1. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Convergent Evolution - How Predictable?

    Discussion in 'The Lounge' started by Steerpike, Jul 22, 2013.

    Conventional wisdom long held that the evolutionary development of organisms isn't predictable (as stated by Stephen Gould in the article I link, below). More recently, the idea has been challenged. A new paper published in Science deals with convergent evolution of lizards on different islands. Interesting to think about. I can't get the full paper from Science. The editor's summary is as follows:



    And an article about the paper can be found here: http://arstechnica.com/science/2013/07/lizards-rewind-the-evolutionary-clock-but-end-up-the-same-every-time/
     
  2. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    Interesting.

    Much has been written as to the logic of certain very general body plans having a higher likelihood of succeeding over others. Like the idea that the sensory package (our face) would very likely be forward of the rest of the body, and that there would be a tendency to raise this sensory package up from the body in order to gain greater sensory input.
     
  3. Lemex
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    Lemex That's Lord Lemex to you. Contributor

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    I really love things like this, and find them infinitely fascinating. Thanks for sharing. :)

    Stephen J. Gould is a name I've encountered before, and so anything by him will spark my interest.
     
  4. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Yes, it is an interesting topic. There are also interesting questions relating to whether evolution is limited to random mutation, followed by natural selection, or whether there might be more at work within the ecosystem that we don't understand. In bacteria, for example, you sometimes find adaptive antibiotic resistance, instead of just selection of fit members of the population that already have resistance before the antibiotic is introduced (which is how it was traditionally thought to work). The adaptive resistance mechanism would have had to evolve, presumably under traditional models. We don't always know as much as we think, however.
     
  5. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    No problem.

    Gould was an interesting guy, and wrote a lot that is worth reading.
     
  6. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    Yeah, I have heard of that. I remember reading that it is believed that plasmids might somehow be involved, trading genetic information between species that are not related. A kind of chromosomal .txt file. Usable be pretty much anything.

    There is also the question of how much of that kind of seemingly predictive behavior is attributable to quorum sensing.

    [sidenote]Quorum Sensing is something that Greg Bear explored in Darwin's Radio and Darwin's Children to my deep and utter fascination.[/sidenote]
     
  7. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    The "tape of life" that is referenced in the original article may also be subject to constraints in what a creature can and cannot do from an evolutionary standpoint, leading to a limited number of end outcomes that remain viable.

    A squillion years ago I started a thread asking why certain traits in animal groups seem to be set in stone while others are so variable. My example question was the constraint on the number of neck vertebra within mammals, being seven. No more, no less. Now obviously this number comes from a common ancestor who passed that number to the rest its descendants, but from that point forward, why should that particular number of neck vertebra be an inviolable rule while other fundamental "options" can vary, like oviparity and viviparity. One would think a giraffe would benefit from a few extra neck vertebra, but no, it's stuck with the same number as a bat or a human.

    Came across this abstract just now from the NCBI:

    http://www.ncbi.nlm.nih.gov/pubmed/10327647

    Now, granted, it is ony an abstract for a proposed hypothesis, but it would appear that there are factors that account for these kinds of constraints that may well be playing a hand in the little lizards being studied right here where I live. :)
     
  8. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    Evolution is a product of natural selection acting on random mutation. Some things are going to be random, and might have developed differently early on. Insect eyes and mammal eyes, for example went down two separate paths. But detecting the environment is required for higher organisms so you can expect some means of perceiving the environment to be universal.

    Locomotion is a universal need in animals, but fish swim with a side to side undulation and marine mammals with an up and down motion. Seaweed doesn't need to move but to reproduce it has to send out seeds or branches. You would expect these problems to be solved different ways but not completely different.

    Feet and hands evolved on land and in water.

    Birds developed hollow bones to lose the weight, bats developed thinner bones. Both need lightweight bone structures but achieved them different ways.

    I don't know that observing convergence in a critter that already has a defined body plan says much about such convergence being universal.
     
  9. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    That's an oversimplification. There are other mechanisms by which evolution can occur - genetic drift, for example. There has also been some interesting work done on evolution of characteristics in a population as a result of purely physical processes.
     
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    It's purposefully oversimplified, it wasn't practical to add a whole discussion of selection pressures positive, negative and neutral.

    And I didn't say anything about sexual reproduction and the spread of genetic material via a half dozen other mechanisms for the same reason.


    But genetic drift is selection acting on mutation. I'm not sure why you see something else. Perhaps you meant shift?

    Fun fact: Complex organisms like ourselves have to have existing variation already present in the genome in order to tolerate major environmental hazards like a new pathogen. We couldn't survive if we had to wait for a mutation in an infant to protect from the hazard.

    But microorganisms can afford to rely on mutations that occur after the hazard appears. Some microorganisms actually shut down genetic repair pathways resulting in an increase in mutation rate when confronted with a toxin.
     
  11. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Genetic drift isn't really selection. By definition, genetic drift is a result of random processes, and is not selection (i.e. if selective processes are at work, it's not genetic drift anymore). You can also have things like Founder effects, which may or may not be the result of selection. A founder effect can occur as a simple result of geographical isolation, and not as a result of selective processes.

    I'm aware of fitness curves already, which is what you're referring to when you talk about the variation already built into a population. But the idea that natural selection isn't the only means by which evolution takes place is well-accepted.
     
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    You are talking past me and I see why now: Genetic drift
    That's one definition. I'm in the infectious disease field and I think of genetic drift in terms of the results.

    The fact many mutations have a neutral impact on the organism doesn't change the principles of evolution. Like I said earlier, I purposefully oversimplified the process, it wasn't practical to add a whole discussion of selection pressures positive, negative and neutral.
     
  13. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    The end result is fixation of an allele, right? But to my recollection, there's no selection going during the process that leads to it. Still, I think these things are all intertwined, and there are a number of things going on, many of which we understand and some of which we don't, the ultimately explain the totality of the evolutionary process.

    Interestingly, back in the 1990s someone did an evolutionary take on the old daisyworld parable, trying to show at least hypothetically how a very simple physical feedback process could result in evolution of a population. It was interesting as a hypothetical, though when you look at what's going on you're really talking about 'evolution' in terms of distribution of individuals across a population, rather than something like speciation, which is what a lot of people equate with evolution.

    It has been a while since I was working in evolutionary biology, and things move pretty rapidly. I suppose the thing to do would be to subscribe to some of the primary literature to try to keep up with it.
     
  14. GingerCoffee
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    While looking at the same glass, you can see it as half-empty, no selection is occurring (neutral mutation), or as half-full, the environment those new organisms now exist in doesn't magically disappear. We are not disagreeing here.

    I find genetic science absolutely fascinating, and of course I'm exposed to infectious disease science which is heavy on genetics.
     
  15. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Infectious disease is fascinating. Have you ever read Guns, Germs, and Steel? I've almost picked it up a dozen times, but never had. Wondering if it is worth the read.
     
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    GingerCoffee Web Surfer Girl Contributor

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    I read it quite a long time ago, but wasn't as impressed as other people seemed to be with it. Doesn't mean you wouldn't like it.
     
  17. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Hmmm. Well, the infectious disease part is the only bit that interest me. For a book on the pre-Columbia new world, I recommend 1491, by Charles Mann.
     

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