Farewell to Species - reticulation

[Thomas Schlemmermeyer]

According to my knowledge, traditional nomenclature in fact assumes that taxon
is any group of organisms, from species up to more inclusive ones.

That this is so and not different, can be explained by the history of taxonomy.
Phylogenetic concepts are relatively new and did not accompany all taxonomic
efforts. Nor should the whole of taxonomy be seen phylogenetically.

Taxonomy has two functions: The storage and retrieval of informations, and,
from a more ultimate point of view, accumulation of systematic, phylogenetic
knowledge.

The first goal mentioned (storage and retrieval of information) can be obtained
already without available phylogeny. Or should one start to name species only
when the complete phylogeny is known? Certainly, this would be nonsense.

Let us not forget that the search for ancestors (although evolution goes from
ancestors to descendants, the search goes from descendants to ancestors) is a
highly integrative and multidisciplinary one. To decipher the enigmatic
direction of time, often additional evidence from embryology, paleontology, and
geology is consulted.

Thus, it is only logical that taxonomy itself cannot and should not be based on
ancestor-descendant relationships already in the first take, rather
ancestor-descendants relationships may be products that come out of good
taxonomies.

   my 2 centavos,   cheers, have a funny week,    Thomas









On (         Sun, 13 Feb 2000 18:13:52 -0500
),         Thomas DiBenedetto <TDibenedetto at DCCMC.ORG> wrote:


>Hubert Turner wrote:
>[in reference to an example where '3' refers to the base of a Y-shaped
>lineage, and'1', and '2' refer to the arms -- and in response to a rather
>obvious point I made about how a species level taxon evolves into a higher
>taxon]
>What rubbish!!!!! 3 is a branch on the network. When it was terminal,
>it was a species (by your own convention!) When it split into
>branches 1 and 2, it became an internal branch. According to the
>phylog. species conc., branch 3 stopped being a species then.
>--------------------------
>No. You just dont seem to get it. 3 does not become an internal branch. It
>becomes an internal branch with 2 terminal branches subtended from the
>internal branch. In other words, its descendants are PART OF IT. Just like
>ALL of the descendants of the original mammal species are part of Mammalia.
>Just like Homo and Pan etc. are PART OF Primates (as you seem to
>understand!). It is only possible to see taxon 3 as an internal branch only,
>by arbitrarily cutting off the descendants. It is probably the most basic
>point of phylogenetic systematics, that taxa are meant to refer to real
>monophyletic groups. When a taxon, ranked as a species (because it is
>terminal) diverges, then it is not equal to the internal branch, it is equal
>to, as always, the original ancestor and all of its descendants. It has
>evolved into a higher ranking taxon.
>----------------------
>tdib previously:
>>If a fossil species were ever to be identified as actually being
>>ancestral to later species, then I would have no problem saying that it WAS
>>a species at some time. Now it may just be part of a higher taxon.
>----------------------
>H.T.
>No, that particular chunk of the genealogical network still is a
>species! In addition it is part of a higher taxon, but so is a
>terminal species extant right now (Homo sapiens is part of the taxon
>Primates is part of the taxon Mammalia is part of the taxon
>Chordata). These are not incompatible designations.
>-----------------------
>By what logic or definition must it still be considered a species? What is
>so problematical about using the past tense to describe something that no
>longer exists? Species is a rank. As a rank, it has conventionally been
>applied to taxa deemed to be terminal. When a taxon is terminal and
>unbranched, it is ranked as a species. When it aint, it aint. When it is
>branched it is a higher taxon. When it is internal, and defined in isolation
>from its descendants, it is an artificial, paraphyletic assemblage.
>-------------
>tdib previously:
>The taxon is the ancestor and all its descendants.
>---------------
>HT:
>As I said, rubbish!!! In traditional (i.e. nomenclatural) usage,
>taxon is any grouping of species, from the least inclusive (1
>species)  to the most (phyla). Don't try to redefine the meaning of
>"taxon".
>-----------------
>Its not me doing any redefining. The definition I presented has been
>standard for quite some time.
>
>Tom DiBenedetto
>tdib at dccmc.org
>