Re: Evolution Statement

Date: Mon Dec 10 2001 - 08:45:50 EST

  • Next message: Michael Roberts: "Re: Evolution Statement (corrected)"

    In a message dated 12/8/01 3:51:05 PM, writes:

    << Bob wrote...


    >I accept the (DWM) as a partial definition of evolution, but with

    >a minor proviso that this definition holds best within recent species

    >and is more problematic the farther one goes back in the history of

    >organic life. The statement fails to mention that, and would be

    >improved if it did. >>

    Tim: <Hmm... Let's look at another set of historical events...

    I accept that meteoric bombardment is at least a partial description of

    how the moon came to be so pock-marked, with the minor proviso that

    this applies best to recently acquired craters and becomes more

    problematic the farther one goes back in the history of the lunar

    surface and the record becomes obscured by time and more recent


    <Thus we should not rule out the possibility that many of the older,

    more disrupted lunar craters could have formed supernaturally and are

    not the products of natural causes. (Or, pace Moorad: We never

    saw the impact which produced Bessel crater, so why couldn't it have been

    made by elves? Science can't apply to any crater formed before 10000 BC,

    because there weren't modern humans or instruments to record it. Let it

    forever be an enigma!)>

    ..end speculations here...>>


    I don't know why you threw in the concept of the supernatural in your moon
    example, which I suppose was meant to address my statement. Did I say
    anything about the supernatural? No. So why do you?

    Bob: >The statement fails to address the critical question: What is the

    >that brought about DWM? That brings us to the heart of the matter, because

    >the answer must be, natural selection. Nicht wahr? (True, genetic drift and

    >neutral mutations possibly direct genetic exchange in very early organisms

    >are sometimes invoked as change agents, but they are relatively minor causal

    >factors.) If natural selection is not the major change agent in the overall

    >course of DWM, please correct me and tell me what is.>>

    Tim: <Genetic variation is the major change agent. What locks a particular

    into a population or affects its frequency in a population includes:

    natural selection, neutral drift, and other factors. It is actually a hot

    debate about which of the two, selection or drift, are the most influential

    agents of change. Certainly neutral mutations accumulate in a genome faster

    than selective ones.>

    While I can understand the mechanism of selection, I find it difficult to
    understand what drives neutral drift. I'd appreciate it if you would explain
    it. It seems to me to be a radical departure from natural selection. What is
    the significance of their "faster accumulation in the genome" that you

    Bob: >But to do so would introduce a problem that the statement probably

    >wanted to avoid, namely, that the only direct evidence we have that

    >natural selection is the causal factor in DMW is bacterial resistance

    >to antibiotics, and what Gould called "short-term evolution" (STE)

    >studies, such as the finch's beak, peppered moths, spotted guppies,

    >and so forth. These studies are the only basis for the claim that

    >natural selection is the causal factor for all changes we see in the

    >fossil record and the tree of life. The operation of natural selection

    >throughout the entire tree of life is an extrapolation from such studies.

    >Or to say it differently, evolutionary biologists hold that socalled

    >macroevolution, or large innovative changes in DWM is microevolution

    >WRIT LARGE. This claim, however, is not a fact. Thus while DWM itself

    >is factual, its mechanism is not.

    Tim: <<Descent with modification can arise from multiple mechanisms, some are

    selective, others are not. I do agree that in most cases, it is a practical

    impossibility to determine what specific factors played a role at specific


    Bob: >To continue, such an extrapolation is unwarranted because of the simple

    >fact that changes observed in STE studies and bacterial resistance are

    >_reversible_. While finch's beaks become more robust in times of drought

    >when seeds have tougher shells, they revert to the more slender shape when

    >climate returns to normal and seed shells less hard to crack. Such

    >reversibility disqualifies STE from serving as the mechanism of DWM, or

    >at least raises serious questions about it. The statement would be more

    >forthright and therefore improved if it acknowledged this.>

    Tim: <<Reversibility is irrelevant and in fact, many of the changes are not

    reversible at the genetic level. Remember that there is a gaping chasm

    between genotype and phenotype. The mapping between the two domains is

    anything but linear in all but the rarest situations. Point mutations

    can confer antibiotic resistance. However, given the odds of hitting that

    exact site again to exactly reverse the point mutation, it's more likely

    that a mutation that eliminates resistance will occur in another

    portion of the genome. Thus a phenotypic reversal (short-term or otherwise)

    does not equate to a genomic "reversal". And we have a recently described

    case where a bacterium acquired streptomycin resistance in a "long-term"

    manner such that loss of the resistance, even in the absence of the

    antibiotic, was selected against (A secondary mutation occurred which

    effectively "locked in" the first one). So, we can say that ratchet-like

    evolutionary progression has been observed even over short timescales.>>

    One case doth not a theory make. Moreover this is not a ratchet-like
    evolutionary progression, as you claim. It is step one. Has anything been
    observed that builds on step one to produce step two? Unless it has you do
    not have a progression. You have merely a locked-in bacterium

    Tim: <<I suspect that true reversibility is a relatively uncommon phenomenon.

    Should we be surprised? I think not. In the mind-bogglingly huge

    morphology- or genetic-space available to organisms, it's not

    likely that one could take more than a couple steps in any direction

    and then return to exactly the same starting place.>>

    I suspect you are overstating your case. Does your "bacterium [that]
    acquired streptomycin resistance" that you mentioned earlier have
    "mind-bogglingly huge morphology- or genetic-space available to it"? I doubt
    it. If so, tell mme what it is.

    Bob: >Finally, DWM has produced the enormous diversity of life forms in the

    >tree of life. This is acknowledged briefly in the statement. Natural

    >selection is ideally suited to produce diversity.>

    Tim: <<Actually, neutral drift also contributes to the production of

    Bob: >But what is more difficult to explain is _disparity_, or the highly

    >organized nature of the organic world, with its deep discontinuities

    >between the major families of organism, roughly designated as phyla,

    >using natural selection as the operating change agent. Dobzhansky stated,

    >"fundamental characteristics of organic diversity-- [are] its

    >discontinuity and hierarchical organization." If such a giant as

    >Dobzhansky made such a statement, shouldn't the statement under

    >consideration at least acknowledge that existence of the hierarchical

    >organization and discontinuities in nature, instead of silently passing

    >by on the other side of the road?>

    Tim; <<Nobody is failing to acknowledge the hierarchical pattern of life and

    discontinuities. These are what led to the conclusion of descent with

    modification in the first place.>>

    Your first sentence in the above paragraph is simply not true. Read the
    statement that Dick Fischer presented and see if you can find hierarchical
    organization and discontinuities in it. Moreover, evolution abhors a
    discontinuity. Many evolutionary biologists are busy trying to iron them out.

    Tim: <<Discontinuity is a product of speciation (a mechanism of evolution)


    Show me.

    Tim: <<Such discontinuities tend to manifest more in the

    morphological arena than the biochemical one. Also, hierarchical

    organization is a manifestation of the rates of change and the nature

    of speciation and organismal genetics. Understanding the timing and details

    of specific steps behind evolution is real challenge, IMHO.>>

    Although these words may make sense to you, they don't to me.

    I think our brief discussion illustrates my point that the statement
    presented by Dick is incomplete, and I add, even misleading. It suggests
    that evolutionary theory is a done deal. I continue to hold that descent
    with modification needs a robustly supported mechanism (which in my view it
    doesn't have) and in addition, an unambiguous refutation of intelligent
    design, to substantiate its claim to be the all encompassing theory it wants
    to be.


    Tim Ikeda>>

    Thanks, Tim,


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