How can evolution explain body symmetry?

When you look at most animals, you see a very symmetrical body that can be split down the middle into two mirror halves. How can evolution explain this? To me, this clearly points to an intelligent designer, and not natural selection. Let me elaborate.Take the human ear. If evolution is correct, then I suppose that sometime long ago, some sort of cells started developing that were sensitive to sound waves, and eventually they formed into an ear with the various organs. But two ears are better than one because they allow the animal to distinguish which direction the sound is coming from. So somewhere along the line, via a mutation, an additional ear appeared, and over time slowly migrated to the opposite side of the head where it was in optimal position for stereo hearing. But the ear would still be a copy of the original ear, and not a mirror image. How can evolution explain this? All humans should have one of their ears facing backwards, or maybe upside down if they evolved naturally by the above process.Furthermore, how is it that almost all animals exhibit this symmetry of the body, yet all animals are different in their features? For instance, an ear of a human is very different than an ear of an elephant, but both ears of an elephant are identical and symmetrical and both ears of a human are identical and symmetrical. If all ears of animals were totally identical to other animals, it would be a little easier to accept. But having both pairs of ears evolve identically just doesn't seem possible. If evolution was responsible for the creation of the animals, then once an original pair of ears was formed on some ancient creature, they would start evolving, but you would not expect both the left and right ears to evolve exactly the same. They might have two ears, but you would expect their shape and size to be quite different as they evolve over time. How is it possible that trillions and trillions of beneficial and lasting mutations happened to all the animals, but that almost every single one of them happened to both the left and right sides equally and symmetrically? Even if evolution was true, the statistical odds that mutations would happen in that way are just absolutely incredible. Even to have one single mutation happen to occur simultaneously and identically and symetrically on the opposite side would be amazing, but to have each and every mutation do this is simply impossible.One additional point with respect to symmetry is the evolution of various appendages that eventually form limbs, wings, and other features. First of all, we should be seeing lots of not yet fully formed appendages occurring in animals, which we don't, but that is a totally different subject. But given some sort of appendage that is forming, you would expect that it would start out as just one single appendage, and then eventually it might duplicate itself into an additional appendage. But if this appendage is formed by random mutations, you wouldn't expect it to always be formed along the center line of the symmetrical body. Appendages would happen at random points on the body and then possibly migrate to more optimum positions. I can't say that it doesn't happen, but I can't recall ever seeing a generally symmetrical animal with an appendage off to one side. Why is that? Unless evolution happened long ago and then suddenly stopped, you'd expect to see all sorts of appendages that are not in line with the general body symmetry.In short, it is my opinion that the only way such a high degree of symmetry of the external body without any significant amount of non-symmetry could occur in all the species is by intelligent design, and not by any natural random process.This message has been edited by CrackerJack, 05-29-2004 11:07 PM

