicemia (blood infection) from a minor leak, an animal easily could. That gap would prove a perfect place for dirt and debri to collect and allow and easy entryway for bacteria. The enclosed space, with or without blood, would be a fertile breeding ground for bacteria.

If the wheels were to function essentially as separate organisms, having their own, mouth, digestive system, lungs, etcetera, no blood would need to be passed to and from the wheels. They still would gain an advantage by remaining attached, if essential parts of the sensory apparatus (eyes and ears) and information processing (brain) were to reside in the main body. The only things that would have to be passed back and forth would be mechanical forces and information. Ball bearings can pass mechanical forces. Pairs of luminescent and photosensitive cells (passing each other every second or so) can pass information.
The information such a system could pass would be extremely limited. The human nervous system operates at a peak frequency of about 1kHz per neuron, and even then we need a massive number of neurons and significant lossy information compression in order for it to operate effectively.

[Relmuis]

How much information would have to be passed to and from a wheel which is an autonomous organism?

To: instructions to go faster, or slower, and whether to ingest food or water, when food or water is present. (The sensory apparatus discerning these things and ascertaining that they are safe -- i.e. not rotting or polluted -- would reside in the main organism.)

From: information concerning the state of the surface (hot, cold, hard, soft, firm, squishy) and of the organism itself (hungry, thirsty, fatigued, wounded).
The sensory apparatus in the main organism would have to determine the location of a wound, and it would be the task of the main organism to do something about it (sucking on the wound, having it turned inward, applying bandages, calling an ambulance, whatever).

One thousand pairs of luminescent and photosensitive cells would give a bandwidth of one thousand bits per second, or more if the luminescence can be variable (other than just "on" or "off").

[TheBlackCat]

How much information is needed it move a leg, and get feedback from its sensory neurons? Well, a lot judging from the number of neurons innervating it. And the leg doesn't have to eat, drink, get hungry, get thirsty, breathe, or digest things. It doesn't have its own heart, own digestive system, own immune system, own lungs, own excritory system. This would be like combining a leg with the entire abdomen and the lower half of the head, which would take a lot of sensory communication. What advantage could this have over more conventional movement system, or over an organism that is just a wheel?

Another problem is that the human nervous system is line-labelled. A given neuron carrier a very specific type of information. Since the CNS knows what type of information any given neuron is carrying, all it has to do is carry that information on to the next stage of processing. However, in your system the actual information carried by each light/sensor pair will be different. As the wheel rotates, each sensor will be looking at a different light. There will have to be some way for each light to tell each sensor what information it is carrying, which will add a huge amount of redundant information, especially if the wheel is rotating quickly and each light only gets a couple pulses before the sensor moves on to a new light. This would give an upper limit on the speed of the wheel, it could never spin greater than the flashing rate of the lights. What is more, it will require a sophisticated processing system on the other side to figure out what input it is getting and transferring that on to the proper part of the nervous system. This would probably take a something along the lines of the human cerebral cortex, which is needed to extract specific patterns from the information being presented.

Imagine having a phone conversation while randomly changing which wires are connected to which pins in the phone jack. Now multiplay this by a thousand or more, all connections changing several times a second, and have the system try to keep up with that.

What is more, the thousand data points per second is about the data transfer rate of a single neuron. And we are talking thousands, maybe tens of thousands of such neurons in just the leg. What you are talking about is input along the lines of the entire human spinal column, or at the very minimum a quarter of that.

[Ara Pacis]

I dunno about everyone else, but I was not thinking of a biological wheel as a living appendage. I figure it would grow in a bud fashion, as someone else pointed out, and then it would essentially be dead tissue and discarded and replaced periodically. It could be a wheel of bone or antler type material, maybe with a chitin tire and the bone axle would be a cam. Multiple muscles/ligament and cartilage systems would compress the cam in sequence to rotate forward or backward with more muscle/conective tissue possibly steering it by internally leveraging the axle.

At the outer dermis would be a sphincter or muscle/ligament/cartilage to seal the opening, perhaps with a spindle or flange on the bony axle. The fluid inside of the sphincter in the axle cavity would contain immune system components (white blood cells, etc) possible cycled through a spleen or filter.

