Centre of origin digression

John Grehan jgrehan at SCIENCEBUFF.ORG
Tue Apr 5 10:37:31 CDT 2005


> -----Original Message-----
> From: Don.Colless at csiro.au [mailto:Don.Colless at csiro.au]
Obviously a story could be cooked up to explain any track
> at all; but what we need (if possible!)are ones that gain credibility
by
> fitting other available evidence - the way "Antarctic" distributions
> fitted so well with continental drift. Of course Wegeners are pretty
thin
> on the ground; but let's keep our eyes out.

Thanks for the feedback Don. 'Gain credibility' is an interesting
concept. If 'credibility' is simply a matter of conforming to 'available
evidence' then biogeography would seem to be not much good at all as it
does not advance knowledge beyond what is already known (its just story
telling on top of storytelling). On the other hand, I agree that one can
cook up a story to 'explain' any track at all. This being the case I
would argue that the question comes down to whether the story advances
knowledge. 

Thus, for the trans-Pacific distributions (which are identified by
everyone (or virtually so whether they profess to be dispersalists or
vicariance/cladistic biogeographers) using panbiogeographic criteria of
minimum distance and main massing) the story concocted by Croizat was
that the general pattern was the result of former land in the Pacific.
This story led to the testable prediction that the Americas are a
geological composite. When he made this prediction there was no
'available evidence' from geology, so using Don's criterion this story
wasn't credible, yet later geologists corroborated Croizat's prediction.


I would argue that Croizat's story was better than that of the
dispersalist/center of origin biogeographers as it was able to predict
facts beyond current knowledge. Some time back one dispersalist
dismissed this achievement as being the product of 'coincidience' so it
seems that even if a method works its not sufficient for people to take
it seriously.

> I don't know about "geographic artefacts", but surely distributions
> contain historical evidence.

I agree that they do - although the nature of the evidence is not
necessarily recognized by everyone. My view about disjunctions being
geographic artifacts is that disjunctions are not defining features of
biogeographic homology. A distribution may be 'disjunct' by one meter, a
kilometer, or half the world away. The mileage is of no biogeographic
significance (at least in panbiogeography as I understand it). I think
of the other list postings made a similar point in the context of areas
of endemism.

John Grehan

> 




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