Biological symmetry

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Discussion by: EricFSM

I was having a discussion (argument) with a creationist about evolution and he brought up a point that I have never heard discussed before.

He said that if evolution were true we would have two right hands and feet, or two left hands and feet. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

I had to just say I don't know how this works, but saying that "God did it" does nothing to explain it. (He thought he had won that round.) I tried to Google this but found nothing, so I am wondering if anyone out there can explain how biological systems work, for example is there just one blueprint for making a finger, and that is somehow repeated 20 times to form left and right toes and fingers?

42 COMMENTS

  1. I don’t know all the details myself, but here are a few important points.

    There isn’t a blueprint for any body part. Genes don’t tell a body what to look like; they tell a cell to divide, migrate, change type etc. depending on chemicals’ concentrations. The sequence of cell activities which form a foot are repeated in a mirror image on the other side because bilateral symmetry as a whole emerges from the details of the rules for cell behaviour and initial symmetry in chemicals’ distribution.

    Having said that, sometimes the genes which cause a body part to form end up forming multiple identical body parts due to either re-use or multiple copies of the genes being present. For example, along the bilaterally symmetric length of a millipede, the same “one-leg-on-each-side” segment is repeated many times.

    There’s a whole chapter on embryological development in Richard Dawkins’s The Greatest Show on Earth. There are two issues here: how does the development work, and how did the answer to that question come into existence by evolution? And, if memory serves, the book tackles both.

  2. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

    he’s correct. natural process is not intelligent at all hence the fact that the vast majority of all life dies before reproducing which can only be a clue to blind natural selection or a particularly hateful deity

    the argument also assumes that you’d have to “transpose” one gene into a left version and a right version.

    ignore the complexity of human digits, go back to where they came from, even further back than the first lobefish and you see that bilateral symetry at no point took a copy from one side and reversed it onto the other, they evolved independently.

    if you look at embryos (always the best place to argue for evolution) you don’t see fingers and toes being created as seperate organs, you see fins growing to webbed hands and feet before the webbing between is reabsorbed to carve out human hands

    the section on embryology in TGSOE is a great place to look. nature builds on what it’s got, you started off as a worm, “you” not just human life, with all the modular design attributes of an ancient segmented sea worm then segments start to seperate into new evolved designs. you’ll never see an embryo grow a hand that gets copied in reverse form. thats just how they grow.

    all land dwelling animal life is bilaterally symetrical. it evolved from things that lived in water with sea bed below and atmosphere above. this carved life into something that could survive, escape, hunt, find mates (eventually crawl out of the water). under that basic environment, bilateral symetry is the simplest working plan for anything that might need to move quickly and not go round in circles.

    left and right as a concept is a human construct. up and down exists thanks to the pull of gravity, fore and aft exist thanks to the requirement to move (especially as eyes evolved such a long time ago), side to side is on average the same each way you look at it.

    there is no digit blueprint. that would require a designer, there are genes that code for proteins, which control cell development and replication. as well as an argument from personal incredulity (all ID arguments are since they rely on a nebulous “too complex…” term) it’s a straw man argument probably based on the oversimplification geneticists use when they say a gene codes for a phenotype

    [edit] yeah what Jos said!

  3. Tell the creationist that all that is needed is a general over-arching rule of development: add new bits in pairs, arranged symmetrically vis-a–vis the centre line. Then it is the exceptions, where only 1 of something or more than 2 is added, that require special instructions. So we get 2 lungs, 2 kidneys, 2 testicles by default but only 1 heart, liver and ovary by a process to be discovered. I don’t know what is known about how this comes about and how it can go wrong.

  4. @OP He said that if evolution were true we would have two right hands and feet, or two left hands and feet. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

    Can you imagine a monkey of an ape trying to swing through the branches at speed using two right hands and two right feet? Natural selection does not need to be “intelligent”. It just has to favour systems which work!