Regeneration of a damaged wheel might be done via sill living tissue on the inner axle bone. The axle bone would not be conected via a circulatory system, but cells near the surface would survive via nutrition in the axle fluid. In fact, I would expect the axlebone cells that are alive to be dormant, and to only become active for spurts of growth or repair. When the wheel is chiped or broken, possibly detected via chemical messenger or even cognative biofeedback, then the flange is sealed for a while until it is grown into a large enough wheel. The cam next to the flange is grown into the flange shape.

This is just a rough design though.

[Halcyon Dayz]

Spare wheels, just as a shark has spare teeth.
Wheel broken, discard it.

[umop ap!sdn]

That sounds like the most practical design - but it would require at least 5 or 6 of them.

As far as communicating information by means of luminescence and photoreceptors, one avenue that evolution might take would be to use a radially symmetrical pattern of lights rather than a direct one light - one signal correlation. The hardness of the surface, for example, might be indicated by the spacing between bright spots, whereas injury might be communicated via a solid line along the exterior side with a bright spot near the site of the injury.

[Relmuis]

Exactly. My point was that if the wheel is a separate organism, no intensive communication is necessary, because the organism can mostly fend for itself, unlike a human leg or arm. The wheels might even have ears and understand spoken commands. The oldfashioned telegraph between a ship's bridge and the engineering section comes to mind: it had only a few positions. (Steering is possible, merely by making some wheels turn faster than others.)

There is no need to convey detailed sensory information either, because the wheels themselves can act on this information. They might even have mouths to protest with if the main organism wants them to ride over broken glass or into molten rock.

Think of a beehive; how much bandwith is there between the queen bee and one of her underlings? If they convey information by, say, pheromones, the wheels and the main organism can do likewise.

By the way, the luminous cells can be arranged in circles, to ensure that communication is never interrupted. If each cell is 10 microns wide while the inside of the wheel is 10 centimeters wide, 10,000 concentric circles might convey 10,000 bits per second (or much more if the light can be modulated and relaxation times are smaller than one second).

[pranab]

As a Post graduate and Post Doctoral Teacher in Pathology ,in Institute of Post Graduate Medical Education Research & Training ,Kolkata-20, I think that before one is planning for body design of any bacteria, or an allien or, the first uinicellular life that may/will evolve in other planets of this / other star, we should at first think the design of DNA of those Extraterristrial life. What ever form of life may exist in outer worlds the first basis is the evolution of life must be the self replicating RNA and its transcription mechanism and evolution will strart from a self replicating RNA or a DNA virion.- Not the bacteria at first. In our Earth the basis of DNA is carbon hydrogen and poshates as base and aminoacids as ladder. The structure of DNA is so complex and so perfect. The mechanism of translation of signals for protien synthesis is so complex and so precise and perfect in earth. What is the basic of DNA and RNA if at all evolved in Extraterristrial life in other worlds? The structure and design of the DNA is so important.
Dr. Pranab Kr. Bhattacharya MD (Cal), FIC path, FIA path, FNASc, FISCA. FRSTM&H(UK)- ASSociate Professor, Dept. Of pathology, IPGME&R, Kolkata-20 WWW. Unipathos.com

[Relmuis]

If I have to guess, I would expect that most, if not all, alien life will use the same DNA and RNA molecules as terrestrial life does. The way they code for amino acids may be different, though. And they might be mirror-images of "our" molecules.

But I think that DNA is versatile enough to code for essentially anything which we may think of, whether it is wheels or whatever. So that wheels or whatever could develop if natural selection demands it. So why would we have to think of DNA first on this thread? If we do, the thread would stop, because nobody in the world can even describe how human DNA establishes the number of fingers in the human hand. Let alone describe how DNA might establish some structures we have only imagined.

[SkepticJ]

If I have to guess, I would expect that most, if not all, alien life will use the same DNA and RNA molecules as terrestrial life does. The way they code for amino acids may be different, though. And they might be mirror-images of "our" molecules.

But I think that DNA is versatile enough to code for essentially anything which we may think of, whether it is wheels or whatever. So that wheels or whatever could develop if natural selection demands it. So why would we have to think of DNA first on this thread? If we do, the thread would stop, because nobody in the world can even describe how human DNA establishes the number of fingers in the human hand. Let alone describe how DNA might establish some structures we have only imagined.

