[Taxacom] Rational holophyly and deological extinction
jcclark-lists at earthlink.net
Mon Mar 16 22:40:10 CDT 2009
On 2009-03-16 11:50, Richard Zander wrote:
> I think there is a rational (sort of) justification for using holophyly
> in classification. It goes this way: ...
First, ancestors. There are organisms alive today that are ancestors of
other living organisms (I am one of those, although I take umbrage at
being called paraphyletic), but the cases where the ancestor is
generally considered to be of a separate species from the descendant are
Second, it is well-established that some species are ancestors of other
species. If one assumes that species are real, this has some
evolutionary meaning (if species are not real, it's religion), but it is
not possible to interpret all of evolutionary history as a nested set of
Third, it is generally impossible to say with any certainty that any
given fossil is the ancestor of an organism alive today (although it is
quite credible to say that it is a relative).
Fourth, higher taxa can be ancestral to other higher taxa only if they
are paraphyletic. Ancestor-descendant relationships are thus an artifact
of the way a taxonomist chooses to draw up the taxa. One could argue
that in the case of two lineages, one derived from an ancestral species
and another from one of its peripatric descendants, the former is
irreducibly paraphyletic, but I see that as equivalent to saying that I
am irreducibly paraphyletic: not of much use except as a straw man.
We all know that there are ancestors in evolution. But history has shown
that they are devilishly hard to pinpoint, much less to develop testable
For a cladist to say that ancestors are unimportant is perhaps arrogant,
but for a cladist to say that our time is better spent looking at
sister-group relationships is a nod to reality.
Curtis Clark http://www.csupomona.edu/~jcclark/
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University Web Coordinator, Cal Poly Pomona
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