atom feed26 messages in edu.ku.nhm.mailman.taxacomdispersal fantasy
FromSent OnAttachments
John GrehanJun 24, 2002 10:17 pm 
W.WusterJun 25, 2002 9:10 am 
John R. GrehanJun 25, 2002 11:19 am 
Jong, R. deJun 25, 2002 12:46 pm 
pierre deleporteJun 25, 2002 2:21 pm 
John R. GrehanJun 25, 2002 3:59 pm 
pierre deleporteJun 25, 2002 7:39 pm 
pierre deleporteJun 26, 2002 2:27 pm 
Ken KinmanJun 26, 2002 7:19 pm 
Adolf CeskaJun 27, 2002 9:38 am 
Robin LeechJun 27, 2002 10:25 am 
pierre deleporteJun 27, 2002 12:50 pm 
John R. GrehanJun 27, 2002 2:45 pm 
P.HovenkampJun 27, 2002 10:27 pm 
John R. GrehanJun 28, 2002 1:58 pm 
pierre deleporteJun 28, 2002 6:42 pm 
John R. GrehanJul 1, 2002 10:19 am 
John R. GrehanJul 1, 2002 11:25 am 
Tom DiBenedettoJul 1, 2002 2:41 pm 
pierre deleporteJul 1, 2002 6:51 pm 
Ken KinmanJul 1, 2002 10:15 pm 
John GrehanJul 2, 2002 7:40 am 
pierre deleporteJul 2, 2002 12:02 pm 
John R. GrehanJul 2, 2002 4:03 pm 
Ken KinmanJul 2, 2002 5:18 pm 
pierre deleporteJul 3, 2002 4:28 pm 
Subject:dispersal fantasy
From:John Grehan (jrg@PSU.EDU)
Date:Jun 24, 2002 10:17:27 pm

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.