    As for copies? Evolution of complex organisms works by making copies and modifying some of them to provide different functions. – Hence the string of segments on an insect. Segments or parts of segments, can be shown to mis-copy (Antennapedia ) with parts from other segments, when mutations occur switching on or off, the genes relevant to development of that segment!

    http://www.unc.edu/depts/our/hhmi/hhmi-ft–earning-modules/fruitflymodule/phenotypes.html

  5. BTW,
    Not everything is symmetrical. And, things that seem symmetric are NOT.

    Hold a mirror up to half your face and see just how symmetric your face is. Internally you are NOT symmetric at all.

    Sponges are not symmetric. Many organisms show radial symmetry. Some organisms have radial symmetry for a time then change to bilateral symmetry (embryo to adult for example)

    Even molecules that when drawn on paper look to be symmetric or even mirror images are, in fact, NOT NOT NOT either. They demonstrate chirality.

    Also, life is LEFT HANDED. All of the amino acids that are part of proteins are levorotatory. As for hands and overt physical structures, as folks have said here, they are NOT governed by a gene. A battery of genes operating in sequence! A cascade of timed molecular events!!!

    This person fucking thinks that evolution can be “intelligent” enough to pull off getting just the levorotatory enantiomer of 20 amino acids (and ONLY 20) —NON SUPERIMPOSABLE MIRROR IMAGES of molecules…. and then the issue of right hands and left hands will confound explanation?

    As for hand formation, the limb starts out as a “bud”. It elongates and grows into what looks like a paddle. Then, ON CUE, cells start to die (google “apoptosis”). The cells that die CARVE out your fingers. If they all do not die on cue, you have webbed fingers! Google “evo-devo” and read read read.

    Then go back to this person and tell them all you’ve learned!!!

    Good luck.

    • In reply to #6 by crookedshoes:

      Also, life is LEFT HANDED. All of the amino acids that are part of proteins are levorotatory.

      I had a creationist pose this as evidence of design. “Then why is all life left-handed?”, he asked thinking he had journeyed into a realm beyond my scope. I replied, “because left-handed aspartame crystals are slightly more stable against heat.”

  6. What amuses me continuously is that all creationists do is poo-poo evolution (while at the same time not understanding a damn thing about it), and being unable to bring anything tangible themselves.

    And I’m not talking about Intelligent Design, I’m talking about a real scientific theory, with testable hypotheses, predictions, experiments.

    He said that if evolution were true we would have two right hands and feet

    Why?!? Tell him to read up on bilateral symmetry, its advantages, and its evolution.

  7. Evolution is a historical record of what survived and what did not. There is no need for any intelligence. It is a trial and error process. We have symmetrical limbs now because our ancestors with more symmetry were better able to survive and reproduce than those with less symmetry and this lead to the level of symmetry we have now. Alan4discussion put it very nicely with. “hard to swing through the trees with 2 right hands”. Symmetry produces greater agility which allows animals to better avoid predators and capture prey.

  8. He said that if evolution were true we would have two right hands and feet,

    This is mere science fiction. If the evolution of a specific being benefited from having two right hands or having eyes on only one side of the body like a flounder fish it would be like that. There is no need to understand the way DNA is coded. It is simple to observe in the fossils of our ancestors.

    At one point humans did not walk erect, we have proof of that in their fossils. Later they started to walk. It would be logical to assume that this was of benefit to the species. Maybe it was a freak accident that stuck in the genetic code. Much like genetic disorder that are disfiguring. Possibly Dwarfism is an example of a freak DNA coding accident. And also that perfection is not always the result thus negating any concept that somehow it is predisposed in our DNA to be perfect or symmetrical .

    There are good common sense reasons why some evolving changes happen. It really has to do with adaptation.The need for an organism to adapt to it’s location in order to survive is the spark of evolution . Change in environment rules what the organism will turn out to be. Organisms that have adapted to pretty much anything have not evolved or changed since they had no apparent need to do so.

    And because of this, some creationists have come up with their own theories, basically that these fossils could not possibly be millions of years old because the same or similar organisms can still be found today in their almost identical form..

