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View Full Version : How realistic are Xenomorphs (Aliens)



Plat
2012-Jun-11, 03:25 AM
Inspired by the Prometheus movie, do they look too humanoid?

Zeek64
2012-Jun-11, 05:15 AM
Totally unrealistic. They grow ridiciulously fast with very little if any nutrition.

Plat
2012-Jun-11, 06:34 AM
I was talking more about how they look, their physical features.

publiusr
2012-Jun-11, 10:15 PM
We have parasitic wasps here--so you might see that.

kzb
2012-Jun-14, 05:30 PM
Totally unrealistic. They grow ridiciulously fast with very little if any nutrition.

This irks me as well. In the book of the first Alien movie, they found that the baby alien had been feeding off one of their cargo grain stores. So that kind of made it all right. In subsequent films it got daft and biologically illogical.

JustAFriend
2012-Jun-15, 03:01 PM
If you start looking for logic in horror movies, you're going to be sadly disappointed....

As to the aliens looking too humanoid (I'm assuming you're talking about the Engineers), the whole point of the movie was that we came from them.

Jeff Root
2012-Jun-15, 04:12 PM
I haven't seen the movie and all I know about it is what
Neil deGrasse Tyson said on NPR this morning. It sounds
like the same idea as an episode of Star Trek: TNG, in
which a message from ancient humanoid aliens is found
encoded in the DNA of life on many planets, revealing
all that life to be related. Tyson very aptly pointed out
the big flaw: Humanoids are an "end" product of billions
of years of evolution. It makes no sense that humanoids
would be a necessary result of a humanoid-designed
beginning with bacteria.

-- Jeff, in Minneapolis

SkepticJ
2012-Jun-15, 07:32 PM
I haven't seen the movie and all I know about it is what
Neil deGrasse Tyson said on NPR this morning. It sounds
like the same idea as an episode of Star Trek: TNG, in
which a message from ancient humanoid aliens is found
encoded in the DNA of life on many planets, revealing
all that life to be related. Tyson very aptly pointed out
the big flaw: Humanoids are an "end" product of billions
of years of evolution. It makes no sense that humanoids
would be a necessary result of a humanoid-designed
beginning with bacteria.

And it makes no sense that a hypothetical engineer would make people that way. Unless they're having a contest at who can devise the most circuitous, inefficient way to accomplish a goal. Interstellar Rube Goldbergs.

ravens_cry
2012-Jun-15, 11:29 PM
We have parasitic wasps here--so you might see that.
Yes, but they don't bond with the hosts DNA, already pretty impossible, but viruses do *something* like this, yet have blood that is so acidic it melts through several layers of metal.

Zo0tie
2012-Jun-25, 05:50 AM
Inspired by the Prometheus movie, do they look too humanoid?

They are silly and they make no sense unless you're a creationist. A crazy creationist but a creationist nevertheless.
Ridley Scotts original but rejected premise for the original movie made more sense. A largely mechanical organism that only used the life processes of living victims to make more copies of itself and then reverted to a non living state to endure the harsh conditions of space. Very much like a virus.

BigDon
2012-Jun-25, 12:07 PM
Totally unrealistic. They grow ridiciulously fast with very little if any nutrition.

But they do inspire fear in every gamer when introduced into the plot line by a good Game Master and played along the lines of the first two movies, at least..

Nobody thinks they are "badder". Even high level hard cases that hunt vampires for sport hunker their shoulders and look at the shadows really hard. Even folks who think they are ready to take on Balrogs say "Crap." (or worse) under their breathes when the evidence for Very Bad Things becomes unignorable. Like the dessicated remains with tell-tale skeletal damage.

"Hmmm, either this guy ate a pound of bacon with every meal or he was killed by a chest burster..."

I had one group of gamers...

The gaming world I've been running since the mid-seventies has several advanced societies, not a few of which ingage in interdimensional exploration much like our world engages in space exploration.

And since the goverment in question had methods of remotely veiwing new locations before making a physical connection they were able to compile a list of places to go...and places not to go.

But goverments being goverments...

The no-go places we're concerned about in this game were places that had empty cities planet-wide. Makes all those salvage and intellectual property rights issues moot.

They wrote me up a list of their safety precautions that were quite impressive, starting with doing all operations on an offworld moonlet and a two week quarantine coming back, etc, etc..

This game got played about once or twice a month for almost three years before this teams luck led them to that last world. In the interum their exploits increased their home's tech level HUGELY. And there were some really close calls. Like playing hide and seek with Clankers AKA Berserker boarding units. Fortunately not only did the entire party have the pertunatural ability to move silently and hide in shadows, a requirement for joining this outfit, but their magical support leaned heavily on the stealth and misdirection magics.

Several times having to hold really, really still while robotic monstrosities scurried or hovered within meters of them. (they couldn't teleport through the hull material.)

Their reward was two auto-docs, which can fix anything still breathing and an archway that retightened and rebuilt your DNA, effectively returning you to twenty years old.

They recieved a lot of attention after that. Their budget exploded. They recieved permission to outfit with the cool weapons forbidden planet-side. And that was the second of 12 excursions total.

By the time their luck changed there were equipped with a plethora of weapons and armours and driving a soviet amphibious APC, either the BMP or the BTR I forget which. They had had the power plant removed and replaced with a dwarven made one the size of a toaster that burned coal. A lump of coal could get you a hundred miles at full speed. A diamond the same size would last for months.

Anywho.

So their last dead world they go to loot has smoked glass skyscrapers, airports, monorail systems, the works. And the players see dollar signs because the street signs translate as "Spaceport, twentyfive miles.".

Now the guys know I have a whole long hidden list of world ending disasters and didn't know which one won the draw this time.

The group's ranger/tracker correctly estimates this place has been dead for twelve or so years. The party as a whole drives out to a high point overlooking the city and they send out their two best scouts, the ranger and a wizard who astral projects.

The wizard found the bad news first.

Drifting around a street corner, wondering where the bodies of the people who lived here might be, (in case they were inclined to sneak up on him and try to eat him. Happens you know.) the wizard basically runs into one of the big gnarly soldier forms. It seemed to regard the normally undetectible astral projecting wizard as an item of curiousity and didn't try to attack. Nobody sitting at the table felt any better when, after about ten seconds, the xenomorph turned and disappeared rapidily down a storm drain.

Even astral, the wizard declined to follow.

The ranger hears about all this and tiptoes all the way back to the APC. And they all beat a hasty retreat back to their moonlet to plan this out, using their updated information.

The group is still up for this because they know I'm a firm believer in risk equaling reward and they see beaucoup risk galore.

Three of the eight players had been in straight up sci-fi campaign that included xenomorphs twice. They warned the other players, and I had to agree, xenomorphs seem to generate bad luck even in openly rolled encounters.

and the battles are always sudden, fast and very hectic. Bring your "A" game and your best toys.

