How can evolution explain body symmetry?

The one eyed, one horned flying purple people eater?

---

Aslan is not a Tame Lion

Well, who says even a perfect designer would have any concern about symmetry at all? If anybody's making assumptions about what designers are like, isn't it you in your opening post? I had thought my point was pretty obvious - your opening post is based on a false premise. You ask why such perfect symmetry exists, but the problem is, it doesn't. There's only as much symmetry as we would expect from evolution. Uh, right, that was the purpose of Point 2. Duh. That hardly means they have no ability to sense symmetry. Plus, most of the species you're talking about are aquatic. No, of course not. But they do tend to prefer mates that appear symmetrical. Perfect symmetry doesn't exist.Look, it's proven fact that humans prefer symmetrical faces. Even infants prefer them. Why on Earth would that require counting? How stupid. All you have to do is look at the organism. If one side is different from the other side, it's not symmetrical.Everybody does this, and it doesn't even take thought. For instance, this famous picture:Ah, a masterpiece. And that smile - so enigmatic, so mysterious. The smile that has captivated poets and lovers for centuries. What is it, exactly, about this famous gaze that defies us to look away?As it turns out, it's a clever asymmetry in the picture that your brain notices immediately, but your consious mind fails to see. If you look closely, you can see that the horizon on the left is lower than on the right. It's a visual impossibility that immediately triggers "wrongness" in your brain but your conscious self wouldn't have noticed if I hadn't pointed it out.Like all vertebrates, your brain has hardware that detects symmetry. The reason you detect it is because often, asymmetry represents poor health or injury, which are not things you want in a mate. Of course they don't observe all minor asymmetries. That's why minor asymmetries persist, like your ears and stuff.You don't seem to be getting it yet. We're not perfectly symmetrical. We're only asymmetrical up to the point that a potential mate might notice, because asymmetry is selected against.We're not perfectly symmetrical. We're only as symmetrical as evolution predicts.There's a third potential explanation for the persistence of symmetry - it's genetically simpler. It takes a lot more genes to code for two separate sides than than to provide the genes for one side and simply duplicate for the other. That's the "evo-devo" explanation, I guess.But ultimately the answer is pretty simple - why does symmetry persist? Because in most cases it's better than asymmetry. And again, your inital premise is false, anyway - nothing's perfectly symmetric. We're only as symmetric as evolution predicts. Get it, yet?

quote:

---

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.

​

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

---

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.

quote:

---

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

---

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.

quote:

---

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.

---

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.

quote:

---

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.

---

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?

quote:

---

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

​

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

​

Polydactylism in cats is symmetrical.

---

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.

quote:

---

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.

​

Evolution doesn't make that prediction.

---

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.

quote:

---

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

​

Why do you insist that we ignore internal asymmetry?

---

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.

quote:

---

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

---

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.

quote:

---

We still have them.

​

They are mostly internal.

​

Why do you ignore them?

---

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

quote:

---

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.

---

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.

quote:

---

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

---

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.

quote:

---

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

---

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.

quote:

---

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.

---

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.

quote:

---

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?

---

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.

quote:

---

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

---

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

quote:

---

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)?

---

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.

quote:

---

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.

---

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.

quote:

---

quote:
--------------------------------------------------------------------------------
Non-advantageous mutations should very often occur piggybacking on advantageous ones.
--------------------------------------------------------------------------------

​

Why should this happen "very often"?

​

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

---

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.

quote:

---

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

​

Fundamentally, they are the same.

​

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

​

Why does it matter, anyway?

---

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.

quote:

---

quote:
--------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------

​

NO IT DOESN'T!

​

Evolution does not predict that every single creature be symmetrical.

​

Nor does it predict that every single creature be asymmetrical.

​

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

---

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.

If that's supposed to be true, what do you think all those doctors do? What do you think all those medicines are for? I imagine that your average junior high school student wouldn't have designed the human retina backwards.

quote:

---

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

​

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.

​

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

---

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.

quote:

---

Symmetry is useful for walking on land, too.

