What are the odds of humans evolving on a different planet?

[by-tor]

I realize that no one knows the exact odds but listing the factors and an estimate of the odds is what I am asking.

My friend keeps insisting that humans are likely on other planets and I keep telling him that a zillion different random mutations would have to happen in all sorts of species for that to be so. His argument is that there are so many stars and so much time that it is bound to have happened.

I also had to try to dissuade him from the idea that evolution progresses towards intelligence as opposed to intelligence just being another adaptation.

Perhaps if I direct him to this thread he will be persuaded by more eloquent and knowledgeable posters.

[Q.E.D.]

The odds are close enough to zero that you might as well go ahead and just call it zero.

[lieu]

The more I read about our own evolutionary odyssey, as well as some of the meteoric and terrestrial cataclysms we had to overcome, the more I'm amazed we came into being on this planet.

[Mr. Slant]

SNIP
My friend keeps insisting that humans are likely on other planets and I keep telling him that a zillion different random mutations would have to happen in all sorts of species for that to be so. SNIP

To narrow down your question, is he positing that:
1. An animal very SIMILAR to a human would have to evolve somewhere out there eventually.
OR
2. Honest to God, actual humans that you could impregnate with human DNA would have to evolve somewhere out there eventually?

[Bricker]

Depends on where the life came from.

If you're talking two planets completely separate, both evolving life from scratch, then effectively zero. (Although I might argue that some general similarities in form are likely -- evolution suggests that things that wiggle must precede those that crawl, and crawling must proceed walking/running, so some generic similarity in form may be comparatively likely).

If the Chariots of the Gods type aliens came along and transplanted life from one place to another at some stage, then obviously the odds of human life get better.

[Lemur866]

Evolutionary biology has been trying to shed teleology ever since Darwin, and is apparently still failing judging from popular notions about evolution.

There is such a thing as convergent evolution. A fish, a dolphin, a shark, and an ichthyosaur all look very similar on casual inspection. But these animals are already very closely related, all being in the same phylum.

What non-vertebrates have evolved to look the same? The closest convergence from a non-vertebrate would probably be a squid...it has a similar shape...if the tentacles are tucked up. And of course the squid swims by water jets rather than wiggling it's tail, which it doesn't have. And on and on. A squid is a fast swimming pelagic predator like a dolphin, but it isn't much like a dolphin despite sharing the exact same environment.

If a creature that is similar to a human is likely to evolve on another planet, then just about every species on earth would be likely to evolve. Why would something resembling humans be likely, but not golden bamboo lemurs, or kangaroos, or narwhals, or pandas, or naked mole-rats, or giraffes, or ostriches?

When you consider the evolutionary history of Homo sapiens, you realize what a long strange trip it's been since the primordial ooze. We were once single-cell protozoans, then colonies, then wormy things, then fish, then amphibian-y creatures, then mammal-like reptiles, then little mousy things, then tree-climbing little mousy-things, then monkeys, then tail-less monkeys, then ground-dwelling tail-less bipedal apes. It's easy to imagine that if one saber-tooth tiger had killed one too many of our ancestors, humans would never have evolved, we'd be extinct. And it is many times more likely for a human-like creature to re-evolve via convergent evolution here on Earth than on some other planet, even if millions of planets have complex life.

Think about bipedalism. There have been hundreds of bipedal organisms in the history of our planet, but NONE of them looked much like a human. There have been lots of large brained creatures in the history of our planet, but none of them were much like humans, except for our ancestors and sister species. An intelligent alien is just as likely to resemble a squid or an elephant or a dinosaur as it is to be a hairless bipedal ground-dwelling but former-tree-climbing ape. Which is, not very likely at all. It's likely to resemble NOTHING ON EARTH.

And that's not even getting into the biochemical issues. All life on earth is related, and has the same basic biochemical machinery...DNA coding for RNA, ribosomes that create protein from RNA, only 20 amino acids out of the thousands possible, phospholipid bilayer cell membranes, and on and on. We have no idea how much of this machinery is required for life, and how much is simply due to how the first living thing arose on earth. But it's pretty likely that any alien life would have a radically different biochemistry from earth life.

[WarmNPrickly]

I'm not sure that you can make the assumption that DNA is as random as you would presume. It seems to me, that since so little is known about abiogenesis, it can't be assumed that early life-forms on another planet wouldn't be exactly as they were on earth. From a chemistry standpoint, it makes sense that molecules would "gravitate" towards the lowest energy configurations.

We do know that only changes in DNA that result in an evolutionary advantage will survive. It's likely that certain mutations are more common than others. I tend to think that evolution is fairly ordered. That is not to say that for every planet with a reasonable biosphere humans with 46 chromosomes two arms and two legs would evolve, but ultimately intelligence is an evolutionary advantage. Certainly four legs is an advantage for survival early in evolution, and this ultimately leads to two arms and two legs. Maybe there is an advantage to 46 chromosomes.

Nevertheless, with all the possible permutations, the possibility of getting something that we would define as human is pretty negligible.

[by-tor]

Mr. Slant, I am not sure but I think he means completely human.

[Exapno Mapcase]

I'm not sure that you can make the assumption that DNA is as random as you would presume. It seems to me, that since so little is known about abiogenesis, it can't be assumed that early life-forms on another planet wouldn't be exactly as they were on earth. From a chemistry standpoint, it makes sense that molecules would "gravitate" towards the lowest energy configurations.
The energy configurations is true, but the rest isn't. And from what you say afterward you're making the mistake of thinking that these energy configurations must lead to a common product.

Probably not. We know that simple amino acids are easily formed, even outside of conditions that would support life. There are 20 amino acids that earth life uses, but we know of others that exist. We don't know enough about the transition to say for sure, but there seems to be no reason at all that the progression from amino acids to proteins to reproducing molecules to DNA must take place in the way it did on earth. That's one reason why intelligent design/irreducible complexity arguments fail. Once life does form it seems reasonable to assume that it will outcompete any newly formed alternate life, so there is no niche for that. On another planet, however, that original niche could be filled by anything that allows for reproduction of genetic material. It does not have to be like our life in any way.

We do know that only changes in DNA that result in an evolutionary advantage will survive.
Not true. Neutral changes will also survive. Most of our DNA is non-functioning as far as we now know, although some hints that the supposed non-functioning sections may have roles to play.


It's likely that certain mutations are more common than others. I tend to think that evolution is fairly ordered. That is not to say that for every planet with a reasonable biosphere humans with 46 chromosomes two arms and two legs would evolve, but ultimately intelligence is an evolutionary advantage. Certainly four legs is an advantage for survival early in evolution, and this ultimately leads to two arms and two legs. Maybe there is an advantage to 46 chromosomes.
We don't know any of these things are true. We don't know how common any mutations are. We don't know that intelligence is an evolutionary advantage (though we're certainly disposed to think so). We don't know that four legs is an early advantage and we don't know that this leads to two legs. We don't know that 46 chromosomes is better than any other number. You're being biased by a sample size of one.

Nevertheless, with all the possible permutations, the possibility of getting something that we would define as human is pretty negligible.
At last, this is something I can agree with.

[sturmhauke]

If the universe is truly infinite, then the chance that there are other humans out there, independently evolved but fully genetically compatible with us, is 1. But our chance of ever meeting them is close to zero.

[Lemur866]

Yes, but the odds that there are independently evolved exact duplicate humans who meet independently evolved exact duplicate humans is 1. But the odds that we'll be either one of those instances is near 0.

Of course, it doesn't seem as if the Universe IS infinite in space and time, so it's kind of moot.

Back to the biochemistry argument.

Sure, we have life on planet Earth, and every instance of that life on planet Earth uses the same biochemistry. But the trouble is that we've only got Earth life to go on, we really have no idea how likely it is that a second biogenesis would create life with similar biochemistry. Maybe it is extremely likely, maybe it is extremely unlikely, but it seems to me that we have no good reason to believe that non-Earth life would have exactly the same features. Even if it used DNA or a molecule extremely similar to DNA, I can't imagine that the exact same codons would code for the exact same amino acids. Except every life form on earth uses exactly the same DNA code for exactly the same 20 amino acids.

[anson2995]

I'd like to suggest that a good place to start looking for answer to the OP's question would be the Drake equation (http://en.wikipedia.org/wiki/Drake_equation). The intention was to calculate the likely number of extraterrestrial civilizations in our galaxy with which we might come into contact. While it doesn't offer any definitive answers, it's a good starting point for an informed discussion of the subject.

Another reasonable launching point would be the Fermi paradox (http://en.wikipedia.org/wiki/Fermi_Paradox), which argues that the overwhelming lack of evidence for extraterrestrial life suggests it just ain't out there.

[WarmNPrickly]

Probably not. We know that simple amino acids are easily formed, even outside of conditions that would support life. There are 20 amino acids that earth life uses, but we know of others that exist. We don't know enough about the transition to say for sure, but there seems to be no reason at all that the progression from amino acids to proteins to reproducing molecules to DNA must take place in the way it did on earth. That's one reason why intelligent design/irreducible complexity arguments fail. Once life does form it seems reasonable to assume that it will outcompete any newly formed alternate life, so there is no niche for that. On another planet, however, that original niche could be filled by anything that allows for reproduction of genetic material. It does not have to be like our life in any way.

I remember reading research from one professor (I think at UC Riverside) where he had changed the DNA simply by changing the connection points from 3',5' to something else. I think it may have been 3,5. The result was DNA that had a larger helix. As a result, the DNA could not hydrogen bond to form the double helix. In this example, it appears that even a minor change in the structure of DNA resulted in a molecule that was a dead end. I suspect that DNA is organized the way it is, because that is the most likely arrangement that is not a dead end.

We don't know any of these things are true. We don't know how common any mutations are. We don't know that intelligence is an evolutionary advantage (though we're certainly disposed to think so). We don't know that four legs is an early advantage and we don't know that this leads to two legs. We don't know that 46 chromosomes is better than any other number. You're being biased by a sample size of one.


One more thing we agree on is that we don't know. Since we don't know, we can't make any assumptions. I am only basing my judgments on a sample size of 1, but it is the only sample we have. I know of no land vertebrates that have evolved with more than 4 limbs. I'm guessing that there may be a reason for this, but I am just guessing. I see no reason to believe that your guess is better than mine.

