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Evolution and the Second Law of Thermodynamics

  1. Oct 2, 2008 #1
    I'm not quite sure where to put this, in Physics or Biology. Mentors, please move this to the most appropriate location.

    A common argument put forth by creationists/intelligent design proponents is that evolution/abiogenesis violates the second law of thermodynamics, by causing a decrease in entropy. Of course we know this argument is ridiculous, as any local decrease in entropy on Earth is more than balanced by an increase in entropy in the Sun.

    I was thinking though, does evolution/abiogenesis even cause a local decrease in entropy? I have never seen it proven. If anyone knows the answer/can link to a proof either way let me know.

    PS. I do not want to discuss creationism/intelligent design, or their argument that evolution violates thermodynamics, as these topics are a violation of the guidelines. Please keep the discussion on topic about whether or not evolution and abiogenesis are a local decrease or increase in entropy, thank you.
     
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  3. Oct 2, 2008 #2

    mgb_phys

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    1, There is a rather larger increase in entropy in the sun.
    2, The 2nd law only applies to closed systems not a single animal.
    3, Entropy/order/disorder have different meaning in thermodynamics than in tidying your room. A human is not any more ordered than a chimp.

    If they really believed this then they couldn't have any life created or evolved - unless they assumed that God overruled the 2nd law everytime someone ate a plant.
     
  4. Oct 2, 2008 #3
    Thank you for not staying on the topic I asked you to stay on.
     
  5. Oct 2, 2008 #4

    mgb_phys

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    Evolution isn't really a thermodynamic concept.
    I suppose the creation of a single Eukaryotic cell takes more energy than a simple cell, but this only applies to individual chemical reactions not the evolutionary process.
     
  6. Oct 2, 2008 #5
    I don't know that this question has an obvious answer. Evolution isn't a process that can be readily observed. I'm no biologist, but my guess is that biologists don't even have any evolutionary pathways with the level of specificity that your question requires. Rather, as a physicist I would say that it might be easier to reduce this to a more simple problem, such as the formation of a lipid bilayer and the process by which it isolates cytosol from an external environment. Then perhaps at least one could use some statistical mechanics to calculate the entropy change involved in such a process.

    Conceptually speaking, my guess is that any hypothetical evolutionary process would require a decrease in entropy. After all, a protein is a lower energetic configuration than a liquid of freely floating amino acids. It makes sense that any evolutionary process which might occur would necessitate a local decrease in entropy.
     
  7. Oct 2, 2008 #6
    The question is very open ended, any arguments/discussions about even a particular small scale evolutionary change are welcome, as well as more general discussions. I guess one way to look at it would be the planet as a whole. Would a planet with life have lower entropy than an (otherwise equivalent) planet without any life? Would a planet with relatively primitive single celled organisms (or even just self replicating molecules) have higher entropy than one with more complex organisms? Or else: Does life, as a product of the chemical reactions involved in it's continuation, decrease the entropy of the earth?
    I don't suppose anyone has any links to anyone who's actually done such calculations? (or should I make this a masters project...)
    Is it? I thought it took a fair bit of energy to produce a protein? If a protein is a lower energy state, shouldn't they form spontaneously (or do they? I don't know much biochem)?

    Thanks for the answers guys, I know the question is very open ended, feel free to interpret it however you want, as long as you stay on topic.
     
  8. Oct 2, 2008 #7
    No, but it is still a process and therefore the change in entropy should be quantifiable (maybe over some particular evolutionary step, or over a longer term, like from the point of abiogenesis to now)
    Just because it takes more energy (does it?), doesn't mean it's necessarily lower entropy. I don't suppose anyone has ever done a comparison of the entropy in a simple eukaryotic cell and a simple prokaryotic cell?

    Thanks.
     
  9. Oct 2, 2008 #8
    Maybe a good question would be "Could life and evolution have occured without the energy from the sun?"

    Perhaps if there were sufficient heat from geothermal activity that would last for a long enough period. Though maybe a planet could not maintain such a level of energy out put from its core for very long. One way or another I would guess that a source of ambient heat/energy would be required for genesis and evolution.
     
  10. Oct 3, 2008 #9

    Moonbear

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    This is the trouble with trying to use some part of a non-scientific argument to begin a scientific argument. There are usually so many things wrong with it that it's a stretch even to find something to start the argument with.

    Evolution is just the change in species over time. There is no reason to think that the switch or change in a gene or gene expression required any more energy than the previous complement of genes expressed in an organism or species.

    It's also the bias of the intelligent design proponents that evolution requires all organisms get more complex with time, which is simply another wrong understanding of what evolution means. Usually, when trying address this particular issue with them, we just point out the sun to them and end the debate, because it's enough to kill their argument. However, there are many more things wrong with it, one of them being that they don't even know what entropy really means. There is no way to apply it to evolution, per se. So, that's another problem is they are conflating life, development, growth and maintenance of organisms with evolution, which is patently wrong. And, even in that context, they manage to conveniently ignore that organisms also die, decay, and basically return to the soil as raw ingredients. Other than using energy from the sun for some assembly, life is a big recycling program...take a bunch of raw materials, assemble them, reuse them for a while, eventually the organism can't keep up the maintenance and dies and all the raw materials are returned to the recycling center again.
     
