Phylocode, Cladistics and Eclecticism ...

[Ken Kinman]

     We've been down this road before, so I'll just summarize.  I agree that
after a complete speciation event has occurred, there are two relatively
independent lineages then exist (although some limited hybridization is
often still possible).
     However, one lineage is the original mother species and the one with
the new character(s), i.e. apomorphy(ies), is the daughter species.  If both
lineages continue to speciate, separate groups (higher taxa) are created,
which can be arbitrarily grouped into species groups, subgenera, genera, and
so forth as they continue to diverge and speciate.
      The likelihood of a true sister group split (mother and daughter
simultaneously evolving separate apomorphies) is very low, and the
probability that two such true sisters would both evolve into higher taxa
gets even more remote.  Mother-daughter relationships are the norm, and
sister-sister groups are the rare exception.  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).  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.  That kind of reasoning is dangerously
circular, with false premises leading to false conclusions.  Or as Larry
Martin might say "garbage in, garbage out" (which can be just as true for
human brains as it is for computers).
                ----- Ken Kinman
******************************************
>From: Thomas DiBenedetto <tdib at oceanconservancy.org>
>To: 'Ken Kinman' <kinman at HOTMAIL.COM>, TAXACOM at USOBI.ORG
>Subject: RE: Phylocode, Cladistics and Eclecticism ...
>Date: Thu, 14 Mar 2002 12:26:14 -0500
>
>-----Original Message-----
>From: Ken Kinman
>      Where American cladism (in particular) got off track was that they
>took
>Hennig's sister group "convention" and turned it into a "definition".
>...we now have a whole generation of biologists having been taught
>that sister groups are REAL, rather than a methodological convention.  From
>that incorrect premise, they can argue that paraphyletic taxa are unreal,
>unscientific, and are mistakes that must be corrected (destroyed).
>********
>I do not think that anyone questions the fact that after a speciation
>event,
>there are (at least) two isolated lineage branches. These branches share
>with each other, and with no other taxon, a most recent common ancestor
>(the
>pre-speciation lineage). This is the sister-group relationship. It is
>beyond
>my comprehension how Kinman, or anyone else, can pretend that this
>relationship is not real.
>**********
>Kinman:
>      If you try to argue from the perspective that paraphyletic species
>are
>real, they will just argue either (1) that species are arbitrary and thus
>not real; or (2) species and higher taxa are just "apples and oranges" and
>can't be compared.
>******
>Niether of these arguments are the ones that are consistently raised
>against
>your postion. Wouldn't it be wonderful if we could all choose the arguments
>raised against us?!
>***
>Kinman:
>      To me, clades are real (although their boundaries are unavoidably
>fuzzy
>and arbitrary).  Sister clades are NOT real, but they are a useful
>convention within the context of cladistic analysis.  When this distinction
>(clades vs. sister clades) is brought to the attention of today's students
>who were taught by a strict cladist, many of them feel they have been
>misled.
>*********
>Well, I am as eager as the next person to be shown how I have been misled.
>Could you please explain to us this distinction that you see - that clades
>are real, but the notion that a real clade might share a "most recent
>common
>ancestor" with another real clade is not real?
>
>Tom DiBenedetto



_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.