dispersal fantasy

Jong, R. de Jong at NATURALIS.NNM.NL
Tue Jun 25 12:46:29 CDT 2002

May I suggest that leaving out the suggestion that 99.9% of the systematists are of an abysmal scientific quality and only 0.1% have seen the light would help elucidate the arguments made by John Grehan?
Proof of what exactly happened in deep history only exists in science fiction.  We have to be content with more or less circumstantial evidence. This comes in many forms, essentially as hypotheses, about phylogenetic relationships, geological processes, genetic processes, fossils, etc. To dismiss a particular hypothesis as a narrative (to me a narrative is a story lacking factual evidence) does not help discussion. To dismiss a hypothesis because it is based on incorrect facts, incorrect interpretation, or whatever, is OK, but to dismiss it by calling names does not help us further. The strength of the Hennigian approach of systematics that came to replace traditional systematics in the second half of last century was, in my opinion, that it was based on arguments, not on opinions. If we disagree with a hypothesis, let us talk about what is wrong about the arguments, not about what is wrong with the person who proposed the hypothesis.  
As to evidence, distribution is not evidence of a process in the past, only an observation. Disjunctions can be the result of different processes, vicariance, dispersal from one area into the other, dispersal from a third area with subsequent extinction. If we want to explain a disjunction, we must search for evidence in favour (or against) any of these possibilities. To favour one explanation over the other (be it dispersal or vicariance) without evidence makes the explanation a narrative. The explanation may be utterly wrong because the underlying hypotheses are wrong, but once noticed we know how to improve it. So I suggest that we help each other improving our arguments and hypotheses.
This is not a rebuttal of John Grehan's arguments, since his arguments are not entirely clear to me. I agree with him that alternative explanations are possible  starting from different hypotheses. The hypotheses on which Raxwothy et al.'s paper was based may be wrong, but let us talk about these hypotheses then. What is wrong with a geological hypothesis other than that it is a hypothesis? If an author has wilfully omitted hypotheses that are not welcome, he can be critized for that, not for the fact that he used hypotheses from other disciplines. If I understand it correctly, the main criticism of John Grehan is "a complete absence of any integration between biology and geology." This is a methodological matter. The desirability of this integration and how to do it is a subject of debate, but this debate was not the subject of John Grehan's criticism, it was taken for granted. 
Rienk de Jong

Dr Rienk de Jong
Department of Entomology
National Museum of Natural History
PO Box 9517
2300 RA Leiden
phone +31 71 568 76 52
fax +31 568 76 66
e-mail: jong at naturalis.nnm.nl

> -----Oorspronkelijk bericht-----
> Van:  John Grehan [SMTP:jrg13 at PSU.EDU]
> Verzonden:    dinsdag 25 juni 2002 4:17
> Onderwerp:         dispersal fantasy
> I will present some comments here on a paper that was recently drawn to my
> attention and give, in my opinion, and example of an absolutely abysmal
> scientific quality for a 'biogeographic' study. I say this knowing that
> 99.9% of systematists practice exactly the same kind of biogeography and
> therefore would accept the scientific credentials of this paper as being
> first class. I acknowledge, therefore, the likelihood that most on this
> list will share that view. However, I make my comments for the few that may
> be seriously trying to think about biogeography in a different way. For
> those who believe my criticisms are misguided, I will be interested in any
> rebuttal.
> The paper is by Raxworthy, C. J. et al. 2002. Chameleon radiation by> 
> oceanic dispersal. nature 415: 784-787.
> In the conclusion of the paper they claim that their analyses provide
> evidence for considerable oceanic dispersal of chameleons, and support the
> hypothesis that dispersal, rather than continental break-up, was the
> precursor for species radiation. Far from providing 'evidence' my
> contention is that this was the view the authors read into their
> non-biogeographic data. This 'data' comprised preconceived ideas about the
> historical significance of matching biological area cladograms to
> geological narratives. According to the authors a (vicariance) geological
> history is supported where biological area cladograms match a postulated
> geological history, whereas the absence of a match is 'evidence' of
> dispersal. This approach demonstrates a complete absence of any integration
> between biology and geology. Instead biogeography is simply the narrative
> invented according to a selected geological narrative.
> Of course the authors use the propaganda tool of asserting the geological
> narrative is "well documented", but its still a story. They also appeal to
> dispersal by accepting the precedence of their 'molecular' clock
> reconstructions that are also incongruent with the postulated geological
> ages of the areas occupied by the lizards. They do not bother to consider
> that they may have novel evidence that the geological age is wrong. Neither
> do they consider the possibility that the molecular evidence may be wrong,
> and the lack of congruence between biological area cladograms may be due to
> differentiation independent of the postulated geological splitting events.
> Another argument about dispersal also comes from geology, rather than
> biogeography. They claim corroborating oceanic dispersal' by the presence
> of lizards on the Comoros islands that 'never had contact with other
> landmasses leaving only oceanic dispersal (note the similarity to the
> Galapagos dispersal argument. Their contention may in actual fact be
> correct, but notice its based on the acceptance of a geological theory. It
> is not 'evidence' from any biogeographic analysis.
> The claim (abstract) that the study 'further highlights the importance of
> oceanic dispersal as a potential precursor for speciation' which may be a
> misrepresentation of their actual work. Far from highlighting the
> importance of oceanic dispersal, their study seems to highlight the
> continued acceptability and credibility of dispersal fantasies based on
> geological and genetic narratives - in a supposedly leading scientific journal.
> Food for thought and rebuttal.
> John Grehan

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