How did Evolution produce Symmetry?

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Can't engage in these clowning incoherent responses; its dreadfully and fearfully clear to me, redemptive-ID being responsible for all the cursed yet complex excellencies being derided at.
If you want to deride these excellencies, I'm out of here (fast).

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Bye then.I bet I've got an example of stupid design for each "excellency" you have. Want to take that bet?Say, precisely what sort of curse can re-route a nerve from its obvious path, so that it instead runs from the neck, loops under the aorta by the heart then goes back up again to the larynx -- and still work? (How exactly is that a curse?) What sort of curse can form the lifecycle of cicada-killer wasps? What sort of curse gives humans our wonderful ear-wiggling abilities? What sort of curse, in short, has creative abilities?I'm afraid I can engage with your clowning incoherent response, even though it is dreadfully and fearfully clear to me that you have no answer to these points.Maybe I'm just cruel, engaging in a battle of evidence with an unarmed opponent. But surely no more cruel than your alleged designer.TTFN, DT

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Originally posted by DOTF:

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Further thought will be required by all.

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Well, by one of us at least.

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I've never heard this topic actually broached before.

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Why am I not surprised?

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But it seems clear that, while some symmetry is good for survival, much is not. An extra eye on one side of our head would be asymmetrical and probably beneficial as well.

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Not, presumably, as beneficial as one more on each side. What were you saying about more thought?Say, if it’s such a great idea, why didn’t god give us these extra eyes? Hell, why didn’t he give us cephalopod-type retinas, and so have retinas that could far less easily detach?

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Why is it then that if you divide the shape of a human body in half you get bilateral symmetry?

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Might it be because we derive from an arrow-formatted creature, as I mentioned above? Nah, too obvious...

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Ten fingers (2*5),

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Never! Let’s see... two... times... five... two lots of five... erm, fingers... six, seven, eight, nine... ten! Hey, you’re right! And my fingers confirm it!Well blow me if I’d not realised this. Well that’s evolution buggered, obviously.

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two arms (2*1), two eyes, ears, and a nose precisely in the middle.

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With two nostrils.

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Sounds simple but it's actually quite perplexing from an evolutionary standpoint.

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Sounds simple, but it's actually quite perplexing from an ignoramus’s standpoint.

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For example, if eyes evolved from light-sensitive cells, why didn't these cells pop up all over the place?

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You mean like on some butterflies’ genitals? (See Eberhard 1983, Sexual Selection and Animal Genitalia, Harvard University Press.) You mean like the extra sets of eyes that spiders have? Eyes are outgrowths of the brain. Where would you like some more? And if these more are such a good idea, how come your god forgot to give them to us?

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What we have is two perfectly aligned eyes pointing forwards.

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Yep. With their retinas in backward, with the bit of the brain at the opposite end of the brain from where the eyes are.What of the not-aligned eyes that point sideways in cows? What of the not-aligned eyes that point sideways in our own embryos? What of the eyes that do not work in creatures that do not need eyes at all?

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And of course there are the decorations, such as completely symmetrical designs on butterfly wings. How did evolution come up with that?

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Go learn some developmental biology; I’m not about to start giving lessons, so try Gilbert’s textbook. (Actually, start with Spot Learns Biology and work your way up.) Heres a hint though: Hox genes.Oh, and yes, this is what’s called ‘ridicule’. It’s almost too easy to ridicule the ridiculous. But then, I’m a sucker for the easy option. Unlike your god, who’d rather do things in the most unnecessarily complicated ways he can find.TTFN, DT[This message has been edited by Darwinsterrier, 10-23-2003]

That was an unnecessarily rude response, Darwinsterrier.

I think in general the idea of necessity applies also to
plants.They don't move and don't have a head-tail division, but are
subject to gravity and have a top-bottom division (roots down,
stems up). Even leaves have an underside.

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For example, if eyes evolved from light-sensitive cells, why didn't these cells pop up all over the place?

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If our heads were covered with eyes, we wouldn't have a skull to protect our brain. Every time we got hit in the head with something remotely sharp, we could die.Having two little holes for our optic nerves is a big risk. It is mitigated by the advantage of having visual input to direct us. Just a trade-off between physical protection and a sensory system.Do you purposely avoid finding explanations for the way things are? It seems you're arguing from incredulity here, an incredulity that wouldn't last long in the face of open-minded inquiry.