    This is so appalling to read because it is purely misinformation of the highest degree it should be illegal to spread this sort of crap!!

    http://www.nwcreation.net/fossilsliving.html

    This however is very interesting and point to my theory that hermaphroditism is the way of the future !! (joke but true for insects)
    http://www.livescience.com/44906-female-insect-with-penis-found.html

    evolution never stops amazing me…

    • In reply to #10 by GFZ:

      If the evolution of a specific being benefited from having two right hands or having eyes on only one side of the body like a flounder fish it would be like that. There is no need to understand…

      Not necessarily – there has to be a gradual path of advantageous increments from A to B. Our bodies would be much more efficient if the laryngeal nerve didn’t loop all the way down underneath the heart and then back up again. But there has never been a significiant enough advantage to the necessary intermediate steps for this major rewiring to take place.

  9. Mirror Mirror on the wall………Who’s the smartest of them all ?…Not Creationists that’s for sure…..
    There ain’t much alive that isn’t symmetrical…perhaps slime moulds etc seem to be formless shapes but they are a colony of tinier symmetrical forms….It would be quicker to name things that aren’t symmetrical…..Like that guy’s two right brains

  10. I can’t add much to what some others have already said but I do want to make one additional point: if anything the fact that so many organisms are symmetrical IMO counts as excellent evidence for evolution. I may be wrong but it seems to me evidence that at some time, a very, very, long time ago as a common ancestor evolved a right-left symmetrical mutation happened and that mutation turned out to have a lot of advantages that made it flourish and from that point on all the descendents: insects, mammals, reptiles, etc. had symmetry.

    Whenever someone talks about intelligence in the design of evolution I think it’s a good idea to explain that random mutations combined with natural selection over millions of years results in things that seem intelligent. And then give them a pointer to some of the great computer examples from Dawkins in Climbing Mount Improbable.

  11. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

    I might also ask, what’s this “gene” thing he refers to? I’m fairly sure the bible doesn’t mention it, where might he have stumbled across such a word?

    when a psuedo-scientists invokes a scientific term, they must be put on the spot to explain what they’re talking about. For us, genes are the pieces of DNA that demonstrate heredity among lving things, they are the bits of code that show how closely all life is related. It’s the unit of evolution. You don’t get to pick and choose bits out of a science book that you think make you sound clever. In truth we all know the answer. As with all discussions with theists the “bombshell” argument they put forward is one they heard from someone else. someone who has a political or financial benefit from spreading misinformation.

    If you don’t have the counter argument to hand when this sort of thing comes up, don’t worry, just keep pressing; play ignorant if need be. keep asking “what does that mean? what’s a gene? why have genes got anything to do with hands and feet? explain ‘transpose’ to me… why is it harder to make an opposite copy? how intelligent is ‘intelligent enough’? how do you measure it?”.. etc etc.

    they will always crumble in the end. they’ll refer to the website or book or cleric who fed them the line and say “just see for yourself..”

    Embryology has been mentioned more than once and it’s always a good argument to bring in as well. if god made life without evolution, who makes babies? if it’s god making the baby in every womb, why does he go to all the trouble of making a single-celled organism go through division and all the stages of what seems like evolution? Aptosis has been mentioned as well. why build something out of living tissue only to kill it off again? humans apparently popped into existance on day 6 yet their descendants all take 9 months of pretending to evolve through a range of simpler life forms.

    tell him to stick that in his word-salad!

  12. He said that if evolution were true we would have two right hands and feet, or two left hands and feet.

    This doesn’t follow. Evolution is the survival of life forms that are best suited to their environment. Nobody said the development of those life forms had to be easy to understand, that takes study.

    He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

    The process of bilateral symmetry is not intelligent and began a very long time ago (500 million to 1billion years) when life was very simple. Have a look at “The Primitive Streak”, which is common to all embryos that develop into symmetrical animals – from simple worms to blue whales. This occurs very early in the development of an embryo.

    Not everything in an animal is symmetrical and those that are are not perfectly so. It should be simple to see that certain parts of an embryo will grow symmetrically due to their position in the early stages (limbs, eyes, ears, lungs, etc.) and others will not (heart, liver, etc.).

    Natural selection will ensure that creatures that are born where this system fails, will probably not live long enough to reproduce.

    You might find this video interesting and useful.

  13. The universe is composed of geometric fractals. That is what we perceive as being symmetrical . A repetitive pattern. From the smallest to the largest. That is the real beauty of it all. You can see it in the leaves of a tree, in the trunk and the roots. In molecular shapes.
    It would take a real trigonometry genius to recreate this without a computer. It follows logic that it would be this way. That everything is made up of repetitive patterns .Bellow some cool pics to demonstrate the beauty I am talking about.

    http://th03.deviantart.net/fs24/PRE/f/2007/311/5/6/Natural_Fractal___Close_up_by_WindyPower.jpg

    http://fractogene.com/full_genome/fractal_lung.gif

    https://c2.staticflickr.com/8/7061/6777670728_d5f5519f7d_z.jpg

    Leonardo Da Vinci already noted that the sum of the area of the sections of all the branches of a tree at a given height , is constant throughout the tree . The passage of the sap nutrients from the roots (also branched to provide absorption and stability optimization ) to the leaves should be kept at a constant flow regardless of the ramifications . This is done according to the law of the sections above . If we think of a binary branching process , we can express the previous result to the equation:
     
    fp = a ( f1 + f2)
    where fp denotes the value of the diameter of the main branch and f1, f2 indicate the diameters of the two branches that arise . The parameter was estimated by Da Vinci value 2 for the trees. In branched fractal generation has been shown to be a critical parameter. For example , a = 2.7 allows us to model the circulatory system with realism and for the case of lung good models are obtained by taking a = 3 .
       
    The fractal dimension in these cases becomes an indicator of complexity in the organization, the ability to take up space or store information.

  14. He said that if evolution were true we would have two right hands and feet, or two left hands and feet. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

    Fold a piece of paper. Open it up and paint a large “L” on the right side. Close the paper and rub open it up to reveal
    the mirrored effect. Ask him what part of symmetry he doesn’t understand. He’s overlooking symmetry in which one half reflects the other and seems stuck on duplication that is attached. In reflective symmetry arms, legs, wings extend outward from a central point. In his version of having two right feet, arms,legs, wings, etc. would extend outward from a central point and then need to be rotated. It would be as if two separate, same wings would be created and then fused in the center. Sorry if this isn’t making sense, but I think the folded paper does.

    • In reply to #18 by QuestioningKat:

      He said that if evolution were true we would have two right hands and feet, or two left hands and feet. He claimed that a natural process is not intelligent enough to transpose one gene into a left and a right anything.

      Fold a piece of paper. Open it up and paint a large “L” on the right side. Close the paper and rub open it up to reveal the mirrored effect….

      This is basically what happens to the developing embryo. In a process called gastrulation, the ball of dividing cells flattens and folds itself into a tube-like structure where the inside becomes the digestive system and the outside becomes the rest of the body parts. One end of the tube becomes the mouth and the other end the anus. The line where the folded group of cells join becomes the back. This is the beginning of cell differentiation, and the beginning of top-bottom, front-back, and a symmetrical left-right.

      • into a tube-like structure where the inside becomes the digestive system and the outside becomes the rest of the body parts. One end > of the tube becomes the mouth and the other end the anus. The line where the folded group of cells join becomes the back.

        So at the most basic level we are just tubes for turning food into poo. Excellent.

  15. Non-biological things display symmetry. There are lots of mirror-image molecules . . . isomers, (see: http://en.wikipedia.org/wiki/Isomer ). Sucrose sugar comes in two forms, or isomers: dextrose and laevose, that are mirror images. Snow flakes show rotational symmetry, (6-fold).

    It is not difficult to see how a biological system can also produce symmetries, including mirror-image outcomes, in a purely physical way, ie. non-supernatural/god-induced. Small genetic influences can have big phenotypic outcomes.

    Philosophically, I see no problem with evolution coming up with bi-lateral symmetry. And of course if such a thing arose in ancestry long ago, then it would be adapted and modified into the huge suite of symmetries we now observe.

