Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Evolution and Thermodynamics.

  1. May 13, 2012 #1
    Is evolution(biological) feasible thermodynamically? Why and why not?
     
    Last edited: May 13, 2012
  2. jcsd
  3. May 13, 2012 #2

    russ_watters

    User Avatar

    Staff: Mentor

  4. May 13, 2012 #3
    How?
     
  5. May 13, 2012 #4
    No part of evolution violates any part of thermodynamics.
     
  6. May 13, 2012 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    If you look for a closed system, you have to take at least the whole solar system (and find some way to "catch" outgoing radiation). Within the solar system, there is a huge entropy exchange between earth, sun and space.
    Without closed systems: the sun provides a (nearly) endless supply of high-energy, low-entropy radiation (visible light), while the earth emits a lot of low-energy, high-entropy radiation (infrared).
     
  7. May 13, 2012 #6
    I had asked why or why not? I want reasons.
    Thanks!
     
  8. May 13, 2012 #7

    jtbell

    User Avatar

    Staff: Mentor

    Why do you think evolution might not be feasible thermodynamically?
     
  9. May 13, 2012 #8

    Ken G

    User Avatar
    Gold Member

    As has been said, evolution is not only consistent with thermodynamics, it is an excellent example of thermodynamics. Thermodynamics says that order does not appear spontaneously, and neither does evolution. "Creationism" is a story of spontaneous appearance (from the scientific point of view) of order-- it just "poofs" into being. But in evolution, "spontaneous" appearance of order means appearance of order with no disorder somewhere else that accompanies the order. Instead, in evolution you would always look for the appearance of disorder to accompany the order. That's essential in the whole concept of "natural selection"-- the order is selected from a wide array of different possibilities, the vast majority of which are essentially "discarded" by the selection process. That vast majority of discarded outcomes is what carries the disorder that allows the order to appear in the first place.

    To take an example, imagine seeds falling from a plant. They go everywhere, at random, but a select few find fertile soil to grow in. The vast majority do not, however. Later, you see small plants growing from the fertile spots-- do you think "wow, someone must have carefully selected those spots to plant the seeds, I wonder how they know those spots would be fertile?" No, that would be a creationist view of how seeds grow, requiring a breakdown of thermodynamics for the seeds to be specially planted. But natural selection is perfectly compatible with thermodynamics-- seeds find the fertile spots (an example of order) expressly because they also sampled all the nonfertile spots too (an example of disorder). The order arises from the disorder, that's natural selection, and that's thermodynamics.

    Bottom line: anyone who thinks thermodynamics favors creationism over natural selection doesn't understand thermodynamics at all.
     
  10. May 13, 2012 #9
    I am not with any of the two as I was looking at counter arguments of both evolutionists and creationists and I didn't get points of both the sides so I posted the question here.
     
  11. May 13, 2012 #10

    jtbell

    User Avatar

    Staff: Mentor

    If you post the points that you don't understand, then we can address those specifically, instead of wasting time trying to guess what you're looking for.
     
  12. May 14, 2012 #11

    Rap

    User Avatar

    Absolutely feasible. Thermodynamics says the entropy of a system never decreases. If a seed lies on fertile ground, that's (roughly speaking) high entropy. When it grows to a plant, that's lower entropy. The soil (and some of the atmosphere) have been converted from high entropy to low entropy, so you might think thermodynamics has been violated. But, by thermodynamics, only the entropy of a CLOSED system cannot decrease. The plant and the soil are not a closed system, they are getting light and heat from the sun. So the closed system that you have to think about also includes the sun. The sun is like a nuclear furnace, its entropy is increasing. The light that hit the plant that made it grow came from a bunch of hydrogen molecules fusing to form helium and light in the sun. That was a case of low entropy going to high entropy. When you add it all up, you will find that the entropy of the seed and the soil and the hydrogen atoms in the sun is less than the entropy of the grown plant and the soil and the helium formed from those atoms in the sun. Total entropy has increased, just as thermodynamics predicts.
     
  13. May 14, 2012 #12
    I got it, but I have a last question, when hydrogen fuses to form helium, does entropy increased or decrease?(explaining it using organized complexity)

    Thanks
     
  14. May 14, 2012 #13

    Rap

    User Avatar

    Entropy increases. If you look at the Wikipedia page on nuclear fusion, you can see that what starts out as four hydrogen nuclei winds up as a helium nucleus, two hydrogen nuclei, two neutrinos, two positrons, and two photons. I think you can get a feel for the fact that the products of the reaction are much more "disordered" (have a higher entropy) than the original four hydrogen nuclei.

    When one of those photons travels to the earth and is absorbed by a plant leaf, another reaction occurs. In very simple terms, the photon, the chlorophyll in the leaf, and carbon dioxide in the air react to form chlorophyll, carbon and oxygen. Again, entropy is increased, but the carbon is used by the plant to "organize" itself, creating all the carbon-based organic chemicals that it needs to live and grow. That's where the decrease in entropy happens. But if you take the entropy increases of all the reactions, nuclear and chemical, that occurred to produce that "organization", it far outweighs the entropy decrease that happens when the plant lives and grows.
     
    Last edited: May 14, 2012
  15. May 14, 2012 #14
    Note also that with the advent of molecular biology, evolution is explained by random errors in DNA copying. Actually tracking all of the entropy changes in a biological system is very hard, but the fact that evolution is emergent from random processes, many of which don't progress the species, should make it intuitively clear that it is not actually increasing order. The idea I'm trying to get at is that for every positive trait, there are many that hurt the species. The increase in order that we perceive is only due to the fact that we ignore all of the bad mutations.
     
  16. May 15, 2012 #15
    Thanks to all! I got that!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook