Farewell to Species - reticulation

Thomas DiBenedetto TDibenedetto at DCCMC.ORG
Sun Feb 6 11:22:53 CST 2000

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]
Indeed, 3 becomes the ancestral lineage of the
clade (1+2+3), but that does not mean that the name of 3 must remain
attached to the clade. As you write yourself:
>The name adheres to a taxon. A taxon
>represents an ancestor and all of its descendants. All of lineage 1
>is a descendant of the ancestor of 2 & 3.
When did a terminal branch(no descendants!) stop being a
Huh? I dont understand your question at all. There are three taxa. Taxon 3
originated at the base of our example. It, being a good monophyletic taxon,
includes that ancestor and all of its descendants. That means all the things
that we also call 2 and 1. 2 and 1 are also taxa. Terminal taxa. Call them
species. That is a nice rank we ususally give to termianl taxa. 3 however is
a higher taxon. I did not say anything to imply that terminal branches are
not taxa!
Lineages 2 & 3 were seen as a single terminal lineage
(species). I don't see a reason for retaining the name of a
particular lineage (such as 3) when that lineage branches up into
several new ones.
But how can we not do that? The taxon is the ancestor and all its
descendants. The name applies to that group of critters. If the taxon
diverges, if the ancestor now has more descendants than it did yesterday,
how can we strip the taxon of its name? It seem obvious to me that if the
ancestor at the base of our example (at the base of the Y) and its
descendants (i.e that taxon), has been given a name, then that name must
remain the name of that ancestor and all its descendants form henceforth.
 And what about all those fossil species? Do you really think
that they are either dead ends in evolution, or actually not chunks
of the genealogical network between permanent splits (those are what
I would call a branch, although actually only permanent splits
accompanied by fixation of an evolutionary novelty in at least one of
the descendant branches (i.e. apomorphies)are the ones that matter in
demarkating sets of branches that together can be called species) but
rather that all their descendants should be included?
Sorry, but I dont understand the question. It actually makes my head hurt.
I'll venture a guess as to what you might mean. Maybe it would help if I
said that, being a historical biologist, I have no problem using the past
tense. 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. Since
those critters are no longer part of a terminal branch, they no longer are
part of a species-level taxon, but they were when they were alive.
but why can't taxon 3 bear its own
(specific) name, rather than the very vague 'taxon 3' you would like
to use? Of course, the clade (1+2+3) can also be named, not
necessarily with a particular rank.
To me, taxon three does bear its own name (higher than specific). Look,
there are a bunch of organisms running around boinking. Some are off in a
little isolate - we call them species 1. Others are occupying the
traditional habitat of their ancestors. We call them species 2. Both sets
are part of the higher taxon 3. If we start digging up the bones of the
previous generations, we come to critters who would not have been considred
to be in either species 1 or 2, because they lived before the split. They
(along with their living descendants) are part of taxon 3. When they were
alive, 3 was ranked as a species, because it was terminal. They were in
species taxon 3. Now their descendants are in higher taxon 3 and species
taxon 1 or 2.

Tom DiBenedetto
tdib at dccmc.org

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