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Is life a matter of evolving chemistry?

  1. Dec 29, 2015 #1

    mjs

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    is life a matter of constantly evolving chemistry?
     
  2. jcsd
  3. Dec 29, 2015 #2

    Ygggdrasil

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    Can you explain your question in more detail? I'm not quite sure what you're asking? Life is constantly evolving, and life is based on chemistry.
     
  4. Dec 29, 2015 #3

    mjs

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    What is the difference between chemistry and biology (If any?)
     
  5. Dec 29, 2015 #4
    Biology is about living things. Chemistry is about both living and non-living things. Chemistry of living things only is ...<drum roll>... biochemistry.

    So, what's the difference between biochemistry and biology? It is a matter of scale. The study of big structures like organs and bones is biology. The study of atoms, molecules, and cells is biochemistry. Tissues are sort of in between.

    Atoms don't evolve, nor do basic molecules like water. More complicated molecules like DNA improved over time, so they evolved, as did cells, tissues, and organisms. I don't know that there is any room for DNA to improve any more, but it is hard to be sure about that.
     
  6. Dec 29, 2015 #5

    Ygggdrasil

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    I agree completely with @Hornbein's answer. Biology obeys all of the rules of physics and chemistry, so in theory, biology is just applied chemistry. However, biological systems are very complicated, with a huge diversity of molecules interacting in a very small, confined space. Although we've worked out the rules of chemistry for certain, much simpler systems, we don't have enough experience with systems exhibiting as much complexity as biological systems to be able to model them from physical and chemical principles alone (though efforts are being made to computantionally model simple organisms like bacteria).

    What's the dividing line between a non-living bag of chemicals and a living bag of chemicals? These questions are questions that scientists who study abiogenesis (i.e. the origin of life) wish to address. This is very much still an active area of research where we don't understand the complete picture, but here are some previous PF discussions on the topic:
    https://www.physicsforums.com/threads/what-gives-dna-replicating-ability.846493/#post-5310125
    https://www.physicsforums.com/threads/a-question-about-natural-selection.743420/#post-4690960
     
  7. Jan 2, 2016 #6

    mjs

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    So you mean that biology maybe is very complicated chemistry that was selected?
    And what about thermodynamics then?
     
  8. Jan 2, 2016 #7
    Biology is the study of living things in general, biochemistry is a specialisation within the general field of biology which focuses very specifically on what is happening at the molecular level.
    It turns out that biochemistry is almost exclusively about the chemistry of Carbon.
    Carbon atoms have unique ways of bonding both with other carbon atoms, and to other commonplace atoms and substances such as water and nitrogen.
    (A small amount of less commonplace elements such as calcium and phospherous play a part too).
    The result is that there are millions of possible chemical reactions involving millions of possible carbon based molecules.
    Some of these reactions have been harnessed by lifeforms for example as a way of gathering energy from sunlight.
    No doubt that DNA and it's simpler cousin RNA are the crowning masterpeices of natural biochemistry though,
    These long chains (sometimes rings) of carbon based molecules are responsible for reproduction.
    They also encode information which leads to the building of proteins, and these proteins perform many tasks, for example they provide much of the building blocks from which the actual physical parts of a plant or animal are assembled.
     
  9. Jan 5, 2016 #8
    You're really asking a question regarding a classification of interaction, and scales of causative relationships. Yes... Biology breaks down (in a reductionist fashion) to chemistry. But chemistry similarly breaks down to physics. So, ultimately, biology is an application of physics.

    But the relationships described in biology are an upper level of "emergent" behavior in complex systems. You'll have to look into the concepts of emergence to understand the differentiation. That will raise questions regarding the nature of causation in biological systems that some find both intriguing and perplexing. So, the effort might be worthwhile for you.
     
    Last edited: Jan 5, 2016
  10. Jan 7, 2016 #9

    mjs

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    Chemistry can indeed break down into physics. However there are difficulties into breaking down biology into (selected) complex organic chemistry, because there is a problem mainly with respect to thermodynamics and creation of order… But can we overcome this uncompatibility one day if really biology is a part of chemistry??
     
  11. Jan 7, 2016 #10
    Suppose we had only to work with that. First, consider the four basic properties of life:
    (1) Containment,
    (2) Replicate,
    (3) Metabolize,
    (4) Evolve.

    Then as we know life, constantly evolving chemistry in an ocean would not be considered life as it's not contained (in a cell). The same holds for replication and metabolism. So no, life is not a matter of constantly evolving chemistry. Rather life is a "contained" chemical system capable of metabolism, replication, and evolution.
     
  12. Jan 7, 2016 #11

    mfb

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    There is no such problem.
    Every biological process increases total entropy. Usually in the form of produced heat from either chemical energy or sunlight, sometimes with more exotic energy sources (like radioactivity).

    It is an interesting question how systems evolved that use low-entropy energy sources and high-entropy energy drains efficient enough to create some order, but this is a purely biological question, not a problem of thermodynamics.
     