[garygnu]

It doesn't give the odds that the beings are human, but Drake's equation (http://en.wikipedia.org/wiki/Drake_equation) is pertinent here:

N = R* x fp x ne x fl x fi x fc x L

where:

N is the number of civilizations in our galaxy with which we might hope to be able to communicate;
and

R* is the average rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can potentially support life per star that has planets
fl is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space.
The values of all those variables is almost entirely speculative. You'd have to add at least one more variable to that for the human-ness of the species.

[PoorYorick]

Hey, where were you guys when I got flamed by fanboys in a "What don't you like about Star Trek" thread (or something of that nature). I said that I couldn't get around all the humanoid species from other planets whose only differences might be forehead ridges or elf ears. I went on to talk about even if a planet had exactly the same history and environment, the chances that a human would come about would be negligible.

Man, it was like I touched an exposed nerve. Of course, they brought up convergent evolution more than once. I just sighed and moved to the next thread.

[David Simmons]

The odds are close enough to zero that you might as well go ahead and just call it zero.Odds were heavily against humans evolving on this planet. Odds are against any animal, plant, amoeba or what-have-you that is selected in advance ever apprearing anywhere.

[WarmNPrickly]

I remember reading research from one professor (I think at UC Riverside) where he had changed the DNA simply by changing the connection points from 3',5' to something else. I think it may have been 3,5. The result was DNA that had a larger helix. As a result, the DNA could not hydrogen bond to form the double helix. In this example, it appears that even a minor change in the structure of DNA resulted in a molecule that was a dead end. I suspect that DNA is organized the way it is, because that is the most likely arrangement that is not a dead end.

I just looked this up. It was professor Christopher Switzer at UCR. It turns out that it was RNA that was being modified. Apparently he has been somewhat more successful since I met him in 2001. Nevertheless, I still tend to believe that DNA was made the way it was, because that is the most stable and easily formed structure that exist. I don't see why my guess would be any less valid than anyone else's.

[Darwin's Finch]

My friend keeps insisting that humans are likely on other planets and I keep telling him that a zillion different random mutations would have to happen in all sorts of species for that to be so. His argument is that there are so many stars and so much time that it is bound to have happened.

We are more than the sum of our mutations. There are several events during our history, much less the history of life on Earth in general, wherein things could have gone very differently. No terminal-Cretaceous asteroid? Mammals might well still be living in the shadow of giant dinosaurs (or, at least, probably not evolved to the point where we could appear). Or, if the (or another) asteroid struck in a different place / time, it could very well have wiped out the first humans.

Geological time is punctuated by numerous mass extinctions, each of which paved the way for adaptive radiation by the survivors. In order for honest-to-Og Homo sapiens to evolve on another planet, the entire evolutionary history of life on that planet would have to play out virtually the same as it did here. Even the structure of our planet has played a role in our history, as the motion of the plates has resulted in changing oceans, which in turn has affected the climate. So, we're talking a planet that pretty much has to be Earth in order to evolve the same life forms.

[WarmNPrickly]

you can also take the point of view, that no matter what order or sequence these events occured, evolution would ultimately lead to the "low energy" result. Ultimately, an intelligent bipedal mammal may be a very likely possibility no matter how events occured.

[Stranger On A Train]

If the Chariots of the Gods type aliens came along and transplanted life from one place to another at some stage, then obviously the odds of human life get better.Even then, if the Great Green Google-Eyed Ones raced down on their Cosmic Hot Rods, scooped up some primitive life, and dropped it on another more-or-less Earth-like world, we'd still not expect something reproductively compatible, or likely even more than crudely similar, to humans. Even saying that it would require "a zillion different random mutations" understates the unlikelyness of this; these mutations (and the external pressures to make them selectively optimal) would have to occur in order. The odds of the same sequences of DNA--including non-nuclear DNA in mitochondria and elsewhere--being compatible are beyond astronomical, even above and beyond the presumed rarity of worlds which went through an Earth-like development and ecosystem to begin with.

Citing convergent evolution is a parlor trick; convergent evolution gives similar end results for the same problem--say, vision or aquatic mobility--but these aren't necessarily the only solutions, nor is the result the same in the details. The vertebrate camera eye and that of sophisticated cephalopods like squid and octopus are dramatically different in construction, even though they fulfill the same essential function. And these are creatures that evolved in the very same environment; unrelated species evolving on different worlds, with different competitor and prey species are likely to have very different solutions even to similar problems.

Here's what we can say about possible intelligent, corporeal alien life: they're likely but not assured to be homothermic, and capable of adapting to a variety of environments,
be tool users with some kind of gripping appendages,
have the senses of vision, touch, and taste/smell,
use respiration (rather than fermentation) to process energy,
have a cellular physiological structure, organized into discrete organs for various bodily functions,
have a complex central nervous system with a substantial portion dedicated to signals processing, communication, and conceptual thought,
and have a vast library of sensory information dedicated to the preparation of food and table settings.There's no guarantee that they'll be bipedal, even if they are something like a mammal that evolved on savannahs, and indeed, bipedalism has some substantial drawbacks, the offseting advantages of which are probably unique to human development and unlikely to be arbitrarily reproduced.

The only reason aliens depicted in science fiction television and movies are largely humanoid is because it's both far cheaper, and far easier for viewers to relate to. This has absolutely no bearing on the likelyhood of human-like life evolving elsewhere.

Stranger

[Stranger On A Train]

you can also take the point of view, that no matter what order or sequence these events occured, evolution would ultimately lead to the "low energy" result. Ultimately, an intelligent bipedal mammal may be a very likely possibility no matter how events occured.This rationale is beyond simplistic. First of all, the human form can hardly be considered "low energy", nor can we view it as some teleogically ultimate result; it's what dominant intelligent lifeform on Earth is now, but perhaps not in the future. Second, it's a mistake to think that any ongoing process like evolution comes to a thermodynamic equilibrium. While thermodynamics plays into evolutionary biology to an extent that we're only beginning to quantify, it's is a decidedly nonequilibrium (NET) situation. The plantigrade bipedal form is the result of intelligence emerging from monkeys; had, say, ursines or equines beaten us to the punch, the form could have been very different. (And please, no repeating the Larry Niven-penned simplification that it takes no intelligence to sneak up on a blade of grass; there are plenty of herbivorous species which demonstrate intelligence, and predator species which show very little.)

Humans or something like us are not an inevitable result of evolution; to believe so is the same kind of blind thinking that lead to heavenly epicycles and élan vital. We just got mostly lucky and demonstrate every evidence of being an unfinished, undesigned, imperfect product.

Stranger

[WarmNPrickly]

There's no guarantee that they'll be bipedal, even if they are something like a mammal that evolved on savannahs, and indeed, bipedalism has some substantial drawbacks, the offseting advantages of which are probably unique to human development and unlikely to be arbitrarily reproduced.

Doesn't bipedalism lend itself to tool use?

[Stranger On A Train]

Doesn't bipedalism lend itself to tool use?Elephants, octopus, and many speces of aves have all demonstrated tool use, sometimes to a sophisticated degree. (Admittedly, birds are technically bipedal, but they don't use their other members as a gripping appendage.) Bipedalism was important for hominid development, so that we could grip and carry tools, and of course there are many species of monkeys and apes which are only intermittently bipedal which use tools to a greater or lesser extent. In fact, it was probably less tool use than the need to cross wide ranges of savannah on foot and see above grasses that is most likely to explain the progressively plantigrade bipedalism and increasing height of hominids which were derived from brachiating apes. You can make the point that the upright mode of locomotion led to tool manufacture (for better hunting prowess against herd animals) and allowed proto-humans to carry tools on migratory processions, but that's a composite logic and not really a solid claim by itself.

In short, there's no particular reason to except any arbitrary intelligent creature to be bipedal, unless they've evolved from brachiating ape-like creatures in a migratory lifestyle, and even then, it's not a guaranteed solution; it just happens to be the one that worked for the singular data set that we have. Generalizing from one scenerio doesn't make for a firm footing to claim that it's the best or most likely of all possible worlds; it's better viewed as the least worst of all options given a particular starting point. Adaptation is never an optimax solution; it's always a compromise between what you'd do if you planned it out and the resources and initial conditions that selective pressure has to work with.

Stranger

[Mangetout]

I think there are things we could expect not to be unique to Earth. Consider the number of times flight, or the eye has independently evolved. Of course lots of things are possible, but how about this (all speculative, I know):

-If you're going to crawl about, it helps to have legs on the bottom of your body.
-If you're going to eat things, process them, and excrete the waste, having the eating bit at the opposite side or end from the excreting bit makes a fair bit of sense.
-If you're going to move in any kind of fast, specialised way (such as pursuit of prey), choosing part of your body to always be the front probably isn't a bad idea.
-The front isn't a bad place to put the visual apparatus - more than one of them if you want depth perception..
-Several factors above favour some kind of longitudinal symmetry
-If your food tends to fall to the ground under the force of gravity, your eyes are better off above your mouth.

-And so on...

I don't think it's at all unlikely that some kind of vaguely humanoid bipedal alien lifeforms could be out there (although I think we'd still have to be incredibly liberal with the definition of 'humanoid'.

[Lemur866]

Sure. Bilateral symmetry is a consequence of cephalization and gravity. If you've got a mouth, it's a good idea to put sensors near the mouth to facilitate getting food into that mouth. If you've got sensors it's a good idea to put the central nerve clusters near the sensors. And so the "head" is born, with it's corollary the tail. Now add in the fact that gravity pulls down, and your creature has a top and a bottom. Uncephalized creatures tend to be radially symmetrical because gravity still exists even in the water, and so we have starfish and jellyfish. If you want to move limbs of some kind are helpful. If you're a large creature an internal skeleton makes more sense than an exoskeleton. If you've got 4 limbs but want to have manipulating organs, walking on two limbs and manipulating with the other two makes sense, although plenty of creatures seem to have perfectly fine hands on their front legs.

But such a creature shouldn't be thought of as humanoid, if that's the definition of humanoid velociraptors, kangaroos, and iguanadons are humanoid. And note that all those creatures are close relatives to humans, all being tetrapods. And note that there were dozens, probably hundreds of bipedal dinosaur species, but how bipedal mammal species can you name? Hominids and Macropods are about it.

[Chronos]

Quoth Lemur866:Of course, it doesn't seem as if the Universe IS infinite in space and time, so it's kind of moot.There's no evidence one way or the other, at this point. Which you prefer is mostly down to philosophy and aesthetics.
Quoth Stranger on a Train:(And please, no repeating the Larry Niven-penned simplification that it takes no intelligence to sneak up on a blade of grass; there are plenty of herbivorous species which demonstrate intelligence, and predator species which show very little.)Mind you, that's not an argument that Niven actually supported; it's presented as an argument made by the Kzinti, who of course have their own set of biases.

Back to the OP, there are a lot of aspects of evolution for which it's very difficult to calculate probabilities. But let's look at a few of the places where it is possible. For instance, for an alien species to be truly compatible with humans, they would need to use the same genetic code as us. Let's even suppose that they use the exact same sort of DNA as us, and the same 20 amino acids, and the same number of bases in a codon (all of these are unlikely, but the probabilities are among those that are difficult to calculate). Even stipulating all of that, we have to assign 64 different codons to 21 different results (the 20 amino acids plus a stop codon), such that each of those 21 has at least one codon. By my figuring, that leaves a number of possibilities ((64! / 43!) * 2164). That comes out to 8.8*10120 different possible genetic codes. So the chance of the life on any given planet having the same genetic code as Earthly life, even if it has the same fundamental DNA-protein biochemistry to begin with, is only about 1 in a thousand billion billion googol. And that's just to get something which has a vague resemblance to anything Earthly... The tiniest bacterium shares that much in common with us. That life would still have to go through the billions of years of evolution (in exactly the same way it happened here) to reach humans.

[Stranger On A Train]

-The front isn't a bad place to put the visual apparatus - more than one of them if you want depth perception.A good list, but it's worth noting that depth perception doesn't require binocular vision, and at range the vary narrow parallax of hominid eyes (and in general those of forward looking mammals) is insufficient by itself for estimating depth, which is instead done by some very complicated visual processing plus integration of other sensory information. Up close, however, that parallax definitely comes into play, and we might expect two or more eyes to be very useful for a toolmaker evolved to works on complicated tools at close range. Plus, having at least two allows for some redudancy should one become damaged or covered, and for virtually all terrestrial mammals eyesight is a primary sense that is in constant use.

Gross anatomical symmetry seems likely--with very few exceptions virtually all mobile creatures in terrestrial or aquatic environments demonstrate either some kind of bilateral or longitudinal symmetry, or have an atavistic symmetry which was modified due to some environmental pressure, like the flounders--and there are some reasonably strong rationales for why this would be more generally so, but it's not a guarantee. Moties seem unlikely, but not impossible.

Stranger

[Stranger On A Train]

Quoth Stranger on a Train:(And please, no repeating the Larry Niven-penned simplification that it takes no intelligence to sneak up on a blade of grass; there are plenty of herbivorous species which demonstrate intelligence, and predator species which show very little.)Mind you, that's not an argument that Niven actually supported; it's presented as an argument made by the Kzinti, who of course have their own set of biases.Niven repeats it elsewhere, however; at least, in my recollection, in one of the Draco Tavern stories, and perhaps in Footfall as well. In general, Niven's grasp of evolutionary theory is weak, or at least highly simplified for the purpose of dramatic conflict.

Stranger

[John Mace]

If the Chariots of the Gods type aliens came along and transplanted life from one place to another at some stage, then obviously the odds of human life get better.
Not really. What are the odds that our closest relatives on earth, chimps, will evolve into humans? Again, so close to zero that it might as well be zero. So, unless these aliens actually transplanted humans onto another planet, we won't be seeing them on other planets. Remember, the OP is asking about humans evolving on other planets, not being kidnapped and planted on other planets.

[Exapno Mapcase]

This rationale is beyond simplistic.
True, but since I always get slagged when I say things like that, I'm curious to see what reaction you'll get. :D

[John Mace]

Just to finish the thought in that last post...

Suppose that 4M years from now, chimps will have evolved into upright, largely hairless apes with the capacity for language. These new Pan sapiens (for lack of a better term) would still be more distant, genetically, from us than than chimps are today. The odds of them having the same mutations at the same place to get the be upright, largely hairless apes with the capacity for language are so close to zero that they might as well be zero.

Not to mention the fact that we will have evolved quite a bit in the next 4M years, too. So not only would Planet X have to have humans on it, it would have to have them at the same time humans existed on earth. No way. Simply now way (unless we postulate an infinitely large universe, and then everything is possible).

[Mangetout]

But such a creature shouldn't be thought of as humanoid, if that's the definition of humanoid velociraptors, kangaroos, and iguanadons are humanoid.I'd say those are *fairly* humanoid, in the context of this particular question, so aliens approximately as similar to us (morphologically) as kangaroos are, I think could be quite rightly regarded as humanoid... ish.

[Musicat]

Doesn't bipedalism lend itself to tool use?More than tripedalism or octopedalism?

Many's the time I wish I had three arms. Two just aren't enough when you're fighting off large, toothy predators or carrying groceries.

[WarmNPrickly]

More than tripedalism or octopedalism?


And yet for some reason, in vertibrates, these characteristics are very rare if they have been heard of at all. I think there may be an evolutionary reason for this. No matter how many arms you think would be useful now we had to evolve from four legged creatures. Maybe six legs isn't efficient for running. I don't know.

[Musicat]

We do know that only changes in DNA that result in an evolutionary advantage will survive. But is the change we observe the ONLY one that will provide the evo advantage? There might be many of nearly equal utility, and each one will lead us on a much different road.

For those who are bringing up Drake's Equation, since all terms are multiplied, all it takes is ONE element to be questionable to make the entire equation useless. But here ALL (or almost all) elements are unknown or highly speculative, making the equation more useless than useless. It's only of philosophical interest; it's not a scientific law with a more precise answer than something in the range from yes to no, zero to one.

[Biggirl]

As one professor aid when asked the same question: That squirrel shares at least 70% of my DNA and it looks nothing like me. Why would one expect an extra-terrestrial to?

[Stranger On A Train]

I'd say those are *fairly* humanoid, in the context of this particular question, so aliens approximately as similar to us (morphologically) as kangaroos are, I think could be quite rightly regarded as humanoid... ish.Not really. Birds and theropod dinasaurs are digitigrade in locomotion, where as kangaroos are macropods that move primarily by saltation. Both would disqualify it for being classified as humanoid by virtue of being significantly different from the plantigrade motion that hominids developed. No anatomist could consider them vaguely morphologically similar to a humanoid. A bear or elephant could claim greater similitude in in that regard.

Stranger

[WarmNPrickly]

But is the change we observe the ONLY one that will provide the evo advantage? There might be many of nearly equal utility, and each one will lead us on a much different road.

As Exapno Mapcase correctly pointed out, mutations may be neutral and still survive. In fact, I would guess that genes could be mildly detrimental and still survive.

[Mangetout]

Not really. Birds and theropod dinasaurs are digitigrade in locomotion, where as kangaroos are macropods that move primarily by saltation. Both would disqualify it for being classified as humanoid by virtue of being significantly different from the plantigrade motion that hominids developed. No anatomist could consider them vaguely morphologically similar to a humanoid. A bear or elephant could claim greater similitude in in that regard.

StrangerSure, but anatomists, although undoubtedly best qualified to make the judgment, wouldn't be the only folks drawing the comparisons.

[sturmhauke]

As Exapno Mapcase correctly pointed out, mutations may be neutral and still survive. In fact, I would guess that genes could be mildly detrimental and still survive.
The only genes that die out are the ones that make reproduction impossible, or at least highly difficult. Even so, there are a number of rare genetic disorders that are clearly very detrimental to humans, yet are still around.

[Bosda Di'Chi of Tricor]

Doesn't bipedalism lend itself to tool use?

The Robin on my front lawn is bipedal, but I ain't seen him use a cigarette lighter, lately.

T Rex could, though. That's why he's extinct--too many ciggies.

[WarmNPrickly]

The only genes that die out are the ones that make reproduction impossible

I don't think that is true. With two slightly different species competing for the same resource, the more efficient species is going to win out. Given millions of years, even mild advantages can be the difference between extinction and survival. Additionally, simple mate selection can make some characteristics dissappear very quickly.

Even so, there are a number of rare genetic disorders that are clearly very detrimental to humans, yet are still around.

Many of the genes that we consider to be detrimental in humans may have positive benefits that we haven't found yet. The most obvious example is sickle cell anemia, which with two copies causes a problem but with one copy makes one immune to malaria.

[John Mace]

And yet for some reason, in vertibrates, these characteristics are very rare if they have been heard of at all. I think there may be an evolutionary reason for this. No matter how many arms you think would be useful now we had to evolve from four legged creatures. Maybe six legs isn't efficient for running. I don't know.
Terrestrial vertebrates evolved from lobe-finned fish, which just happened to have had four lobed fins that evolved into limbs. All tetrapods are descended from that same ancestor some 350M years ago. It's certainly possible that fish with more than 4 lobed fins could have evolved, in which case it's certainly possible that terrestrial vertebrates with more than 4 limbs could have evolved. Four might be optimal in some way, but 6 or 8 might well prove optimal in some other way.

[WarmNPrickly]

The Robin on my front lawn is bipedal, but I ain't seen him use a cigarette lighter, lately.

Is somebody making the argument that all bipedal animals are intelligent?

[John Mace]

The only genes that die out are the ones that make reproduction impossible, or at least highly difficult.
No. Genes can "die out" due to simple genetic drift. (http://en.wikipedia.org/wiki/Genetic_drift)

[John Mace]

As Exapno Mapcase correctly pointed out, mutations may be neutral and still survive.
Yes. Let's remember that, in humans, non-coding DNA makes up about 80 - 90% of the our genome. Any mutation in the non-coding sections is most likely going to be neutral.

In fact, I would guess that genes could be mildly detrimental and still survive.
Unlikely that they would survive over time. Unless they also confer some additional advantage, they will disappear. But remember, they have to be detrimental to reproduction. Just being detrimental to survival isn't enough.

[Gorsnak]

Moties seem unlikely, but not impossible.

Stranger
I thought the Moties' asymmetry is supposed to be understood as arising out of genetic engineering the Moties had performed on themselves at some point many many cycles ago. Hence you still have four-armed porter castes, and the closely related little Watchmakers. Is that not the whole point of the sequence in The Gripping Hand at the Blaine Institute where they're talking about symmetry?

[WarmNPrickly]

Terrestrial vertebrates evolved from lobe-finned fish, which just happened to have had four lobed fins that evolved into limbs. All tetrapods are descended from that same ancestor some 350M years ago. It's certainly possible that fish with more than 4 lobed fins could have evolved, in which case it's certainly possible that terrestrial vertebrates with more than 4 limbs could have evolved. Four might be optimal in some way, but 6 or 8 might well prove optimal in some other way.

We agree then. You can take the position that it was by chance that we evolved from tetrapods, or you can believe there was some evolutionary advantage to 4 limbs. I choose the latter.

Yes. Let's remember that, in humans, non-coding DNA makes up about 80 - 90% of the our genome. Any mutation in the non-coding sections is most likely going to be neutral.


Since non-coding DNA has no effect on whether something is humanoid or not I don't see the relevance.

Unlikely that they would survive over time. Unless they also confer some additional advantage, they will disappear. But remember, they have to be detrimental to reproduction. Just being detrimental to survival isn't enough.

For neutral mutations I would guess that the probability of survival is around 50%. For less advantageous mutations I would guess that the survival rate does not immediately drop to 0%.

[John Mace]

We agree then. You can take the position that it was by chance that we evolved from tetrapods, or you can believe there was some evolutionary advantage to 4 limbs. I choose the latter.
Remember, though, this is GQ. Unless you have some evidence that it was the latter, then it's just your opinion. The original point you made, and which I was responding to was this: "I think there may be an evolutionary reason for this." Without any compelling argument one way or another, the simpler explanation is that it just happened that way by chance.

Since non-coding DNA has no effect on whether something is humanoid or not I don't see the relevance.
Because people are jumping all over the place in this thread-- one minute talking about humans and the next minute making sweeping statements about genetics and evolution in general.

For neutral mutations I would guess that the probability of survival is around 50%. For less advantageous mutations I would guess that the survival rate does not immediately drop to 0%.
Which is why I underlined "over time" in that post. I clearly was not talking about something that happened "immediately".

[Darwin's Finch]

And yet for some reason, in vertibrates, these characteristics are very rare if they have been heard of at all. I think there may be an evolutionary reason for this. No matter how many arms you think would be useful now we had to evolve from four legged creatures. Maybe six legs isn't efficient for running. I don't know.

Meet my friend, the "evolutionary constraint". Not everything that could evolve in theory can evolve in practice. Terrestrial vertebrates evolved from a common ancestor, which had a specific body plan. That body plan happens to be very conservative; even though we find quite a bit of variety in the form of the four limbs, we still have only four limbs. Some groups have reduced that number, but none have increased it. That would imply that there is a good reason that it can't happen. Most likely, it's a result of Hox (aka Homeobox) genes; these gene suites are master developmental genes, and mucking with them, even a little, can have drastic effects for the developing embryo. As such, there isn't as much room for variation in those genes as there are in others. Even in some of the peripheral Hox genes, such as those that control phalangeal development and growth, we only see a reduction in the number of phalanges, never an increase (at least not since the days of 8-9 phalanges in our very early ancestors).

And even in the case of reductions, it tends to be that the genes are simply turned off (i.e., the expression of those genes has been altered, but not necessarily the genes themsleves), not actually eliminated. Thus, we still find the occassional three-toed horse, or whale with vestigial hind limbs.

Because of our particular body-plan, we will most likely never gain limbs or even digits, regardless how useful they might be simply because the required mutations would be vast; we'd basically have to shift body plans, and that just doesn't happen.

[WarmNPrickly]

Remember, though, this is GQ. Unless you have some evidence that it was the latter, then it's just your opinion. The original point you made, and which I was responding to was this: "I think there may be an evolutionary reason for this." Without any compelling argument one way or another, the simpler explanation is that it just happened that way by chance.

The key in that statement is "I think". I think this because my experience as a chemist suggests that things tend to move through the easiest pathway. As I have mentioned before in this thread, we know very little about how evolution happens. This thread has been almost entirely conjecture.

Because people are jumping all over the place in this thread-- one minute talking about humans and the next minute making sweeping statements about genetics and evolution in general.

I don't know what sweeping statements you are refering to. I have given my opinion on how things worked. Many people have not liked what I have to say.

Which is why I underlined "over time" in that post. I clearly was not talking about something that happened "immediately".

I think you are misunderstanding "immediately". I meant that mutations that lead to only mildly detrimental attributes would survive nearly indefinitely. On that point, I think we dissagree.

[Bosda Di'Chi of Tricor]

Is somebody making the argument that all bipedal animals are intelligent?

No, somebody suggested it promoted tool use, & I refute the notion.

[Blake]

I think this because my experience as a chemist suggests that things tend to move through the easiest pathway.

But evolution isn't chemistry. It involves chemsitry just as it does physics, but that doesn't make arguments based on the second law of thermodynamics relevant, nor does it make arguments based on chemical principles relevant.

We know that evolution doesn't move through the easiest pathway, it moves through whatever pathway promotes reproduction for the individual regardless of how easy or hard that is. Bipedalism in humans isn't easier in any sense than walking on the knuckles, nonetheless it evolved. that's because because despite being more energetically expensive and risking spinal injury and making birth difficult and a multitude of other difficulties it conferred benefits that aided reproduction. Nothing to do with being easy thermodynamically or chmically or even physiologically. Purely and entirely based on reproductive rates.

I meant that mutations that lead to only mildly detrimental attributes would survive nearly indefinitely. On that point, I think we dissagree.

I hope everyone disagrees because it's not true. Once you declare that something is evolutionarily detrimental then you have also by definition said that it will be eliminated given sufficient time. If it won't be eliminated given sufficient time then it isn't detrimental, not even mildly.

I think your problem may be that the term "mildly detrimental" is almost meaningless in a discussion concerning evolution. Either a mutaion decreases reproductive succes or it does not. Some mutations will have a less evere effect on reproductive success, which is the only possible interpretation of "mildly detrimental" that make sany sense.

But if that is the sense that you mean then the statement is out-and-out incorrect. Mutations that only mildly affect reporductive success can't survive indefinitely because by definition individuals that carry them have a decreased reproductive rate compared to the general population. Doesn't matter if they are only eliminated with 0.00000001% greater frequency than the general population, the fact that they are elminated at a greater rate means the mutation must vanish.

[David Simmons]

No, somebody suggested it promoted tool use, & I refute the notion.Some birds use tools. (http://en.wikipedia.org/wiki/Bird_intelligence)

Of course so do some apes and monkeys and they aren't really bipedal.

[Blake]

Some birds use tools. (http://en.wikipedia.org/wiki/Bird_intelligence)

Of course so do some apes and monkeys and they aren't really bipedal.

So do otters, dogs and caddisflies. That totally misses the point.

The point is that there are countless bipedal animals on this planet that have never, ever been observed to use a tool, and a handful of species that have.

There are also countless quadripledal, hexipedal and octipedal creatures on this planet that have never, ever been observed to use a tool, and a handful of species that have.

There is no evidence whatsoever that bipedal animals are more prone to tool use than quadripedal or hexipedal or octipedal. Anyone claiming that bipedlaism promotes tool use neede to explain this observation before there claim can be taken seriously. If bipedalism promotes tool use then why are extant bipedal species no more likely to use tools than quadripedadal, hexipedal or octipedal species?

[John Mace]

The key in that statement is "I think". I think this because my experience as a chemist suggests that things tend to move through the easiest pathway. As I have mentioned before in this thread, we know very little about how evolution happens. This thread has been almost entirely conjecture.
OK, but again... unless there is some reason to think that, then I don't find the argument very convincing. At any rate, we don't really know why the first lobe finned fish had 4 lobed fins as opposed to more. Maybe it's just that it helps to have two in front and two in back and having more isn't of much help. But the reason all land vertebrates have 4 limbs is because some fish a long time ago had 4 lobed fins.

I don't know what sweeping statements you are refering to. I have given my opinion on how things worked. Many people have not liked what I have to say.
Here's an example, from one of your posts:

I don't think that is true. With two slightly different species competing for the same resource, the more efficient species is going to win out. Given millions of years, even mild advantages can be the difference between extinction and survival. Additionally, simple mate selection can make some characteristics dissappear very quickly.
That's a general statement about evolution and genetics, not about what makes a human a human. It is one that I believe is correct, but it is a very general statement nonetheless. Nothing wrong with that, in the same way there was nothing wrong with my statement about non-coding DNA.


I think you are misunderstanding "immediately". I meant that mutations that lead to only mildly detrimental attributes would survive nearly indefinitely. On that point, I think we dissagree.
Do you have a cite for that claim? Because, as I read it, it contradicts one of the fundamental tenets of the theory of evolution by natural selection. As I noted earlier, I'm reading "detrimental" to mean detrimental to reproductive success. If you simply mean that a mutation that is detrimental to something like life span, then you might be correct-- it might hang around for a long time, but whether it "would" do so is hard to say without knowing the specifics of that mutation.

[beowulff]

I think the odds are incalculable.

Literally.

[Exapno Mapcase]

I think the odds are incalculable.

Literally.
Well, duh.

[beowulff]

Well, duh.
Well, if it's so obvious, why is there two pages of pointless ramblings?

Any attempt to calculate the odds is just so much mental masturbation, seeing as there is no way to prove any hypotheses at this time.

[Stranger On A Train]

Well, if it's so obvious, why is there two pages of pointless ramblings?

Any attempt to calculate the odds is just so much mental masturbation, seeing as there is no way to prove any hypotheses at this time.'Cause "mental masturbation" is both fun and keeps you in practice for the real thing. ;)

Seriously, the o.p.'s question was answered, seconded, and repeated in the first dozen or so posts, and the bulk of the remainder of the thread has gone onto this rather odd tangent about bipedalism and whether it does or does not promote/allow/essential to tool use, plus some kind of random, unstructured claims about thermodynamics and chemical equilibria, which has served to demonstrate that applying simplistic analogies don't hold up well to a complex phenomena like evolution.

