Farewell to Species - reticulation
TDibenedetto at DCCMC.ORG
Fri Feb 4 11:20:39 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]
If a name was applied to specimens in lineages 2 & 3
before the existence of lineage 1 was known, it does not all of a sudden
become the name for a clade (1+2+3).
Huh? Why not? 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.
>But the name of the original taxon was meant to apply to all descendants of
>the common ancestor of the original taxon.
> The original taxon is a higher taxon.
No! It is still a single lineage between two nodes: but now, the
terminating node is not terminal, but internal.
Huh? This seems to imply that descendants can somehow no longer belong to
their history! I think it is a fundamental point that, from an evolutionary
perpsective, taxa derive their identity from their history. Humans are not
animals because we have or dont have any particular characters; those are
only guides. We are animals because we are descendants of the common
ancestor of Animalia. Nothing that can ever happen in the further evolution
of our lineage will ever cause any of our descendants to not be an animal.
It is a matter of defintion. I think it is simply a matter of taking
evolution seriously. That is why it is so frustrating sometimes to see e.g.
so-called "evolutionary systematists" try to deny that birds are reptiles.
For the same reason that humans are animals, vertebrates, mammals, primates
etc, and birds are also animals, and vertebrates and reptiles and
archosaurs, so too taxon 1 and taxon 2 in our example are part of the
lineage emanating from taxon 3. If taxon 3 were named at any point, then
this name applies to taxon 1 and 2 as well.
If taxon 3 were the primoridal mammal, and taxon 1 was the primordial
monotreme and taxon 2 the primordial therian, then is it not the case that
all three are part of the higher taxon Mammalia?
In your view, Archaeopteryx
( or maybe Protoavis) is not a genus, but an order (=Aves). Try getting
that past a nomenclaturist!
This is of course, why ranks are being abandonded. If Archaeopteryx is the
sister group to Aves, well then,,, it is the sister group to Aves, what can
we say? Thats reality. That is how it happened. Some branches sputter out,
others go on to diversify greatly. Knowing that means that we know something
about the evolutionary process. I am not sure what the system of ranks
applied to taxa tells us about evolution.
tdib at dccmc.org
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