Their whole premise is they aren't here to battle, rescue anyone or seek trophies. They were going to use a special device aquired at enormous risk that pinpointed the most valuable items in an area, go there at high noon in the APC, teleport to the locations directly, scoop the goodies, pop back to the APC, then get the heck gone before anybody is the wiser. They have guns, grenades and spells.

What could possible go wrong?

They didn't want to push their luck and stay longer than two hours, tops. Half hour into town, an hour of wholesale looting via teleporting, a half hour back.

They bomb into town to a large skyscraper, led by their treasure finding device. The wizard astral projects to the location, finds it clear of goobers and returns to his body. Then as a group they teleported up to the 110th floor of a high end research and developement corperation for some interdimensional copyrite infringement.

Than was the idea anyhow.

In complex games like this I use charts and graphs from multiple different role playing games that best suit both story telling and gaming.

So one of the guys asks to do a Weapons Check, which gave a +1 bonus when freshly done prior to the poop hitting the rotary air mover. A free stackable +1 bonus is nice, and with xenomorphs in the picture you go for every stacking bonus you came scramble for. The other three tanks all agreed this was a good idea as did the healer, wizard, ranger and sage (specialist, dead worlds).

Except...there is that mere 5 per cent chance you can dramatically blow the weapons check right out your keister. For instance...

The healer, armed with an M-16, had a rather inconvieniant, if not serious weapons malfunction and fired a long burst into the wizard, cutting him in half, from his right hipbone to just under his left ribcage.

Everybody was shocked speechless a moment. The above sentence being the product of about eight different roles and two wildly blown saving throws.

Once again, everybody was stunned speechless, mainly because the wizard was the only one who could teleport and they were 110 stories up in a xenomorph infested buiding.

Wow, what a bummer.

One of the tanks was an elf and I informed him that, indeed, "they heard that." and were beginning to stir.

So with the healer now on perminant point duty they try to get back down via the stairway and after descending three floors, and after losing the healer and one of the tanks, decide rapelling/traversing down the outside of the buiding sounded like a better solution.

They actually snuck down 40 floors before they got the attention of one on the inside. The firefight they needed to drive it off once again ratted them out to every xeno within half a mile. Sixteen more floors down and they had lost three more members. The remainder felt like sitting ducks and broke back into the the buiding. Leaving behind gnarly and expensive magical boobytraps as they went.

All the better to let me keep them informed as to how close the monsters were behind them.

The 20th floor and it's down to just my heavily armed friend, Ol' Weird Bob.

Getting down to the fifth floor involved him making three different saving throw or die situations. He had been flat-out snatched up, carried to the stairwell (and downward and before it could paralyse him he was able to discharge a preprepared spell, shocking grasp, that the now defunct wizard had given everyone. "Just in case something goes wrong."

This causes them both to fall down the center of the stairwell. But Bob's web gear hangs up on a railing after three floors while the xenomorph keeps falling.

But not far enough. It catchs itself after five more floors and starts to come back up for Bob, who is messed up, man-handled and brutalized. It was effortlessly snapping his limbs, (left arm, right leg) while he beat on it like an angry five year old.

Which, of course, made positive problem resolution difficult, not even counting the three story sudden stop and inverted position. More saving throws, these constitution based, that still gave him no more than a fifteen percent chance and he got a telling, one-handed burst off with his assault rifle.

Now while this may have hosed Sigourney Weaver, she didn't get to use healing potions!

Bob had six. He used two. And decided to risk the elevator. This surprising enough, worked for him.

and by he finally emerge in the parking garage he was completely out of ammo, spells and grenades. The only thing he had left was a .357 magnum revolver and two speed loaders.

18 rounds.

I rolled how far away that tiny rectangle of daylight was from him and came up with 330 yards.

In a blacked out parking garage, with abandonned cars and, of course, all sorts of overhead duct work and large exposed conduits.

And xenomorphs.

Well, two to be exact. and a .357 with 18 rounds is barely adaquate for one.

Bob makes it to the APC with one round and 6 of 57 hit points.

And gets all the way back to the portal.

And the guy on the portal watch is beautiful.

"Xenomorphs huh? And how long was your vehicle out of your sight? Sorry. I won't let it through. Park it over there and I'll let you through. Better hurry though."

This led to a lively across the table debate.I gave points to the gate watch on the premise of good role-playing.

Wish I could remember how that turned out.

publiusr
2012-Jun-29, 10:27 PM
Reminds me of a dream I had once. There the night sky was like the demi-urge--dripping substances down that would stand up and run. Shades of Kuttner's Zulchequon, an astronomer who had blinded himself was smashing a telescope mirror.

"Don't you understand?" he said.

"They're not stars--they're eyes!"

primummobile
2012-Jun-30, 08:55 PM
It's all about numbers. If you have enough alien worlds with life, there is some point where other humanoid-like organisms have evolved.

However, I would think that the chances of an intelligent alien life form evolving to a humanoid-like shape is not that outlandish.

I think that birds could have evolved to rival humans in intelligence, but they traded intelligence for flight. Flying requires much too high of a caloric intake to have the time to develop things like sophisticated tool-making skills. Marine mammals traded intelligence for their life under water. You could add to this list for quite a long time, I would think.

The most efficient means of locomotion for land-dwelling animals are legs. We could imagine all kinds of other means, but I can't think of anything other than legs that allow the control and ability to move in and around objects that legs provide. The most energy-efficient configuration is to have two legs. Intelligent creatures would need some appendage they could use to manipulate their environment, either directly or through the use of tools. One appendage would work, but I think that two is the optimal number. More than two appendages of this sort could be too energy-intensive to have an evolutionary advantage. They would need some biological mechanism to grasp objects. Mechanical grasping with some type of an opposable thumb is probably the most efficient means of doing that. An organism could grasp objects using something like vacuum pressure or electromagnetic attraction, but those require more energy and they are not as reliable as mechanical grasping.

They would need some place for their bodily function mechanisms, such as gas exchange, waste removal, energy consumption, and so on, to reside. (I obviously don't know how their bodies would consume energy, but I think it's a pretty safe bet that it would be from the immediate environment and that it would use chemical reactions to extract that energy) It would not be evolutionarily efficient to have the those mechanisms in their appendages. The loss of an appendage would mean death and therefore either no or less offspring. So that would require some type of a bodily mass, probably centered, where those mechanisms would reside.

So what we have is a centered mass with at least two appendages for locomotion and at least two appendages for manipulation of the environment. Evolutionary processes, at least on Earth, are very energy-conscious. Whatever organism is able to compete the best with the least expenditure of energy is usually the more successful. In fact, this is the reason nearly all organisms on Earth die. It takes less energy to create a new organism than what it takes to indefinitely maintain an existing organism. We don't know that this would be true elsewhere, but life is not going to evolve anywhere beginning with a fully-functioning intelligent being. That would imply offspring, and by necessity, death.