Regarding the biped/quadraped issue, it is, as the sage Darwin's Finch points out, a mistake to think that the process of evolution explores all possible pathways. Why do spiders and other arachnids have eight legs, while most insects have only six legs, and mammals and reptiles have four extant or deprecated limbs? There's no especially good reason that any of these numbers have to be thus (though having an even number of limbs is dictated by symmetry), and only in the case of aves can we even make a reasonable claim that parsimony demands the absolute minimum. An entire class of reptiles certainly gets by having dispensed with legs at all, and the cephalopods seem to have far more than any reasonable creature needs (and live fine should they lose two or three).

With natural selection there's no planning ahead, or running a trade study to see if 13, 17, or 23 limbs will work out better than two; you start with the form you have and modify from thus, and the more complex form your initial specimen has the harder it is to make gradual modification that still fit in the overall scheme, hence why the finches of Galapagos, while being speciated by their adaptations to subsist on various niche food sources, show a common form rather than the diversity seen in mainland birds. Intelligent life evolving on another planet would likely--to a point of certainty--take different paths even if faced with the same gross evolutionary pressures, and the end result may be very different; instead of a savannah-hiking mammal-like biped, it might well be an litoral-dwelling quadralobe, or a social birdlike scavenger/predator, or a furry forest-and-praire-dwelling omnivore. It's likely that it would even be something far different from any of our terrestrial life classifications. To say that the biped for is innately superior or even necessary to the development of higher intelligence and tool use is a blindly homo-centric view, unsupported by either reason or a useful body of data.

Stranger

[Exapno Mapcase]

If you read through the whole thread, you'll see that several people have already said that the odds are not calculable. However, much of the discussion was on what factors would be needed to make the odds calculable, starting with an analysis of what happened on earth to reach our current point. Hardly masturbation if you understand the science involved.

Admittedly, if you don't understand any of the underlying science, I can see how it would seem worthless, but that would be true for any science thread, not just this one.

[JKellyMap]

Of course, they brought up convergent evolution more than once.
:p

[WarmNPrickly]

But evolution isn't chemistry. It involves chemsitry just as it does physics, but that doesn't make arguments based on the second law of thermodynamics relevant, nor does it make arguments based on chemical principles relevant.

In my experience, everything always takes the path of least resistance in most sciences. I see no reason to expect that the rules change for evolution.

We know that evolution doesn't move through the easiest pathway, it moves through whatever pathway promotes reproduction for the individual regardless of how easy or hard that is.

Ironically, I would consider something that promoted reproduction to be the easier pathway so your are proving my point. Obviously, you have a different definition of easiest pathway. I would also consider the paths that are more statistically probable to be easier.

Do you have a cite for that claim? Because, as I read it, it contradicts one of the fundamental tenets of the theory of evolution by natural selection. As I noted earlier, I'm reading "detrimental" to mean detrimental to reproductive success. If you simply mean that a mutation that is detrimental to something like life span, then you might be correct-- it might hang around for a long time, but whether it "would" do so is hard to say without knowing the specifics of that mutation.

You are right, I am not talking about genes that are specifically detrimental to reproductive success.

Regarding the biped/quadraped issue, it is, as the sage Darwin's Finch points out, a mistake to think that the process of evolution explores all possible pathways. Why do spiders and other arachnids have eight legs, while most insects have only six legs, and mammals and reptiles have four extant or deprecated limbs? There's no especially good reason that any of these numbers have to be thus (though having an even number of limbs is dictated by symmetry), and only in the case of aves can we even make a reasonable claim that parsimony demands the absolute minimum. An entire class of reptiles certainly gets by having dispensed with legs at all, and the cephalopods seem to have far more than any reasonable creature needs (and live fine should they lose two or three).


Insects and other non-vertibrates have an entirely different building structures from vertibrates. It's valid to take the position that all vertibrates evolved from tetrapods by random chance. I don't think it was random at all.

With natural selection there's no planning ahead,...

I'm not talking about planning ahead. I'm saying that random chance is likely give you something relatively close to what we already have. A bird is not likely to develop a large brain size due to the weight constraints of flight and a forest and prarie dwelling omnivore would probably be bipedal to make tool use efficient, but that would strike me as being rather close to what we have. Octopusses are an interesting option, just because I haven't found a reason they aren't likely to develop intelligence doesn't mean a reason doesn't exist.

To say that the biped for is innately superior or even necessary to the development of higher intelligence and tool use is a blindly homo-centric view, unsupported by either reason or a useful body of data.


To say that it isn't more likely is equally unsupported by reason or a useful body of data. I had to change "superior" to something I've actually said.

[John Mace]

You are right, I am not talking about genes that are specifically detrimental to reproductive success.
OK, then you're not talking about evolution.

Insects and other non-vertibrates have an entirely different building structures from vertibrates.
Different structure, but the genes are remarkably similar, as DF mentioned upthread.

It's valid to take the position that all vertibrates evolved from tetrapods by random chance. I don't think it was random at all.
All vertebrates did not evolved from tetrapods. If you have a goldfish at home, that's a vertebrate and it is not now a tetrapod nor was it ever one in its evolutionary history. Tetrapods got their 4 limbs from lobe finned fish which got their lobed fins from even more primitive fish which had the basic 4-lateral fin body plan we see today even in sharks (two pectoral and two pelvic fins). This body plan would seem to go back more than 400M years. Why only 4 of these fins, we do not know. But that is why we, today, have 4 limbs. As DF noted, it's a conservation of an ancient body plan that had nothing to do with walking on land.

[Lemur866]

In my experience, everything always takes the path of least resistance in most sciences. I see no reason to expect that the rules change for evolution.

And here is what I think is the nub of the discussion.

Life itself is not the path of least resistance. Living organisms are an extreme example of chemical disequilibrium. Of course, the reason living organisms are in such a state is due to the constant input of energy to create that disequilibrium, and when an organism reaches chemical equilibrium we biologists call that organism "dead".

And it's the same with evolution. It just doesn't make sense to argue that the creatures we see living today are there because they are the most likely sorts of creatures to evolve. Just look back 65 million years ago to the Cretaceous and you'll see a vastly different suite of animals and plants. If a body from space hadn't hit the Earth back then, it's very likely that the suite of animals and plants on Earth today would be much more similar to that Cretaceous biosphere. And go back 225 million years and you'll find that the Permian had a much different suite of organisms compared to the Triassic, and if the Permian extinction that wiped out the mammals hadn't occured, the dinosaurs never would have taken over.

So are the fish and marine mammals that dominate the oceans today more thermodynamically likely than ammonites and marine reptiles that dominated the oceans in the Mesozoic? I don't think so.

[Stranger On A Train]

In my experience, everything always takes the path of least resistance in most sciences. I see no reason to expect that the rules change for evolution.First of all, you're applying a simple mechanical principle to a complex, non-equilibrium process. "The path of least resistance", thermodynamically speaking, wouldn't lead to any kind of life. Indeed, life can be seen as an organized resistance to entropy, an attempt to graduate the flow of energy through a variety of self-organizing and self-replicating processes which defy--or at least defer--the normal workings of equilibrium thermodynamics and chemical reactions. The entire process of respiration and the Krebs cycle (http://en.wikipedia.org/wiki/Citric_acid_cycle) is a very strong and complex extropic process which can't in any way be described as "the path of least resistance." Clearly, evolution doesn't not favor "least resistance", but rather optimum extraction of energy from the local environment with acceptible risk.

Insects and other non-vertibrates have an entirely different building structures from vertibrates. It's valid to take the position that all vertibrates evolved from tetrapods by random chance. I don't think it was random at all.You keep throwing up "random chance" as a kind of straw man which you can hang from the gallows. I don't believe anyone--certainly no one who has a more than superficial understanding of natural selection--views the progress of evolution as being "random chance". Indeed, it is very much the opposite; it proceeds based on the overall strategy of maximal success in competition, and is decidedly nonrandom in pruning out unsuccessful strategies.

But it does not automatically follow, nor have you demonstrated in any qualitative or objective sense, that the bipedal form is somehow necessary or even overwhelmingly beneficial for the development of conceptual development and tool use, nor that there is any reason to believe that intelligent life would converge upon the bipedal form as optimal to support intelligence. Of the most intelligent non-primate-derived animals, only ursines and procyons come even close to the human form, being capable, albeit slowly, of plantigrade bipedalism. (They of course prefer movement on four legs, but can and so stand upright to use their forelimbs for manipulation.) Other animals of comperable conceptual or problem solving intelligence, learned behavior, and/or social complexity to the great apes are equines; in particular, Equus asinus (donkey), the aves of Corvus and Psittacinae (ravens and parrots), the more complex cephalopods (octopus), many members of order Cetacea, and some other litoral marine mammals like sea otters. With the exception of the birds, none are bipedal, and for these birds bipedalism is not the primary means of locomotion.

It is a mistake to view adaptation as being either an open process that finds an optimum engineering solution to any problem, or one that seeks the least energetic solution to a challenge. Natural selection merely favors the solution, however ad hoc the expressed phenotype (and it's clear from even a superficial study of animal anatomy and molecular genetics that ad hoc, stopgap solutions are the nature of the business) that gives the greatest advantage to the carrier of the gene in the current environment, against existing competition, and built upon cummulative genes and expressed forms. Convergent evolution is a result of common challenges, but the routes and specifics of parallel adaptations are often strikingly different; for instance, the structure of wings on insects is very different than on birds, and different again for bats. Eyes, which have been independently evolved an estimated 40 times are very different in structure between independent approaches. The propulsive tails of cetaceans and other marine mammals that have them are horizontal (deriving from extension and modification of previous quadrapedal structure) while that of sharks and fish are vertical, even though both perform the same function.

Neither convergent evolution nor "path of least resistance" are strong principles adhered to by natural selection. Moderationg of energy gradients and accumulation of adaptations are. Please try reading Ernst Mayr's What Evolution Is (http://www.amazon.com/What-Evolution-Ernst-Mayr/dp/0465044263) or Richard Dawkins' Climbing Mount Improbable (http://www.amazon.com/Climbing-Mount-Improbable-Richard-Dawkins/dp/0141026170/) to get a better understanding of how evolution proceeds and why the easy or obvious solution--the one that is "the path of least resistance"--is often not the one selected.

