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Re: Popper and Palaeontology (was: Re: "running" elephants - locomotary analoges)



> On Monday, April 21, 2003, at 01:17  AM, David Marjanovic wrote: 
> 
> > The way I see it at least, 
> > every cladogram represents the following 2 hypotheses: 
> > 1. The cladogram is the most parsimonious (or, for molecules, often 
> > most likely) way to represent the data. 
> > 2. Evolution is most parsimonious (respectively, what we call "maximum 
> > likelihood" is really that), or at least it's parsimonious enough that 
> > the few extra reversals and convergences would not change the 
> > cladogram, except if we had lots more data and would use those to make 
> > the cladogram. 
> 
> We don't know that evolution is parsimonious "enough". 
 
True. As I wrote, this is a hypothesis. 
 
> If we assumed it was, this would 
> serve as an axiom of evolutionary biology (see below). 
 
OK. 
 
> >> Popper's ideas certainly do provide a robust philosophical framework, 
> >> but they are notoriously difficult to apply to biological sciences. 
> > 
> > Why do you think so? 
> 
> [...] It has to do with Popper's characterising 
> scientific theories as positing laws that forbid certain things 
> - which seems to be very difficult indeed to apply to biology, 
 
Well, for example in biomechanics, it looks rather easy. Take the 
hypothesis that tetrapods with immobile ankles can't run. This forbids the 
existence of one with immobile ankles that can run nevertheless. Find one, 
and the hypothesis is falsified. Or ethology: The hypothesis that a 
peacock's tail feathers are maintained by sexual selection can be tested 
by taking a statistically relevant number of peacocks, cutting their tail 
feathers off, and presenting them to a statistically relevant number of, 
er, peahens. Back to cladistics: any hypothesis that two characters are 
correlated (rarely made explicit but encrypted in data matrices) -- find 
one organism which has one but not the other, and you've falsified that 
hypothesis. The other way around, a hypothesis that two characters are 
_not_ correlated... hm... requires that an organism with one but not the 
other exists, but I can't think of a way to falsify such a hypothesis. 
<headache> Right, it can be difficult. Is that Popper's asymmetry? 
 
> where it is questionable that there are any laws at all. 
 
You mean like Dollo's "law", Cope's "rule" and Marsh's "law"? 
 
> So, is the evolution of science parsimonious? ;-) 
 
How do you mean? How would you make a character matrix...? ;-) 
 
> As a potted history of science that ain't so bad I suppose - but the 
> whole area is minefield of controversy. "Smoking guns" are difficult to 
> find in the history of science - they tend to be played up later on. 
 
Sure, and the definition of "smoking gun" is very subjective. 
 
> Popper argued that it was not important where a hypothesis came from - 
> [...] I hope that's clearer now. 
 
Yes, thanks. 
 
> Of course, Popper also thought that the most falsifiable hypotheses 
> (i.e. the ones with the largest empirical content - and so by his 
> definition the most parsimonious) are the best, and should be first in 
> line for testing. But their being the most falsifiable is not in itself 
> the test. So, where does the testing come in cladistics? 
 
The testing of the hypothesis that that cladogram is the most parsimonious 
outcome of the data? As I wrote, rerun the analysis. Of the hypothesis 
that the most parsimonious outcome is the one that's closest to the truth? 
That's the problem, I agree. Just how parsimonious evolution is has AFAIK 
not been tested. 
 
> Phylogenetic hypothesis are rejected solely on the basis that they 
> are not the most parsimonious. This method may not be wrong - 
> that's not what I'm arguing - just that it is not obviously 
> derivable from Popper's philosophy. 
 
On the level that we just want the most parsimonious representation of all 
the data, it is derivable. On the level that we want the one that's 
closest to the truth, it isn't. 
 
> > What could be such axioms? 
> 
> [...] 
 
thx 

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