To be clear, I by no means think that I or anyone else have covered or even imagined all the different paths that life could take. And I am not saying that the always humanoid-like take we see in science fiction is even close to correct. All I am saying is that I don't believe that the chances of a body plan superficially similar to our own evolving independently are as small as what some people think.

Jeff Root
2012-Jul-01, 03:39 AM
I think that's a pretty good analysis and agree with your
conclusion.

One thing I'd make more clear is that the body plan
comes first and intelligence comes after. The body plan
could change after reaching intelligence, but in that case
I'd guess that the two become somewhat independant
of each other.

The two characteristics of humans that seem most likely
to have lead to our intelligence are communication and
using tools. Our ancestors may have communicated with
each other to hunt cooperatively. They used their hands
to use tools. At some point (probably way back) they
began communicating to each other (teaching) how to
use the tools. At that point there could have been a
greatly increased pressure for those who understood how
to use tools and could communicate the information to
others to survive, and for the others not to survive.

So they needed hands and an ability to make sounds or
other complex signals before they could start becoming
highly intelligent.

I think bilateral symmetry is highly likely in any creature
that becomes intelligent. Four legs would seem to be a
very likely starting point, though, so I'd expect four-legged
intelligent people to be at least as common as two-legged.
If you have four legs, four arms might come with. There's
no obvious place to attach another set of arms to humans,
but if you're built more like an ant or a spider, it could be
easier.

-- Jeff, in Minneapolis

Selfsim
2012-Jul-01, 05:33 AM
All I am saying is that I don't believe that the chances of a body plan superficially similar to our own evolving independently are as small as what some people think.I think that's a pretty good analysis and agree with your conclusion.The conclusion is identical to the premise, and if things were different, they would be different ...

So many words so much philosophy so little science !

eburacum45
2012-Jul-01, 09:42 AM
...I don't believe that the chances of a body plan superficially similar to our own evolving independently are as small as what some people think.
Well, it all depends on how superficially similar you mean. A creature with two legs, two manipulating appendages and some kind of encephalisation could look very dissimilar to a human. The bodyplan of a kangaroo or a tyrannosaur would also fit the bill, and both of those creatures are quite closely related to humans.

There are no vertebrates anywhere else in the universe apart from here, unless they have been taken there from Earth; there may be creatures with some sort of backbone out there that resemble vertebrates in some, or many ways, but they will have a completely separate origin and evolutionary history. If we ever encounter such creatures, it seems likely that we will be more aware of their differences from Earth life than the similarities, and this may be even more true if they resemble humans even superficially.

primummobile
2012-Jul-01, 02:07 PM
The conclusion is identical to the premise, and if things were different, they would be different ...

So many words so much philosophy so little science !

Science is the systematic study of the universe with the goal of producing testable explanations and predictions about what we observe. Since we have never studied any type of life outside of our own world, that automatically places speculation about how alien intelligence will look squarely into the ring of philosophy.

But we do know that intelligent beings would need a means of independent locomotion as well as a way to manipulate their environment. I don't doubt that there aren't many different ways that could be accomplished. All I am saying is that the general layout of our bodies gives us pretty proficient ways of doing that. If you disagree, please explain yourself. Hit and run statements dismissing everythin I said aren't very conducive to either one of us learning anything. I'm an engineer, not a biologist. So I'm open to listening to what those more knowledgeable than I have to say about it, but you have to say something about it if you want me to listen.

primummobile
2012-Jul-01, 02:19 PM
Well, it all depends on how superficially similar you mean. A creature with two legs, two manipulating appendages and some kind of encephalisation could look very dissimilar to a human. The bodyplan of a kangaroo or a tyrannosaur would also fit the bill, and both of those creatures are quite closely related to humans.

There are no vertebrates anywhere else in the universe apart from here, unless they have been taken there from Earth; there may be creatures with some sort of backbone out there that resemble vertebrates in some, or many ways, but they will have a completely separate origin and evolutionary history. If we ever encounter such creatures, it seems likely that we will be more aware of their differences from Earth life than the similarities, and this may be even more true if they resemble humans even superficially.

Yes a T Rex is superficially similar to us. It walked upright on two legs and had two arms and a head with sensory organs. You'll notice that I was silent on alien intelligence having a head. I would consider anything that walks upright and has arms to be superficially similar to us.
The point to it having only two "arms" and two "legs" is that two is probably the lower bound for usefulness and that it is more energy efficient to grow and then use two than what it is to grow and use three or four. I never said anything about vertebrae or any other internal structures other than that aliens would need a way to consume energy and excrete the byproducts.

The point was that aliens who walk upright on "legs" and have "arms" isn't that farfetched.

Selfsim
2012-Jul-01, 11:21 PM
Science is the systematic study of the universe with the goal of producing testable explanations and predictions about what we observe. Since we have never studied any type of life outside of our own world, that automatically places speculation about how alien intelligence will look squarely into the ring of philosophy.

But we do know that intelligent beings would need a means of independent locomotion as well as a way to manipulate their environment. I don't doubt that there aren't many different ways that could be accomplished. All I am saying is that the general layout of our bodies gives us pretty proficient ways of doing that. If you disagree, please explain yourself. Hit and run statements dismissing everythin I said aren't very conducive to either one of us learning anything. I'm an engineer, not a biologist. So I'm open to listening to what those more knowledgeable than I have to say about it, but you have to say something about it if you want me to listen.Greetings primummobile!
My post contained observations. I didn't dismiss anything.
Feel perfectly free to pursue the knowledge you seek .. we're all in that pursuit together.
Selective listening however, would seem to be a sure way to miss knowledge of what is not known.
Regards

Noclevername
2012-Jul-02, 12:34 AM
The humanoid shape of the Xenomorphs is only one factor. The many other specific characteristics (they can gestate in and digest human, canine and alien bodies, absorb genetic material from their host no matter what species, secrete a corrosive deadly to all their hosts, have a two-stage reproductive process (haploid/diploid?) with only one form being humanoid and the other a vaguely arthropodal stage etc.) all add cumulatively to the massive genetic and physiological complexity required for such a lifeform, and thus the more things that can go wrong and inhibit its survival.

primummobile
2012-Jul-02, 01:10 AM
Greetings primummobile!
My post contained observations. I didn't dismiss anything.
Feel perfectly free to pursue the knowledge you seek .. we're all in that pursuit together.
Selective listening however, would seem to be a sure way to miss knowledge of what is not known.
Regards

I wasn't trying to imply that I wouldn't listen to you. I was merely stating that, by definition, any talk of alien life is usually not very scientific. I am just speculating about why humanoid forms may not be that uncommon.

