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

[Jason Mate]

Dear John,

Regarding the fossils, do you object to them because of misidentification then? Objectivity and accuracy (e.g. accuracy of the identification) are not the same, so I am not sure what you mean. Assuming fossils are accurately identified and placed (i.e. phylogenetically we "know" their approximate relation to the other taxa of the monophyletic group we are looking into), then they can approximately pin down the age of a node and hence are the only truly objective timing data available to us currently. From these "prime" nodes you can estimate the others, with increasing uncertainty particularly backwards or if the taxon sampling is poor. In the former case (the root problem) the uncertainty comes from the highly skewed probability curve. But this probability curve is not infinitely long and can be established based on outside data. Yes, the data may be imperfect but it improves the initial estimate and their time accuracy improves with additional data (fossils). Sometimes your initial biogeographical hypotheses are proven wrong by ugly facts and others they live another day. 

Cladistic biogeography has weaknesses, but it still recognises dispersal and vicariance (as do most biogeographers) as valid mechanisms to explain current distributions. To which we could add extinction of course, but to prove this you need factual, objective data (fossils again). On the other hand not only does panbiogeography function in the absence of phylogenetic information (more in the next paragraph), but in addition it can function in the absence of dispersal (or explain it away). Surely organisms can move around and sometimes hit the insular or contienetal jackpot. Calling names like dispersalists seems to me like a tactic to draw attention away from the limitations of the panbiogeographical methodology.

Panbiogeography, in its essence, doesn´t use phylogenetic/cladistic information (maybe you´d prefer to call it misinformation ;) ). Apparently you find this statement untrue, but as practitioners have explained over an over again, tracks are basically a cartographic method of connect-the-dots, which then you sort into matching patterns to prove the existence of ancient communities that have been moved apart by vicariance events of one sort or another. Yes, you acknowledge the importance of phylogeny but you don´t use the relationships to determine if your tracks are actually joined in this way or that (i.e. does the sequence match known geologic events) or the timing (before or after) or even if you are comparing like for like (biogeographical homology). Furthermore you state that this method can predict the existence of previously unknown geological events. Does that mean that your tracks stay in some sort of biogeographical suspended animation until a matching geological event is found? i.e. you can prove but not disprove panbiogeographical tracks? Neat. That is what I meant by saying that you subordinate patterns to evidence. If what I have said is false then show me an example.

If you want to argue about the finer points of biological philosophy, great. But please don´t draw a fictitious line in the sand between dispersal and vicariance. We all know things can stay put or disperse or become extinct and, as Robin has pointed put in a rather amusing way, the world is a big casino and sometimes the same number can come up 10 times in a row. Describing the the pattern of numbers that comes out of the roulette can be fun or even instructive but it will not help you win when you place that bet.

Good night

Jason