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How does evolution work?

  1. Feb 1, 2008 #1
    How does evolution work?

    It seems that evolution has determined many of the circumstances of the world we find ourselves in. Here are a few examples:

    (1) Cosmologists tell us that our present astronomical universe --- a conglomeration of planets, stars and clustered galaxies, together with dark stuff, all immersed in a sea of radiation and dark energy ---- evolved over 14 or so billions of years out of a hot, compact and quite uniform plasma of particles and fields ---- the early universe of some 14 billion years ago.

    (2) Biologists tell us that all the teeming plants and creatures that occupy the surface of this planet evolved over half a billion years or so from less numerous and simpler forms of life --- from “worms and worse”, as I’ve heard it put.

    (3) Political theorists tell us that modern representative democracy has evolved, from the simpler and harsher social systems of ancient times, to the complexities of the current presidential elections in the U.S.

    (4) Historians tell us that technology has evolved from fire and wheel to the complexities of modern life, like short circuits and traffic gridlocks.

    (5) And as you read this, silicon intelligence may be busy evolving a substitute for our ephemeral biological intellects.

    The details of how evolution (if this is indeed the right term to use) operates in each case are of course different. The purpose of this post is to ask folk who take an interest in the whys and wherefores of such matters (those who have a philosophical bent and some knowledge of physics?) if there could be a common factor that defines “evolution”.

    For a start I suggest that the existence in each case of some kind of self-promoting process might fit the bill. Since these are physics forums I focus on an example of physical evolution, that of our universe.

    Cosmologists seem to agree that ever since gravity began to transform density fluctuations in the almost homogeneous fluid of the primeval universe into the structures we know today, the second law of thermodynamics has ruled on a universe-wide scale.

    Consider the action of the second law as described by Penrose in his book The Road to Reality (Chapter 27) . Penrose presents his discussion of the second law in the context of what I will call the “landscape” of phase space, to borrow a term from fringe cosmology. Phase space is a well-known concept used in the discipline of statistical mechanics. It is an abstract multi-dimensional coordinate space in which the state of the system being considered is specified by a single point. As the system develops dynamically this representative point traces a trajectory through phase space. In the case of the universe it passes through a “landscape” that Penrose depicts as “boxes”
    of phase space with boundaries that are sensibly but rather subjectively chosen. Large boxes contain many states judged to be too similar to be distinguished. Small boxes contain only a few such states.

    It is implicitly assumed in Penrose’s persuasive graphic description of the action of the second law that the landscape of phase space remains distinct and unchanging as the universe ergodically explores its phase space; phase space is assumed to be an unchanging background, as it were, for the developing trajectory of the point that represents the state of the universe. It is in this context that one can assert with confidence that the chances of structures like stars and galaxies spontaneously assembling themselves without gravity are entirely negligible --- as are the chances
    of all the molecules of a gas in a macroscopic container spontaneously collecting together into one of its corners (or of all the atoms in a molecule of DNA spontaneously assembling into a double helix).

    How then did gravity then force the evolution of the complex and heterogeneous universe that astronomers now observe?

    Consider a modification of Penrose’s description of how the second law operates. Suppose that the boundaries of “boxes” that define the landscape of phase space, as envisaged by Penrose, are changed by the action of gravity as the universe’s representative point traces its trajectory through phase space. For example, suppose that the trajectory of the early, near- uniform universe passes through a box of states in which the universe has a single overdense patch. The attraction of gravity draws matter towards this patch, and in doing so moves or creates new box boundaries. I am here suggesting that gravity is an agent that can dynamically reshape the landscape of phase space while the universe evolves, and that this is possible because gravity stimulates self-perpetuating processes: i.e that gravity is an agent of auto-catalytic change.

    From a broader point of view, this is evident in many situations. For instance, in geomorphology gravity stimulates self perpetuating processes like the hydrodynamic dissection of a smooth slope by the formation of a drainage network of rivers and streams. In this process the phase space of fluid flow over the smooth slope is, I suggest, dynamically reshaped by the action of fluid flow itself, and therefore ultimately by gravity.

    And seems to me that it is indeed appropriate to talk of the evolution of the universe, because the principal agent of change that is involved is gravity, which stimulates self-perpetuating processes. In this respect physical evolution is like biological evolution, whose essence is the reproductive capability of DNA. The difference is that gravity is a phenomenon of the physical world determined by its geometry, whereas DNA is a physical structure made possible by the laws of nature.

    Is evolution in general characterised by processes that are self-perpetuating?
     
    Last edited: Feb 1, 2008
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  3. Feb 1, 2008 #2

    mgb_phys

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    The word evolution is used rather loosely above. Saying that gas clouds evolve into stars and planets is like saying a dropped egg 'evolves' into a mess on the pavement.

    Evolution is only really defined in a biological sense where it simple means a change such that further change in the same direction is more likely.
    eg. you don't need atoms to spontaneously evolve into DNA, you just need a few atoms together to create the right electro-chemical properties for the next atom to stick in such a way that adding the new atom means the properties ar ebetter for more to stick.
    Look up self catalysing reactions for an explanation.
     
