Farewell to Species - reticulation

Thomas DiBenedetto TDibenedetto at DCCMC.ORG
Tue Feb 15 08:11:27 CST 2000

Hubert Turner wrote:
All I want is to be able to refer to a particular internal branch by a
particular name. And that name is sometimes already available, namely a
species name.
Could you give me an example of an internal branch that bears a species
name? I am sorry, but Archaeopteryx lithographica doesnt cut it, because it
is not an internal branch, at least not in any rigorous analysis that I have
seen. One might speculate that it was a direct ancestor of all other birds,
but there is no evidence whatsoever to back up that hypothesis. Nor is there
any evidence for any other species to be designated as an ancestor. As I
imagine that you know, there has been a long and extended discussion of
these issues in the systematic and paleontological literature stretching
back to the seventies.
It has been pointed out many times that we simply do not have the empirical
tools by which to support a hypothesis of direct ancestry.
When that branch was terminal, it was referred
to as a species, so why not continue to do so? Of course it is also part of
a larger clade which also includes all of its descendants, but it is also
part of a still larger clade that includes all vertebrates, which are part
of an even larger clade that includes all metazoans, etc. etc.
But we can discuss the principle if you wish, even if we cant ever really
identify ancestors. Let us refer back to the example that was tossed around
a few months ago. The Homo sapiens lineage diverges because a colony on Mars
becomes genetically isolated. I contend that the name "sapiens", as a name
for a taxon, must always refer to that taxon, and that taxon now encompasses
both the descendants who remain on earth and those who live on mars.
Therefore they are all "sapiens"; therefore sapiens is no longer the name of
a terminal unbranched taxon, but is the name of a branched taxon, a higher
taxon. And so I would propose calling the descendants on earth "Sapiens
terrestrius" (sorry I still havent learned latin!) and the ones on Mars
"Sapiens marsi". And if you wanted to refer to the organisms, like you and
I, who lived on earth before the split, you could continue to refer to them
as Homo sapiens. It should be obvious from the context that sapiens was, at
one time, a species level taxon, and so if you wish to refer to organisms
that lived at that time, you could call them by a name that has "sapiens" in
the species postion of the name.
You could infer from this that if it were ever the case that A.
lithographica were somehow proven to be the direct ancestor of all other
birds, that I would propose "lithographica" as a replacement for "Aves" (or
 What is the objection against referring to that particular branch (starting
at a split and ending at the very next split) by a name at species level?
As I mentioned above, I do not know of any way in which one can actually
place specimens on internal branches. But if it were to be possible, then
the branch could bear a name that has, in the species position of the
binomial, the name of the taxon of which it was a founder. For example, if
you discovered and were able to identify specimens of the primordial mammal
species, you could call it Amniotus mammalia, or something like that.
  I feel you confuse the term 'taxon' with the term 'clade'.
Guilty as charged. Except that, being a concious decision, I dont think it
should be called confusion. I support the notion that taxa should be
monophyletic, which equates them with clades. That is the whole point of
phylogenetic systematics.

Tom DiBenedetto
tdib at dccmc.org

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