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Re: different drummer

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  • Cliff Lundberg
    ... I include pygidial ribs as segments. The awkwardness of terminology here is a sign that this area needs more attention. For me, all skeletal segments, not
    Message 1 of 10 , May 3, 2002
      Derek McLarnen wrote:
      >Sheldon's trilobites did not gradually add segments. Sheldon's trilobite
      >specimens, when separated by genera and sorted chronologically according to
      >the stratigraphical evidence of the shales in which they were found, form a
      >staggering series whose general trend only is toward an increased number of
      >pygidial ribs. Reduction in numbers of pygidial ribs over time is *almost*
      >as frequently observed as increase.

      I include pygidial ribs as segments. The awkwardness of terminology here
      is a sign that this area needs more attention. For me, all skeletal segments,
      not merely the larger axial segments, fall under the rule of decreasing
      Random mutation can gradually *reduce*, but cannot gradually *elaborate* an
      of homologous segments. Random mutation of an array of symmetrical elements
      should produce reduction and distortion, and that is in fact what is seen
      in the

      The Ordovician was a long time ago, when the world was buzzing with trilobites
      in every niche, and Sheldon's 3 my is a rather thin slice of this long era.
      In this case the unusual plethora of data allows a variety of interpretations,
      but IMO if Sheldon had proper awareness of the pattern of reduction he would
      not have set out the sequences he did. He was aiming to show gradualism,
      and he could have done that with reductive series that would have avoided
      the objection I raise. I'll get by a library soon to read the paper and comment
      further then.

      >When arranged in chronological order, Sheldon's trilobite specimens do not
      >"form a simple-to-complex series". As I have previously argued (probably
      >without success) an increase in the number of pygidial ribs in a trilobite
      >population is hardly "simple-to-complex", or even
      >complex-to-slightly-more-complex; it is only

      'Complexity' is only a scientific term if you can quantify it. I define it
      in this context as simply the number of discrete parts. The basic point
      being that you can't gradually elaborate a set of homologous parts in
      the sense of increasing their number. Pygidial ribs are of course
      serial homologs.

      >While it may be "no trick to arrange specimens from the vast array of
      >variations to form a simple-to-complex series", you have presented no
      >evidence that Sheldon did this and did not arrange his specimens in
      >chronological order, based on stratigraphical evidence of the shales in
      >which they were found. Once you present such evidence (provided it stands up
      >to the intense scrutiny it will receive), you will have indeed justified
      >your claim that "Sheldon is a modern-day Kettlewell or Haeckel" and you
      >should be afforded the same recognition that was given to those that exposed
      >Kettlewell and Haeckel.

      The fudging I complain about is not directly related to, or necessary for,
      Sheldon's point. I only seize upon it as one example of how the pattern of
      reduction is ignored by neo-Darwinians. (And many others). Even if his
      stratigraphy is correct, that is not proof of such an evolutionary pattern;
      other interpretations are possible. Consider all the controversy in the much
      more recent evolution of the modern horse and its loss of lateral digits. You
      just can't pin these things down very well. Consider how rare are these
      supposed sequences showing gradual elaboration, and how odd therefore
      it is that Sheldon should find *8* such sequences in arranging his mass of

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