Re: "Common ancestor" in cladistics

["Jaime A. Headden" <qilongia@yahoo.com>]

John Bois (jbois@umd5.umd.edu) wrote:

<It's an actual thing.  You and your sister share a common ancestor--your
mother.  The idea is that your sister becomes reproductively isolated and
her progeny lead to new species in time.  As others have said, it would
not be possible to ID this in the fossil record. Students buy the idea of
evolution by n.s., but tell them that their own existence depended upon
the survival of a certain fish in the Devonian and they will balk.>

  You have TWO common ancestors with your sibling, as BOTH of your parents
are progenitors. The concept of a "common ancestor" in phylogenetics,
however, is more abstract than my line back to the beginning. A species,
by divergence, separates from either a single species, or there is a
schism and there are two species that diverged from ancestral stock. At
the base of that genetic divergence, the descendant organisms would not be
distinct from their ancestors except by whatever finite element you've
labeled as instructive in this division. In this matter, such a concept is
both physically demonstrative, as well as abstract, as it requires
creating an unknown element in phylogeny to  point to a moment we cannot
either prove, or demonstrate a likelihood in method of division.

  Cheers,


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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