MD Randomness & Evolution

From: Jim Ledbury (
Date: Sun Oct 17 2004 - 00:58:10 BST

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    Hi Platt, Mark, Scott ...

    the context of random in terms of evolution means that mutations are
    supposed to occur without purpose. This is because they are imagined to
    arise through copying errors in cellular replication or through
    environmental factors (radiation, chemical mutagens...) hence they occur
    without any regard to consequence. Whether there are other causes of
    mutation a different matter, but given that such purposeless mutations
    *do* occur it is currently considered as sufficient by biologists to
    drive the variations required for evolution by natural selection: the
    deciding factor is that they are survivable and are advantageous. As I
    have said elsewhere, given the tangles that evolution does get into, I
    have little reason to believe that there is anything other than an
    essentially purposeless, haphazard variation involved. This fits the
    dictionary definition of random perfectly.

    Randomness as used as a modelling tool in statistics is a different
    matter. It simply means that we are not interested per se in the causes
    for variations in initial behaviour, we simply assume that there is a
    certain distribution of tendencies and run with it. Whether or not we
    can attribute an underlying cause for the distribution is generally
    immaterial. The turn of a dice or the fall of the balls in the UK
    lottery is assumed to involve sufficient mixing of initial conditions
    that an even distribution of outcomes is an article of faith, although
    it can be backed up (or refuted) by statistical analysis.

    In physics, randomness is asserted at the quantum level. Some
    interpretations of quantum mechanics state that the outcome of a given
    experiment is actually globally determined. It's just we can never
    access the global information necessary to determine the outcome of a
    given experiment, so we are forced to assume a random albeit weighted
    outcome. Other interpretations say the randomness is intrinsic, so we
    end up doing the same calculations anyway. Here I would add that
    'consciousness' obviously does have an influence on QM randomness as I
    end up typing the keys I want to (usually).

    'Random' number generators used by computers are actually deterministic
    algorithms, frequently involving modulo arithmetic, and are correctly
    termed pseudo-random. They just give a decent distribution for
    modelling say dice throws or card orders in games but not for instance
    in deriving the keys for encryption where decent analysis will uncover
    the fact that the 'random number' generator is not actually that
    random. There are web-sites devoted to providing a better set of random
    numbers than are produced by the bog standard random number generators
    available to most computers ( The best
    description of a random distribution is rather subtle and requires that
    there is no simpler description of the distribution than the set of
    random numbers themselves (as opposed to a generating function). This
    has no bearing on the assertion that evolution is random.

    Randomness in chaos is down to the existence of 'strong mixing' in
    strange attractors. This is similar to random number generators
    discussed in the last paragraph but all it means here is that
    arbitrarily small differences in initial conditions ultimately lead to
    vastly different end points (the so-called butterfly effect).
    Mathematically this is modelled by completely deterministic formulae,
    but is generally taken to completely independent of quantum mechanical
    randomness (although a different formulation of QM could I guess make
    use of strong mixing) and in any case has absolutely no bearing on what
    is considered to be the random nature of mutations as the source of
    evolution. Even if the world is wholly deterministic, the cause of
    genetic mutation is completely without regard to the consequence of the
    mutations so can safely be presumed to be haphazard, purposeless and
    hence 'random' - unless you want to get into universe spanning
    manipulators of fate, which personally I don't. I don't believe in the
    synchronicity espoused by Jung to explain the utility of the I Ching

    I accept the possibility of purposeful manipulation of the genetic code
    on a cellular level as determined by the cells themselves
    (neo-Lamarkism): I just think it would inevitably be incredibly
    shortsighted therefore not much better than randomness if at all, but
    given the actual existence of random, purposeless, haphazard mutations
    as opposed to a hypothetical puroposeful adjustment, I am comfortable
    with this as an explanation for evolution.

    In short, I'll accept the assertion of "random mutation acted on by
    natural selection" as a reasonable working hypothesis, and I don't think
    I'm being dogmatic about it. :-)


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