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Thread: News 21 May 2011: Genetic drift, complexity and prions

  1. #1 News 21 May 2011: Genetic drift, complexity and prions 
    Moderator Moderator TheBiologista's Avatar
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    This week, Nature features a letter from Ariel Fernández and Michael Lynch, which argues that genetic drift is a major driving force towards complexity in living things and that the rise of prion diseases in multi-cellular organisms is a direct result of this influence. They also argue that as life becomes more complex, the negative impact of these diseases will become every more significant.

    The Achilles' heel of biological complexity -Nature News commentary by Philip Ball

    Summary:

    The letter builds on previous work by Lynch which suggests that the smaller effective breeding population sizes seen in multicellular species (which are orders of magnitude smaller than those of microorganisms) magnifies the influence of genetic drift versus natural selection on the spread of variety. Thus, larger numbers of non-adaptive variants become common in the population. Complex protein-to-protein interactions arise because they restore fitness to proteins made unfit due to their spread through the population via drift. But, the authors argue, this quick and easy method of circumventing the effects of flawed protein function lacks foresight (as evolution always does) and in fact merely creates more opportunities for the emergence of problem variants via drift.

    To me, it seems like this ought to be a self-limiting process. The accumulation of risky genes in the population must surely be policed by natural selection. There must be a protein network complexity 'tipping point' at which the lack of fitness of a given set of genes results in productive selection against them.

    The work is none-the-less fascinating, and I think it raises questions worthy of very careful consideration and a great deal of research.

    The original letter (open access, with great figures): Non-adaptive origins of interactome complexity


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    Forum Professor Zwirko's Avatar
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    I've read quite a few of Lynch's papers before, got a few in my library (er, folder on laptop): "The frailty of adaptive hypotheses for the origins of organismal complexity" and "The Origins of Genome Complexity". He's very much into highlighting the role of non-adaptive processes in evolution.

    So, he's got a common theme going here, although the prion angle seems to be a new direction I've not encountered before.

    I agree with all the non-adaptive approaches in evolutionary studies - that's something I'm keenly interested in. But I'm not too convinced of their reasoning here. I've always wondered why so many eukaryote enzymes exist as dimers and multimers or are found in huge multi-enzyme complexes. It leaves one wondering why so many other enzymes are not found in such arrangements; are they immune from drift? Perhaps they are more sensitive to change?


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    Moderator Moderator TheBiologista's Avatar
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    Quote Originally Posted by Zwirko
    I've read quite a few of Lynch's papers before, got a few in my library (er, folder on laptop): "The frailty of adaptive hypotheses for the origins of organismal complexity" and "The Origins of Genome Complexity". He's very much into highlighting the role of non-adaptive processes in evolution.

    So, he's got a common theme going here, although the prion angle seems to be a new direction I've not encountered before.

    I agree with all the non-adaptive approaches in evolutionary studies - that's something I'm keenly interested in. But I'm not too convinced of their reasoning here. I've always wondered why so many eukaryote enzymes exist as dimers and multimers or are found in huge multi-enzyme complexes. It leaves one wondering why so many other enzymes are not found in such arrangements; are they immune from drift? Perhaps they are more sensitive to change?
    It all has a bit of a whiff of grand theory to it- like someones building a case for some sort of terminal evolution via excessive complexity story. As you say, there seems to be some possible holes in the evidence, but it's early days yet.
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    Forum Professor Zwirko's Avatar
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    "Psi Wavefunction" over at the excellent SkpeticWonder blog has a good post on this paper. After reading it I feel that I have a much better grasp of what the authors of the paper were discussing. I must admit to finding the Fernández & Lynch piece somewhat impenetrable in places.
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