Let me give an example to make my point clearer. I know someone who has one extra digit on their right hand, but only the normal five on their left. The same with his mother, grandfather, etc. back through his family history. So his body is not symmetrical. Polycats are an example of such extra digits in cats. Their extra digits are often not symmetrical. I've seen many other mutations in humans and animals that produce non-symmetrical results. These sorts of mutations that cause asymmetry are quite common, so why haven't many such asymmetries propagated throughout the history of evolution? Certainly there would have been at least one asymmetrical mutation in the history of the evolution of man which was beneficial enough to have been retained or even if not beneficial would have piggybacked on a beneficial mutation being propagated. But the fact that there isn't any is very strong evidence that evolution never happened. In order for evolution to be true, beneficial asymmetrical mutations must never occur, or are somehow culled and not allowed to propagate. Can you supply any evidence that either of these is true? I highly doubt it. If extra digits are such a common result of mutation, we should see all sorts of animals with differences in the number of digits between their left and right side.Furthermore, regardless of how present life came into being, over time we should see many occurrences of non-symmetry due to mutations. If you were to breed cats or any other animal for a certain asymmetrical feature, eventually you would expect that mutation to become dominant and you would have "created" a new asymmetrical creature. Given enough time, such occurrences should happen naturally, given geographical isolation. So the fact that we do not see many such asymmetrical features on generally symmetrical animals indicates that either not enough time has passed since they were created / came into being, or there has never been enough geographical isolation from the main population for such mutations to propagate. For such a high degree of symmetry to remain, I see only one of two possibilities. 1. There was an intelligent designer created life not so long ago and chose a symmetrical design which has not had time yet to degenerate into any asymmetries. 2. Mutations have not propagated the way evolutionists say they do and the chances of population isolation allowing a mutation to become dominant is extremely rare and could never account for all the mutations required for evolution to have occurred.Now if there was some biological mechanism that forces symmetry, even in the face of asymmetrical mutations, then asymmetrical mutations should never be passed on from one generation to the next, and the internal body should be just as symmetrical as the external body. The fact that the internal body is not totally symmetrical, and that asymmetrical mutations are easily passed from one generation to the next proves that this is not the case. How is it that evolution "chose" to create an internal body that is asymmetrical yet an external body that is always totally symmetrical? It doesn't make any sense.So, in summary, the fact that asymmetrical mutations do occur so frequently places extreme doubt that evolution could have ever occurred unless some mechanism can be shown to explain why asymmetrical mutations do not propagate while symmetrical mutations do so very frequently.

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First, for a trait to continue it must offer an advantage to the population for survival. It is not individuals that evolve but populations. There is no plan to it, no direction.

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Precisely. "There is no plan to it, no direction." So why do we not see asymmetry in our evolution? Why is it that NO asymmetrical mutations are beneficial? What is so special about symmetrical mutations that makes them beneficial and asymmetrical mutations not? If, as you say, there is no plan or direction to the mutations, then symmetry should be a rare occrence, and not the norm.

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That you do not see it simply means it didn't happen.

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That says absolutely nothing about Evolution.

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Then what does it say? If someone says to me that there are one trillion mutations that were necessary to bring us to modern man from some prehistoric creature, yet not one of these mutations deviated from the symmetry, that, in terms of statistical odds, says a LOT about evolution. Statistically, evolution could never have happened or you need some better explanation as to why asymmetries do not occur.

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Language in humans evolved to be processed in the left hemisphere of the brain.

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This is an asymmetry that is shared by nearly all humans today.

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Your premise is shown to be false.

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Sorry, I thought I clearly stated in the first post that I was referring to EXTERNAL features, and not internal features. I was trying to make my posts more readable by not adding the word "external" to every single reference, but I probably should have mentioned it, so now I will. Unless I state otherwise, I mean external symmetry. Now I totally agree with you that the internal body is not completely symmetrical. Why do you suppose it is that evolution chose such perfect symmetry of the external human body and of most creatures, while choosing an asymmetrical internal body? It doesn't make any sense to me why evolution is supposedly so random, yet seems to be so selective in this case as if it is some designer doing the selecting.

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If extra digits are such a common result of mutation,
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It's not all that common.

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I know of two different cases of extra digits, so I would say it is fairly common, based on my observations, but whatever. I have personally only seen mutations that were asymmetrical and none that were symmetrical. But being I haven't made any scientific analysis of what are the probabilities of each type, I can't make any definite statement about that. The point is that asymmetric mutations are certainly not rare when compared to mutations in general.

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I found the following information in about 2 minutes after doing a quick google on "asymmetrical animals".

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Maybe you forgot to try to find out if there actually were asymmetries before declaring that there weren't?