    Other symmetries exist in living nature, such as radial and spherical, and those too are found in purely physical, non-living things. I suggest your creationist friend think more deeply, EricFSM, as well as looking for symmetries in all kinds of non-biological things.

  16. Why would evolution select for two left hands? Look at your left hand and try to picture it on your right arm. How would that work? Would the palm face outwards (hands at your side) or would the thumb point backwards? And, again, where is the selection advantage in this?

    For the tree dwelling primate, or an earlier rodent/ferret-like mammal, or a reptile where would the selection advantage be? For a fish, if it were to have a left pectoral fin instead of a right one, where would the selection advantage be?

    Your friend is assuming he is right without having to explain, even to himself, why it should be true. His premise of non-symmetry is unsupported, faulty and (not coincidentally) wrong. And of course faulty premises generally lead to faulty conclusions. The fact of evolution remains unchallenged despite his misunderstanding of basic reality.

  17. Wow, where do you start? How about how come babies are not born with two left hands or feet? How about a foot where a hand should be?
    Is that happening now? No. Babies are born with their right parts on the right side for most normal births.

  18. Here is a nice hypothesis for the virtues of bilateral symmetry in animals. They make a cogent case for it as the most effective symmetry for locomotion.

    And here is a convincing argument for its origins in sea anenomes before the evolutionary split of Cnidaria and Bilateria, facilitated by the Hox gene and DPP growth factor.

  19. Its only the creationists genetics that are not mirror image….that’s why they walk around and around in circles with their two left feet since they evolved…..just like their thinking patterns…..

  20. I wonder what happened to my Left Liver or my Right Spleen.

    I wonder why my heart is so crooked, and why one side of the lymphatic system only drains 1/4 of the body and the other drains 3/4.

    What is wrong with the Broca center on the right side of my brain?

    No, humans are only superficially symmetrical.

    • In reply to #27 by zengardener:

      I wonder what happened to my Left Liver or my Right Spleen.

      I wonder why my heart is so crooked, and why one side of the lymphatic system only drains 1/4 of the body and the other drains 3/4…

      Ah, but they do all start symmetrical and in the midline. And strictly speaking, the flow of blood does observe left and right division. I’d ask the creator why He had to have the heart develop in front of the mouth and then move into the chest to differentiate into the chambers afterwards. If He just learned to do his bricklaying in-situ, I wouldn’t have to think about heterotaxy syndromes or why the liver starts as 6 bits which decide to create blood cells along the way to becoming a chemical factory…

      • In reply to #30 by Docjitters:

        In reply to #27 by zengardener:

        “I’d ask the creator why He had to have the heart develop in front of the mouth and then move into the chest to differentiate into the chambers afterwards.”

        Too true. The question of why things have to move all over the place during development is a whole other category of weirdness.

    • In reply to #27 by zengardener:
      >

      No, humans are only superficially symmetrical.

      Symmetry is quite limited in vertebrates (basically “Bilateral symmetry”), when compared to some plants and marine organisms with radial symmetry or spherical symmetry.

      Symmetry in biology

      Echinofossulocactus multicostatus

      Echinocactus grusonii – File:Singapore Botanic Gardens Cactus Garden 2.jpg

      http://en.wikipedia.org/wiki/Echinocactus-grusonii

  21. Yes, there must be blueprints, because, after all, it took some time for animals to evolve into those with front side and back side, then ones also with belly and spine and then also with sides. Anyway as far as I know an embryo is not developing from one side to another, but from midline otwards so the the fact that we have both right and left hands and legs seems reasonable.
    But thing about fingers is really complicated (but do not tell it creationists), since it involves different processes, including apoptosis. Actually quite a lot of embryo must die to develop normally.

  22. Stick your left thumb in your left ear, and your right thumb in your right ear and pretend you are an embryo. The cells in the centre of your head start producing a chemical. It diffuses across your body. The cells nearest the source turn into thumbs, the cells furthest away turn into pinkies. No, it doesn’t happen like that, but it is easy to see how symmetry can be generated from very simple rules.

