Phylocode, Cladistics and Eclecticism ...
tdib at OCEANCONSERVANCY.ORG
Thu Mar 14 15:40:51 CST 2002
From: Ken Kinman
I agree that after a complete speciation event has occurred, there are two
independent lineages then exist
However, one lineage is the original mother species and the one with
the new character(s), i.e. apomorphy(ies), is the daughter species.
This discussion is about justifying the distinctions you make, not merely
asserting them once again.
The likelihood of a true sister group split (mother and daughter
simultaneously evolving separate apomorphies) is very low,
This might be the Kinman defintion of sister-group, but it is not the
cladistic defintion. And we are discussing the cladistic defintion here.
What makes you think that you can be considered a serious commentator on
these subjects if you simply ignore the meaning of words as they are used in
the field, and make up your own definitions - and then go on to assert that
this defintion is wanting?
Sister-groups are defined by RELATIONSHIPS, not by the simultaneous
evolution of apomorphies.
Mother-daughter relationships are the norm, and sister-sister groups are
the rare exception.
In all cases, a previously coherent terminal lineage branch has evolved into
two isolated lineage branches. "Mother-daughter" is an inappropriate
metaphor for this situation. I imagine that you find it compelling because
one of the new terminal lineage branches seems to be the same, in terms of
characters, as the pre-speciation lineage. But we are classifying by
relationship, not by characters. The appropriate metaphor is
Mother-daugher+daughter. Both new terminal branches have the exact same
relationship to the mother. And both have a unique sister relationship to
each other. Whatever the character distributions, these are the
relationships, and in cladistics, we classify by relationship.
We only pretend (by Hennigian convention) that mother-daughters are really
sisters because it greatly
simplifies cladistic analysis, and it works well because our data sets are
so incomplete (especially for fossil forms).
Who is this "we" that pretends? You mean "you".
In my opinion, sister groups
should be taught as a convention, not as a reality-----and it is especially
misleading to use such a convention to then argue against the reality or
"naturalness" of paraphyletic taxa.
In my opinion, you should not be pretending to teach cladistics to anyone.
That would be a case of really misleading students!
Paraphyletic taxa represent the recognition of arbitrarily truncated lineage
systems. They have no place in a phylogenetic classification - and this is,
and has been a consistent position of all cladists since Hennig first
articulated the reasons why such groupings are artificial in any system that
seeks to represent the true history of evolutionary lineages.
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