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No, not at all. I purposely didn't give any examples because I wanted someone who is defending evolution to help prove my point, which you did nicely. First, I didn't say that there weren't any asymmetrical features in any animals. I was referring to man, and a large group (majority) of animals that are symmetrical. The fact that such a large class of creatures exhibit external symmetry, without any significant deviation, shows that at no point in their history were there any asymmetries, or else somehow they were culled out. The fact that you came up with a few examples of asymmetries just proves my point that there is no reason why non-detrimental asymmetries should not occur as part of evolution. But in general they do not. Why are there a few animals that exhibit clear asymmetries while the majority don't? Even by your own claim, you say that the asymmetries in these few examples are the result of the evolutionary process. Thus, by your claim there should not exist any evolutionary process that culls out all asymmetric mutations because such mutations are clearly visible in the examples you brought up. So what happened to all the asymmetric mutations that occurred throughout the history of the evolution of man? Why can't we see them? If evolution isn't deselecting them, then what is? Why are humans left with only the symmetrical ones?Now the main reason given as to why asymmetric mutations don't in general propagate seems to be that they are not of any benefit and have no reason to be selected. I say that this is a totally unfounded argument for the following reason.Trying to say that EVERY SINGLE mutation that has led to modern man/animals was beneficial, and that each mutation becomes dominant in the population before the next beneficial mutation can occur is totally absurd. It is an absolute impossibility that evolution could have ever occurred in the timeframe given if that was the case. And the full-range of transitional forms would be very evident. I don't think any knowledgeable biologist would ever try to make that claim given the current evidence. But in order for non-beneficial asymmetrical mutations to be absent in so many branches of the evolutionary tree, that would have to be the case, or else we would expect to see many of these non-beneficial mutations present and dominant in today's species.Let me elaborate. According to evolution, when a certain part of a population exhibits a positive mutation that gives them some advantage over the rest of the population, they then have a chance of squeezing out the others because of their advantage. But when selecting for some positive mutation, nature can't pick and choose and has no idea where evolution is taking it. It merely picks based on having some current advantage - a total advantage. So while sometimes the advantage may be just one single mutation, it often will be multiple mutations, with some being positive, some being negative, and some being neutral. If the net effect of all the mutations present in the new candidate species is positive, they have a chance at becoming a new branch on the evolutionary tree. If the net effect is negative, they will likely not make it. So along with some positive trait, it is only natural and extremely likely that many minor mutations will piggyback on the one or multiple positive mutations. Thus, even if no positive asymmetrical mutations ever occurred in the evolution of man, you would expect to to have some retained due to this piggybacking effect.Most biologists today agree that punctuated equilibrium, or some other method of rapid evolutionary change is needed to explain the fossil record. If such a large number of mutations happen in such a short period, you are certain to get some neutral and some slightly negative mutations happening at the same time as the positive ones. Statistically, it just isn't possible to have such rapid change and not have some of these additional mutations included. Evolution has no way of examining the DNA and throwing out slightly negative or neutral mutations, it only can select branches that have an overall advantage and deselect branches that have an overall disadvantage. The same statistical odds apply equally to positive mutations as they do to neutral mutations when deciding if both male and female sharing the same mutation(s) pass it along to their offspring as a dominant trait(s). So statistically you are bound to get these neutral mutations in some of the evolutionary steps. Maybe not all of them, but statistically it is impossible that some won't be included. The only possible way they could have been excluded is if evolution happened much more slowly than is generally accepted and mutations happened so slowly that there was statistically almost no chance that there were any other mutations piggybacking on any of the evolutionary steps.

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Vertebrates all evolved from water dwelling, swimming creatures, and there is VERY good reason for a swimming creature to be symmetrical. Once the symmetry is established, why do you expect it to be abandoned so much? And of course, when there's a good reason, it is abandoned (see the pics in previous post).

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You make a very good point about swimming sea creatures. If evolution was true, that would be a very good reason why symmetry was selected in those creatures. But the migration from sea to land happened long ago, yet the symmetry still exists with very little deviation in spite of huge evolutionary change in the creatures. If very little change had occurred since the start of land creatures, you would have a very good point. But given all the time, and all the multitude of mutatations, I don't see the significance of your point with relation to land creatures.

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Unless it offers an advantage you will not see it.