Stranger

[WarmNPrickly]

It seems we have two fundamental philosophies here. One suggests that evolution is just as likely to come up with an intelligent six legged flying hippopotamus as an intelligent humanoid. The other philosophy suggests that evolution is controlled by rules that ultimately led to an intelligent humanoid. It's true, the latter philosophy is more difficult to prove as it requires one to study how evolution works to prove that rules exist. Nevertheless, it is what I believe.

My suggestion of bipedal intelligence comes from the fact that no vertebrate with more than four limbs has ever been discovered. Tool making is much easier with two free hands, and that leaves two legs to walk on.

Of course, my belief requires the burden of proof, and assumes a more complex system. Occam's razor is scientific folly.

[Darwin's Finch]

Insects and other non-vertibrates have an entirely different building structures from vertibrates. It's valid to take the position that all vertibrates evolved from tetrapods by random chance. I don't think it was random at all.

I get the feeling that few people actually read what I write these days. Not least of all because I made a pretty glaring error in my previous post about constraints...namely, I said "phalanges" when I meant "digits". Anyway....

You've got the sequence backwards: tetrapods evolved from vertebrates, not the other way around. And I made a case for why the four-limbed status quo among most terrestrial vertebrates is what it is. Not because of random chance, not because it's adaptive, but because that pattern has been "locked in". Granted, early on, when body plans were still being experimented with during the Cambrian, that might not have been the case. But once developmental complexity reaches a certain point, there's not as much "wiggle room" to modify that plan. Insects remain six-legged, arachnids eight-legged, vertebrates 4-legged, etc. You can reduce the numbers of limbs / digits / phalanges / whatever by shutting off gene expression, but you can't go up from the bauplan defaults.

[WarmNPrickly]

You've got the sequence backwards: tetrapods evolved from vertebrates, not the other way around. And I made a case for why the four-limbed status quo among most terrestrial vertebrates is what it is. Not because of random chance, not because it's adaptive, but because that pattern has been "locked in". Granted, early on, when body plans were still being experimented with during the Cambrian, that might not have been the case. But once developmental complexity reaches a certain point, there's not as much "wiggle room" to modify that plan. Insects remain six-legged, arachnids eight-legged, vertebrates 4-legged, etc. You can reduce the numbers of limbs / digits / phalanges / whatever by shutting off gene expression, but you can't go up from the bauplan defaults.

And I'm saying that the number four may have been picked because thats the only way (or at least the most likely way) that it could work. I don't have it backwards, of course tetrapods evolved from vertebrates.

[Chronos]

About the "path of least resistance"... Things in other sciences don't follow the path of least resistance. What they do is follow multiple paths, and follow those paths which have less resistance more often. As an example: Suppose I have a network of parallel resistors. I've got, say, one 1-ohm resistor, one 2-ohm resistor, and one .5-ohm resistor. I then hook this network up to a voltage source, so a current flows. Most of the current will end up flowing through the .5-ohm resistor, since it's the path of least resistance. But some will flow through the 1-ohm, and a lesser amount through the 2-ohm.

But now suppose that the voltage source I use is very low voltage. It's so low voltage, in fact, that the total current is only 1.6*10-19 amps. And I only leave the voltage source turned on for a single second. In other words, I'm only sending a single electron through my network of resistors. Which one will it go through? Most likely the least resistance. But it might go through one of the others instead.

And this is the situation we have here. All of the terrestrial vertebrates descended from a single ancestor, which happened to have four limbs. Maybe four limbs was the path of least resistance, or maybe it wasn't. If we had a great many examples of independant evolution of terrestrial vertebrates to study, we might be able to say which path offered the least resistance. But with only one case to study, all we can do is make feeble guesses.

[John Mace]

It seems we have two fundamental philosophies here. One suggests that evolution is just as likely to come up with an intelligent six legged flying hippopotamus as an intelligent humanoid.
No one has suggested that.

The other philosophy suggests that evolution is controlled by rules that ultimately led to an intelligent humanoid. It's true, the latter philosophy is more difficult to prove as it requires one to study how evolution works to prove that rules exist. Nevertheless, it is what I believe.
No, the rest of us understand the how evolution works and that is why we are saying that bipedalism is no prerequisite for sentience. You are setting up a false dichotomy.

My suggestion of bipedal intelligence comes from the fact that no vertebrate with more than four limbs has ever been discovered. Tool making is much easier with two free hands, and that leaves two legs to walk on.
And yet tool using preceded bipedality. Besides, your observation is limited to what happened to have occurred on earth, with it's unique history and physical characteristics. A world covered almost entirely with water might well develop intelligent species that never became terrestrial and might have 50 limbs or 8 or 1.

[Darwin's Finch]

It seems we have two fundamental philosophies here. One suggests that evolution is just as likely to come up with an intelligent six legged flying hippopotamus as an intelligent humanoid. The other philosophy suggests that evolution is controlled by rules that ultimately led to an intelligent humanoid. It's true, the latter philosophy is more difficult to prove as it requires one to study how evolution works to prove that rules exist. Nevertheless, it is what I believe.

Actually, you left out the more fundamental philosphy, which I'd bet the majority of posters here subscribe to: that evolutionary pathways are contingent on both previous history and current environmental variables (in addition to more esoteric notions, such as "degrees of freedom" for mutations; not every mutation is equally probable). We got to where we are not because of predestination or fixed rules which dictate that a bipedal intelligent form must arise, or even from infinite plasticity and we just happened to win the mutational lottery, but because of our contingent history. If you change that history, life as we know it would be very different. As such, since no planet is exactly like Earth, we cannot reasonably expect to find alien lifeforms which look like those found on Earth. Sure, there may be similarities, based on convergent evolution (comon solutions to common problems, and all that), but the end results will still very likely differ in substantial ways.

My suggestion of bipedal intelligence comes from the fact that no vertebrate with more than four limbs has ever been discovered. Tool making is much easier with two free hands, and that leaves two legs to walk on.

No vertebrate with four limbs will ever be discovered. If we do find aliens with spines on some distant planet, they won't be vertebrates (as in, members of Vertebrata).

[WarmNPrickly]

Consistent with that analogy Chronos we end up with multiple species. What we don't see is current jumping between the parrallel wires. The "path of least resistance" analogy is not perfect, but it demonstrates the idea.

[Stranger On A Train]

It seems we have two fundamental philosophies here. One suggests that evolution is just as likely to come up with an intelligent six legged flying hippopotamus as an intelligent humanoid. The other philosophy suggests that evolution is controlled by rules that ultimately led to an intelligent humanoid. It's true, the latter philosophy is more difficult to prove as it requires one to study how evolution works to prove that rules exist. Nevertheless, it is what I believe.This is a grotesque and hyperbolic misrepresentation of what has been stated, to the point of invoking argumentative fallacy. No reasonable person would suggest that an "intelligent six-legged flying hippopotamus" is likely or even possible; evolutionary processes obvious favor forms that are realiziable within the allowances of basic physical mechanics, and there are certain general preconditions that we can estimate as being necessary for the development of intelligencel see lists in previous posts of this thread for examples thereof.

However, you are stating that a very specific form--a bipedal, human-like anatomy--is either a necessity for or a consequence of intelligence. You haven't demonstrated this in any factual or rational way, other than to assert that gripping appendages like hands are necessary. Even this claim is circumspect--an octopus, while having a very articulate manipulative capabiltiy, has nothing like a vertebrate hand--but even if we accept this to be true, it does not follow that any intelligent, extraterrestrial species would be derived from a four-limbed ancestor and would therefore devote two of the formerly locomotive limbs to manipulation and tool use to become a biped, much less humanoid.

My suggestion of bipedal intelligence comes from the fact that no vertebrate with more than four limbs has ever been discovered. Tool making is much easier with two free hands, and that leaves two legs to walk on.

Of course, my belief requires the burden of proof, and assumes a more complex system. Occam's razor is scientific folly.There are no vertebrates on Earth with more than four limbs (and for that matter, none that have fewer except for those who have deprecated limbs, and even these still show up in embryonic forms). This is a consequence of cumulative adaptation from an original terrestrial vertebate form with four lobes/protolimbs. Fantasy creatures aside, adding more limbs to a complex anatomy based on an internal skeleton would require a massive retooling of the vertebrate body form which is beyond unlikely. A "hopeful monster" with six or more limbs is hardly likely to be reproductively successful for any number of anatomical and competition based reasons, even assuming such a mutation would breed true, and the addition of nascent limbs (the predecessors of which likely existed for functions other than locomotion) in a complex form is unlikely to offer any significant survival or reproductive advantage long enough to bring it to functionality.

If it had been a six-lobed fish that crawled up on shore (metaphorically speaking...the evolution of terrestrial vertebrates is much more involved than that, of course) then we'd expect to have six-legged creatures which might deprecate or modify two or more locomotive appendages due to adaptive pressure, and thus we might anticipate a centuar-like intelligent species rather than a biped. Or a four-legged creature might have used something else--say, lips, or a prehensile tongue, or an extended probiscus--for manipulation and tool-use. Arguing that the biped form is an inevitable consequence of or requirement for intelligence and tool use because all examples we have of this are bipeds, even if it were true (which it's not) is making a claim from a highly restricted set of data without a definitive and uniquely sufficient causal link; a combination of arguing the general from the specific and the cum hoc, ergo propter hoc fallacies. You states that "evolution is controlled by rules", but except for the rules of physics and biochemistry there are no "rules" or "guidelines" by which evolution progresses in terms of selecting form; it simply adopts the most reproductively successful adaptation or modification of current form.

Stranger

[Lemur866]

Ever seen an elephant? Here's a highly social, highly intelligent quadripedal herbivore, that doesn't use it's front paws to maniuplate objects, but rather a specialized organ derived from the muscles of the nose and lip. Elephants have brains as large as a human. It's easy to imagine a civilization of human-intelligent elephants a million years in the future. But those elephants wouldn't be bipedal, and they wouldn't use their front feet to manipulate objects like Babar.

No land vertebrate is going to grow six legs, sure. But while an elephant's trunk isn't a fifth limb, it functions as one, just like the Panda's thumb that isn't a thumb.