If the third eye would be beneficial why didn't
god put one there?In terms of a body-plan one could claim ANY form to indicate
a designer, since a designer is free to do anything they
wish (given sufficient resources).That we see a consistency of form across the continents would
tend to lean away from a designer rather than toward
surely ....

Hi Darwinsterrier,
And don't you just love when creationists say "I have never heard this subject broached before"?Then why are there studies likeProc Natl Acad Sci U S A. 1996 Dec 10;93(25):14279-86. Related Articles, LinksFrom symmetry to asymmetry: phylogenetic patterns of asymmetry variation in animals and their evolutionary significance.Palmer AR.Department of Biological Sciences, University of Alberta, Edmonton, Canada. Rich.Palmer@UAlberta.CAPhylogenetic analyses of asymmetry variation offer a powerful tool for exploring the interplay between ontogeny and evolution because (i) conspicuous asymmetries exist in many higher metazoans with widely varying modes of development, (ii) patterns of bilateral variation within species may identify genetically and environmentally triggered asymmetries, and (iii) asymmetries arising at different times during development may be more sensitive to internal cytoplasmic inhomogeneities compared to external environmental stimuli. Using four broadly comparable asymmetry states (symmetry, antisymmetry, dextral, and sinistral), and two stages at which asymmetry appears developmentally (larval and postlarval), I evaluated relations between ontogenetic and phylogenetic patterns of asymmetry variation. Among 140 inferred phylogenetic transitions between asymmetry states, recorded from 11 classes in five phyla, directional asymmetry (dextral or sinistral) evolved directly from symmetrical ancestors proportionally more frequently among larval asymmetries. In contrast, antisymmetry, either as an end state or as a transitional stage preceding directional asymmetry, was confined primarily to postlarval asymmetries. The ontogenetic origin of asymmetry thus significantly influences its subsequent evolution. Furthermore, because antisymmetry typically signals an environmentally triggered asymmetry, the phylogenetic transition from antisymmetry to directional asymmetry suggests that many cases of laterally fixed asymmetries evolved via genetic assimilation.orCiba Found Symp. 1991;162:94-120; discussion 121-7. Related Articles, LinksTwo types of bilateral symmetry in the Metazoa: chordate and bilaterian.Jefferies RP.Natural History Museum, Department of Palaeontology, London, UK.The chordate sagittal plane is perpendicular to the sagittal plane primitive for the bilaterally symmetrical metazoans (Bilateria). The earliest metazoans, when symmetrical at all, were probably radial in symmetry. The axis of symmetry was vertical and the mouth, when present, opened either upward or downward. The Bilateria evolved from the primitive metazoan condition by acquiring bilateral symmetry, mesoderm, a brain at the anterior end and protonephridia. Perhaps in the stem lineage of the Bilateria a hydroid-like or medusoid-like ancestor fell over on one side onto a substrate (pleurothetism). If so, the anteroposterior axis of Bilateria would be homologous with the vertical axis of radial symmetry in coelenterates. The bilaterian plane of symmetry arose to include the anteroposterior axis. The Deuterostomia (the Hemichordata, Echinodermata and Chordata) evolved within the Bilateria by producing the mouth as a secondary perforation. Within the deuterostomes the echinoderms and chordates constitute a monophyletic group named Dexiothetica. Hemichordates retain the primitive bilaterian sagittal plane. The Dexiothetica derive from an ancestor like the present-day hemichordate Cephalodiscus which had lain down on the primitive right side (dexiothetism) and acquired a calcite skeleton. The echinoderms evolved from this ancestor by losing the ancestral locomotory tail and gill slit, becoming static, moving the mouth to the centre of the new upper surface and developing radial pentameral symmetry. The chordates evolved from the same ancestor by developing a notochord in the tail, losing the water vascular system, evolving a filter-feeding pharynx and developing a new vertical plane of bilateral symmetry perpendicular to the old bilaterian plane. Evidence derived from certain bizarre Palaeozoic marine fossils (calcichordates) gives a detailed history of the early evolution of echinoderms and chordates and shows how the new bilateral symmetry was gradually acquired in chordates. This symmetry began in the tail (which contained the notochord and was also the leading end in locomotion) and advanced forward into the head.or even in plantsProc Natl Acad Sci U S A. 2003 Oct 10 [Epub ahead of print]. Related Articles, LinksDifferential regulation of symmetry genes and the evolution of floral morphologies.Hileman LC, Kramer EM, Baum DA.Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138.Shifts in flower symmetry have occurred frequently during the diversification of angiosperms, and it is thought that such shifts play important roles in plant-pollinator interactions. In the model developmental system Antirrhinum majus (snapdragon), the closely related genes CYCLOIDEA (CYC) and DICHOTOMA (DICH) are needed for the development of zygomorphic flowers and the determination of adaxial (dorsal) identity of floral organs, including adaxial stamen abortion and asymmetry of adaxial petals. However, it is not known whether these genes played a role in the divergence of species differing in flower morphology and pollination mode. We compared A. majus with a close relative, Mohavea confertiflora (desert ghost flower), which differs from Antirrhinum in corolla (petal) symmetry and pollination mode. In addition, Mohavea has undergone a homeotic-like transformation in stamen number relative to Antirrhinum, aborting the lateral and adaxial stamens during flower development. Here we show that the patterns of expression of CYC and DICH orthologs have shifted in concert with changes in floral morphology. Specifically, lateral stamen abortion in Mohavea is correlated with an expansion of CYC and DICH expression, and internal symmetry of Mohavea adaxial petals is correlated with a reduction in DICH expression during petal differentiation. We propose that changes in the pattern of CYC and DICH expression have contributed to the derived flower morphology of Mohavea and may reflect adaptations to a pollination strategy resulting from a mimetic relationship, linking the genetic basis for morphological evolution to the ecological context in which the morphology arose.Like defender said, nobody has ever addressed this subject...don't we feel like fools there goes evilution down the toilet...cheers,
M

