Farewell to species (but not yet!)

[Jong, R. de]

I have always wondered why some people make such a fuss of distinguishing
between paraphyly and polyphyly. If a paraphyletic group is defined as a
group not including all descendants of a common ancestor, so is a
polyphyletic group. If we agree that an orchid and an elephant have a common
ancestor (be it far back in history) than the group orchid+elephant is a
group that does not include all the descendants of their common ancestor.
Nobody will be prepared to distinguish such a group, but yet it provides
some information about kinship and maybe even about the time elapsed since
their lineages separated (somewhere hidden in their DNA code). Apparently it
depends on the number of descendents excluded whether we call a group
paraphyletic or polyphyletic, an arbitrary decision. Is there a threshold
number of excluded descendents beyond which a small sin becomes a deadly
sin?
Sometimes a paraphyletic group is defined as a group defined by
plesiomorphies, and a polyphyletic group as a group defined by
convergencies. In that case the distinction is made on the basis of common
possession of homologous (paraphyly) and non-homologous (polyphyly)
characters. It may seem a clear-cut distinction, but then the use of the
terms paraphyly and polyphyly is confusing, because they refer to ancestors
and tree topology, while plesiomorphies and convergencies refer to
characters.

IMO the main problem with the terms monophyly, paraphyly and polyphyly is
the aversion of many people to change. In Europe many national currencies
will cease to exist in two years time. There is much aversion to it, but in
a year or so everybody will be accustomed to it, if only because denying it
will be very costly. In systematics such a financial pressure does not
exist, but if we take our discipline seriously, we should stop talking about
the relative merits of paraphyly and polyphyly, and stick to monophyly. And
if a journalist uses the term reptiles in a newspaper, so be it, as long as
it is not a systematic paper.

Rienk de Jong

> -----Oorspronkelijk bericht-----
> Van:  Thomas Lammers [SMTP:lammers at VAXA.CIS.UWOSH.EDU]
> Verzonden:    zondag 6 februari 2000 19:43
> Aan:  TAXACOM at USOBI.ORG
> Onderwerp:    Re: Farewell to species (but not yet!)
>
> At 07:53 PM 2/4/00 -0800, Curtis Clark wrote:
>
> >Paraphyletic groups are fine, until someone assume they provide
> >information about kinship.
>
> They do.  All their members are descended from a common ancestor.   That's
> kinship.  You've just left some fellow descendent(s) out of the group.
> So
> you haven't got ALL the facts on kinship expressed.  Not good.  But it
> seems a small sin compared to polyphyly, which indeed provides no
> information about kinship.
>
>
> Thomas G. Lammers, Ph.D.
>
> Assistant Professor and Curator of the Herbarium (OSH)
> Department of Biology and Microbiology
> University of Wisconsin Oshkosh
> Oshkosh, Wisconsin 54901-8640 USA
>
> e-mail:                     lammers at uwosh.edu
> phone (office):         920-424-7085
> phone (herbarium):  920-424-1002
> fax:                         920-424-1101
>
> Plant systematics; classification, nomenclature, evolution, and
> biogeography of the Campanulaceae s. lat.
> -----------------------------------------------------------
> "Today's mighty oak is yesterday's nut that stood his ground."
>                                                  -- Anonymous