And even if we look at creatures that use their front paws to manipulate objects, how many of those are bipedal? And when we look at bipedal animals throughout evolutionary history, we see that although bipedalism has evolved many times, our sort of bipedalism is unique. Any quasi-vertebrate intelligent biped is much more likely to resemble a bipedal dinosaur rather than a tail-less ape with its torso cranked up 90 degrees.

One more thing to consider. Evolution DOES tend to find optimum solutions for engineering problems. But the caveat is that these are local optimums, rather than global optimums. So if you've got bony animals, evolution can find all sorts of novel ways to reduce weight and increase strength of bones...but no animal that depends on a strong skeleton is going to ditch calcium phosphate bones and start using aluminum, even if aluminum bones would be much stronger. Once an organism is dependent on a particular structure evolution will refine and refine that structure, but the organism can't throw the structure away and start from scratch. So giant arthropods from the Paleozoic couldn't evolve internal skeletons, even though internal skeletons are much more effective than exoskeletons for large animals. Animals are often stuck with their evolutionary legacy, with no way to improve it, even though obvious improvements might exist, because every animal has to exist and reproduce as a whole animal.

[Anaglyph]

Because of our particular body-plan, we will most likely never gain limbs or even digits, regardless how useful they might be simply because the required mutations would be vast; we'd basically have to shift body plans, and that just doesn't happen.
Actually, polydactyly (http://en.wikipedia.org/wiki/Polydactyly) (having extra digits) does occur in humans and other species: The condition has an incidence of 2 in every 1000 live births, although the frequency is higher in some groups (an example is the Amish in the United States, due to the founder effect).

[Stranger On A Train]

Consistent with that analogy Chronos we end up with multiple species. What we don't see is current jumping between the parrallel wires. The "path of least resistance" analogy is not perfect, but it demonstrates the idea.Setting aside for the moment the point that argument by analogy is a dreadful way to extend a logical argument, I fail to see how this advances your case at all. We certanly don't see species jumping from one order to another (except in the case of misclassification, which is an artifactural problem with taxonomy, not the theory of natural selection) it reinforces the argument that your end result is predicated by the path you've previously taken; four legged terrestrial vertebrates are a consequence of the ancesterial anatomy having four motive limbs, and the bipedal stance with forelimbs being rededicated to manipulative digits is a consequence of that plus what comes after, specifically brachiating primates. If intelligence had instead advanced to tool manufacturing stage in aves, we'd anticipate a more complicated manipulative beak and tongue structure (which in fact can be seen in the birds with high intelligence and the propensity to make use of "found" tools).

Evolution isn't about "least resistance" or even optimal parsimony; indeed, the most generally adaptive creatures are ones that retain extra or seemingly unnecessary capabilities which come in handy when survival pressures change. Having a "bag of tricks" up your genotypical and phenotypical sleeve is a credible evolutionary strategy up to the point that carrying them around fatally compromises your ability to survive.

Stranger

[Stranger On A Train]

Actually, polydactyly (http://en.wikipedia.org/wiki/Polydactyly) (having extra digits) does occur in humans and other species: The condition has an incidence of 2 in every 1000 live births, although the frequency is higher in some groups (an example is the Amish in the United States, due to the founder effect).This isn't an adaptation to external sitimuli but a mutation that is generally anatomically inconsistant, i.e. the extra digits are (generally) only partly functional or impair normal use, though it is possible that such mutations could be selected for if they offered an reproductively advantagous capability. (Please, no jokes about triple-breasted whores.) At any rate, adding additional fingers or toes isn't comperable to the complexity of adding whole limbs, particularly motive implements, which would require a massive restructuring of the skeletal system to accomodate. At any rate, no vertebrate species has evolved to add additional limbs as part of the species anatomical archetype.

Stranger

[WarmNPrickly]

It doesn't seem that anybody is really presenting any proof of any kind. People say that six legged creatures could have been the first to walk on land, but they don't offer any proof of that. An elephant can be held up as an example of something that is a quadruped that uses tools, but an elephant is pretty limited in what it can do wth them. As I mentioned earlier, an octupus is an interesting example. I don't know why octupuses haven't developed intelligence. It could be that an ocean environment is bad for the development of language. Maybe the mutations that would lead to intelligence are only feasible in vertebrates.

Playing like your giving me information I haven't already considered isn't going to convince me of anything. Tell me something new.

[Darwin's Finch]

Actually, polydactyly (http://en.wikipedia.org/wiki/Polydactyly) (having extra digits) does occur in humans and other species: The condition has an incidence of 2 in every 1000 live births, although the frequency is higher in some groups (an example is the Amish in the United States, due to the founder effect).

However, as I note in this post (from a different thread) (http://boards.straightdope.com/sdmb/showpost.php?p=2333516&postcount=7), polydactyl digits are not "new inventions"; they are the result of one or more genes being expressed multiple times during development. The extra digit / phalanx retains the developmental identity of the digit / phalanx it is copied from.

While the genes which control expression would be heritable (thus increasing the likelihood of polydactyly in certain groups), that extra finger or toe is, in itself, not.

[Stranger On A Train]

It doesn't seem that anybody is really presenting any proof of any kind. People say that six legged creatures could have been the first to walk on land, but they don't offer any proof of that. An elephant can be held up as an example of something that is a quadruped that uses tools, but an elephant is pretty limited in what it can do wth them. As I mentioned earlier, an octupus is an interesting example. I don't know why octupuses haven't developed intelligence. It could be that an ocean environment is bad for the development of language. Maybe the mutations that would lead to intelligence are only feasible in vertebrates.

Playing like your giving me information I haven't already considered isn't going to convince me of anything. Tell me something new. You've made an affirmative claim, to wit: tool-manipulating intelligence can only occur in bipeds, and have failed to present proof of it, despite examples to the contrary.
There is no "proof" that any number of other legs would be ideal, useful, or possible for a terrestrial vertebrate in the form of example because it hasn't happened, and indeed the purpose of that line of reasoning is to indicate that evolution of life on Earth hasn't demonstrated an exploration of all possible alternatives and dismissed them in favor of quadrapedal (and later, bipedal) locomotion. Four limbs (or deprecations thereof) are endemic of terrestrial vertebates because that number was, as far as we can tell, the number of existing lobes on primative lungfish. Furthermore, we have every reason to believe--from the study of anatomy, evolutionary zoology, and molecular biology--that adding more locomotive limbs to an existing complement is irreducibly difficult. Four is the number because it was arbitrarily first, not because it is some kind of evolutionary optimum, as evidenced by a wide variety of other numbers of limbs in insects.
Various species of octopus have demonstrated very high levels of conceptual and problem-solving intelligence, and while not social creatures in the sense of habitat or defense, they show a remarkable degree of visual communication skill in experiment. As they lack vocal or sound-generating capability (not a part of their cumulative form, see) they don't have the ability for speech or hearing, but they have an enormous brain compared to body mass, and have a visual cortex roughly comperable in complexity to primates. The main restriction, it would seem, in more extensive evolution to developing social intelligence and capability is their reproductive cycle; they die (by function) not long after impregnating or laying eggs, and thus don't have the kind of extended social or familial contact that is common among the more intellegent vertebrates.At this point, you seem to be dedicated to defending your thesis despite a complete lack of rationale beyond appealing to the extant but highly limited dataset of life on Earth, and are in your own words adverse to considering even contraditions therein, rather than engaging in honest discussion or debate. Evolution and natural selection are not simple processes that are readily analogous to simple chemical reactions or mechanical thermodynamics, and generally can't be boiled down to a simple set of rules that follows a linear and inalterable path toward a preconceived or universally optimum solution. The fact that you don't understand this suggests that you need to spend some more time reading up on the field rather than preserving a facile and unsupported claim.

Stranger

[John Mace]

It doesn't seem that anybody is really presenting any proof of any kind. People say that six legged creatures could have been the first to walk on land, but they don't offer any proof of that.
Uhm, invertebrates adapted to terrestrial life before vertebrates, so we know that creatures with more than 4 legs were the first to walk on land. The earliest footprints found are well over 500M years old and belong to some type of arthropod.


An elephant can be held up as an example of something that is a quadruped that uses tools, but an elephant is pretty limited in what it can do wth them.
Why are they limited, and why couldn't the trunk evolve to be more useful in manipulating tools?

As I mentioned earlier, an octupus is an interesting example. I don't know why octupuses haven't developed intelligence. It could be that an ocean environment is bad for the development of language. Maybe the mutations that would lead to intelligence are only feasible in vertebrates.
Depending on how you define intelligence, octopuses have developed it. And there are many aquatic animals that communicate quite well-- there is no reason to think that that environment is not amenable to the evolution of language.

[Darwin's Finch]

It doesn't seem that anybody is really presenting any proof of any kind. People say that six legged creatures could have been the first to walk on land, but they don't offer any proof of that.

We're arguing hypotheticals; how can you reasonably expect proof of anything hypothetical? Heck, you haven't offered any proof for your own hypothetical. Either the logic behind our explanations is sound, or it is not. I am of the opinion that it is; constraints are known to exist, body plans are known to be difficult, if not impossible, to modify in a substantial manner. Intelligence has manifested itself in non-humanoid, even non-vertebrate, forms here on Earth. There is no reason at all to believe that human (or human-like, if you prefer) intelligence is the only viable form of intelligent life.

An elephant can be held up as an example of something that is a quadruped that uses tools, but an elephant is pretty limited in what it can do wth them. As I mentioned earlier, an octupus is an interesting example. I don't know why octupuses haven't developed intelligence. It could be that an ocean environment is bad for the development of language. Maybe the mutations that would lead to intelligence are only feasible in vertebrates.

Language is necessary for telling someone else what you know; it's not necessary for being able to figure things out on your own. Cephalopods and elephants may not be building skyscrapers or flying saucers anytime soon, but that doesn't mean they don't have their own sort of intelligence (not to mention, they do possess forms of communication).

Playing like your giving me information I haven't already considered isn't going to convince me of anything. Tell me something new.

Given that we have not evolved telepathy, we don't know what's new to you. We can only infer, based on your arguments here.

[brazil84]

If the universe is infinite, then there is not only 1 other planet with humans on it. There is an infinite number.

And there is an infinite number of planets with a straight dope message board on them.

