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Re: Phylogeny and Distance



Ken Kinman (kinman@hotmail.com) wrote:

<The most primitive neognaths and the most primitive paleognaths
are admittedly virtually equally related to any other group,
including Archaeopteryx, Velociraptor, or even Homo sapiens.

  But from that point, the differences in evolutionary rates
(generally greater amongst neognaths) results in a growing
differential of relatedness as time progresses.

  Compared to the common ancestor of paleognaths and neognaths,
a crow, hummingbird, or other present-day neognath will have
fewer genetic similarities with such a form than will a tinamou
or even a ratite.>

  What is the evolutionary rate of a paleognath relative to ...
say ... a hoatzin, or most cuculiform birds [which vary _very_
little from one another]? Even most passerines are quite similar
to one another, varying mainly in plumage count, color, and
intrinsically in the syrinx.

  Now, as for what makes neognaths different from paleognaths,
the latter are more plesiomorphic of the carinate condition than
are neognaths ... the latter have modified more greatly along
the way, but still waterfowl and gallinaceous birds are outside
that level, and you can step up this in some phylogenies,
leading to some "most derived from the plesiomorphic condition
of all" group. This says nothing for the paleognaths, who still
aren't closer to velociraptors than *Passeres* is, but says
something for *Passeres*, who has all these wonderful novel
adaptations that *Struthio* and *Chauna* don't.

<Even Darwin recognized this and based his taxonomic philosophy
upon it.>

  Darwin did not have a taxonomic phylosophy, he had a phyletic
one; one of relation, not names. Not assumptions. This _is_
nitpicking on my part.

<****What is not being recognized here is that "relationship" is
not the same thing as "relatedness", and therefore neither are
the degrees of relationship and relatedness. Siblings may share
a common relationship, but the number of genes they share in
common can vary from 100% (in identitical twins) to extremely
low percentages in rare instances (the disparity in relatedness
can be enormous even among the closest of relatives).>

  I thought we'd gotten out of the discussion regarding "halfway
houses" when the paradigm of descent through modification is
rendered as mutual acquisition (about a month ago this
discussion was?)? Two animals that stem from a common ancestor
will have features in common with that ancestor and _it's_
ancestor [plesiomorphy] but to state that these features now
mean something other than it wasn't altered through descent
would be like saying eight limbs in spiders and octopus [pl.] is
a common ancestral thread shared exclusively, rather than
modified by further organisms to six or less, or more. A
plesiomorphy is useless in a phylogenetic context unless it's to
use it as a "evolutionary rate count" in organisms.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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