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I have to totally disagree with you there for the reasons I mentioned in one of my previous posts. Non-advantageous mutations should very often occur piggybacking on advantageous ones.

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But the very things you have mentioned, that there is no symmetry internally, shows that there is no preference for either symmetry or asymmetry.

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Again, I must totally disagree. There is some degree of internal symmetry, but certainly not the same as externally. So there seems to be a definite preference for external symmetry, and a much less preference for internal symmetry. Now can you offer some explanation for this difference between internal and external? Why would symmetry be so much more preferred for the external body and not the internal? But yet, in terms of mutations, you are totally correct because there doesn't seem to be a preference there for either symmetry or asymmetry. That is the clincher. Mutations don't prefer symmetry or asymmetry. They are random. But the evidence of existing life forms shows a high degree of preference for external symmetry. Thus evolution via mutations cannot be adequately explained in light of such obvious symmetry.

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Plus, look at all the critters out their that are not symmetrical. Plants, are a great example. Look at handedness. Asemmetrical. Look at snail shells, look at fiddler crabs, look at trees, look at many spyder, bee and other insect's eyes. Often there are three of them, asymmetry.

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Yes, plants do not exhibit the same degree of symmetry as found in animals. But I never mentioned plants in my post and fail to see what that has to do with anything being plants and animals are totally different life forms. As I already mentioned in another post, your few examples of asymmetry in an otherwise symmetrical world just proves the existence of asymmetrical mutations which flies in the face of the evolution of symmetrical creatures. But rather it tends to give more credibility to the suggestion that nature was created by an intelligent designer.

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Just to add, ask any barber and you'll find out that everybody has asymmetrical ears - one is always a little higher than the other.
Most people have a facial asymmetry to one degree or another. Not to mention one longer arm, one longer leg, one larger foot.

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I don't think you understand my point, because your argument seems to be helping to prove my position. Of course there are minor differences. But overall, the external body is very symmetrical. Now, what is the cause of these minor differences and does it prove that the left and right halves evolve separately? If the left and right sides are slightly different because of genetic evolution, then it totally blows evolution out of the water, because the left and right side should evolve independently and there is no reason why there should be much symmetry at all. That is back to my original point of how is it that two opposing body features managed to almost exactly duplicate each other's mutations such that they look exactly the same unless carefully examined for the small differences in size, position, etc as you pointed out. Why didn't elephants develop a left ear like an elephant and a right ear like a human? Or why didn't we develop a human ear on one side and a rabbit ear on the other? Either something is forcing symmetry, or it isn't. If nothing is forcing symmetry, which you seem to be saying, then you've got a big problem with your theory because symmetry is just about everywhere you look. If something is forcing it, then you've got a problem explaining why it is so selective.Now, if the left and right halves evolve together (symmetry is forced), then why are there these minor differences? That would mean that they are not the result of lasting genetic mutations but rather individual aberrations which are not consistent across the general population and so they have no significance with respect to this discussion because they are not inherited traits. I have not researched the reason for these minor differences you mentioned, but I suspect it has much more to do with growth and development than with genetics.So take your pick. You either brought up a point of no significance, or you helped prove my point.

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For everyone out there: YOUR PERSONAL EXPERIENCES AND OBSERVATIONS DO NOT CONSTITUTE VALID DATA SETS FROM WHICH ANYONE MAY DERIVE MEANINGFUL STATISTICS.

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I get your point and completely agree. And I certainly didn't mean to imply that my limited data sample set any sort of statistical precedence. On the other hand, the data I mentioned has little effect on my overall argument. Anyways I will try to research such data better in the future an provide meaningful statistics rather than personal experience. Thanks for the suggestion.

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It's actually you who doesn't understand your own position, or at least, the very obvious consequence - if we're the product of intelligent design, and that designer is a perfect God, then we shouldn't have just some overall, large-scale, exterior symmetry.

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We should be perfectly symmetric, inside and out. We're not, so we're obviously not the product of a perfect designer.