Why only DNA? You don't think some other type of molecule could code for the production of chemicals?



You can't just wave it off like that, yeah, we don't know how fingers are told to form the way they are, but we do know why fingers look and work the way they do. We know their evolutionary history, all the way back to little bones in the fins of fish. Your idea for the wheel being it's own organism is a way to explain it, but otherwise, how would a wheel evolve? Every step has to have a survival advantage, can you work out a rationalization for all the parts performing another job until they make a working wheel? Now it could be possible that the organism was more complex and became simpler, that's how venus flytraps evolved. But can you show how that would happen? What would be the history of those parts? What did they do before it became more simple to form a wheel and axel? Also you need to answer where would these wheels be useful? Try ridding a bike off of any road, path or any kind of trail sometime. Pretty worthless piece of junk without roads, isn't it? Nature doesn't have roads. Now there's flat dried up lake beds, but what's to eat out there on those salt flats? Nothing, really. So, what place is there for wheeled(has wheels, not curling up and rolling, the latter has evolved) animals in nature?

[Relmuis]

To start with the last of these objections: alien worlds are supposed to be alien: they may contain landscapes completely unknown on Earth. And even Earth has its level plains, it salt flats and its tidal shoals.

A bicycle is useless in most landscapes, because its tires are narrow. A jeep, or landrover, however, can fend for itself in various forms of landscape. (No, not on mountain-tops or in marshland, so don't bother to mention them.)

There are several ways for an amalgamated organism to evolve, as each eukariotic cell is such an amalgamated organism. In the case of wheels, one might think of separate wheelformed beings, congregating for safety and/or warmth, and of special types developing who can think better, but roll worse, than the average wheel. But another route would be parasitism om symbiosis by a different species, and yet another route would be incomplete separation during early development (akin to "Siamese twins").

But all of this is completely beside the point I was trying to make. The point being, that we might as well stop discussing the probable body shapes of alien beings if we feel required to discuss the way these must be coded for in the germplasm. One might as well require someone discussing the likely geography of alien worlds to first derive their geology from the Standard Model of subnuclear physics.

[eburacum45]

Or discuss the influence of the English alphabet on the complete works of Shakespeare.

[SkepticJ]

To start with the last of these objections: alien worlds are supposed to be alien: they may contain landscapes completely unknown on Earth. And even Earth has its level plains, it salt flats and its tidal shoals.

A bicycle is useless in most landscapes, because its tires are narrow. A jeep, or landrover, however, can fend for itself in various forms of landscape. (No, not on mountain-tops or in marshland, so don't bother to mention them.)

I wasn't thinking of those, I was more thinking of in a forest. Can you see a jeep making it's way through a jungle(or any place with trees and bushes), no matter how hard the soil is, without roads? Sure, jeeps can go on *bleep*-poor roads, but they still need roads when there's stuff in the way(like trees, fallen or not). Also, think about the massive amounts of torque that those machines have to their wheels, how is an animal going to match that? Does the animal have a driveshaft to a motor? If so, how did the motor evolve? What does it run on? Or does it kick along with some hind legs? If the latter, why not just have more fully working legs? A wheeled animal would be a evolutionary dead end at the very best: when that environment changed they'd go extinct. When those environs you mention go away, how are they going to get to another place like them? They can't roll there, that's for sure.

[Relmuis]

No, jeeps don't need roads. That's why they are called jeeps. (From G.P., or General Purpose.)

Anyway, of course there are environment where wheels won't work. Just as there are environments where lungs don't work. There are, however, environment where wheels will work, and that is the point.

[Ara Pacis]

Wheels might be useful in aquatic environments.

[SkepticJ]

No, jeeps don't need roads. That's why they are called jeeps. (From G.P., or General Purpose.)

So how do jeeps get through solid trees then? Knock 'em down as they go? I really don't know how to make this any more simple, when there's stuff in the way, jeeps need roads. Now the road may be very, very poor, with basketball sized rocks poking up here and there, but it's still a road.

[SkepticJ]

Anyway, of course there are environment where wheels won't work. Just as there are environments where lungs don't work. There are, however, environment where wheels will work, and that is the point.