Like I said I'm an engineer, not a biologist. So I don't understand evolution the way some people do. But I am involved in quite a bit of robotics work and I can tell you that the best ways we have found to do things are based on human anatomy. Yes, evolution has no end result and is based entirely upon chance happenings. But if given long enough, pretty efficient designs are going to arise. But as engineers, we don't have to rely on chance happenings. The best way we have found for a robot to grasp is by giving them arms with hands on the end. (If the robot isn't just grasping the same thing again and again.) The best way we have found of making it possible for a machine to traverse uneven land is to give it legs. Altogether, it's a pretty good design that happened relatively quickly on Earth, and given enough habitable planets, I think it likely it would repeat itself. I'm not even trying to guess the odds of it happening, I'm just saying that I believe if an alien spaceship landed on Earth we would be more likely to see a being walking out on legs rather than a squid sliding along the ground leaving a slime trail.

I'm just judging this from my personal experience, and I think you would agree that it is impossible for an observer to have no bias. But in my personal experience, if I were to design an intelligent being it would not be all that different from us if it was to be a land-dweller.

eburacum45
2012-Jul-03, 08:29 AM
... if I were to design an intelligent being it would not be all that different from us if it was to be a land-dweller.
Then again, a creature resembling a theropod or a kangaroo, not necessarily with a definable head or backbone, would fit the rough definition of 'a creature with a minimum of two manipulatory appendages and two locomotary appendages'; this is rather pushing the boundaries of the term 'humanoid' somewhat.

primummobile
2012-Jul-03, 09:22 AM
Then again, a creature resembling a theropod or a kangaroo, not necessarily with a definable head or backbone, would fit the rough definition of 'a creature with a minimum of two manipulatory appendages and two locomotary appendages'; this is rather pushing the boundaries of the term 'humanoid' somewhat.

The point was that if two legs and two arms is an efficient design then there would probably be beings who are rather humanoid looking.

You were talking about T. Rex the other day, weren't you? Take a T. Rex and make his arms a little larger and more functional. Lose his tail. Maybe shrink him a little. Now you're looking at one pf the invaders from 'V', which is quite a bit more similar to us than to a dinosaur.

primummobile
2012-Jul-03, 11:39 AM
Let me try to make this a little more clear. I haven't heard anyone say that the general humanoid 'design' is not an efficient one. If anyone has any counter-argument to that I would really appreciate hearing it.

I'm going to make some assumptions here. I know that assumptions are very very bad, but if we don't make any assumptions we can't have a meaningful conversation about this.

Let's assume that there is, on average, one intelligent species per galaxy. Let's further assume that there are 100 billion galaxies in the observable universe. So, we have 100 billion intelligent species in the observable universe.

Now, let's stop there for a second. Obviously, evolution does not follow any design. But what evolution does do is try out a whole lot of different things so that the "end" result seems like it was designed. Let's further assume that having appendages that function like legs and arms is beneficial and efficient. So much so, that this body plan arises 5% of the time. Let's further assume that there are twenty different ways for this body plan to be accomplished effectively, and that one of those is humanoid. That would mean that there are 250 million other intelligent humanoid species in the observable universe.

Obviously, this is entirely speculative---from the first assumption to the last. Any of those being wrong (which they most undoubtedly are) could throw the final number off either way by several orders of magnitude. But I don't think that the logic is any more tortured than the logic that Tyson, and formerly Sagan, uses to speculate that the humanoid body style is very unlikely.

I used to spend a great deal of time reading Carl Sagan's books. I have a lot of respect for him. But when he was discussing the possibility of alien life, it was sometimes difficult for me to get past his pontificating about humanity and find the science in his work. Especially in his later years, Sagan seemed to have a pretty strong disdain for humanity. I can't help but think that that disdain colored his judgement when he spoke of what forms alien intelligence could take.

I, on the other hand, am pretty impressed by what humans have accomplished in the 50,000 years since we have reached full behavioral modernity. Of course, that may color my judgement the other way. I don't know. As Selfsim pointed out, this is more philosophy than science. So, it is my belief that the humanoid form would not be as rare as Tyson or Sagan would have you think.

eburacum45
2012-Jul-03, 02:58 PM
The devil is in the details. The great difference between a theropod or a kangaroo and a human is the angle of the backbone; tyrannosaurs and kangaroos have a horizontal spine, with a balancing tail and forward pointing head, while humans have an erect spine. The 'erect biped' bodyplan is quite rare in the animal kingdom, with the only examples I know of being the hominids and the penguins; on the other hand a horizontal or near horizontal spine is common among archosaurs, birds and mammals.

I suspect that even among the set of intelligent bipedal aliens, the erect spine is a relative rarity; we might be more likely to meet aliens with cantilevered horizontal bodies than precariously upright bodies, if the history of life on Earth is anything to go by. Cantilevered bipeds don't seem very humanoid to me, unless one compares them to a flying squid or worse.

eburacum45
2012-Jul-03, 03:08 PM
Having said that, the Xenomorph bodyplan is considerably more horizontal than a human's; it is often depicted as crawling along on all fours.

Perhaps the strangest feature is the elongated crest at the back of the head- possibly this crest exists in order to house the long 'mask'-like proboscis or telescopic jaws that it uses to good effect. Quite how it swallows food through these long jaws, or how it sees with no eyes, is a mystery.

primummobile
2012-Jul-03, 07:22 PM
The devil is in the details. The great difference between a theropod or a kangaroo and a human is the angle of the backbone; tyrannosaurs and kangaroos have a horizontal spine, with a balancing tail and forward pointing head, while humans have an erect spine. The 'erect biped' bodyplan is quite rare in the animal kingdom, with the only examples I know of being the hominids and the penguins; on the other hand a horizontal or near horizontal spine is common among archosaurs, birds and mammals.

I suspect that even among the set of intelligent bipedal aliens, the erect spine is a relative rarity; we might be more likely to meet aliens with cantilevered horizontal bodies than precariously upright bodies, if the history of life on Earth is anything to go by. Cantilevered bipeds don't seem very humanoid to me, unless one compares them to a flying squid or worse.

I imagine you are probably correct. This whole discussion seems to boil down to what you would be willing to call a "humanoid" or " similar to a humanoid". My natural bias is to look for similarities rather than differences while other people would approach it differently. That being said, I still find this intensely interesting.

Do you think an erect spine would be a better load-bearing structure than a horizontal spine? I would think the trend in bipedal evolution would be toward no tail and an erect stance.

eburacum45
2012-Jul-03, 09:31 PM
Well, there were thousands of species of theropods and ornithopods and none of them evolved an erect stance. Only a few birds and mammals are erect, so it seems to evolve quite infrequently.

I wouldn't like to correlate an erect stance with sentience or sophonce without more data.

transreality
2012-Jul-04, 12:21 AM
Let me try to make this a little more clear. I haven't heard anyone say that the general humanoid 'design' is not an efficient one. If anyone has any counter-argument to that I would really appreciate hearing it.

So, it is my belief that the humanoid form would not be as rare as Tyson or Sagan would have you think.