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First of all, I never mentioned a perfect designer, I just mentioned an intelligent designer. Second, who says even a perfect designer would create something perfectly symmetrical? In his mind, something less than perfectly symmetrical might be exactly what he intended. If you don't know the designer, how can you guess at what his intentions were?But regardless of that, mutations are an undeniable part of biological life on earth. So even if we were created with a perfectly symmetrical external body, mutations could have easily marred that perfect symmetry. I fail to see any reason why a designer would necessarily choose a perfectly symmetrical interior, as that is not the most optimum design. Take an automobile for example. Most automobiles are designed to be symmetrical on the outside and the visible portions of the interior as that is pleasing to eye of the designer and buyer. But open the hood and you will see something totally asymmetrical. The same with the human body. Strange coincidence there don't you think? A human designer designs a complex piece of machinery much the same way as the human body is designed. Asthetically pleasing and symmetrical on the outside, and asymmetrical but functional and practical on the inside.

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Evolve seperately? Of course not. My left side doesn't reproduce separately from my right, so my two sides obviously won't evolve separately.

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Well, it was you who brought up the minor differences between left and right ears, etc. I didn't know why you were doing that, and thought maybe it was because you thought they were evolving independently. Thus my reply. If you don't think so, then please explain the significance of your initial reply because in light of your current reply I fail to see what was your point was in your first reply.

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Look, your question has been answered twice over. Why are we mostly symmetrical?

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1) Because we're the decendants of organisms for whom symmetry was an adaptation to environment.

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2) Because symmetry is strongly sexually selected for (humans are most attracted to mostly symmetric humans.)

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Well, maybe those were adequate answers in your mind, but to me they fall way short of the mark. Point 1 does explain the initial symmetry of swimming sea creatures, but fails to address why the symmetry has remained in spite of a huge span of time over which asymmetrical mutations should have been common and long ago changed much of the symmetry. Point 2 I will address in response to your next quote.

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Now it's you who doesn't understand my point. Of course something is "forcing" symmetry in humans - sexual selection. But it only forces symmetry with one big restriction: it only enforces symmetry you can see. That has two consequences - one, that the symmetry will only be true enough to fool the eye, and not the mirometer; and two, that the symmetry will only be on the outside.

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Look, it's pretty simple. The source of symmetry goes back to our invertebrate ancestor, who was adapted to an aquatic environment, where bilateral symmetry works better than asymmetry. It persists in our species and others because it's very strongly selected for, sexually.

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Thank you for that thorough explanation. Really! However, I must disagree with that theory. Some creatures are blind, or have such poor eyesight that they could not select for symmetry, yet they remain symmetrical. But even in animals who have excellent eyesight, do you think they examine every part of a potential mate and reject any that are not perfectly symmetrical? Perhaps a human has enough intelligence and insight to do this, but I don't see any other creatures that would be so thorough in their inspection of a potential mate. Do you think lower level animals have the ability to count the digits on their potential mate and count their own and then reject the candidate if the number digits don't match? Come on! A very general inspection of symmetry might be believable, but assuming all the animals are carrying out any detailed inspection that would rule out all minor asymmetries is just farcical. Your theory sounds good at first, but I don't see how it holds any water upon close examination.Actually, I disagree that any sexual selection towards symmetry is taking place based on a visual inspection, other than perhaps in the most highest level animals. Swimming sea creatures who are not symmetrical would tend to not be such good swimmers and less likely to avoid predators, and thus naturally deselected by getting eaten before they could reproduce. There would have been no need to have even developed such a sexual selection. Sexual selection of a mate based on physical characteristics certainly does happen, but I highly doubt that symmetry plays any part of this in creatures of lower intelligence. If you can provide any link to actual scientific studies of this, then please do so. I'd be interested to read about it. I'm not saying such sexual selection doesn't occur, I'm just saying I'm highly suspect that it does unless real solid scientific proof can be provided.

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Also, it's a requirement for walking around on any number of legs on a flat surface.

