Positivism in evolutionary scienc

Tom DiBenedetto tdib at UMICH.EDU
Sat Dec 6 00:37:18 CST 1997

Thomas Schlemmermeyer wrote:

[from Hennig]
> 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
> 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
> the outcome! If you have doubts, show that the outcome is wrong!
> Hennig justifies (in this phrase) this a-priori-confidence in synapomorphy
> hypothesis by simply claiming that, without it, phylogenetics would crash
> down.

I am sure that this is obvious to most readers of this list, but it
shoud perhaps be mentioned that one assumes homology not merely
because it is necessary to make systematics a workable system, but
rather homology is assumed because your homology hypotheses have
already been corroborated by all the tests you impose on them in your
work as a biologist (anatomist, behaviorist etc.). IOW, you have
already accepted them as homologies in light of all your biological
knowledge; the test of congruence is merely one last test.

> That there really are easily
> recognizable synapomorphies and that the few homoplasies can be "outed"
> and shown ?

Homoplasy is incongruence. Those homologies which flunk the
congruence test are therefore falsified homologies; and we must
invoke ad hoc hypotheses (e.g independant origin) to account for

> 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?

No, you are on your own Thomas,,,,,:)

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