If it is so efficient why is it so rare. Arthropods, molluscs etc have been around for half a billion years just like chordates, why haven't they produced lots of humanoid forms. Even something like a praying mantis is only very superficially humanoid like. They've been big (insects anyway), they've been terrestrial. The thing is the humanoid form is reliant on lots of pre-adaptions and most of those are contingent in nature. Dinosaurs do it with hollow bones and efficient metabolisms, humans do it with specialised skeleton and complex nervous and balance systems. Looks to me statistically speaking, the more legs the better.

cathal
2012-Jul-04, 12:12 PM
...Perhaps the strangest feature is the elongated crest at the back of the head- possibly this crest exists in order to house the long 'mask'-like proboscis or telescopic jaws that it uses to good effect. Quite how it swallows food through these long jaws, or how it sees with no eyes, is a mystery.

Perhaps both these questions have the same answer; echolocation. The structure might be a structured sound focusing medium, allowing separation of frequencies and selective active dampening. The Xenomorph has always seemed to prefer darkness, and its colouring seems dark-adapted. The jaws seem to be mostly used offensively.

WRT pressures to resemble humans. Another intelligent species might be bouyant bags with hundreds of manipulatory tendrils, or a parasite on a pack eusocial centipede-style mammals. It's a chaotic system, and only when already very near humans can the pressures even be suggested to push towards us. Frankly, I wish our ancestors had spent a few million years dominating a niche and developed intelligence there, so we solved some of these body-plan issues like spine and knee problems, but that's not how it happened.

An alien intelligence could be equally as poorly adapted. Imagine something like our cephalopods experiencing pressure due to a aridifying climate. They adapt by clumsily splashing from puddle to puddle and experience a pressure toward intelligence by being able to increase their survival probability cooperatively building ever more sophisticated watertraps and engaging in trade. Finally they build the greatest watertrap of their species' history... in space. They have an instant advantage over us in both radiation resistance (water shielding) and acceleration tolerance (being of the same density as their surrounding medium.) They also have the experience working in environment suits that they developed during their renaissance, when they realised that the enormous desert surrounding their ecology wasn't shielding them from water-stealing shark-like demons but from an enormous, if somewhat over-salty, ocean.

There are such a ridiculous number of input variables, from biochemistry to environment that it would be absurd to imagine our form as anything more than one island of stability amongst many in a very choppy sea .

primummobile
2012-Jul-04, 07:08 PM
Well, there were thousands of species of theropods and ornithopods and none of them evolved an erect stance. Only a few birds and mammals are erect, so it seems to evolve quite infrequently.

I wouldn't like to correlate an erect stance with sentience or sophonce without more data.

I don't think we would have developed intelligence if we did not have limbs that were not needed for locomotion.

And I just wanted to know your thoughts on the load-bearing abilities of an erect spine versus a horizontal spine.

primummobile
2012-Jul-04, 07:13 PM
Well, there were thousands of species of theropods and ornithopods and none of them evolved an erect stance. Only a few birds and mammals are erect, so it seems to evolve quite infrequently.

I wouldn't like to correlate an erect stance with sentience or sophonce without more data.

I'm not speaking of all animals. No land animal on this planet with anything even approaching intelligence has any more than four limbs. The most intelligent animals are all able to walk upright, even for only a short distance, so their hands can be freed to use as tools. The exception is the elephant, but they have a trunk with digits. How succesful do you think humans would have been if we had our brains in the bodies of dogs?

ZunarJ5
2012-Jul-12, 07:59 PM
I'm not speaking of all animals. No land animal on this planet with anything even approaching intelligence has any more than four limbs. The most intelligent animals are all able to walk upright, even for only a short distance, so their hands can be freed to use as tools. The exception is the elephant, but they have a trunk with digits. How succesful do you think humans would have been if we had our brains in the bodies of dogs?

First, I want to say that I agree with you for the most part on your stance regarding the probability of humanoid-like intelligent life in the universe.

I did just want to point out that crows and ravens are among the most intelligent animals on earth and have only their beak with which to manipulate tools.

ravens_cry
2012-Jul-14, 10:51 PM
I did just want to point out that crows and ravens are among the most intelligent animals on earth and have only their beak with which to manipulate tools.
They also use their feet to a degree I believe.

primummobile
2012-Aug-09, 05:27 PM
First, I want to say that I agree with you for the most part on your stance regarding the probability of humanoid-like intelligent life in the universe.

I did just want to point out that crows and ravens are among the most intelligent animals on earth and have only their beak with which to manipulate tools.

Yes, I should have probably said "mammals" instead of "animals". Thanks for the correction.

eburacum45
2012-Aug-10, 08:29 AM
I would, as always, caution against the use of the word 'humanoid' when describing aliens. Even bipedal aliens with two arms and some sort of head-like arrangement are likely to look very different to anything on Earth; the fact that they have some remote resemblance to humans will probably make them look more unsettling, rather than more familiar.

Jeff Root
2012-Aug-10, 04:37 PM
Why not the word 'humanoid'? Do you have an alternative?

-- Jeff, in Minneapolis

eburacum45
2012-Aug-10, 06:22 PM
I wouldn't call a velociraptor or a tyrannosaur humanoid, but they would almost certainly resemble a human much more closely than most bipedal alien species.

primummobile
2012-Aug-14, 07:35 PM
I really don't want to rehash this, but I believe I said 'humanoid-like'. I think I specifically said it would be more likely for intelligent life to resemble us, even superficially, than it would be for intelligent life to resemble a squid leaving a slime trail on the ground.

It was just a thought experiment and that's all. I was just assuming a terrestrial creature that is intelligent. And again, I never made the claim it was likely for them to resemble us. I said that it was probably not as unlikely as some may think. If you've ever listened to people like Carl Sagan or his disciples, they are so anti-geocentric that I think it clouds their judgement sometimes and so they take it to the opposite extreme. I've read that there is virtually no chance of there being similar beings elsewhere in the universe. I think that's taking it too far, and I gave the reasons why I think that.

A velociraptor may have had a branch diverge into the Gorn instead of birds. The Gorn I've seen are all pretty humanoid-looking to me.

Noclevername
2012-Aug-14, 09:02 PM
I really don't want to rehash this, but I believe I said 'humanoid-like'. I think I specifically said it would be more likely for intelligent life to resemble us, even superficially, than it would be for intelligent life to resemble a squid leaving a slime trail on the ground.

It was just a thought experiment and that's all. I was just assuming a terrestrial creature that is intelligent. And again, I never made the claim it was likely for them to resemble us. I said that it was probably not as unlikely as some may think. If you've ever listened to people like Carl Sagan or his disciples, they are so anti-geocentric that I think it clouds their judgement sometimes and so they take it to the opposite extreme. I've read that there is virtually no chance of there being similar beings elsewhere in the universe. I think that's taking it too far, and I gave the reasons why I think that.

A velociraptor may have had a branch diverge into the Gorn instead of birds. The Gorn I've seen are all pretty humanoid-looking to me.

