How can evolution explain body symmetry?

quote:

---

Unless it offers an advantage you will not see it.

---

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.

quote:

---

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

---

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.

quote:

---

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.

---

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.

quote:

---

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.

---

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.

quote:

---

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

---

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.

CJ,No worries.

No, I understand.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.We should be perfectly symmetric, inside and out. We're not, so we're obviously not the product of a perfect designer. Evolve seperately? Of course not. My left side doesn't reproduce separately from my right, so my two sides obviously won't evolve separately.Look, your question has been answered twice over. Why are we mostly symmetrical?1) Because we're the decendants of organisms for whom symmetry was an adaptation to environment.2) Because symmetry is strongly sexually selected for (humans are most attracted to mostly symmetric humans.) 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.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. Also, it's a requirement for walking around on any number of legs on a flat surface.Now what about that explanation do you feel falls short?

quote:

---

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.

​

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

---

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.

quote:

---

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

---

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.

quote:

---

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

​

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

​

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

---

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.

quote:

---

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.

​

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.

---

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.

quote:

---

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

---

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.

Cliff.Evolution is evolution. There is not one set of rules for plants and another set of rules for animals.

---

Aslan is not a Tame Lion

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?

---

Aslan is not a Tame Lion

quote:

---

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.

---

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

quote:

---

I know of two different cases of extra digits, so I would say it is fairly common, based on my observations, but whatever.

---

No offense, but your own personal observations are statistically meaningless.We call such information "anecdotal evidence", and it is quite unreliable, because your sample size is tiny and non-random.

quote:

---

I have personally only seen mutations that were asymmetrical and none that were symmetrical.

---

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.

quote:

---

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.

---

You have made a factal claim here. Please provide reliable evidence to support it.

quote:

---

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.

---

If by "animals", you mean "vertebrates", I have already explained that all vertebrates evolved from sea-dwelling creatures, so therefore follow the same basic body plan.

quote:

---

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.

---

Exactly, but not in all cases, as my photographs showed you.

quote:

---

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.

---

Right. All the asymmetries I showed are adaptive.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.

quote:

---

But in general they do not. Why are there a few animals that exhibit clear asymmetries while the majority don't?

---

All animals exhibit clear assymetry, you just want to ignore the internal ones.Why do you insist that we ignore internal asymmetry?

quote:

---

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.

---

That is exactly what I am saying.There are, however, evolutionary pressures to cull out most asymmetries.

quote:

---

So what happened to all the asymmetric mutations that occurred throughout the history of the evolution of man?

---

We still have them.They are mostly internal.Why do you ignore them?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.

quote:

---

Why can't we see them? If evolution isn't deselecting them, then what is? Why are humans left with only the symmetrical ones?

---

1) Evolution does select them out, which is why we don't see them.2) We have plenty of asymmetries, they are just internal. Why don't they count to you?

quote:

---

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.

---

You're right, it is absurd.That's why the above is not what evolution says.There is nothing in the ToE which requires only one beneficial mutation to become dominant in a population before another occurs.If this were true, the entire human population would be genetically identical.

quote:

---

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.

---

But they are here.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.

quote:

---

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.

---

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

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)?Do you think we would do well with the configuration of a side-hill gouger? That is, one leg longer than the other. Would an extra eye on one side of our head offer an advantage? What did you have in mind?After you've found a couple of those then you need to suggest some evolutionary pathways to get to them. Not all advantages configurations can be reached throught evolutionary processes.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.

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?".

quote:

---

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?

---

Alterations to the external body may reduce sexual attractiveness and may impede locomotion.

quote:

---

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.

---

Actually, mutations affecting basic body plan do strongly tend to affect the individually symmetrically, because that is how embryonic development occurs.

quote:

---

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.

---

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?

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.

quote:

---

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?

---

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?This message has been edited by schrafinator, 05-31-2004 10:09 AM

quote:

---

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.

---

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?

quote:

---

Do you mean to say that if some animal had a nose on the side of it's head, it couldn't walk?

---

No, but if it had one leg a lot shorter than the others, it would have a pretty hard time of it.

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.

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.