  4. Feb 1, 2008 #3
    Evolution is when objects change gradually via a natural process. I don't think a natural process has to be self-perpetuating, no. Life processes are fuelled by the outside world.
     
  5. Feb 1, 2008 #4
    Yes -- I'm trying to explore the concept of evolution, so I do use the term "rather loosely", on purpose. A dropped egg doesn't evolve; overall entropy increases when it is dropped and it becomes disordered. When a gas cloud condenses into stars overall entropy increases and local order increases. Evolution is a fair description of star creation, I maintain.

    It is not only in the biological sense that there is evolution. This is the whole point of my listing a set of examples. And I agree that atoms need not evolve to make DNA. It is the structure of DNA that evolves, from what and just how is lost in the mists of our ignorance. But I doubt if DNA arrived on the scene suddenly and spontaneously.

    Thanks for referring to me self-catalysing reactions. They are exactly the sort of self promoting process that I propose as the essence of evolution, although such reactions may also occur independently of an evolutionary process.
     
  6. Feb 1, 2008 #5
    Thanks for your prompt comment
     
  7. Feb 3, 2008 #6
    Just a note, one of the common mistakes people make is in assuming that 'evolution' has a direction. It really doesn't. In the biological sense, it does not mean going from simpler organisms to more complex.

    Evolution is simply adaptation to through natural selection.

    The ant you just stepped on, is just as 'evolved' as you are. Its been through a similar process but ended up differently. Humans are not 'more evolved' than Ants. We simply took a different path.
     
  8. Feb 3, 2008 #7
    It's for once so nice to see this recognised explicitly. I agree strongly that we're not "more evolved", than any of our fellow creatures. But I do think evolution has a direction, in the following sense: saying there is no direction to evolution is like denying the irreversibity forced upon us by the Second Law, or that time (whatever this is) doesn't have a direction from past to future, i.e. that "time's arrow" doesn't exist.

    By the way I'm careful never to step on ants!

    Finally,

    Yes indeed. But is there some recognisably common factor in its different manifestations? I think so, and that the trick is that all kinds of evolution incorporate a self-promoting process.
     
  9. Feb 3, 2008 #8

    Moonbear

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    No, it really doesn't have a direction. It simply means change...in any direction. Organisms can become more simple as much as they can become more complex. Parasites lacking digestive tracts have evolved from organisms with digestive tracts...they've become simpler, they're still evolved.

    Evolution does not need to be self-perpetuating. Indeed, it can be a dead-end. Evolution can result in a species becoming extinct, because it cannot self-perpetuate.
     
  10. Feb 4, 2008 #9
    I admit I've been too simplistic. Evolution is not always from simple to complex, as you correctly point out. But I don't agree that it "simply means change". Physically, systems that change may well become trapped in local minima of free energy, as it were, and cease evolving towards ultimate stability. An example is the rapid cooling of an alloy where metastable configurations form all the time, and may become permanent for all practical purposes. As in the quenching of Damascus steel.

    Another example, beloved of inflationary cosmologists, is the metastability induced by Mexican hat potentials in the inflationary scenario.

    So "dead ends" are also a general feature of evolution. I think one must broaden the meaning of this word beyond its biological applications, or its dictionary definition of "developing by natural processes". Isn't it appropriate to say that the bicycle evolved out of various wonderful bone-shaking and penny-farthing configurations?.
     
  11. Feb 4, 2008 #10
    Im having a hard time understanding your posts. Evolution has to do with biological processes. It is the gradual weeding out of traits that are not benifical to natural pressures in the environment. It is always from simple to complex, thats not what moonbear said. She said its from simple to complex, but that complex may fail due to an environmental pressure; whereas, a similar but slightly different biological form will survive to reproduce. She said its a dead end, she did not say it was NOT from simple to complex. Simple to complex is exactly how natrual selection works.

    I dont know what this minima of free energy has to do with evolution. Your stretching farther than your arms can reach.

    As a side, you have a lot of big words in your posts mixed in with science, and I dont have one clue what your talking about. It makes no sense when I read it from a physics point of view.

    For example,

    Er, not really. Gravity is a phenomenon that occurs whenever there is two bodies of mass. Is there a non-physical world, by the way?

    A 'phase space'....What in the world is that supposed to mean?
     
    Last edited: Feb 4, 2008
  12. Feb 4, 2008 #11

    Garth

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    What Moonbear actually said was:
    I understood that to mean that when the simpler system is better adapted to survival in a particular biological situation then it does evolve from complex to more simple.

    Garth
     
    Last edited: Feb 4, 2008
  13. Feb 4, 2008 #12
    Perhaps I should clarify. The process starts simple. That being said, the parasites still started from simple organisms, developed a digestive track, and then due to environmental pressures survived without it. However, it still started from a simple form. In other words, it could not have started with a digestive track from the get-go. That had to have been evolved first.