  13. Jan 8, 2016 #12

    Ygggdrasil

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    As mfb noted, biological systems locally create order but they increase the overall entropy of the universe because they are dissipating energy (e.g. using sunlight or burning food molecules). Along these lines, there are attempts to understand the theory of how the laws of thermodynamics would drive the evolution of life. Here's a news piece describing work by Jeremy England on the subject:
    http://www.businessinsider.com/physicist-has-a-groundbreaking-idea-about-why-life-exists-2016-1?amp

    Along with the corresponding discussion thread on PF:
    https://www.physicsforums.com/threads/novel-idea-on-the-origin-of-life.851106/
     
  14. Jan 9, 2016 #13
    Is it still not possibly the underlying non-linear dynamics principally responsible for the emergence and evolution of life? I do recall Ygggdrasi, one particular thread here where you proposed if a suitable set of non-linear differential equation were set up appropriately, dynamics we ascribe to living systems could (or might) emerge. I am of that school: if you write the equations of mathematical physics on scraps of paper and throw them onto the kitchen floor, they won't get up and dance. But if the scraps of paper behaved in a sufficiently non-linear manner, I believe something resembling the properties we identify as "living" would emerge. :) Consider the work of Stuart Kaufmann and Camazine in "At Home in the Universe" and "Self-Organization in Biological Systems." Kauffman proposes that it was the dynamics of the primeval earth that gave rise to life, and Camazine submits (non-linear) mathematical models to represent organization in biology. And therefore, in an effort to remain on topic, to answer the question posed by the thread author, some have suggested that life is not just a matter of evolving chemistry, but rather more fundamentally, of sufficiently-complex non-linear dynamics. Consider also the Brusselator: https://en.wikipedia.org/wiki/Brusselator. Interesting how a simple set of coupled non-linear PDEs, just by virtue of the intrinsic non-linear dynamics encoded in their couplings, can evolve spirals and dots from an initial random state: order emerges from chaos by virtue of dynamics.
     
    Last edited: Jan 9, 2016
  15. Jan 9, 2016 #14

    Ygggdrasil

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    Yes, I would agree with this (the post you reference is here). Thinking of life as a large set of non-linear system of differential equations is not at odds with what England has proposed.
     
  16. Jan 12, 2016 #15

    mjs

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    Questions:

    a)How easy it is for these theoretical interpretations to be experimentally tested?

    b)Entropic changes of life as a whole or at a local level are a-priori theoretical assumptions or are they backed by experimental evidence?
     
  17. Jan 12, 2016 #16

    mfb

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    Which theoretical interpretations do you mean?
    Backed by millions of experiments. Trillions of experiments if you include "I made sports, now I am sweating".
    In addition, the interactions of the components of life are studied in great detail. If a living object would violate thermodynamics, it would need some component that does so, and no such violation was observed ever. The fact that entropy is not reduced is more a mathematical statement than a physical one - and in mathematics you can prove things: you can prove that entropy cannot be reduced in a systematic way, no matter how the system looks like.
     
  18. Jan 12, 2016 #17
    In the book, "Self-Organization in Biological Systems," Camazine and others construct among other many examples, a coupled set of three non-linear PDEs modeling the dynamics of termites during the construction of the marvelous clay cathedrals that they construct using three variables: termites, mud, and pheromone:

    ##\begin{align*}
    \frac{\partial H}{\partial t}&=\epsilon M-k_2 M+D\nabla^2 H\\
    \frac{\partial L}{\partial t}&=\phi-k_1 L+\mu \nabla^2 L-\gamma \nabla\left(L\nabla H\right) \\
    \frac{\partial M}{\partial t}&=k_1 L-\epsilon M
    \end{align*}
    ##
    with ##H## being pheromone, ##M## mud, and ##L##, termites.

    Aren't they beautiful! And one should keep in mind that the particular forms of the equations were not just "conveniently" constructed but rather formulated on the best reasonable analysis of how these three variables ACTUALLY interacted based on experimental data. But equally beautiful, out of a random initial state, "mounds" albeit simplified versions, emerge (the ##L\nabla H## is the non-linearity and since the equations are coupled, the entire system is non-linear). So that in the context of the thread topic, we see here some modicum of experimental evidence suggesting life is perhaps a little more than just chemistry but rather non-linear dynamics of complex systems.
     
    Last edited: Jan 12, 2016
  19. Jan 18, 2016 #18

    mjs

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    I am skeptical with assumptions like “oh, life sustains order, because for instance, a cell is much more ordered than its components, so life is about sustaining order and avoiding chaos” or things like that. I think that this is maybe not the whole picture, because we forget that a cell never exists in isolation. It’s a result of the other life that already exists.

    Imagine you have a flask with water that is heated with fire. The molecules of water will start speeding randomly toward various directions. Virtually, what you are doing here with the cell argument is ignoring the fire and the majority of other water molecules and focusing only on 1 or 2 specific molecules. These molecules will be perceived as gaining speed without an obvious (or rational) reason,..


    So the question is if entropy of life as a whole was ever directly or indirectly calculated (for instance indirectly through changes in heat production, or something like that?).

    Or a man as he grows, starting from a baby and becoming an adult or an old man, does his entropy increase or decrease as he ages?
     
  20. Jan 18, 2016 #19

    mfb

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    What does "entropy of life as a whole" even mean?
     
  21. Jan 18, 2016 #20
    There are many interesting ideas being discussed here. And yes, without question, functional causative relationships within complex dynamic systems (such as those frequently seen in biology/ecology) appear at times to decrease entropy in "localized" regions. However, unless you are prepared to argue that true "top-down" causation is achieved as an emergent phenomenon, then biology IS a complex manifestation of chemistry, which in turn, IS a complex manifestation of physics.
     
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