Well, let's look at Earth. The Cambrian Explosion produced multicelled life in every imaginable and some unimaginable forms. Of those, only a handful of animal types are alive today. One of those few lines of developments led to vertebrates, and to us. Now imagine if one slight difference in environment or mutation had not produced that specific line. All "humanoid" life would never have developed, and something else would have taken those niches. Alternately, suppose another line had survived and out-competed ours by just a little bit, then went on to become the dominant species; if cephalopods had developed, say, air-breathing just slightly before we did. Today some Squibbon scholar would be saying "well, it's unlikely that dry-skinned tetrapods could become sapient".

Evolution is a crapshoot. It uses whatever shape works for survival.

primummobile
2012-Aug-14, 09:34 PM
Well, let's look at Earth. The Cambrian Explosion produced multicelled life in every imaginable and some unimaginable forms. Of those, only a handful of animal types are alive today. One of those few lines of developments led to vertebrates, and to us. Now imagine if one slight difference in environment or mutation had not produced that specific line. All "humanoid" life would never have developed, and something else would have taken those niches. Alternately, suppose another line had survived and out-competed ours by just a little bit, then went on to become the dominant species; if cephalopods had developed, say, air-breathing just slightly before we did. Today some Squibbon scholar would be saying "well, it's unlikely that dry-skinned tetrapods could become sapient".

Evolution is a crapshoot. It uses whatever shape works for survival.

I don't think that it's entirely a crapshoot. Whatever form is the most efficient with the fewest resources (such as food for the mother) needed to develop is going to win out. Whatever form can survive the best on the fewest resources is going to be superior, with all other things being equal. If we had four legs we would probably be superior to what we are now, but we would need to consume more calories to survive which would have put us at a disadvantage to our two-legged counterparts back when it was a struggle to find food.

I've been through all of this earlier in the thread. I'm not saying that humanoid-like life is likely to be encountered. I'm saying that others have said that the chances are nil that it has devloped elsewhere. I'm just saying that maybe it's not nil. Maybe the probability is .0000000001 that it would develop as the dominant form of life on an earth-like planet. I realize that there are a lot of ways for life to evolve, especially given all the options. But given enough time, you are going to find organisms that are exceedingly fit to physically survive in their environment. Our shape is exceedingly fit to survive on Earth, and you'd be hard pressed to identify a more fit form for us to take.

It should also be noted that when I say 'humanoid-like' I'm not referring to something that would have to be a vertebrate. I think in my first post on this I said that legs are the most efficient method of land locomotion we have discovered. (if you don't have naturally occuring roads to travel) In addition, it seems that one leg would not be very useful and three legs are one more than you need, which would mean extra energy required to maintain that leg. Intelligence would need something with which to grasp and manipulate objects in their environment, which would be something like a hand. There are other ways, yes, but a hand is the most universal tool for grasping objects. Some animals may evolve vacuum pressure to pick up objects, but as soon as something with a hand came along it would out-compete them. I also said that vital organs spread throughout the body would not be advantageous because the loss of a body part could mean death. A one-legged woman can still reproduce. If you heart was in your leg, losing a leg and surviving would not be an option.

My definition of humanoid-like was any being with a center mass, something like a head, something like two arms with hands, and something like two legs. Because its arms would need to be free to manipulate the environment it would probably walk upright.

It's also likely that life developed independentally many times in the early Earth. I don't think it likely that the first self-replicating molecule just happened to be RNA and we stuck with that. But with that in mind, it could mean that RNA-DNA is a very efficient means of carrying genetic information compared to some of the other possibilities that may exist. Therefore, given the same intitial conditions, it's not outlandish to think that something similar to DNA would eventually evolve.

On the other hand, what you said is true. Life doesn't need to be the most fit to survive and pass along its genes. It merely needs to be fit enough to survive and pass genes. That means that probably almost all of the time we would expect to find life quite different from what we have here. All I'm saying is that given enough time, you're bound to get organisms that are more fit than what came before. Given my belief that the humanoid form is very fit for intelligent organisms, I don't think it's unreasonable to say that we probably aren't the only humanoid-like organisms in the universe. Of course, that's assuming that intelligent life has developed elsewhere.

I think you're reading more into what I'm saying than what I am really saying. But unless you're talking to me about electrical engineering, scuba diving, or motorcycles I'm usually pretty non-committed in what I say. My speculation is much more along the lines of what could happen rather than what does or is likely to happen. In this case, I'm saying that humanoid-like life developing elsewhere from similar initial conditions isn't as impossible as some would believe.

ravens_cry
2012-Aug-14, 09:35 PM
I don't think we are that likely to see complex tool using intelligence that doesn't have some kind of manipulator.
A manipulator could be a tentacle, a trunk, a hand like appendage, a prehensile tail, a claw beak combination or something else entirely.
I wonder how common a centauroid body plan will be, a centauroid being a creature whose manipulators did not evolve from a locomotive limb. For example, an elephant's trunk.

Noclevername
2012-Aug-14, 10:18 PM
My speculation is much more along the lines of what could happen rather than what does or is likely to happen. In this case, I'm saying that humanoid-like life developing elsewhere from similar initial conditions isn't as impossible as some would believe.

Not impossible, no, but-- and I'm sure you've heard this argument before-- living things are like snowflakes, they melt if it gets too warm. Or something like that. ;)

primummobile
2012-Aug-14, 11:27 PM
Not impossible, no, but-- and I'm sure you've heard this argument before-- living things are like snowflakes, they melt if it gets too warm. Or something like that. ;)


I thought they melt if they get wet.

primummobile
2012-Aug-14, 11:32 PM
I don't think we are that likely to see complex tool using intelligence that doesn't have some kind of manipulator.
A manipulator could be a tentacle, a trunk, a hand like appendage, a prehensile tail, a claw beak combination or something else entirely.
I wonder how common a centauroid body plan will be, a centauroid being a creature whose manipulators did not evolve from a locomotive limb. For example, an elephant's trunk.

I agree with that. In fact, I think I used the example of an elephant trunk earlier in this thread.

ravens_cry
2012-Aug-15, 01:26 AM
I agree with that. In fact, I think I used the example of an elephant trunk earlier in this thread.
Why bless my soul and whiskers, you did.:)

JCoyote
2012-Aug-18, 03:54 PM
I don't think that it's entirely a crapshoot. Whatever form is the most efficient with the fewest resources (such as food for the mother) needed to develop is going to win out.

I initially agree with the idea but when I look at the Cambrian explosion a few things occur to me.

1: Establishment is strength. An established successful organism in its niche is hard to displace by different organisms that would share its niche. An organism could be more efficient, but if not initially present in large enough numbers could fail and go extinct. There is strength in numbers, breeding partners and territory control.

2: Failure to succeed in the environment is not purely based on body morphology. Some body formats may have been superior in some ways, but appeared in lineages with insufficient defense against disease, inadequate processing of useful available proteins, etc.

All I'm saying is it is more complex than just body shape, and once something succeeds even marginally it is hard to displace. I've said it before, nonlethal mediocrity is a valid outcome in selection.

primummobile
2012-Aug-18, 04:16 PM
I initially agree with the idea but when I look at the Cambrian explosion a few things occur to me.

1: Establishment is strength. An established successful organism in its niche is hard to displace by different organisms that would share its niche. An organism could be more efficient, but if not initially present in large enough numbers could fail and go extinct. There is strength in numbers, breeding partners and territory control.

2: Failure to succeed in the environment is not purely based on body morphology. Some body formats may have been superior in some ways, but appeared in lineages with insufficient defense against disease, inadequate processing of useful available proteins, etc.

All I'm saying is it is more complex than just body shape, and once something succeeds even marginally it is hard to displace. I've said it before, nonlethal mediocrity is a valid outcome in selection.

I don't disagree with any of that. In fact, that's why I don't think there will be any significant steps in human evolution unless we leave the planet or most of us die off. We're too fearful of anything different to allow that to happen.

SkepticJ
2012-Aug-27, 07:42 PM
. . . or how it sees with no eyes, is a mystery.

Is it necessarily true that a large creature would have large camera eyes? What about patches of compound eyes? Maybe evolved* phased arrays?

*Or not, in the case of the created Xenomorphs.

publiusr
2012-Aug-27, 10:47 PM
With that dome for a head--I would think sound as vision

SkepticJ
2012-Aug-28, 09:54 PM
The real answer, of course, is that the lack of eyes makes it creepier. Alien being a horror movie.

H.R. Giger's original art, Necronom IV, had eyes.

Jeff Root
2012-Aug-29, 05:31 PM
Could you provide a link to an image of one of these
eyeless movie aliens? I'm confused now as to which
alien (or possibly aliens) you are referring to.

-- Jeff, in Minneapolis

SkepticJ
2012-Aug-29, 08:32 PM
Could you provide a link to an image of one of these
eyeless movie aliens? I'm confused now as to which
alien (or possibly aliens) you are referring to.

-- Jeff, in Minneapolis

The movie is called Alien. It's from 1979. Starred Sigourney Weaver, Ian Holm, and others. Directed by Ridley Scott

It had a sequel called Aliens. 1986. Sigourney Weaver, Michael Biehn, Paul Reiser, and others. Directed by James Cameron.

The aliens, or xenomorphs, in these movies lack visible eyes.

The movie Prometheus is set in the same universe as the above two fine films, as are four other movies that aren't worth the film they were recorded on.

Strange
2012-Aug-29, 09:03 PM
The real answer, of course, is that the lack of eyes makes it creepier.

Oooh. I had never noticed that before. The things you learn on BAUT/CQ.

eburacum45
2012-Sep-01, 09:54 AM
With that dome for a head--I would think sound as vision
This would be more reasonable if the Alien were an aquatic animal. Dolphins use the 'melon' organ in their large domelike head as a lens to focus their sonar emissions. However I'm pretty sure this wouldn't work very well in air. The density of the air is much lower, so the focus of the lens structure would be all wrong.
According to this wiki page,
http://en.wikipedia.org/wiki/Melon_(whale)
one function of the melon is 'impedance matching'; specifically 'creating a similarity between characteristics of its tissue and the surrounding water, so acoustic energy can flow out of the head and into the environment with the least loss of energy'. The Alien's head would need to be quite differently arranged to match impedance with the surrounding air, and it would need big ears to recieve the echoes too.

eburacum45
2012-Sep-01, 10:19 AM
The Xenomorph's stance has some differences to the normal human 'erect biped' stance,or so it seems to me; it often seems to move in a crouching fashion, and it has a long tail, which would probably impede a fully erect walking motion in any case. No doubt the 'crouching' is just another example of an attempt to make it look creepier, but when I saw the film on its first release the scariest moments came when the monster was mostly concealed; it could have been almost any shape for most of the film.

ravens_cry
2012-Sep-03, 09:41 PM
I found the almost, but also certainly not, human teeth and jaw to be the scariest part, especially when connected to the lack of visible eyes.

Joe13
2013-May-29, 08:20 PM
Totally unrealistic. They grow ridiciulously fast with very little if any nutrition.

Evolutiononaly it is possible for a creature to evolve that can grow that quickly, we have some examples on Earth like some types of insects.

Seaumas
2013-May-30, 12:25 AM
Hey, if you want to be in the movies you have to look a little recognizable. Just kidding. They were probably designed with insects in mind. I'm sure an entymologist and an arachnidologist were involved with H.R. Giger back there drawing like mad. If you think they look too human, then check out a preying mantis.

TooMany
2013-May-30, 09:46 PM
I don't think that it's entirely a crapshoot. Whatever form is the most efficient with the fewest resources (such as food for the mother) needed to develop is going to win out.

There is considerable evidence of convergent evolution that probably occurs for this very reason. Some things work better than others.

The eye of an octopus and the human eye have evolved independently but are remarkable similar.

The main difference in these eyes is that in an octopus, the nerves that do pre-processing and transmit signals from the retina to the optic nerve are behind the retina. In humans, the arrangement is opposite which results, for example, in our blind spot. So actually the octopus eye is more efficient. This difference is an accident of evolution. Such a major difference is unlikely to change. And yet other than this, the two "designs" are virtually the same.

I just read an article that says that it is possible that "comb" jellyfish have evolved muscles and nerves independently from other animal forms. The suspicion comes from major differences in genetic structures between these jellyfish and all other animals. If true, this may change some people's view about how random evolved systems are and demonstrate that multiple paths can lead to similar structures that evolve simply because they are effective.

TooMany
2013-May-30, 10:06 PM
I don't think we are that likely to see complex tool using intelligence that doesn't have some kind of manipulator.
A manipulator could be a tentacle, a trunk, a hand like appendage, a prehensile tail, a claw beak combination or something else entirely.
I wonder how common a centauroid body plan will be, a centauroid being a creature whose manipulators did not evolve from a locomotive limb. For example, an elephant's trunk.

Crows are amazing dexterous with their beaks and elephants with their trunks. But these types of appendages are far less dexterous than our hands.

It's a bit difficult to imagine an octopus-like set of appendages that would be more dexterous than a couple of hand-type appendages. Using a large number of "fingerless" appendages to get the same dexterity as a single main appendage with fingers may not be biologically economical. It is things like this that make an argument for advanced creatures that are more human like than many of the strange creatures that live in the ocean or others that we might imagine.

My suspicion is that we have hands because of our arboreal ancestors who climbed in the trees and picked fruit. This also accounts for our good binocular and color vision. Both are necessary to make brain development a huge advantage (the advantage being tool-making).

If you accept that it is likely that trees evolve on alien worlds, then you might make an argument that intelligent life will evolve from tree dwellers for the same reasons it did here.

When I see things like the six-legged horses in Avatar, I can't help but notice that they don't seem to provide any particular advantage over four.