​

Try walking with one leg shorter than the other.

​

Also, Why do you think that asymmetrical mutations should have become dominant long ago if they are not adaptive?

---

Yes, symmetry is important with respect to the length of legs, size/shape of feet/paws, and if it affects balance. But mutations that would effect these points are only a small fraction of all possible asymmetric mutations. Non adaptive mutations would have become dominant just by chance by being present at the time of an evolutionary step. For evolution to work, it requires a lot of mutations and a lot of chance happenings in making those mutations dominant in a population. I already explained that evolution can't work on only one mutation at a time because it would greatly expand the time required for current life to have evolved. So there must be many mutations happening simultaneously. In order for the statistics to work for the good mutations, they are also working for the neutral and bad mutations. Most of the bad mutations are culled out due to their negative effect, but the neutral mutations cannot be culled with respect to these statistics. Thus the piggybacking effect.

There are, though. That's been the point of about ten messages to you, so far.

quote:

---

quote:
--------------------------------------------------------------------------------
Or if I have one extra digit or one less digit on my hand, that means I can't walk?
--------------------------------------------------------------------------------

​

No, but it may impede your ability to grasp and hold things in your hand, like food, weapons, tools or prey. Hands, BTW, are unique to certain primates. They are an extremely recent evolutionary development.

​

Potential mates would probably be less likely to be attracted to you due to your birth defect, too.

---

Totally irrelevant! If such mutations were symmetrical, rather than asymmetrical, they would have exactly the same effect if not more so. If, as you say, an extra or missing digit affects grasping, then a symmetrical mutation would be even worse because it would affect both hands and not just one. Likewise with attracting a mate. "Two" defects are worse than one and are more likely to turn off a potential mate. My comments were made in response to the claim that asymmetry affects locomotion and you're trying to turn the argument into something totally different - neither locomotion nor asymmetry.

quote:

---

quote:
--------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------

​

One leg is shorter than the others.

​

One foot is larger than the others.

​

Your big toe is tiny on one foot and big on the other.

​

You are under some mistaken impression that a mutation has to cause a creature to not be able to walk at all to be tetrimental.

​

My husband is bow legged and flat footed, which is fine now because he is an academic, but a million years ago, on the savannah, he would be at a pretty big disadvantage.

---

Sorry, my bad. Length of legs had already been discussed, but I failed to mention it again there. I apologize for the oversight.

quote:

---

The one eyed, one horned flying purple people eater?

---

Glad to see you have a sense of humor!

quote:

---

Well, who says even a perfect designer would have any concern about symmetry at all? If anybody's making assumptions about what designers are like, isn't it you in your opening post?

---

Yes, I did mention an intelligent designer, because I see that as the only alternative to evolution, which in my mind is impossible given the discrepancies between observed symmetry and the random (asymmetrical) nature of evolutionary mutations. Tell me another way that explains how we came about rather than evolution or an intelligent designer and I'll amend my statement.

quote:

---

I had thought my point was pretty obvious - your opening post is based on a false premise. You ask why such perfect symmetry exists, but the problem is, it doesn't. There's only as much symmetry as we would expect from evolution.

---

Fair enough. You thought I meant totally perfect symmetry, from a perfect designer, and you were trying to show we weren't totally perfectly symmetrical. I now see your point.

quote:

---

Some creatures are blind, or have such poor eyesight that they could not select for symmetry, yet they remain symmetrical.

​

That hardly means they have no ability to sense symmetry. Plus, most of the species you're talking about are aquatic.

---

Sense symmetry? You mean to tell me that a blind creature feels every square millimeter of a potential mate's body first for symmetry? Wow, that is really a new one on me! Could you please give some example of this and provide some link to documentation of this behavior? Plus even if most of the blind or nearly blind species are aquatic, there still are some blind land based animals such as bats and some snakes for instance.

quote:

---

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?

​

No, of course not. But they do tend to prefer mates that appear symmetrical. Perfect symmetry doesn't exist.

​

Look, it's proven fact that humans prefer symmetrical faces. Even infants prefer them.

---

Besides humans, can you prove it? As a test, I suggest you make a fake asymmetrical appendage and attach it to a dog and see if the dog is any less attractive to potential mates. I've seen dogs with all sorts of clothing, ornaments, etc. attached to them by their owners and they never seem to have any trouble attracting other dogs when their owners take them out for a walk. I see a lot of sniffing and barking going on, but the appearance of the dog never seems to be any problem in finding a mate. Not to mention certain dogs and other creatures have very long hair which hides a great deal of their body structure. How do these dogs "sense" asymmetrical mutations hidden under the hair on a potential mate? Do they do it by some sort of magical ESP? In short, I totally reject sexual selection based on asymmetry of the lower animals. If the asymmetry is only secondary to some other defect then it may be deselected. Please provide some evidence of your claim that lower animals can detect asymmetries in their potential mates and reject those mates. And please state why there are exceptions to this such as the crabs and flounders already mentioned. Why do they not select a mate the same as all the other creatures?

quote:

---

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?

​

Why on Earth would that require counting? How stupid. All you have to do is look at the organism. If one side is different from the other side, it's not symmetrical.

​

Everybody does this, and it doesn't even take thought. For instance, this famous picture:

---

For people, this is easy. A person can look at two hands and tell they're not the same, or a picture and tell that the landscape doesn't match. We're not talking about humans here. I agree humans do place a high degree of significance on symmetry. We're talking about lower forms of life who do not have the same level of intelligence and reasoning as humans.

quote:

---

Like all vertebrates, your brain has hardware that detects symmetry. The reason you detect it is because often, asymmetry represents poor health or injury, which are not things you want in a mate.

---

Again, please show me some proof of this. I do not believe all vertebrates are selecting mates based on symmetry.

quote:

---

Of course they don't observe all minor asymmetries. That's why minor asymmetries persist, like your ears and stuff.

---

No, I'm not referring to such minor asymmetries that require measurement. I'm referring to asymmetries that can easily be missed by just looking at some creature. Many asymmetries can be hidden by hair, fur, feathers, scales, etc. Some may be on the underside of the body or require some special angle to be viewed. A quick inspection can easily miss these asymmetries.

quote:

---

You don't seem to be getting it yet. We're not perfectly symmetrical. We're only asymmetrical up to the point that a potential mate might notice, because asymmetry is selected against.

​

We're not perfectly symmetrical. We're only as symmetrical as evolution predicts.

---

I get what you are saying, but I don't agree. And unless I can see some solid proof of sexual selection of symmetry by animals, I will continue to disagree. A test should be easy to conduct, but I predict the results will not be what you are expecting. BTW, any test should measure the attractiveness of a mate with a certain asymmetrical mutation, and compare it to the same mutation but where it is forced to be symmetrical. Doing a test comparing the attractiveness of a normal specimen, compared to a specimen with only an asymmetrical mutation is no test as there could easily be some pattern embedded into an animal's genes which they use to compare when selecting mates. And the test should be also be done with asymmetries placed in hard to locate positions and see if those can be detected. Then the test should be carried out on blind specimens and see if blind specimens can "sense" asymmetries in their potential mates. I dare anyone who believes in evolution, and has the resources, to perform such a test and publish the results.

quote:

---

There's a third potential explanation for the persistence of symmetry - it's genetically simpler. It takes a lot more genes to code for two separate sides than than to provide the genes for one side and simply duplicate for the other. That's the "evo-devo" explanation, I guess.

---

Then why is the external body not symmetrical, and why are there minor, not easily seen, asymmetries of the external body which you already agree exist? And why the exceptions listed, such as crabs and flounder?

quote:

---

can operate on average for more than 50 years without any significant maintenance,

​

If that's supposed to be true, what do you think all those doctors do? What do you think all those medicines are for?

---

Doctors and medicine extend the life, but what about thousands of years ago when there were no doctors? People still survived. And the animal world survives for the most part without doctors or medicine. I dare you to find any car or other similarly complex machine that can go for even 20 years without replacing any parts.