Positivism in evolutionary scienc

[Thomas Schlemmermeyer]

 Hello,
=20
 On Fri, 5 Dec 1997, James Francis Lyons-Weiler wrote:
 >=20
 > Positivism isn't the same as optimism.  I am an optimist, not a
 > positivist.
 >=20
=20
 OK. I agree. When I used the term I had in mind those books which
 you can find more in the non-scientific corners of book shops and which
 deal with the "power of positive thinking" and so on which seems to
 me like a comercialized form of optimism. Sorry, it was just a confusion
 of meanings!
=20
 What Hennig recomended in his 1953 paper (Kritische Bemerkungen zum
 phylogenetischen System der Insekten) seems to be very much like a critica=
l
 optimism. The signal/noise problem mentioned here maybe is a little bit=20
 similar to the synapomorphy/homoplasy problem in Hennig's terminology.
 I feel free to cite here from HENNIG's work (page 17 in his paper):
=20
> ".....ein wenig Ueberlegung zeigt aber leicht, dass die phylogenetische
> Systematik allen Boden unter den Fuessen verlieren wuerde, wenn sie alle=
=20
> Synapomorphien zunaechst als Konvergenzen auffassen und in jedem Falle de=
n
> Beweis des Gegenteils verlangen wollte. Die Last des Beweises muss=20
> vielmehr der Behauptung auferlegt werden, dass bestimmte Synapomorphien
> in Einzelfaellen nur auf Konvergenz beruhen koennten.
=20
 This says: One has to prove that certain synapomorphies are in reality
 homoplasies and not the opposite!
 (Everything is homoplastic and one tries to prove that there are=20
 synapomorphies.)
 Ok, I'm just trying to understand it all, but, put into modern cladistic
 practice, this may say:
 Start your ordering procedure with maximum parsimony and look on=20
 the outcome! If you have doubts, show that the outcome is wrong!
=20
 Hennig justifies (in this phrase) this a-priori-confidence in synapomorphy=
=20
 hypothesis by simply claiming that, without it, phylogenetics would crash
 down.
=20
 OK, let's try to put this, as well, in more modern methodological thinking=
:
 Before running any procedure one should be aware of the process assumption
 involved.
 So, what would be the most basic and generalized process assumption of
 phylogenetics?
 What is it that makes Hennig (and probably the majority of you as well)
 confident that it does all make sense? That there really are easily
 recognizable synapomorphies and that the few homoplasies can be "outed"
 and shown ?
=20
 One may put this in a short, concise phrase?=20
=20
 I don't know how to put it but I guess it must be some very simple
 assumption. In this phrase, there has to come in something like hierarchy,
 origin, ancestor and common descent........
 But can anyone help?
 =20
=20
>"  Hier ist die Feststellung am Platze, dass keine der morphologischen
> Regeln und keines der Kriterien, deren sich die Systematik zur Feststellu=
ng
> der Verwandtschaftsverhaeltnisse bedient uneingeschraenkt gueltig ist.=20
> Sie haben alle zunaechst nur den Wert heuristischer Prinzipien."

Here, Hennig utters some caveats concerning the power of his methods.
He says that his rules and criteria (to recognize homologies, polarize
them and run the deviation rule) are nothing more but heuristic principles.
=20
 Nowadays, it seems to me, that one simply puts the stuff into the computer
 and makes some statistics on it (which I still did not start to study,
 sorry!). But what really should count is WHAT the data set contains!
 =20
 Already the act of defining a character is hypothetic. A character is not
 something real! It is just a man-made hypothesis!
 It is completely useless to run a lot of mathematic procedures on data
 which were not gathered according to sound and critical human judgement.
 Miss Bennett from California out there (Duodeviginti-Thread)! You probably
 know what a heuristic principle is.
 But I think it includes some point of subjective judgement=20
 (greek heureka=3DI see, I understand). The method does not substitute one'=
s
 judgement. They work hand in hand. The method is only a method of making
 methodical judgements. But they continue being judgements.
 =20
> " Aber den haben sie auch. Radikale Skepsis gegenueber der Moeglichkeit d=
es=20
> Erfolges ist auch in der Systematik nicht geeignet, vor den Beginn der=20
> wissenschaftlichen Arbeit gestellt zu werden.
> Das Vertrauen, dass eine richtige Anwendung von Methoden und Kriterien,
> die sich als logische Folgerungen aus theoretisch gut begruendeten=20
> Voraussetzungen ergeben, haeufiger zu richtigen als zu falschen=20
> Ergebnissen fuehrt ist hierfuer geeigneter."
=20
 OK, this last phrase shows Hennig's optimism as a part of his
 method. It's a careful optimism which pleads in favour of carefully chosen=
=20
 theoretical assumptions.
 Sorry, it got quite long, but I just started to study it all, and I'm
 very eager to understand the core of it.
=20
 Yours   Thomas
> -------------------------------------------------------------------------=
-----
> Thomas Schlemmermeyer
> Museu de Zoologia, Universidade de S=E3o Paulo
> Caixa Postal 42694
> CEP 04299-970
> S=E3o Paulo, SP, Brasil
>=20
> Resid=EAncia:
> Thomas Schlemmermeyer
> Caixa Postal 00276
> CEP 14001-970
> Ribeir=E3o Preto, SP, Brasil
>=20
> Fone, Fax: 016 6371999
> -------------------------------------------------------------------------=
-----
>=20