How did Evolution produce Symmetry?

I'd have thought bilateral symmetry was obvious. If you want to go somewhere in particular -- rather than wander aimlessly -- the route you will take will be a version of a straight line. A straight line with directionality (one way or the other) is an arrow.So the bit of you that gets somewhere -- whereverthehell you're going -- first is the best place to put sense organs -- it's no good finding out that you're going to hit a rock after you've already done so -- and this gives you a head end. The rest, that which trails behind and gets 'there' later, is the remainder of your body.All that remains is for there to be a left and a right, rather than being tube-like and any-way-up. But 'up' is the other clue: gravity will tend to define a top and a bottom. The side of the body that is in contact with the ground (or whatever) is the best place to put whatever makes you move along; 'up' and 'down' are useful variables too, so it makes sense to diversify your body plan into a top and a bottom, a dorsal and a ventral side. This could also come about from embryology-development: gravity will tend to have effects on embryological processes, setting for instance grading of hormones (as with bootstrapping of early 'advanced' embryos).And voila, bilateral symmetry, from nothing more complex than 'needing to go somewhere in an environment with gravity'.But the alternative, having sense organs all the way round, also works too, producing radial symmetry -- and plenty of animals have gone that way, such as echinoderms. But since evolution is constrained by history, once a lineage went down one route, it was stuck with it. It might be useful to have eyes in th eback of your head, but we just can’t have 'em!Cheers, DT

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Originally posted by Philip:
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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Most of us infer that a potter fashions the pottery, an artist the painting, etc. How much more might I (we) infer an excellent universe, quantum chemical science, life-form, and/or person to be directly fashioned by an awesome Maker.

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Albeit doubts and fears must always taunt me (us) in this matter. A real curse of sin and blindness in my (our) mind(s) which repeatedly refuses to acknowledge the glorious truth of cosmic design.

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Oh yes Philip, I entirely concur. I freely accept that design "strongly infers" an "awesome Maker". The only problem is that the designer strongly inferred it is an incompetent idiot and a sadistic bastard. That, matey, is the "glorious truth" about this designer.TTFN, DT

Oh yeah, DOTF... "... perfectly crafted creatures... ", eh? See my first link above.DT

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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]

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

Fair enough, old chap (chapess?) I just took exception to DOTF thinking we needed to be told that ten fingers means five each side, and the ludicrously panglossian ideas he offered. I mean, not having an asymmetrical head with an extra eye on one side being a problem for evolution?! As I thought I made (oxmoronically) implicitly obvious, that would leave you (extra-)eyeless on the other side!Put those things together in the same short paragraph, and I -- perhaps too quickly -- pegged him as low-grade creationist nitwit. It's a hazard of discussing these matters too much I'm actually delighted on the rare occasions when a creationist asks genuine questions, seeking knowledge, trying to see who is right. But that's not the general habit: they start absolutely certain that, no matter what they are told, that they are right nevertheless. (For a classic example, see Philip’s reference to ‘excellencies’ in this very thread. Fingers in the ears and singing LA-LA-LA-LA at the top of his inefficient (see below) lungs.) The general habit is Argument from Incredulity. When one is deficient in knowledge of a subject, to then use that argument smacks of -- hell, is -- a form of arrogance.So, sorry DOTF. By all means prove me wrong! Please. I insist.Ref old Dr Pangloss, I found it amazing that DOTF expected such best of all possible worlds to be produced by evolution... when in fact the concept of there being a vastly intelligent designer -- his own concept -- is by its nature utterly panglossian.'Look how perfectly so-and-so is/works! Look at how great bilateral symmetry is, two perfectly aligned eyes pointing forward!' and so on. And so the irony meter goes fzzzt-BANG! when evolution is expected to put eyes all over the body. If that would be better, then why did god not do that?!This is actually a damned good question. There are many instances of not if X is better why didn't god give us it, but since X is demonstrably better, why did god not do it?Here's an example.Birds have through-flow lung ventilation, whereby the air travels a circuit through their bodies. Mammals have a tidal system: the air goes in and out through the same tubing. The mammalian system therefore mixes the used air with the fresh, and some of it is re-breathed. Because the bird system does not mix the fresh air with the used, it is demonstrably, measurably, massively more efficient than the mammal system -- one website says it is ten times more efficient.Now, the creationist might say "So? God can do it however he likes." But on the one hand, we humans are allegedly the pinnacles of creation. Are there no instances when better -- much better -- breathing would be useful to us? How about just running?And on the other hand, there seems no functional logic to which creatures got which system. All birds have through-flow; fair enough for hawks and hummingbirds, peregrines and pigeons. But ostriches? Penguins? Kiwis? Sure, it's good that they’ve got it, I'm sure they're very pleased to have it. But if -- not if, but since -- through-flow is so much better, one has to wonder why no mammal was deemed to have needed better breathing than it’s got. No long-distance runner, like wolves or hunting dogs, have it; no sprinter like cheetahs have it. And crucially, no bat has it. What makes bat lifestyle so different from bird lifestyle that a bat could not immediately benefit from avian through-flow respiration?And another example, pinched from what I wrote for the EvoWiki:

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As photographers will tell you, a 'pinhole camera' is an effective way to form an image out of light; the small aperture at the front forms an image on the screen behind it. The smaller the hole, the sharper the image. The down side is that the smaller the aperture, the less overall light gets in. To solve the problem, camera designers add a lens. A lens is an obvious improvement, since it allows both a sharp and bright image. We might therefore expect the Intelligent Designer of organisms to use lenses in eyes.

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And the 'designer' did. Octopus and squid eyes have lenses... vertebrate eyes have lenses.

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There is however one cephalopod mollusc, the nautilus (Nautilus pompilius), which is considered more primitive than octopuses and squid, since it has an external shell. And it lives at considerable depths, where light is at a premium.

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The nautilus has a very good pinhole camera eye; considerable thought presumably went into its design. But the designer apparently saw fit not to give that eye a lens. Its eyes are therefore far less efficient than it easily could have been. Did the designer just forget?

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Erm, sorry, I appear to have wandered off topic Okay, butterfly pattern formation. There’s tons of stuff about this, and while (as with everything) we don’t know everything about it, it ain’t no Black Box for evolution. The best place I’ve found to start is here. This page gives a load of references, including pdfs of the actual papers. I’d only seen one of these papers before, and it’s why I mentioned Hox genes. (Incidentally, it is the homeobox Ultrabithorax that is also involved -- not surprisingly, really -- in the formation of fly halteres, and a mutation in Ubx is what can turn these impressive balancing organs back into what they once were, ie wings.As to why they tend to be symmetrical: it’s the way genes get expressed. In short, genes work in cascades, with one set controlling the next level, and those the next. All cells (yeah yeah, red blood cells etc etc, smartarses! ) contain all the genes, and it is the cascades that arrange which are switched on in which cells where to form the required tissue, by reference to the cells already around it. This means that in practice, a particular cell gets told something like ‘if you find yourself at the end of a limb bud / in a wing / in a liver / whatever, do this’.So when a limb is forming, the left hand doesn’t need to know what the right hand is doing. They are both doing the same thing, automatically and generally symmetrically, just in opposite directions out from the starting point. Same with butterfly wings.And thanks for the references, Mammuthus! Fascinating!Cheers, DT

Hi WK, nice to see you over here!"Way forward"? Nah, it's simply the formula:'Idiotic post' --> 'Short, sharp response'. 'Fraid this is nearly Pavlovian with me. I know it's a bad habit, but ring my bell and my fangs get bared.The better formula is:'Ignorant but open post' --> 'Detailed, hopefully informative response'. This too is nearly Pavlovian. I suppose it amounts to the old "Ask a stupid question..."As to referring people to a load of textbooks... well, just where do you start when ignorance runs so deep?When someone says 'evolution can't explain X', the first thing one should say -- and soooo often, you don't realise it should have been the first thing till much later -- is not 'yes it can because this this and this', but rather, 'what do you know about evolution?' If the answer is already obviously the square root of f**k all, what should one do? Give them a course in evolutionary biology before you can even attempt to answer the specific point? Sod that. Tell them to go away, sit down with a straightforwad textbook on the matter, then come back if they still have a problem.The alternative -- a detailed response -- will simply not be understood. I've had such responses plain ignored and followed by a restatement of the alleged problem ('you didn't answer my question!'), and sometimes thrown back at me for being deliberately complicated -- when the matter is complicated and/or relies on a load of other knowledge.So, the point is seriously made: if the amount that needs to be explained to answer the point is beyond the sensible capacity of anyone on a bulletin board to provide, go read a textbook.And as to Hox genes, they are a bit like shielding in chemistry. A large proportion of the answers will come from them. Sure, Hox genes aren't the be-all and end-all of butterfly wing patterning (or anything else genetic-developmental). But in looking up that bit of the basics, the answers and/or where to look for them should become apparent.Cheers, DT (Oolon Colluphid)

Hi ReiOkay, I've looked at the Framsticks thingybob site. Looks rather more clever than my old DarwinPond (though my five-year-old daughter likes feeding and killing the swimmers ). Which version / option should one download to just play with it a bit?Cheers, DT

I'm still waiting to hear how an intelligent designer can fashion very stupid designs, and still be called intelligent.DT