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Re: summer science quiz #2

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  • Re: summer science quiz #2

    Re radial "vs." bilateral:

    > One thing that distinguishes bi-laterally symmetric
    > animals from asymmetric ones is that the former move
    > faster (relative to the viscosity of their media).
    > Thomas A. Stoffregen, Associate Professor
    > Department of Psychology
    > University of Cincinnati

    Not a tenable statement, really, and that depends on
    whether you are speaking of dynamic or kinematic viscosity.
    Even though they seem to be bilaterally symmetrical
    molluscs, squid (while jetting) can be considered largely
    radially symmetrical about their long axis --- a streamlined
    spindle water jet reaction rocket --- and they are among
    the fastest creatures, some are even capable of leaping
    clear of the water.

    A point of terminology: we should use the term "radially
    symmetrical" instead of "asymmetrical" here...a paramecium
    or coral reef is more properly asymmetrical, and there are
    other forms of symmetry...

    As for either/or arguments in general: it should be clear
    that the existence of such an argument often precedes the
    widespread realization that the "answer" is a mixture of
    the two (witness genes/environment) or that insufficient
    information exists about a situation, perhaps indicating
    that it will prove to be more complex than a simply
    "bilateral" breakdown. This would apply to bilateral /
    radial symmetries, and dumb luck / function. As for the
    latter pair, luck happens (dumb or smart) and function
    (physics) matters.

    > Why does bilateral symmetry predominate in the animal
    > kingdom would perhaps be a better question.

    Does it? Define your use of "predominate," or better,
    what do you mean when you say "animal kingdom" ?

    Chuck Pell

    Rule of Functure [sic]:
    "Function without structure is a ghost, and
    structure without function is a corpse."
    --- Wainwright and Vogel, 1968

    Thomas Stoffregen wrote:

    > Some comments on the origins and utility of bi-lateral symmetry
    > (i.e., even numbers of limbs) in animals.
    > >My solution: Bilateral symmetry in the animal body plan produces the even
    > >number of limbs, but those animals that develop with radial symmetry (like
    > >the starfish) can have odd numbers of limbs. Why does bilateral symmetry
    > >predominate in the animal kingdom would perhaps be a better question. My
    > >answer to that question is: pure dumb luck.
    > Dumb luck is possible, but before we accept this non-functional
    > explanation, we should consider whether bi-lateral symmetry might
    > have a functional role that lead to its being selected for (rather
    > than merely tolerated) in the evolutionary history of animals.
    > Bi-lateral symmetry is locomotor appendages is not universal, cf.
    > star fish, and snails (the latter have only one foot, an odd number).

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