Sure, but oceans aren't small and don't just dry up(here anyway, looks like that may have happened on Mars). Tidal flats, salt flats etc. go away after a time. HOW are they going to move from their disappearing home to another place when they can only move in environments like their home? You didn't answer this, and I think it's a killer. Legs of some kind work on any kind of terrain, even very soft mud.(some birds have feet that make snowshoes look pathetic), the same can't be said of wheels.

[SkepticJ]

Wheels might be useful in aquatic environments.

Maybe, but why roll when you can float? Using wheels underwater is like driving when you have the option to fly.

[pranab]

[QUOTE=Relmuis]If I have to guess, I would expect that most, if not all, alien life will use the same DNA and RNA molecules as terrestrial life does. The way they code for amino acids may be different, though. And they might be mirror-images of "our" molecules.
Pranab
Then the DNA and RNA molecules must have to come from space time in the earthn and also in the other planets where life might have evolved as extraterristerial. Might be Astreoids or commets as a source of DNA and RNA molecules there and carried life everywhere where life evolved. But I wounder that when commets or asteriod strikes the planets atomosphere it developes so huge heat . How that DNA and RNA molecule survive then?

[pranab]

[QUOTE=Relmuis]If I have to guess, I would expect that most, if not all, alien life will use the same DNA and RNA molecules as terrestrial life does. The way they code for amino acids may be different, though. And they might be mirror-images of "our" molecules.

Pranab
In that case, organic aminoacids,the DNA or RNA molecule must have to appear in the space time and to be carried to the planets [where life has evolved ] either through the astreoids or through the commets' But I wonder that when the asteriods or commets strikes the earths orany other planets atmosphere ,[where we are considering possibilities of extraterristerial lifes existance, and planning for its design] it produces huge heat at Gev level and then how the DNA or RNA or organic molecules escaped that heat to remain functioning and self replicatingone? or life appeared in this earth simply by chance factor and what are these chance factors in other planets through out our galaxy. what is miror DNA molecule? Is it like antiparticles? or mirror particles? or mirror immage of double helix?

What other molecules similar to DNA /RNA and of what composed of Fe?Si? Zn? mg? Mn? or by C
The basic molecules of gases required to evolve an amino acids are H2o, Co, Co2, CH3OH and NH3. That the life appeared in this planet reqiuired many things a) blanket of Co2- perhaps a thousands time heavier then present time.b) great masses of calcium carbonate shells as lime rocks .c) Dissolving of those rocks in acidified water,d) requirement of of sea water to generate co2 from caco3 stone rocks and volcanoes e) presence of volcanoes f) atmospheric co2 dissolved in rain water to form carbonoc acid g) an optimal atmospheric temperature h) production of dimethyle sulphate in sea water g) then production of basic molecules of life in gasious form H2o, Co, Co2, CH3oH, NH3
Dr. Pranab Kr. Bhattacharya
Mr. Rupak Bhattacharya

[Relmuis]

No, I don't assert that DNA spreads from world to world. It might, but it might not.

What I do suspect, is that DNA is the easiest or even the only plausible way to encode genetic information in a CHON environment, and therefore will always be the one that evolves.

However, this is still beside the point. If there is some other viable way to encode genetic information, this way must be as versatile as DNA, and have the potential to code for wheels as well as hands, feet, wings, flippers or whatever. Otherwise it would not be viable, and DNA would outcompete it.

[Ara Pacis]

Maybe, but why roll when you can float? Using wheels underwater is like driving when you have the option to fly.

You're thinking two-dimensionally. Almost all human water vehicles use a wheel.

[SkepticJ]

You're thinking two-dimensionally. Almost all human water vehicles use a wheel.

Doh, that's right *smacks self*. Still doesn't help the case for macroscopic biological wheels though, because the shape of fish, marine mammals or the extinct marine reptiles from the age of the dinosaurs all were a nice hydrodynamic shape and all used fins. This is because they couldn't evolve otherwise, but assuming they could evolve wheels, they still wouldn't, because the fish shape and how they flap their tails is a far more efficient way of getting through water than our turbine using subs. Turbines can allow far faster subs than fish that exist, but fish kick their bleeps on fuel economy. That's why MIT's tow tank and robo tuna is looking into how tunas swim, beyond just general curiosity. We want subs and ships that can do whatever it is that fish do to work so well.