The four-limbed plan is very old, perhaps it persists not just by accident.

Spacedude
2013-Jun-04, 09:39 PM
If Xenomorphs do exist (what's not possible?, we hardly know that yet) I'm just glad they can't build spaceships. They always hitch a ride.

MVAgusta1078RR
2013-Oct-09, 07:05 AM
I thought the xenomorphs were created by the Engineers as a sort of bioweapon. Like Umbrella's creations in Resident Evil. So isn't it kind of pointless to try to see how realistic they are to something that nature made when they weren't even created by nature. We genetically engineered glow in the dark puppies in Korea. An alien civilization thousands of years ahead of ours probably could genetically engineer something like the xenomorphs or even better.

Noclevername
2013-Oct-12, 10:13 AM
Crows are amazing dexterous with their beaks and elephants with their trunks. But these types of appendages are far less dexterous than our hands.

It's a bit difficult to imagine an octopus-like set of appendages that would be more dexterous than a couple of hand-type appendages. Using a large number of "fingerless" appendages to get the same dexterity as a single main appendage with fingers may not be biologically economical. It is things like this that make an argument for advanced creatures that are more human like than many of the strange creatures that live in the ocean or others that we might imagine.

My suspicion is that we have hands because of our arboreal ancestors who climbed in the trees and picked fruit. This also accounts for our good binocular and color vision. Both are necessary to make brain development a huge advantage (the advantage being tool-making).

If you accept that it is likely that trees evolve on alien worlds, then you might make an argument that intelligent life will evolve from tree dwellers for the same reasons it did here.

When I see things like the six-legged horses in Avatar, I can't help but notice that they don't seem to provide any particular advantage over four.

The four-limbed plan is very old, perhaps it persists not just by accident.

Evolution is not engineering. It uses what is available, not what is most efficient. The four limbed plan is limited to a single line of development-- vertebrates. We have four limbs because early fish happened to have four limbs. And that didn't give them a notable advantage of tool use or tree climbing, it was luck of the draw. If our ancestors had tentacles, we'd have tentacles.

To paraphrase a popular saying, whatever genes don't kill you get passed on to your descendants.

eburacum45
2013-Oct-13, 12:04 AM
Crows are amazing dexterous with their beaks and elephants with their trunks. But these types of appendages are far less dexterous than our hands. But on another world there may be creatures with trunks that have opposable finger-thumb analogs, and so on. And I would expect there to be a large variation in mouthpart dexterity; arthropods have complex mouthparts which have evolved from limbs, and an alien with an array of enlarged mandibles and maxillae might use these in very complex ways.


It's a bit difficult to imagine an octopus-like set of appendages that would be more dexterous than a couple of hand-type appendages. Using a large number of "fingerless" appendages to get the same dexterity as a single main appendage with fingers may not be biologically economical. It is things like this that make an argument for advanced creatures that are more human like than many of the strange creatures that live in the ocean or others that we might imagine. Molluscs have numerous structures which could evolve into useful manipulators- as well as tentacles, squid have both arms and beaks, and gastropods have radulae which can be very complex. But of course molluscs are only found on Earth, so this sort of comparison can only work as an analogy.


My suspicion is that we have hands because of our arboreal ancestors who climbed in the trees and picked fruit. This also accounts for our good binocular and color vision. Both are necessary to make brain development a huge advantage (the advantage being tool-making). This might be only one of a very large number of circumstances that would allow advanced toolmaking to develop. Circumstances on other worlds could be very different.


If you accept that it is likely that trees evolve on alien worlds, then you might make an argument that intelligent life will evolve from tree dwellers for the same reasons it did here. Some nesting behaviour in birds is so complex that I wonder if this might lead to culture on other worlds which have forests - but the details could be very different indeed to Earth life.


When I see things like the six-legged horses in Avatar, I can't help but notice that they don't seem to provide any particular advantage over four. On a high gravity super-earth, six legs could be very useful. The thing that annoys me about Pandoran evolution is that the six-legged monkey-things evolved into humanoids with perfectly normal proportions and skeletal/muscular arrangements. This would not happen.


The four-limbed plan is very old, perhaps it persists not just by accident.Tetrapods might be very common on planets that are exactly like the Earth, but planets come in a very wide range of shapes and sizes, with different densities and mineral compositions, different atmospheric densities, windspeeds and atmospheric physics, different hydrosphere compositions, depths and percentage cover, different degrees of geophysical activity and impact history, different orbital characteristics and obliquities, digfferent gravity regimes and rotation speeds, and so on. Tetrapods might only be favoured on a fraction of those worlds.

Noclevername
2013-Oct-13, 12:27 AM
Tetrapods might be very common on planets that are exactly like the Earth, but planets come in a very wide range of shapes and sizes, with different densities and mineral compositions, different atmospheric densities, windspeeds and atmospheric physics, different hydrosphere compositions, depths and percentage cover, different degrees of geophysical activity and impact history, different orbital characteristics and obliquities, digfferent gravity regimes and rotation speeds, and so on. Tetrapods might only be favoured on a fraction of those worlds.

And only a small fraction of Earth's life is tetrapods. We only see them as "favored" here because we're tetrapods and we like things that remind us of ourselves. Most of the more successful species are not.

Noclevername
2013-Nov-02, 11:26 PM
It's a bit difficult to imagine an octopus-like set of appendages that would be more dexterous than a couple of hand-type appendages. Using a large number of "fingerless" appendages to get the same dexterity as a single main appendage with fingers may not be biologically economical.

Actually, octopus arms can open jars and bottles, something most monkeys haven't demonstrated. They're arguably the most dexterous limb articulation possible:doh: currently known to exist.

ravens_cry
2013-Nov-03, 07:01 PM
Actually, octopus arms can open jars and bottles, something most monkeys haven't demonstrated. They're arguably the most dexterous limb articulation possible.
Rather. Instead of thinking it as many separate limbs, imagine it as one hand with a set of fingers with practically infinite joints.
On the subject of ravens and crows, They are known make changes to the things they pick up to use as tools, something that pretty rare among primates and other tool using critters. I know chimps do it, and, of course, we do it, but it's still fairly rare.

Noclevername
2013-Nov-04, 04:27 PM
Instead of thinking it as many separate limbs, imagine it as one hand with a set of fingers with practically infinite joints.


I've seen octos using one arm by itself, or several at once, to handle objects. So it could be considered as one or more hands with a variable number of fingers per hand, always adding up to eight. With suckers.

ravens_cry
2013-Nov-04, 08:54 PM
I've seen octos using one arm by itself, or several at once, to handle objects. So it could be considered as one or more hands with a variable number of fingers per hand, always adding up to eight. With suckers.
Which are like, well, suckers. Fascinating creatures. Make them social and give them a life span past child rearing, and things might start to get interesting. Yes, I have read Baxter's book, but I had a love for Cephalopoda even before then.