Who is the postivist?

Tom DiBenedetto tdib at UMICH.EDU
Thu Dec 11 05:08:46 CST 1997

 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? :)

>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
Birds and crocs are sister taxa - is this the type of grossly
disimilar terminal relationships you would like your method to

>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!

>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.

>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

>>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.

> 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.

> 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?

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