cladism's greatest weakness

Tom DiBenedetto tdib at UMICH.EDU
Tue Sep 28 18:15:39 CDT 1999

Richard Zander wrote:

>Tom DiBenedetto wrote:
>>Cladists believe in classifying in a
>> manner that mirrors the reconstruction.

>The problem is there is commonly no probabilistic reconstruction. By
>probabilistic, I mean that no really acceptable basis is offered for an
>expectation that at least more often than not you would be correct if you
>acted upon the hypothesis.

But cladistic systematics is an empirical science. We prefer the
hypothesis which is best supported by empirical evidence. I dont see
how probabilism enters into the equation. If you wish though, I will
play with this idea a bit. Given our assumption that the history of
species divergence is recoverable from an analysis of the distribution
of character states ( an assumption which is, I think, necessarily
shared by all systematists), then one could imagine a probability
function which indicates an increasing probability for a hypothesis as
a function of increasing empirical support for that hypothesis. Such a
perspective is, I think, fundamental to any empirical science.

>Well, choosing not to present a single answer when only a "best" answer is
>available out of many different answers that are also supported by the data
>and which are also not evolutionarily unreasonable.

But the amount of support differs for each hypothesis. We accept the
hypothesis with the most support. I dont see why you find this

>Tom, a poorly supported cladogram is an optimization, which is good.
>Grouping similar taxa by any optimization maximizes phylogenetic info. That
>makes it fine for a classification, sure enough. The difference is that
>these optimized classifications are passed off as reconstructions -- not
>well supported reconstructions but none-the-less very detailed poor
>reconstructions. The devil is in the detail, and no attempt is made at

Once again, I dont really see the problem. They are not passed off as
ultimately true reconstructions, they are presented as the
reconstructions which are most in accord with available evidence. As
all scientists do.

>Bayesians deal with probability as psychological expectation.

Seems to me to introduce a confounding factor of the most problematical

>> See both Edward's
>> book on Likelihood, and Popper's works on the scientific method for
>> critiques along these lines.

>I have puzzled over both of these authors. Their books add to my ongoing
>compilation of ingenious ways to explain away doubt and generate funding.

I dont suppose that this is the proper forum for a discussion of these
issues, but I heartily disagree. I see nothing in Popper's work which
would support a charge of explaining away doubt. Quite the contrary.

>Likelihood does have uses, but can be easily misused.

I agree with that. I think, for instance, that the use of likelihood to
estimate phylogenies is a horrible misuse, given that the fundamental
tenets of statistics are massivily violated by this procedure (e.g. the
independence of samples).

>    Popper uses propositional logic like waving a 4th of July sparkler in
>the dark to create pretty patterns of light, which persist for a while as
>blind spots.

I guess I really dont know what to do with this statement!

>    Sick of philosophy?

Nope, but I sense that you are!

>> Do you think all scientists should abandon their preference for the
>> hypotheses that are most in accord with empirical data in favor of a
>> non-judgemental consideration of all alternatives?

>Again you plunk for a "best" answer and ignore my question in doing so. A
>best explanation is fine for classification but insufficient for a

Well, since we are discussing systematics (making classifications)
perhaps we should leave things on this point of
?agreement?. I am not sure what you mean by reconstruction, or what is
wrong with presenting our state-of-the-art reconstruction until such
time as we learn more.

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