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Really? You could have fooled me there! Do you mean to say that if some animal had a nose on the side of it's head, it couldn't walk? Or if I have one extra digit or one less digit on my hand, that means I can't walk? Some huge asymmetrical appendage might create an imbalance, but other than that I fail to see how an asymmetrical mutation would cause a creature to not walk. Please explain.I really thank you for your thoughtful explanation and look forward to more discussion on this topic if you have the time and desire.

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As a Christian I get really upset when people try to use Intellegent Design as a way to falsify Evolution.
There is no way anyone can look at the designs and say they were done by an Intellegent Designer. Maybe they were a Junior High Science Project but certainly not one the level that any mechanical engineer would hope to produce.

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Don't you realize just how incompetent that makes God look?

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I couldn't disagree with you more. If the designs are so terrible, why is it that man can't even come close to building something that works as well as the human body? All complex machinery that man makes requires constant maintenance to keep it going, replacing of parts when they wear out, etc. Show me someone who can build a human sized robot that weighs the same or less as a man, can walk/run at the same speeds as a man, can operate on average for more than 50 years without any significant maintenance, be every bit as flexible and agile as a human, and can reproduce itself. Then your statement might start to gain a little credibility. Look at all the biological creatures and they are simply an absolute wonderful collection of magnificent designs. From microscopic motors, to flying machines, to aquatic swimmers, to sprinters. I absolutely do not see how you think some junior high school student could produce anything that could even be considered anything remotely close to those designs.

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1) Many creatures are not extrenally symmetrical, as I illustrated.

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I would not call that many. I would say more like a few. When you look at the animal world as a whole, you see external symmetry as the norm, not as the exception.

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2) Why do you discount internal asymmetry as evidence of evolution producing asymmetry? Internal structures evolve in exactly the same way as external, so it makes no sense for you to treat them differently.

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If internal and external structures evolve in exactly the same way, then there should be lots of asymmetry in both. Being there isn't, evolution should be discounted because as of yet nobody has given a good enough explanation to account for such a high degree of external symmetry. And the sexual selection argument doesn't cut the mustard as I've already shown.

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3) Evolution has been shown to proceed by random processes combined with selection, but the selection is done by the environment. No intelligent "designer" needed.

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And there is no need in the environment for such a high degree of external symmetry in land creatures, so no need to deselect asymmetry unless it negatively impacts locomotion due to an imbalance or some other such effect. Proof has already been provided of limited asymmetry, so why is it so selective and not widespread?

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I have a mutation that caused both of my lower wisdom teeth to never develop, and that was symmetrical.

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A woman my husband knew in high school has corckscrew-like pinky fingers and that is symmetrical.

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Polydactylism in cats is symmetrical.

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Ok, I have done some research today on symmetrical vs. asymmetrical mutations and yes there are a fair number of symmetrical mutations as you have pointed out. But polydactylism in cats is not always symmetrical. In general, some mutations are symmetrical, and some are not. So unless someone can provide some actual scientific data on what is the ratio between the two, we can't really say anything more than both types are well known to occur.

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You seem to think that non-adaptive assymmetries (you limit your requirement to only in humans and only external, for some strange reason) should be widespread in a population.

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Evolution doesn't make that prediction.

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No, I don't limit it to just humans. If evolution were true, there should be some probability that some percent of all mutations that are retained will be clearly asymmetrical. Statistically, most asymmetries (not including those that negatively impact the species) should have stopped being deselected once fish became land animals. Being man is claimed to be a descendant of the original land animal, that means that some very early ancestor should have some noticeable asymmetric feature and all descendants from that creature, including man, should exhibit that feature. Along with it, many other asymmetries should have been picked up along the way, and the end result should be a wide range of asymmetries across the entire spectrum of the animal kingdom. If evolution was true, I would expect just about every land creature to exhibit some clearly visible external asymmetry.

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All animals exhibit clear assymetry, you just want to ignore the internal ones.

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Why do you insist that we ignore internal asymmetry?

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I'm not ignoring them. I'm just saying that if evolution is creating internal asymmetry, it should also be creating external asymmetry. There is no reason for it to be so selective.

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There are, however, evolutionary pressures to cull out most asymmetries.

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What do you mean by "most"? And by what means (other than what has already been mentioned) are they culled out? Many mutations, symmetrical or asymmetrical, will create a big disadvantage and should obviously be culled. Asymmetrical mutations that create one longer leg than the other are obviously going to be culled. But would a long ear lober be culled? What about all the positive mutations that have occurred. Take opposable thumbs for instance. Everyone agrees that they are a huge advantage for humans. What if an early ancestor of man evolved an opposable thumb on just one hand and not the other, would that be culled because it was a disadvantage? Of course not. It would be retained. Somewhere along the line, some of the advantageous mutations should have been asymmetrical and retained.

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We still have them.

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They are mostly internal.

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Why do you ignore them?

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If they are mostly internal, that means that some of them are external. Please name the external ones.

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As for external symmetry in humans, it has been empirically shown that symmetry is strongly sexually selected. IOW, asymmetry reduces a human's chance of mating.

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Agreed that in humans, a new asymmetry would be a disadvantage. But if all humans had the same asymmetrical feature, it would be considered normal and not deselected. Lower animals are not capable of the same sort of reasoning and inspection that a human is. So some distant ancestor of man should have had an external asymmetrical mutation that was retained and considered normal and thus not sexually deselected.

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1) Evolution does select them out, which is why we don't see them.

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Why does evolution select them out? The sexual deselection argument doesn't cut it as I've already shown. Please provide a reason that applies to ALL externally symmetrical animals. Why is it being culled out in blind animals? How can lower level animals count and determine an uneven number of digits between the left and right? Sexual selection can only account for deselecting new mutations in humans and possibly other very intelligent animals. It cannot account for the lack of asymmetries in the past or in lower level and blind animals.

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2) We have plenty of asymmetries, they are just internal. Why don't they count to you?

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We keep going over and over this. Because if evolution is true, it should be creating a similar number of external asymmetries as internal asymmetries in the lower level animals. But it doesn't so I want to know why. Nobody has given an adequate answer to my reasons I gave for why sexual selection doesn't work. Please give me an adequate reason that applies to ALL land animals, and I will consider the question answered.

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Humans are FUNDAMENTALLY asymmetrical in nearly all respects EXCEPT for basic body plan, alterations to which are likely to strongly negatively affect either locomotion, sexual attractiveness, or both.

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Again, the same old argument that just doesn't cut it. I just answered it. As to locomotion, again totally off base. Only mutations such as leg length, abnormal paws/feet, or weight imbalance would affect locomotion. Most mutations would have no effect on locomotion.

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But once you set up embryonic development in which all vertebrates are symmetrical in their basic body plan, how long do you think it should take to change it, particularly since there is no great evolutionary pressure to be asymmetrical?

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Agreed that the body should still show a symmetrical shape. But there should be at least some, and in most cases numerous external asymmetries in all or just about all land creatures. There is no evolutionary pressure to be asymmetrical, but likewise there is no evolutionary pressure to retain symmetry either. So the mutations should be a random mixture of the two.

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Furthermore, creatures ARE fundamentally asymmetrical, except for basic body plan, alterations to which may detrimentally affect sexual attractiveness and locomotion.

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See my previous post for answers to both the sexual attractiveness and locomotion arguments.

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Perhaps you could give an example of an external, asymmetrical mutation in man that you think would not be selected against (and while sexual selection has been shown to do this you may ignore that for the moment)?