  11. Oct 3, 2008 #10

    russ_watters

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    The amount of energy stored in an organism's structure (body) doesn't have anything to do with anything. It has nothing to do with how much energy it requires to create that organism. The amount of energy stored in the material in an organism is miniscule compared with the amount spent over its lifetime on the business of living. So if you want to view it in terms you are describing, the process of living itself is virtually all wasted energy. Evolution, then, would be several generations of wasted energy.

    But as said, that's a pretty poor way to look at either evolution or thermodynamics. It's best just to not mix beer and liquer like that: it'll make you sick, even though they are fine on their own. Seriously, though, the second law of thermo just plain can't be applied to evolution.
     
  12. Oct 3, 2008 #11

    russ_watters

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    And even if it did, so what? Sharks have lived virtually unchanged for millions of years, generating lots of entropy in that time. If they had evolved into something that had a more efficient storage structure or simply consumed energy more efficiently in living, and generated less entropy, it wouldn't mean that the law had been violated. For that, they would have to evolve into a perpetual motion machine.
     
  13. Oct 4, 2008 #12

    Chi Meson

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    In terms of "order to disorder" statement of 2nd law:

    In long term evolution, an animal has changed from a simple structure to a very complicated structure: lots of bones, organs, nerves, all in very specific places. So when comparing a creature to its long-ago evolutionary ancestor, it appears to be a huge increase in the state of order.

    But as Russ noted, to get there there were several [million] generations of wasted energy. It's not a single system (one body) that increases in order.

    It is not like a house that starts with bricks, lumber, nails, and mortar lying on the ground; then becomes a small bungalow after work is done on it; then becomes a two story house after more work and materials are added; then becomes a mansion after more rooms and a pool are added on (everything's an architecture analogy with me!).

    So I agree that the second law is poorly applied either way to evolution.

    But if forced to do so, I would say that evolution as a whole, lengthy as it is and using highly inefficient organic processes, does NOT present a local decrease in entropy, because you cannot look at just one creature's body, you have to look at the entire chain of millions of generations of bodies. The "increase in order" of the final subject (even if you could quantify it) would be far outstripped by the energy input all along the way.

    A single body, as it grows from infancy into adulthood, is very much a local decrease in entropy, but that is an extreme case of "non-isolated system."
     
  14. Oct 4, 2008 #13

    Moonbear

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    Don't forget all those dilapidated houses condemned for demolition...the species that were unsuccessful and went extinct. Or the ones that downsized. Again, the ID and creationist proponents, in their flawed understanding of evolution, forget that evolution is not happening in a single direction always getting bigger, better, more organized. There are extinctions that are dead ends...no more evolution. There is evolution toward more simple organisms...parasites lacking organs that their ancestors would have had simply because they were unnecessary.

    The arguments they make are basically taking a whole bunch of poorly understood scientific concepts, smushing them all together in a way that makes no sense at all, toss in a dash of misconception, a cup of willful ignorance, and try to serve up their unpalatable mess to anyone who will buy it. This is why scientists don't like wasting their time arguing with them. You can't just point to one wrong concept or a tiny misunderstanding and say, "there, that's where it went wrong" because it's such a jumble of so many wrong ideas, there's no place to even begin dissecting it, and with the willful ignorance thrown in that they don't want to be corrected, it's futile.
     
  15. Oct 5, 2008 #14
    You should treat their arguements fairly though. Blowing them off only martyrs them in the eyes of a masses who do not understand the arguement and its flaws any better than they do. No one likes to be made to feel an idiot and will likely favour those who appeal to them with kind explinations rather than haughty intellectual superiority. What did you think of professors who treated you like a simplton if you didn't understand the material?

    Creationists generally point to the genesis, or begining of life, for their arguements. If the earth were truely a closed system then abiogenesis (order from disorder) and further 'evolution' into complex organisms in a complex biosphere would seem to contravene the second law of thermodynamics. So in this way creationists seek to show that this theory of evolution doesn't even make sense from a scientific view point. Science contradicts itself and the arguement makes sense if you don't think about the sun as an energy source for life. Recycling of materials does not explain why their arguement is faulty. Really this part of their arguement is based on a often perpetuated idea that the earth is a perfect equilibrium of life, which it is not. Recycling of materials only fits right in. If life can perpetually recycle itself then it breaks the second law which predicts decay, dissipation of energy, and heat death. On an organism by organism basis the second law may not apply but on some level it does. Unless you admit to some special property of 'life' ecological systems are necessarily subject to the same laws as any other system.
     
  16. Oct 5, 2008 #15
    when humans got rid of their tails was that more complex or less? Which is more complex a snake or a lizard? how about a human with no arms or legs? I always hated using entropy and evolution in the same sentence. Which is more complex an octopus or a horse or a human?
    edit: or a centipede? just thought of that one.
     
  17. Oct 5, 2008 #16
    Are you saying parts of me are imaginary?
     
  18. Oct 5, 2008 #17

    vanesch

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    Entropy is a *number*. It is a number one can associate to a given system - there are small ambiguities in the definition itself of that number but for most practical applications, these ambiguities amount to such tiny differences that it doesn't matter for all practical purposes.

    If a system receives heat Q at temperature T, then the entropy of the system increases by Q/T, and if the system gives off heat Q at temperature T, then the entropy of the system decreases by Q/T. If a system exchanges work with the environment in a reversible manner, then the entropy doesn't change.

    If a system consists of several subsystems, the entropy is the sum of the entropies of the subsystems.

    The second law states that for an *isolated system*, this overall entropy can only increase or remain the same by interactions of the internal subsystems.

    The second law doesn't state at all that the entropy of every system must increase. Only for isolated systems, the overall entropy must increase. Otherwise, water couldn't freeze!

    Systems that are coupled to the environment can be modeled as an overall isolated system in which we consider 2 subsystems: the original system and a "heat reservoir" as second system, or several heat reservoirs if necessary.
    In that case, the second law can still be applied to the overall system, and means that the original system cannot have a stronger lowering of entropy than what is compensated by the increase in entropy in the heat reservoirs.

    Now, in order for biological evolution to violate the second law of thermodynamics, one would need to have that the system under consideration (the biosphere) has a stronger lowering of its internal entropy, than the increase in entropy of the heat reservoirs which model the environment. A decrease is allowed for, as long as it is less than the increase in the entropy of the environment (modeled by heat reservoirs).

    Now, it is true that a living biosphere has a *slightly* lower entropy than the same material in thermodynamic equilibrium. So yes, the entropy of the biosphere has been lowered a tiny amount since life developed. However, it is not much. It comes about because of the separation of chemicals in the bodies of the living creatures, which are lower-entropy than would be their equilibrium (dead) values. In the same way as ice has lower entropy than liquid water, although for water and ice, and worse, for vapor and liquid water, the differences are much bigger than for the chemicals in living creatures.

    When you do the calculation of how much entropy has been increased in the heat reservoirs, then the tiny amount of entropy decrease in living organisms is totally dwarfed. So the second law is not violated, by several orders of magnitude.

    But in as much as this argument would make sense (it doesn't), condensing steam or freezing water would violate MUCH MORE the second law then. It doesn't, simply because there is so much increase in entropy in the heat reservoirs (essentially the sun on one hand, and dark cold space on the other, but you can include geothermal effects and all the heat flows (and hence entropy flows) the biosphere is coupled to).
     
    Last edited: Oct 6, 2008
  19. Oct 5, 2008 #18

    vanesch

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    In fact, the tiny tiny tiny "entropy decrease" that could eventually be associated to the "complexity of a biological body organisation" is TOTALLY DWARFED by the entropy balances of the CHEMICALS in the body. In fact, it is of the order of the ambiguities in the definition itself of entropy.

    Entropy is the logarithm of the "number of possibilities of equivalent complexity" in a way. So in order to calculate the entropy increase due to the organisation of a human body with or without tail, you'd have to specify exactly what you consider as the "macroscopic definition" (hence the ambiguity!) of "human being", and then count the number of different ways in which you could arrange that ; and then you'd have to define the "macroscopic definition" of "predecessor of human being",and count the number of possibilities (there might be more).

    So then the "evolution" from "predecessor of human beings" to "human beings" has resulted in a diminishing of the number of possibilities, and hence in a decrease of the entropy. However, these numbers are tiny (and moreover ambiguous because you see that it depends on arbitrary definitions of "human" and "predecessor"), they are infinitesimally tiny as compared to the NUMBER OF MOLECULAR ARRANGEMENTS of the chemicals (the number of ways each of the atoms in the body could be arranged into different molecules and so on). These are tens and tens of orders of magnitude larger than the small numbers we were talking about.

    If you'd separate a human body in all the different chemicals that are present, and put them in bottles, the entropy of this system would be, up to 10 decimals or more, the same as the entropy of the living human being. If you'd separate the body of a chimp in the same way, you'd find about the same entropy (even thought the chemicals might be slightly different). The tiny tiny difference due to "body organisation" is totally dwarfed by the entropy of the chemicals. And that by itself is dwarfed by simple processes such as evaporating water.
     
    Last edited: Oct 7, 2008
  20. Oct 5, 2008 #19

    Moonbear

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    Apparently you missed my point about their WILLFUL ignorance. I see no reason to treat their arguments fairly when they have no intention of considering explanations of scientific concepts fairly. Have you REALLY tried talking to these people? I have...that's how I learned it's futile. They don't WANT to be educated about evolution or any other aspect of science, they just want to rationalize their beliefs to themselves. This is entirely different from a student who is simply confused and wants to learn.
     
  21. Oct 6, 2008 #20
    But the people who listen to their arguements and yours may decide who to believe, not based on the quality of the arguement but, based on whether or not they believe you are treating them fairly. I come across many people who believe creationist and ID arguements have merit and this is the main reason. Education isn't about 'winning' arguements.
     
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