    • In reply to #32 by God fearing Atheist:

      Stick your left thumb in your left ear, and your right thumb in your right ear and pretend you are an embryo. The cells in the centre of your head start producing a chemical. It diffuses across your body. The cells nearest the source turn into thumbs, the cells furthest away turn into pinkies. No, i…

      One set of instructions that is based on the perpendicular distance from the spine measured along the surface can build both a left and a right arm. Since the distance can be plus or minus, there are two solutions, each a mirror image of the other.

  23. He said that if evolution were true we would have two right hands and feet, or two left hands and feet.

    Of course YECs have two left feet.
    There is the one that hops up and down in denial, whenever science is explained to them, and there is the other one, which they plant firmly in their mouths to comically respond whenever evolution is mentioned!

    “YEC Company backward into antiquity by the left, quick march!” “Left!, left, left, left, left right behind the modern world!”

  24. Imagine drawing a tall, thin triangle. This is a perfectly simple object and it has a left corner where the long side reaches up and right towards the central vertex and a right corner where the the long side reaches up and left towards the central vertex. The corners are left-right mirror images of each other. Now imagine that this was a bunch of cells in an embryo. If DNA sends instructions to build a hand thumbs-up on each corner, you get a left hand on the left side and a right hand on the right side. Growth of the cells is contextual; that is to say that cells grow in a way which is affected by where they are. This gives rise to eyes in your head, not your abdomen and so on, so that each part of the body grows in the appropriate place and the proper way round. The technical name for this is cell differentiation. Sometimes after the initial division of the fertilized egg, the cells don’t differentiate, and you get twice the number of everything, i.e. twins.
    The DNA blueprint is not like an engineering drawing: it does not contain a picture of the finished hand, which would have to be either a right hand or a left hand. Rather it contains a series of chemical recipes for building proteins in a certain order. Which proteins get built and where they end up depends on where the cell finds itself in the embryo at the time. That is why, when you cut your finger, you grow new skin cells, not bits of liver.
    What is perhaps more difficult to explain is why, if we have only one heart, it is not symmetrically placed in the centre, but to one side, almost always the left.
    Bill Dixon

  25. He’s idiot. some specific symmetry came about probably because non-symmetrical being did not survive.

    When you speak symmetry I’m guessing you’re referring to digits and limbs and their placement. However bodies not totally symmetrical,. All part of human body are placed in a manner for efficiency and defense. Dome symmetrical some not. The heart, thyroid, spleen etc not counting every hair on the human body are placed in a manner for efficiency only. .

  26. The universe can distinquish between left and right. Who knew! But anyway, they will make up the most ridiculous rubbish to support their ridiculous rubbish, you must find unique and original ways of humiliating such morons.

  27. I’m afraid if you’re talking to a creationist, you will have to dumb it down a little. You can’t teach your cat calculus. They can hear ‘miaow’ or ‘purr’.

    Now why are you talking about genes? If beings could exist immaterially, there would be no need for material. There is material.

    Why does the immaterial being like genes? Why did he take 6 billion bps to write a locust? Twice a human?! Was that intelligent?!

    One can never deny magic, but one can question the wit of the wizard. A child could do better.

  28. Bilateral symmetry of the body would have first formed in Fish. The driving factor would have obviously been the fact that asymmetric bodies would take incredibly complex brains to control the swimming. A fish cannot control its direction of swim to catch prey unless it is symmetric. An asymmetric body shape cannot flow thru water correctly. This is why life that doesn’t need to catch prey is frequently radially symmetric, including starfish, jellyfish, and even trees. If you think about it running across the ground needs symmetry for the same reason. You just can’t move in a deliberate direction unless your body is symmetrical. From the DNA embryo growth aspect organisms grow by series of branching, so once you branch something that will become an arm or a leg, once the branching starts they grow independently so there is no need for “nature” to coordinate one becoming left and one becoming right, because they will be that way because the original branching structure controlled it as the root level of a long series of chain reactions.

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