[Ara Pacis]

Doh, that's right *smacks self*. Still doesn't help the case for macroscopic biological wheels though, because the shape of fish, marine mammals or the extinct marine reptiles from the age of the dinosaurs all were a nice hydrodynamic shape and all used fins. This is because they couldn't evolve otherwise, but assuming they could evolve wheels, they still wouldn't, because the fish shape and how they flap their tails is a far more efficient way of getting through water than our turbine using subs. Turbines can allow far faster subs than fish that exist, but fish kick their bleeps on fuel economy. That's why MIT's tow tank and robo tuna is looking into how tunas swim, beyond just general curiosity. We want subs and ships that can do whatever it is that fish do to work so well.

I know... but evolution doesn't choose the best or most efficient solution, only the adequate solutions. That's the problem with "survival of the fittest" it's a superlative when all you need is a comparative advantage. If an organism's genetics "accidentally coded" for a wheel and it thrived long enough to procreate then that mutation would continue. There's no guarantee that it anything will be around to outcompete it.

[pranab]

Let me assume/immagine that in a planet [call it X planet] of our galaxy or of a near by galaxies, whose bioatmosphere was once a time similar like that of pre arachian bio atmosphere of our planet the earth, in presence of volcanos, seawater, carbonate rocks, methane gas co2, N2 O2 etc by a chance factor life appeared through chemical evolution[ aminoacids] as a self replicating RNA world[ The nature in earth realy did the toughest job of the universe ,that no sofisticated laboratory of earth could develope an artficial self replicating RNA till date] and let me assume that sufficient time was allowed to evolve in that planet for tree and veribrates like a fish to develope and there evolution will take same almost same as darwinian evolution and there then shape & size of the fish or of reptiles or of trees will depend on the oxygen concentration, green house effect Nitrogen concentration of atmosphere of that planet. I immagine there every things are of large size due to high O2 level in biosphere. [ in the X planet]a normal small fish will be of a size of whale of the earth floating & sweaming in the top of air, The trees are of hugely tall, large size and intercommunicating with each others so that they could avoid fall by gravity hindering entry of sun light in the grounds, Microbes developing in the grounds/soils , a little Birds are looking like a dinosores and are able to communicate within themselves , are carniverous and strokers in nature and they have three eyes for vision at 360 degrees if the DNA genome are designed so for purpose of evolution. there.
DR. Pranab Kr Bhattacharya
Mr. Rupak Bhattacharya
www.unipathos.com

[eburacum45]

Sounds quite like National Geographic's Blue Moon
http://www.nationalgeographic.co.in/watch/ProgramDetails.asp?UniId=AG321&SeriesId=529
This programme presents a very good simulation of a life-bearing but not very Earth-like planet, by the way. Worth watching if you haven't seen it yet.

[pranab]

Sorry I have not seen yet National geographic " Blue moon" will You please let me Know how did they design Extraterristerial life at genomic level? Where the planet'Blue moon Exist?. what is the nature of evolution there? of what chemicals the DNA are made of?
Dr. Pranab Kr Bhattacharya
www.unipathos.com

[parallaxicality]

They didn't go into that kind of detail. It was really just gross physiology; wings, eyes, legs, fins. I suppose they assumed, like a lot of the more optimistic exobiologists assume, that since amino acids and other simple compounds are interstellar, then life will probably have relatively similar chemical makeup wherever it appears.

[pranab]

Pranab
Thank You. Life is Extraterresterial origin then. It some how carried to earth through either commets or asteriods. It must be carried in the earth either as RNA molecule or as a microbe. If it was carried in earth as A Big self replicating RNA molecule then it must not be chiral ie RNA/DNA molecule must be Lt handed. But in space & time the DNAif at all exist it must be a chiral molecule
In that case life every where in a planet/moon of any place of our universe must be a carbon based DNA similer like that of earth and evolution of life will be same as that of earth only difference will be in size Shape & structure of evoluting organisms and that will depend s on atmospheric concentration of various gases like oxygen, Nitrogen, CO2, CO, Methane , Hydrogen
DR. Pranab KR Bhattacharya
MR Rupak Bhattacharya
MR. Ritwik Bhattacharya
MRAvishek Chakraborty
www.unipathos.com