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Someone will find something about any example I give and say that it wouldn't be selected because of one reason or another. So rather than try to second guess what sort of a mutation would be advantageous and what wouldn't, why not just take just about any of the existing differences between man and simpler life forms. Being they've supposedly already been selected, there is no refuting their advantage. For example, opposable thumbs. We happen to have two of them. But let's say that at some point we just developed an opposable thumb on our right hand and our left was left with five regular fingers. That would be a clear advantage even though the left side didn't duplicate the mutation. Why were all of the advantageous mutations symmetrical and not one of them asymmetrical? It doesn't have to be opposable thumbs, that is just an example. But take just about any of the evolutionary steps and make it asymmetrical rather than symmetrical and you still get an advantage, with a few notable exceptions.

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Now there is one more point that I think has been mentioned. I'm not sure of this so it may take a bit of digging but I think that our symetrical features are not the result of "left-genes" and "right genes" but one gene for both sides with expression controled by other mechanisms.

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If there was just one gene for both sides, then why would the internal body show such asymmetry? Having single genes for both sides of the external, and separate genes for either side of the internal would be a very strange and I think you would have a hard time explaining why such a mechanism developed. Plus the examples given of asymmetry (crabs and flounder) prove that the left and right sides are different, at least they must be in those cases.

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Non-advantageous mutations should very often occur piggybacking on advantageous ones.
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Why should this happen "very often"?

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Also, please define "very often"; how often is "very often?".

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To define precisely how often it would occur, I would have to collect data on what is the ratio between symmetrical and asymmetrical mutations, then we have to decide on what the mutation rate is when evolution is occurring and do some calculations. Being that current biologists are tending towards rapid mutations in a short time, followed by long periods of stability, I assume the mutation rates they are expecting during the evolutionary steps are quite high. The higher the mutation rate, the more frequent you will see multiple mutations piggybacking on the main mutation(s) responsible for the step. Being we don't observe this type of mutation happening (at least not quick enough to measure), we have no way of knowing what exactly is the mutation rate at the point of these evolutionary steps. Thus no way of calculating it precisely.

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No, plants and animals are not fundamentally different life forms.

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Fundamentally, they are the same.

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The same system of DNA and RNA is found in both plants and animals.

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Why does it matter, anyway?

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From an evolutionary perspective and from your perspective they may be fundamentally the same, but they are certainly not the same from mine. But it really doesn't matter as you say. I was referring to animal symmetry, and not to plants or microscopic organisms and I was not the one who brought up plants.

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As I already mentioned in another post, your few examples of asymmetry in an otherwise symmetrical world just proves the existence of asymmetrical mutations which flies in the face of the evolution of symmetrical creatures.
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NO IT DOESN'T!

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Evolution does not predict that every single creature be symmetrical.

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Nor does it predict that every single creature be asymmetrical.

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It predicts that populations will, over time, adapt to their environments or go extinct.

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Then why do you and everyone else keep harping on selection for symmetry based on sexual attraction and locomotion? On the one hand you are saying that evolution is selecting for symmetry for these reasons, and on the other hand saying it is selecting for the environment. Well you are trying to take both sides of the fence and it doesn't work that way. Pick one side or the other and stick to it. Your showing of these asymmetrical features proves that sexual attraction does not always work. If it didn't work in these cases, you specified, then we first should assume it never works unless it can be proven otherwise. It is certainly proven in humans that it can be a factor, but I have seen no evidence that it is effective in any of the lower life forms. So until you can supply some proof, sexual attraction cannot be used as any sort of proof that evolution has been selecting for symmetry since the advent of land animals.

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If you can't make any testable predictions about how the designer might design something, the ID is useless as science.

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Also, you have been saying all along that suchandsuch is evidence for a designer, but now you say it is impossible to know what or how the designer designed anything.

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Which is it? Do you know, or is it impossible to know?

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Well, I say that the symmetry observed in humans and other creatures cannot be explained by evolution due to the randomness of evolutionary mutations. If life as we know it didn't come about by evolution, and it didn't come about by an intelligent designer, then by what means was it created? Those are the only two possibilities I can think of, and being evolution is ruled out in my mind due to the reasons I've explained, I assume it was an intelligent designer. If you can show another way by which we were created I'd be glad to entertain your idea.