[Taxacom] Robust argument

Bob Mesibov mesibov at southcom.com.au
Sat Jun 27 19:33:47 CDT 2009

With considerable fear and trepidation, this TAXACOMer sticks his head above the battlements and meekly raises a couple of small points of informal logic.

We're agreed that we'd like to reconstruct evolutionary history, as best we can. The following argument seems to have been put forward:

(1) Because the genome is passed on from generation to generation, it contains information we need to infer evolutionary history.
(2) It is possible to infer evolutionary history using information in the genome.
(3) Morphology also contains information of use for inferring evolutionary history.
(4) It is possible to infer evolutionary history using information from morphology.
(5) Literally speaking, morphology is not inherited, so morphological information is second-hand data derived from a heritable source: the genome.
(6) No other kind of information can be used to infer evolutionary history, because no other information is inherited.

(4) has been the basis for evolutionary inference for a long time, (2) for a shorter time. Many people believe that (2) is better than (4) because of (5), and because there is more (1) information than (3) information.

The logic here needs defending. Why should (5) make (4) any less reliable than (2)? (I think this is one of Richard Zander's points.) How do you compare the reliability or resolution of (2) vs (4), given that we have no time machine and no other information (see (6)) that can independently be used to infer past events? How do you know that there is more independent information from (1) of use for historical inference than from (3)?

I think these 3 questions go to methodological assumptions. Should these assumptions be taken as givens, equally reliable from group to group? It worries me that posters have written THEORETICALLY in caps without spelling out their thinking.

I also point to (6), which is nonsense, and comes from thinking about organisms divorced from their geographical location and their ecological associations (think of parasitism, insect/host plant interactions, etc). (6) should not be confused with (7), which might read "It is possible to infer evolutionary history from biogeography and ecological associations." That history might be blurrier than (2) and (4) histories, but how do total evidence enthusiasts justify their insistence on using (1) and (3) evidence to the exclusion of (6) evidence? (Or is it just that *some* evolutionary historians can't be bothered studying all the phenomenally complicated, ungeneralisable facts of what used to be called natural history?)
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195
Website: http://www.qvmag.tas.gov.au/mesibov.html

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