Re: Convergence

From: Bill Spight (
Date: Thu Aug 09 2001 - 06:36:05 BST

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    From: Bill Spight <>
    Subject: Re: Convergence
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    Dear Ted,

    > It's well known that atavistic traits commonly pop up among developing
    > organisms. A feral pig is liable to develop tusks. Horses occasionally
    > grow extra toes. Humans are sometimes born with a small tail. Such things
    > can be expected if we do indeed resonate with past forms. But they can also
    > be explained according to the genetic model. What can't be explained
    > genetically is parallel evolution, or "convergence."

    Convergent evolution is in fact a major support of the theory of

    > Among plants and
    > animals, we continually find new examples of organisms widely separated in
    > their phylogenetic derivation which nonetheless develop remarkably similar
    > forms. In New Zealand we find many kinds of leaves common to Eurasia which
    > serve to fend off herbivores that don't exist in New Zealand. There seems
    > to be no reason why marsupials and mammals would develop such incredibly
    > similar forms.

    Don't be silly.

    > Why should butterflies or fish of different species in
    > different locations develop almost identical color patterns on their wings
    > or scales? In some cases animals mimic others that are poisonous to
    > predators and are thus avoided by predators along with the poisonous
    > varieties. But this explanation fails to apply in the vast majority of
    > cases.
    > Dawkins discusses this dilemma in The Blind Watchmaker: "It is vanishingly
    > improbable that the same evolutionary pathway should ever be followed twice.
    > And it would seem similarly improbable, for the same statistical reasons,
    > that two lines of evolution should converge on the same endpoint from
    > different starting points. It is all the more striking... that numerous
    > examples can be found in real nature, in which independent lines of
    > eovlution appear to have converged, from very different starting points, on
    > what looks very like the same end-point."

    From which Dawkins draws the inference of morphic resonance. Right! ;-)

    > According to Sheldrake's model, organic systems resonate with similar
    > systems. We resonate with ourselves individually, with our species, and
    > with any other species which is similar enough to our own. If flying
    > squirrels, jerboas, and moles are all emerging in both Australia and
    > Eurasia, they will be drawn into similar evolutionary pathways due to their
    > resonance with each other. Outside of this model, there's no explanation
    > for convergent evolution.


    First, there is the simple explanation of similarity of environments.
    Aquatic mammals and fish provide a basic example.

    Second, there are physical and chemical constraints that impose
    structure. Example: similarities in structure of sunflowers, pine cones,
    snail and nautilus shells.

    Third, there is coincidence.

    You need to find characteristics that do not contribute to the fitness
    of the organism, and are not similar for physical or chemical reasons
    (such as minimizing the use of resources), and then compare their
    occurrence with a model that indicates how often such convergences occur
    at random, and show that they occur too often. Otherwise, don't waste
    your time.

    The advent of computers has enabled us to see, by simulation, how
    frequent random coincidences are. It is human nature to seek
    explanations, and statistical argument alone leaves nagging doubts. Thus
    people can easily believe that Design, whether by supernatural or by as
    yet undiscovered natural means, is necessary to explain coincidences. It
    appears that morphic resonance is one such principle of Design. It is
    invoked without much consideration at all of other, scientific
    explanation. And it assumes that there is no coincidence.

    Even if there are patterns and structures in convergent evolution that
    are not explained by general physical or chemical constraints nor by
    fitness in similar environments, the phenomena that are to be explained
    rely on human judgements of similarity. We make such judgements at the
    drop of a hat. They should occur quite frequently for randomly arising
    patterns. Without a model that predicts how often they occur for random
    coincidences, there is no way to tell whether they occur too often for
    that explanation.



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