[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Some thoughts on cladistics



> <The point is that "evolutionary systematics" can,
> additionally, declare species or higher groups as transitional between e.
g.
> reptiles and mammals, reptiles and birds or whatever. Here the cladistic
> criticism is that this kind of transition is a complete artefact produced
by
> the recognition of paraphyletic groups, ...>
>
> Birds are necessarily a paraphyletic group?

Maybe I should have been clearer. Of course reptiles (in the sense above,
but I hate its crown-group definition) are (necessarily) paraphyletic (in
the example) while birds and mammals are not (while both amphibians and
reptiles in their traditional senses are, and remember how long it was
unclear what *Seymouria* is). The cladistic position is that the cladistic
definitions of Mammalia and Aves are arbitrary, but at least both Mammalia
and Aves can be defined as holophyletic groups, so we can define where both
begin in theory and then assign everything we find unambiguously to one side
of this arbitrary border, as long as everyone uses the same definitions.
Because paraphyletic groups are not allowed the discussions whether
something is still a reptile end. "Evolutionary systematics", however, does
not define taxa at all and allows paraphyletic groups, therefore we can
never unambiguously decide whether something should be called a reptile or a
mammal respectively bird and will continue to quarrel about such vanities to
eternity if we stick to that system.

> A system of classification starting from observation of easily
> distinguished, numerous, and widespread modern groups is no more an
> abstraction than any other approach.

Easily distinguished? I've just heard a lecture by a professor who has
published lots on the systematics of diverse marine protostomians and has
described many new species that it is sometimes very difficult to tell
polychaetes and nematodes apart in practice. In theory that should be really
easy, after all, the former are in Lophotrochozoa like molluscs, and the
latter in Ecdysozoa like arthropods! Since Cuvier took Linné's Vermes apart
AFAIK nobody thought they were closely related or should otherwise be
classified together!
Numerous and widespread? *Sphenodon*?

> <...at least for clades, phylogenetic systematics use the last common
> ancestor instead of an archetype. The
> ancestor at least existed :-)>
>
> So, modern birds are an archetype, a non-existent (to our senses) model of
> which living exemplars are only an imperfect image.  However, an
> unidentifiable ancestor whose characters are being educed by a logical
> argument is far more real.

Exactly. Just that the ancestor is not unidentifiable, it is just very
improbable to discover it. The ancestor existed because evolution happens,
and that* is an observed fact. The existence of archetype is untestable, and
strongly contraindicated by evolution.

*OK, microevolution is observed: e. g.

Jonathan Weiner: The Beak of the Finch. Evolution in Real Time, Alfred A.
Knopf 1994

Actually, when species are used as OTUs in a matrix, then the characters of
ancestors are not inferred a priori, but are the outcome of the analysis.
Otherwise the outcomes of such analyses are (hopefully) used to code the
OTUs. I forgot to write that.

> This argument sounds a bit perverse, as I'm understanding it.

???

> He knew something about weight.  So he attempted to utilize that
> understanding to determine what would happen if two similarly shaped metal
> objects were dropped from a tower.  His logic was good, given his
knowledge,
> but his conclusion was outright wrong.
> What was his error?  He used logic in place of direct observation.

Indeed. Cladograms are testable, and they are often tested, just read any
posts by HP Mickey Mortimer where he takes other people's matrices apart
respectively updates his own ones... cladograms are scientific hypotheses.
Cladistics is a science. Aristotelic thinking is not, at least not in the
full sense of the word. Neither is "evolutionary systematics". I'm not sure
about phenetics but nobody uses it anymore anyway...

> So, let's propose a rule:  the further a hypothesis gets from direct
> observation, and the fewer direct observations it's based on, the more
> doubtful it should be considered.

You know, I agree with that :-)

> The idea that a classification system should start with easily observed
> modern groups seems comfortable to me in this context.
>
> Simple, isn't it.  ;-)

Are you calling for _phenetics_? ~:-|
Why should classification start with modern groups? What's so special about
being alive? (You can use the same arguments against crown groups.)

Phylogenetic taxonomy is based on _more_ observation than all other
classification schemes proposed so far, namely the observation of evolution,
of continuity.

Phylogenetic taxonomy leaves the tree intact, it only binds labels to the
places where 2 branches join or where 1 begins. Evolutionary systematics
cuts some branches away and hangs them into the air next to other branches
that are supposed to be of the same rank, and people don't even know where
exactly they cut and where exactly they put their labels!

Who was it who said "100 years without Darwin are enough" in 1959?

*************************************
Congratulations to HP Tom Lipka,
and to Larry D. Martin for telling what sort of evidence could convince him
of a dino-bird link... :-)