And an infinite number of people making this exact post, in English.

[John Mace]

What are the odds that a mod will finally put this thread out of its misery?

[David Simmons]

Language is necessary for telling someone else what you know; Maybe for telling what you know but not for passing on what you know. Female cats teach their kittens to hunt, wolves, bears et al teach their young how to survive.

I saw a movie of an octopus given a jar with a crab inside. It couldn't get the lit off to get at the crab. Thn an octopus who knew how was put in an adjacent tank. This one unscrewed the cap and grabbed the crab. The first one immediately grabbed its jar and after some trying got the cap unscrewed.

It is true though that language is necessary in order to pass on information widely and to those with whom you have no direct contact. If I could read the language I could learn directly from Galileo.

[Blake]

It is true though that language is necessary in order to pass on information widely and to those with whom you have no direct contact. If I could read the language I could learn directly from Galileo.

More importantly language is necessary for passing on information without exposure. I can tell you not to open your jar because it contains a poison, even thoug mine contains a tasty crab dish. An octopus is incapable of doing that.

Passing on information through demonstration alone is actually a terrible way of doing things and little better then trial and error. It is completely useless for teaching about things that are not demonstrably present in the environment right now. A wolf can teach its young how to hunt deeer, provided it encounters deer before weaning. In contrast I can teach my child how to hunt without her ever needing to see see the species.

[WarmNPrickly]

We're arguing hypotheticals; how can you reasonably expect proof of anything hypothetical? Heck, you haven't offered any proof for your own hypothetical.

The problem is, my ideas of how evolution has worked are being summarily rejected without a shred of evidence, yet I am expected to provide detailed proofs that humanoid intelligent life is likely. I've given, my ideas on tetrapods and how they would lead to bipedal forms. I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why we see some forms but not others.

It is just beyond reason to everyone else in this thread that I could have the same information, yet arrive at a different conclusion. As far as i can tell, everyone else has a perfectly valid view of how evolution occurs. My view is valid too. If you have proof that my view isn't valid, then please present it.

[Stranger On A Train]

The problem is, my ideas of how evolution has worked are being summarily rejected without a shred of evidence, yet I am expected to provide detailed proofs that humanoid intelligent life is likely. I've given, my ideas on tetrapods and how they would lead to bipedal forms. I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why we see some forms but not others.You haven't provided any evidence to support your rather strong and specific claim, nor addressed stated examples to the contrary. And now you're arguing to ignorance, to wit, that there are "mechanisms of evolution that aren't understood" which proportedly support your claim, or at least will once someone discovers them. This is a position without factual merit or basis; there is no credibility here to say that bipedalism is an inevitable result or a requirement of high intellect; the most that can be said is that the singular example of a complex, tool-manufacturing species we have available to evidence is bipedal. One data point does not a statistical prediction or basic principle make.

Stranger

[John Mace]

The problem is, my ideas of how evolution has worked are being summarily rejected without a shred of evidence, yet I am expected to provide detailed proofs that humanoid intelligent life is likely. I've given, my ideas on tetrapods and how they would lead to bipedal forms. I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why we see some forms but not others.

It is just beyond reason to everyone else in this thread that I could have the same information, yet arrive at a different conclusion. As far as i can tell, everyone else has a perfectly valid view of how evolution occurs. My view is valid too. If you have proof that my view isn't valid, then please present it.
Not really. You've posted stuff that isn't even about evolution, thinking that it was (ie, genes that don't affect reproductive fitness). You are taking what you know about chemistry and assuming that there must be a parallel in biology. You are insisting that just because form A is present now then form A must be essential in some way, when we know that isn't true. In fact, that's more akin to creationism or ID than to evolutionary theory. I'm sure you're a fine chemist, but you simply don't have a good understanding of evolutionary theory.

I'm not a biologist either-- my training is in physics. But I know enough about evolutionary theory to see that you are just plain wrong. If you don't take if from me, take if from Blake and DF, both of whom are biologists.

[WarmNPrickly]

But I know enough about evolutionary theory to see that you are just plain wrong.

Then tell me what you know that I don't.

[brazil84]

What are the odds that a mod will finally put this thread out of its misery?

I don't know, but if the universe is infinite, then maybe there are an infinite number of "What are the odds of humans evolving on a different planet" threads, many of which have already been closed by the mods.

[Blake]

In my experience, everything always takes the path of least resistance in most sciences. I see no reason to expect that the rules change for evolution.

As others have pointed out, everything doesn't take the path of least resistance, even in chemistry.



Ironically, I would consider something that promoted reproduction to be the easier pathway so your are proving my point. Obviously, you have a different definition of easiest pathway. I would also consider the paths that are more statistically probable to be easier.

In which case your position is entirely circular, and thus entirely illogical, and can thus be discouted out of hand.

You claim that things most frequently follow the path that is easiest. Then you define easiest as paths that are most statistically probable. And you can only determine which paths are most statistically probable by observing wich paths are utilised with the greatest frequency.

Your whole position has beocme hopelessly circular. Unless you claim to have some mathematical method by detecting a priori which path is most likely to be used your argument is completely illogical.

You are right, I am not talking about genes that are specifically detrimental to reproductive success.

All genes are detrimental if we restrict ourselves specifically to defintions that excalude reporductive success. No excuses, no exceptions, all genes are detrimental. Just consider the genes responsible for the bipedalism that you think is so vital. They are massively detrimental to the ability to bar live young and the ability to move without incurring spinal damage.

By "not talking about genes that are specifically detrimental to reproductive success" you have demolished your own position and forced us to accept that bipedlaism is in fact detrimental rather than beneficial.


The problem is, my ideas of how evolution has worked are being summarily rejected without a shred of evidence..

Nonsense.

Your ideas are being rejected because they are based on demonstrably flawed reasoning and are demonstrably not true.

Claiming that there is no evidence that things follow paths of high resistance or that there is no evidence that all genes are detrimental is simply not true.

...yet I am expected to provide detailed proofs that humanoid intelligent life is likely.

That's right, youmade the positive claims, you have to provide evidence. We only need to provide couterexamples to flasify those claims. You're a scientist, oyu should know this.

I've given, my ideas on tetrapods and how they would lead to bipedal forms.

And others have pointed out how those ideas are based on erroneous ideas.

I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why we see some forms but not others.

I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why you are completely wrong.

Where does thta leave us? Does that seem like a good reason to accept what I say? This is the problem with the argument from ignorance, it can be used to support absolutely any position at all.

It is just beyond reason to everyone else in this thread that I could have the same information, yet arrive at a different conclusion.

The trouble is that you have demonstrated that you don't have the same information. There is a lot of information that you clearly lack.

As far as i can tell, everyone else has a perfectly valid view of how evolution occurs. My view is valid too.

No. Science doesn't work on the "I'm OK you're OK principle. Only one view can be a valid reprsentation of reality. That may be a view that isn't being expressed, but it is impossible that two or more opposing views are all valid.

If you have proof that my view isn't valid, then please present it.

We have. Logical fallacies, factual errors and misundertsanding of evolutionary theory all invalidate your view.

[Stranger On A Train]

Then tell me what you know that I don't.See the above Mayr and Dawkins recommendations for a basic starting point in understanding evolution and natural selection as currently accepted.

I don't know, but if the universe is infinite, then maybe there are an infinite number of "What are the odds of humans evolving on a different planet" threads, many of which have already been closed by the mods.Oh no you don't! This is why I prefer Bohmian mechanics to the Many Worlds interpretation. It's all nonlocal hidden variables as far as I'm concerned. Hugh Everett was such a wanker. ;)

Stranger

[WarmNPrickly]

As others have pointed out, everything doesn't take the path of least resistance, even in chemistry.

Oh do please give me that chemistry example.

All genes are detrimental if we restrict ourselves specifically to defintions that excalude reporductive success. No excuses, no exceptions, all genes are detrimental. Just consider the genes responsible for the bipedalism that you think is so vital. They are massively detrimental to the ability to bar live young and the ability to move without incurring spinal damage.

By "not talking about genes that are specifically detrimental to reproductive success" you have demolished your own position and forced us to accept that bipedlaism is in fact detrimental rather than beneficial.

I don't think that the detrimental comment refered at all to bipedalism. I realize now that I made an error here. Given a large enough sample size, a neutral gene will survive 100% of the time. For genes that are advantagous or disadvantagous you need a time variable to determine the % survivability. The longer the time, the steaper the slope, but essentially once you get to infinite tima all genes that are dissadvantaguos will be selected out and all the genes that are advantaguos would be selected for. Still not sure what this has to do with the argument.

That's right, youmade the positive claims, you have to provide evidence. We only need to provide couterexamples to flasify those claims. You're a scientist, oyu should know this.

Yes this is true, but the absence of proof isn't proof that I'm wrong.

And others have pointed out how those ideas are based on erroneous ideas.

I must have missed this. Did someone come up with an example of a six legged vertebrate?

I think there are mechanisms of evolution that aren't understood yet. I think these mechanisms will explain why you are completely wrong.

Where does thta leave us? Does that seem like a good reason to accept what I say? This is the problem with the argument from ignorance, it can be used to support absolutely any position at all.

So you think there are unknown mechanisms of evolution that would preferentially select for a path our planet didn't take? That's interesting.

The trouble is that you have demonstrated that you don't have the same information. There is a lot of information that you clearly lack.

Well, I can't say that your post has exactly broadened my knowledge.

No. Science doesn't work on the "I'm OK you're OK principle. Only one view can be a valid reprsentation of reality. That may be a view that isn't being expressed, but it is impossible that two or more opposing views are all valid.


I haven't seen why my position isn't valid yet. I'm sure you'll clarify it soon though.

We have. Logical fallacies, factual errors and misundertsanding of evolutionary theory all invalidate your view.

Must have missed all that. This last post certainly didn't clarify.

[Colibri]

Must have missed all that. This last post certainly didn't clarify.

[Moderating]

Sorry, Christopher, if you have missed all the ways in which your positions have been refuted in this thread, then the effort is probably wasted. At this point, you seem to be arguing just for the sake of arguing, and not contributing any actual information. I'm going to declare the question asked and answered as far as GQ can take it. If you want to continue this discussion, take it to GD. I'm going to close this thread.

Colibri
General Questions Moderator