You should study some embryology! Symmetry is easy, once a basic symmetrical body plan is established (e.g., a worm). Mutations of many genes produce symmetrical results based on fundamentals of embryological development; evolution does NOT generally have to wait for two mutations, one for each side of the body!These are well-studied issues, not some novel idea at all.So there's nothing "perplexing" about this at all, from what I know.Think your examples through a little...for example:" if eyes evolved from light-sensitive cells, why didn't these cells pop up all over the place? What we have is two perfectly aligned eyes pointing forwards."Well, they mave have popped up all over the place. But if all you have is basic light sensitivity, what use is having light detectors everywhere?Better to organize these in a ways that gives directional sensitivity, like the "eye cups" of simple organisms. When the "cup" specializes further, you can get a focused image, etc.Now, at this point, one might argue that an extra "eye" would be helpful in humans, but embryological and genetically you now have an extremely difficult problem - how do you make such a huge change to a complex, specialized system?Evolutionary biology shows through fossil records, and embryology shows through its basic principles, that simple body plans are easily altered, but major changes in complex, specialized body structures are slow and rare.So, why don't we have eyes everywhere? Because specialized eye cups have an advantage over randomly placed light detectors. The rest is history. Why are the eyes symetrically placed? Embryology.[This message has been edited by Zhimbo, 10-23-2003]

yeah, i did and i haven't seen symmetrical creatures yet. perhaps i haven't left them to their own devices long enough yet. last night i tried to get the framstick program to run overnight, but a family member closed the program before i got up.I've just been seeing non-symmetrical creatures that move around in little circles. I think a limitation of the program is the options you have for selective pressure. You can make a creatures velocity a significant factor, or you can make the distance they travel a significant factor (or a combination of the two)... but the distance option isn't very significant because it is not distance from the starting position... so creatures that travel in small circles get the same distance score as creatures that walk off into the distance.I'm guessing because of the way the mutations work on this program creatures will never evolve a "genetic" code that has a mutation appear on both sides of their body. Because of this the only way to evolve symmetry would to somehow select for walking a straight line... which the program doesn't allow for.

from a previous message of Philip's:

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But speaking PER SE on cosmic excellencies of symmetry, harmony, and proportion does beg (strongly infer) awesome design (ID) to be sure, so that it seems pointless to argue the matter.

