Who is the postivist?
bryo at COMMTECH.NET
Thu Dec 11 09:50:05 CST 1997
Tom DiBenedetto wrote:
> Richard Zander wrote:
> >Tom DiBenedetto wrote:
> >> Parsimony selects the tree which represents the
> >> set of least falsified grouping hypotheses.
> >That's hypothetico-deductivism. "Wishful thinking subject to correction"
> >according to Quine.
> Hey, I like that! Did he mean to be disparaging? :)
No. He likes it. I just think he doesn't know how it is used in
reconstructing the past.
> >I rather assume like produces like unless
> >macroevolution is demonstrated, and I see parsimony analysis eliminating
> >relationships between grossly dissimilar terminal taxa, and using state
> >changes as a distance measure (patristic).
> How will you demonstrate macroevolution or "like produces like" (do
> you mean saltation vs. gradualism?) outside of a phylogenetic
Yes. You can't. You can't in a phylogenetic context.
> Birds and crocs are sister taxa - is this the type of grossly
> disimilar terminal relationships you would like your method to
You need three taxa, two similar, one disparate and lots of
> >That's okay. In most cases
> >you don't even need a computer to come up with a general classification
> >that assumes your version of evolutionary direction (selection of
> >outgroup). But "reconstruction"?
> What does this mean? You dont need a computer to come up with a
> classification? You must have a big brain, or a very small set of
> taxa and characters!
My point is that a classification is easy...it can be phylogenetic, such
as for ((man chimp) dog) or artificial, such as maximum synapomorphy.
> >The general hypothesis is that all reasonable trees are Darwinian
> >explanations of evolution. Your general hypothesis is convenient for
> >selecting one tree from dozens or hundreds. Looks good but the general
> >hypothesis is wrong to begin with.
> Well thats cute. Make up a hypothesis for me, then call it wrong. Can
> I make up my own?
> >> Anti-realists (by your definition) seem to deny the reality of taxa.
> >> Once again, if that is your position, then why bother with
> >> systematics?
> >Pragmatically, a classification based on overall similarity of taxa
> >groups organisms such that we can best predict things about them.
> And what kind of predictions would you like to make? Those of us who
> are interested in evolutionary questions seem to agree that a
> phylogenetic classification (based on apomorphies, not overall
> similarity) is most predictive.
I'm not sure: phylogenetically similar taxa should have similar genetics
and thus should share qualities: medicines, ecologies, particular genes,
whatever. We agree that the Truth is only approximatable, but the closer
we get to this grail, the better the predictions should be. So far, we
have the equivalent of a bunch of hotrodders arguing the merits of their
different cars, car 1 has MacPhooey struts, chome six-barreled
carburettor, Wolzinski headers and burns nitro fuel, car 2 has a blown
402 in 8.5 cylinder Reo engine, and big back wheels and burns
hydrazine...so which is fastest? Well, race'em, I say. Maybe they won't
even get past the starting line. Which car or tree predicts best? By
what measure? What are we doing this for?
> >Phenetics and cladistics and max likelihood trees are generally alike,
> >and that's encouraging. I would use the tree or dendrogram or cluster
> >that predicts best with external verification.
> What source of external verification do you have in mind. Cladists
> look to biogeography or coevolution; you have something else up your
That's good, and see above. I like classifications that make sense
biogeographically...as long as the possibility dispersal events are not
> >>Given that there are 30-80 million species, and more
> >> possible phylogenies than quarks in the universe, how can any
> >> phylogeny have a probability more than a smidgen above zero? And yet
> >> one is true.
> >Again you assume that the theory has to be the same as Truth, whatever
> >that is.
> No I dont at all.
Okay, I understand.
> > Given lots of (sometimes outrageous) assumptions, statistical
> >phylogeneticists do come up with trees that have probabilities attached
> >to them.
> And those are meaningless I think, certainly if they are considered
> probabilites relative to truth.
No. If they are meaningless, then cladistics can't reconstruct anything
> > I know of a study that presented a tree selected from 10^40
> >trees. The tree is reasonable, but so are a number of other trees
> >slightly less probable. The test is usefulness in a scientific context
> >(a la Piercian pragmatism) and it should be external.
> Usefullness in an evolutionary context would be a tree based on a
> parsimonious ordering of homologies. Each homology, as an independant
> evolutionary novelty, is external to the others.
> Where are you looking for your external test?
Biogeography, coevolution, general usefulness of the classification to
other scientists for things they need to predict.
Richard H. Zander, Buffalo Museum of Science
1020 Humboldt Pkwy, Buffalo, NY 14211 USA bryo at commtech.net
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