    You cant climb mount improbable.
     
  14. Feb 4, 2008 #13
    I'm sorry that this is so, especially since you say you are reading "from a physics point of view". I didn't mean to misunderstanding Moonbear's kind reply, which I am mostly in agreement with.

    You seem to consider evolution as exclusively biological, in which case I can offer no help here.
    About gravity: it is a physical phenomenon, as distinct from some abstract thing. And for about a hundred years physicists have described it in terms of the geometry of space and time.
    About phase space. This was invented by Willard Gibbs around 1901 and has been a fundamental concept in phyics ever since. Try Wikipedia.

    I seem to have made you cross, by using ancient physics, for which I apologise.
     
  15. Feb 4, 2008 #14
    Mount improbable is a nice analogy, but it only addresses 'how we got to complex life from simpler life'. It doesn't imply that this direction is somehow an implicit part of evolution.

    We do know quite a lot about how things evolve and its not always in that direction. Amoebas are not necessarily more complex than the vast majority their ancestors and their are more of them than us. A biological system, organism, will respond to its environment, be it in the gut of another creature or in the gut of the ocean. And it will go in whichever direction seems to present an advantage.... and yeah sometimes that ends badly.

    Evolution doesn't really address how life started however, although there are some interesting applications of evolutionary principles to simple molecules within the framework of how things might have started. One can however imagine a planet where these simple reactions never resulted in more complex interactions.
     
  16. Feb 4, 2008 #15
    What seems to be going on here is attempts to clarify the myth of progress / great chain of being, and why those are myths. "More evolved" would mean high up on this imaginary chain of being. Since it is more like a tree of life, the term could not be used in this way. The only sensible way of speaking of "more evolved" would then be a population where the shift in allele frequency is higher.

    As noted above, the complexity rises and falls all throughout evolution with no particular preference.
     
  17. Feb 4, 2008 #16
    I think we should differentiate between 'evolution', which is a biological term, and evolutionary analogies in other systems.
     
  18. Feb 4, 2008 #17

    Garth

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    Yet nevertheless the history of biological life on Earth has been from single cell prokaryotic bacteria and eukaryotic organisms to multi-cellular eukaryotic celled organisms as shown on the phylogenetic tree of life.

    The overall story has been an evolution or gradual development from simple to more complex, in the sense that complex organisms first originated after simple ones.

    And yes JoeDawg the word 'evolution' is being used with two separate, though related, meanings: as the 'biological process of the survival of the fittest' and in the general sense of 'gradual development'.

    Garth
     
    Last edited: Feb 4, 2008
  19. Feb 4, 2008 #18
    I disagree strongly with this. Evolution (at least in the biological sense) certainly has an overall preference to those mutations which are beneficial to the organism in question's ability to survive and reproduce. Although it is often the case that evolution causes simpler organisms to become more complex i agree and am sure there are at least some cases where an organism becoming more simple would be beneficial. In this case simplicity has "preference".

    -||spoon||
     
  20. Feb 4, 2008 #19
    Not sure if it's interesting but for instance the evolution of the molars and tusks of mammoths in Eurasia is rather intriguing. From the older mammoth species (2,5 My ago) to the younger, Mammuthus meridionalis, Mammuthus trogontherii to the last (woolly) Mammuthus primigenius, we see the general body size decreasing from about 14-15 ft at the shoulder to about 8-9 ft for the latter, the enamel plates of the molars increase from 5-6 to some 35 suggesting transition from browser to grazer while the tusks increased in relative size. The large spiralling tusks of the bulls of the last, the woolly mammoth were absolutely useless for anything else than an ornamental token of strenght, while the straight tusks of its predessors could have been usefull for derooting trees to be able to browse the higher branches, like the modern elephants do. But the woolly mammoth was rather unfamiliar with trees on his large steppe. Also the small more rudimentary tusks of the cows confirm that there was little practical use for tusks anymore.

    When the grassy steppe biotope in Siberia suddenly changed in boreal forests, marshes and swamps, completely unfamiliar for the woolly mammoth, the large tusks may have become a nuisance maneuvring between the trees. It may have contributed to its extinction. A highly specialized steppe animal in a completely wrong biotope.
     
  21. Feb 4, 2008 #20
    There is no special preference for complexity, just novel utility. The two often go together, but this is not necessary. It all matters what you mean by "complex". For instance, dinosaurs are more complex than, say, the H5N1 strain of avian influensa, yet dinosaurs predates H5N1. Examples where selection has worked towards the less complex are the evolution of the venus fly trap, evolution of whales and the size of the hominid brain. There are also many examples of increased complexity leading to less ability for survival.

    Imagine three populations of bacteria. A might outcompete B and B might outcompete C, but C can still outcompete A should the environmental changes make it more probable. There is no "progress" in this sense. The term 'survival of the fittest' is a somewhat outdated and it should really be change in allele frequency in a population over time.
     
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