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So it seems you don't want to argue these points anyway, just assume that there is a designer just from proportions found in the universe. Am I wrong here?So I will ask in a more congenial manner this time.1. If symmetry is proof of a designer, is lack of symmetry (see flatfish) proof of no design?2. Can you give examples of what is designed and what isn't designed with a set of criteria?3. Can you state the mechanisms by which the designer designed?4. How does the Theory of Design explain the current species better than the Theory of Evolution?5. Is it impossible for chance and physical laws to create symmetry and order? One example for chance symmetry and order would be a hurricane which has order and symmetry and comes about due to chance and physical laws.You don't have to answer all these questions if you don't want to, but these are the questions that come to mind after reading message #5. If this is still too incoherent, let me know and I will try and rephrase.[This message has been edited by Loudmouth, 10-23-2003]

I know, but gravity seems to be a barrier to locomotion in animals while I have suggested it may be a facilitator in plants and yet by the current scholarship on symmetry bilateral or otherwise, there would be no way to make this difference unless say the photons do something polar and inverted differently in chlrophyll say vs retinas AND is generalized to all forms on both "sides". I would expect that whatever REPLICATION is insofar as it is a unified notion must move BOTH plants and animals focefully in THE SAME DIRECTUM. Now it could be that indeed replication functions differently such thta plants can THUS take different advantge of g-forces that animals by dint of getting around this simply cant but my first thought was that plants actually cut cell shape around places crystal lattices form in to which serve as "return points" for animals. I do not know which is correct therefore I am necessarily torn. Part of the problem here seems to be due to not enought focus molecular biologically on the horizontal force of base pairs perpendicular to the DNA twist coming BACK from the place the parts fore and aft are at but this I doubt in ration proporations any arse which is why I included the "others" (protozoans, bacteria, viruses).

Mr Jack: I fail to see why it was unnecessary. Unhelpful, perhaps -- though I gave clues to where more info could be found -- by hardly unnecessary. Sometimes a sharp kick in the arrogant backside of an ignoramus (as defined in Chambers: 'one pretending to knowledge not actually possessed' (paraphrased)) is necessary. Or, at least, fun.You did note him pointing out what two times five was, I assume? The fact that we have two (2*1) arms? Well gosh darn if I have no sympathy or empathy with such folks.Maybe you're new to this E/C lark. Stick around. You'll see that being troubled by bilateral symmetry, while in the same ballpark of ignorance, is at the low end, even by creationist standards.TTFN, DT

Can't we all just get along? I beg to differ Darwinsterrier.I believe the majority of people posting on these boards are very intelligent, but without the specific knowledge you have [although probably capable of it] - me included. There's a big difference between intelligence and knowledge. Einstein may not have known much about Biology, but had plenty of intelligence. I'm sure you understand this so I won't bore you.I just think DOTF had some valid points considering his limited knowledge on the topic. It sounds like you have a lot of knowledge about this, and I was interested in what you posted when you were speaking of it. I'd even like to hear more about Hox Genes, but I can Google that.I look forward to more of your useful input on the boards.[This message has been edited by rokit, 10-24-2003]

Darwin's Terrier:It was unnecessarily rude for the following reasons:

• While Defender may have been slightly patronising in his post, he was doing so to demonstrate his point rather than insult.
• The information in your post was valid, but by being so rude and adversarial you add nothing to the debate.
• When one is right, one can afford to be gracious.
• An overly aggressive stance such as yours actually weakens your position, and by association, our position.

How about you keep your assumptions to yourself, hey?

Why does everyone try and simplify any question in evolutionary-developmental biology into HOX genes. In the case of butterfly eyespots this is a completely misleading "Clue". HOX genes are fairly tangential, UBX may have an initial role in the patterning of the wing but it is an insufficient explanation for the development of eyespots, or did you mean homeobox genes in general? Its all very well deriding people for their lack of specific knowledge but telling them to read half a dozen textbooks hardly seems the way forward.