How can evolution explain body symmetry?

And, interestingly, it has been suggested that a reversed retina is a better design for a flat, or cup, eye due to improved directional capability.

Hello everyone,
Been lurking around this forum for a day or so and thought I might leap gamely into this conversation. Hi.I should probably make my position clear from the outset; I am an Evolutionary Psychologist; I study human behaviour from an evolutionary standpoint. I am a scientist, as are all Ev Psych'ers, and I am an atheist. I have no issue at all with scientists who are not atheists. I personally find the principles of evolution incompatible with belief in a deity or deities but that is my own position, reached after careful thought, and I have no illusions that it is a position that is or should be shared by everyone. Having said that, I have engaged, from time to time, in lively debate with creationists and have discovered that scientists and creationists occupy totally incompatible platforms. There is no common language in which to conduct a discussion; science is based on reason, logic and rationality, while creationism (by it's own admission)is based on faith, not reason. Neither group is capable of convincing the other... but that doesn't mean we can't have some fun trying.So... to the subject at hand. Symmetry.CrackerJack seems to have gone walkabout recently, which is a shame, but just in case he's still about (or if anyone else feels like taking up his position); I am a little confused by his argument. Could you explain exactly WHY you would expect terrestrial animals to have evolved away from a symmetrical bodyplan? As far as I can see, you base this on the idea that in the amount of time since we left the sea SURELY some deviation from symmetry should have evolved. Could you explain this position?Secondly, regarding the Gangestad and Thornhill scent of symmetry article (back in message 49), CrackerJack is right in principle. The subjects could indeed be detecting one of a number of things. Healthy people have been shown, in seperate studies, to smell nicer. Men prefer the scent of ovulating women too. However, the study referred to is the result of rigorous scientific analysis in which other effects were controlled for. That women prefer the scent of symmetrical men (especially when at their most fertile) is a statistically significant effect.

I'm inclined to think symmetry must be more fundamental, at the genetic level. This is becuase it accords with certain data principles - it saves storage space to have one design which is oproduced once directedly and once in mirror; you can use one set of data for both sides.However, any errors in the source data will likely be aggravated by this mirroring, much as errors in text become successively worse with photocopying. So an animal exhibiting bad asymmetry probably implies that animal has or had something quite seriously wrong with those processes. This I suspect is the underlying basis for the attractiveness of symmetry.I'd also be less inclined to see this as related to an early water environment; as has been suggested symmetry is valuable in all environments and not in water especially.Furthermore, we often recognise and value symmetry in engineering, where no sexual selection applies. I think it is specifically the itself symmetry we are geared to detect.

Indeed. Many studies have linked symmetry with the quality of an animal's immune system. If bilateral symmetry is the fundamental body plan, as you suggest, it can be referred to as the "target phenotype". Most of the factors that can subvert the body's attempt to produce this target occur during development of the foetus. A developing foetus is under constant stress from environmental factors, including parasites, pathogens and the mother's own immune syste. These factors are called "developmental noise". Individuals who can withstand developmental noise and develop the target phenotype are adept at defending themselves from developmental noise, presumably due to their immune system. Deviation from the target phenotype, then, becomes a marker for developmental instability and poor immunocompetence. This, presumably, is the basis for symmetrical individuals being more attractive.I also see no reason why symmetry should be related to an aquatic environment. I agree that it seems more efficient to have a symmetrical organism that would require the doubling of a single set of genes to construct rather than one set for each side of the body. Our earliest multicellular ancestors were probably symmetrical. There has been no reason to abandon it. I believe the flatfish, that was posted earlier, developed from a symmetrical ancestor.

The first known design of a robot was made by Leonardo da Vinci in 1495, but the first functioning android was made in 1738 by Jacques de Vaucanson. The point of this message is that I find it silly that you're argumenting with that we haven't been able to build a robot that "works as well as the human body" now that we've been seriously working with robotics only for such a short period of time compared to how long it took for the human body to evolve into its current complex form.Sorry for grasping in such a small thing but it really caught my eye.

If you think that your "parts" are not replaced, you are mistaken. On average, of all the atoms that made up your body not so long ago, not a single atom is left today. Your rate of "maintenance" is higher than that of the average dishwasher.

---

We are all atheists about most of the gods that humanity has ever believed in. Some of us just go one god further. - Richard Dawkins

Please first show me but ONE quote "taken out of context". No one has ever, on any web site proved this to me. If I have I will retract, but my guess is that I just had not been clear enough for your competer pogram that might have scrapped a few letter s ijn.I doubt that genetic material actually did code for both sides of the body at the same time. If only for the difference of the relation of Cam and Jims in topobiology, the use of calcium spatially between th salamander and fish lineages in revolutions of the earth, the strucutre of the golgi body, the anatomy of cell death dissections etc. A bullet does not a spandrel make.
EvC Forum: GP Gladyshev's paper (s)or mine?
You must distinguish genetic phsyiology from transmission genetics if you wish to have locomotion but a mechanical thing. Again more water please.
EvC Forum: Distinguishing Baramins
Also this pic shows an asymetry in SIDES

I found an interesting article with lots of examples of asymmetry and the mechanisms by which it is produced: http://www.drmichaellevin.org/Chiralityconf1.pdfHope it is of interest

Heres something to shed a little light on the bad design of the upside down retina:
http://www.godandscience.org/...ution/designgonebad.html#eye

Edited by Sumer, : No reason given.

Aerodynamics.

---

*not an actual doctor

Or possible Hydrodynamics.

---

Aslan is not a Tame Lion

that too.

---

*not an actual doctor

Look around at human vehicles and tell me the answer to that question isn't obvious. How many asymmetric airplanes have you ever seen?

Edited by Sumer, : No reason given.