dispersal fantasy

[P.Hovenkamp]

At 03:59 PM 6/25/02 -0400, John R. Grehan wrote:
>Pierre Deleporte wrote:
>
>>There is independent contribution from biology: the genetic datations and
>>phylogenies, confronted with the geological scenario, and allowing to check
>>for inconsistencies under some interpretative assumptions ("model"). Also,
>>everything is always interpreted in the light of current knowledge. Cannot
>>be otherwise.
>
>The way the paper seemed to work was that the 'contribution' of biology was
>dependant on its degree of conformity to a geological narrative so the
>contribution was not independent (.ie. there were no biogeographic models
>generated from the phylogeny). Similarly, the genetic information was
>another narrative outside biogeography. In reference to current knowledge,
>it is possible for a method to generate predictions that go beyond current
>knowledge.
>
>>Well-argued "narratives", i.e. historical inferences, may effectively at
>>some moment be considered as belonging to background knowledge for further
>>explanation. If the narrative is revised, then background knowledge is
>>modified and the scientific explanation may change. No methodological
>>problem, I think.
>
>If one is confining a research program to making up stories based on
>current knowledge rather than advancing knowledge then I would agree that
>within that constraint one may say that there is not a problem. If one
>prefers a method that is not constrained in this way, then there are
>choices available.

To me, the basic problem here seems to be how we go about confronting
geological theory with biogeographical evidence.
John seems to want to collect a whole lot of biogeographical evidence, use
this evidence to derive a biogeographical statement with some degree of
generality, and then confront geology with that statement.
Pierre seems to accept a "piecemeal" approach, which confronts each piece
of biogeographical evidence with the geological theory separately, and
returns a "narrative" which deals with the similarities and differences.
Is that more or less a correct interpretation?

I suggest that, in the long term (when we're all dead...) it will come to
the same thing: when a lot of conflicting evidence emerges, something will
have to break, and alternative theories will have to be considered. That
may be a geological theory (new evidence for land bridges across the
Mozambique channel), or it may be about the biogeographical evidence
(someone finding chameleons can swim after all..., or revealing fatal flaws
in the cladograms).
Ultimately, it's about strength of evidence. I would need pretty strong
evidence to convince me of the effectiveness of homeopathic medicine - and
some recent transoceanic dispersal hypotheses come close to that in their
implausibility in the light of other evidence...

Peter Hovenkamp

P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at nhn.leidenuniv.nl
http://nhncml.leidenuniv.nl/rhb