[Taxacom] Hedges /Kumar (eds) The Timetree of Life

[John Grehan]

Comments below

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Jason Mate

> I would like to see how you would apply a temporal dimension a priori.

I did not suggest applying a temporal dimension a priori

> You bring panbiogeography to the mix at your own risk. The risk being that 
> you will start subordinating the facts to the pattern. 

Where has that occurred?

Now if I had two 
> sister clades, as in the rodent article, one in South America and one in 
> Africa, it could be vicariance or it could be dispersal. 

Yes. Although in panbiogeographic analysis this would not be treated a fact in isolation.

> The key is timing. We are all in agreement that fossils provide a minimal 
> age but there is (or should) also a reasonable maximal age (best estimated 
> by the fossil record of related groups). Of course with no bottom it 
> becomes impossible (-ish) to refute vicariance. And that is my point with 
> Michael´s article.

Whatever one might consider 'reasonable' is a personal matter. I consider it 'reasonable' that there were no humans in the Carboniferous, but that has no necessary bearing on reality no matter how much I believe it. However, judgments are made and there is nothing wrong with that if identified with respect to some other criterion. The fossil record of related groups may have some bearing on that, or not. Sister group relationships are sometimes invoked where one group has a very old record and the other very young by comparison, so the younger is predicted to be as old as its sister group despite the lack of an older fossil record.

But the molecular method can potentially refute vicariance if the vicariance is later than the estimated divergence date (as Heads has pointed out).


"My reading of biogeographic papers is that most practitioners do indeed assume that the lack of evidence for former land is evidence for a lack of former land."

> In my experience there are not many 4m tall humans. In fact I have never 
> met a single one and neither has anybody else I know. Based on this I make
> the inference that there are no 4m tall humans. This is a logical fallacy, 
> as has been pointed out by Michael. However, and in spite of Popperian 
> flogging, science operates not on certainties but on probabilities based 
> on the available data. So although I cannot prove the non-existance of 4m 
> tall humans, the fact that there is not one shred of evidence til now 
> makes it highly improbable that one exists. However if one were to walk 
> throught the door right now then all my pretty hypothesis would be wrong. 
> I can live with this uncertainty. 

I interpret this to mean that you agree with me that most biogeographers assume the lack of [geological - I forgot to add that term of reference] evidence for former land is evidence for a lack of former land.

> A broken clock tells the right time twice a day. In 10,000 pages I am sure 
> that there are many right guesses.

I find this kind of remark to be remarkable (its not the first time this approach has been used to dismiss panbiogeography). Perhaps in only in evolutionary biology is it seen to be scientific to be condemned for getting the right answer and congratulated for getting it wrong.

 
"The irony of all of this is that the various papers by Heads demonstrates the utility of molecular phylogenies as hypotheses of relationship for many, many groups. While I have my doubts about molecular phylogenies and regard them as provisional with respect to morphological corroboration and problematic when there is substantial morphological incongruence, they do provide many examples that are biogeographically coherent, that often demonstrate classic vicariism, corroborate the standard tracks of the world (which no one has yet falsified), and providing tectonic correlations. One could not ask for more."

> You are moving way beyond the topic here. But in any case tracks are not a 
> method of analysis. You are describing a pattern and then trying to impose 
> it on other patterns. 

Tracks by themselves are not a method of analysis, but identifying their spatial relationships against one or other criteria is - at least if it is not analysis neither is phylogenetic reconstruction which is also a combination of patterns to get a resulting pattern.


> Humans have this tendency to learn a pattern and then look for it. Like 
> finding animals in the clouds or in a piece of wood, just because it looks 
> like something it doesn´t mean it is the same thing.

True - that's the challenge of science in general. Whether panbiogeography is mistaken in some fatal way in this respect remains to be seen. It is certainly the case that dispersal theory has failed to predict novel tectonic correlations with biological distributions whereas panbiogeographic analysis has produced a lot of information on that. Tectonic correlations are a reality, not a cloud or wood figment.

John Grehan

Good night

Jason
 		 	   		  
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