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Re: The iguanodont paper

evelyn sobielski writes:
 > >  > A nice way to explain the problem of nonmonophyletic taxa to
 > >  > laypeople by reductio ad absurdum: consider a taxon
 > >  > "Caerulommatanimalia" - "animals with blue eyes".
 > > 
 > > Sorry to be picky, but this is not a reductio ad absurdum.  That
 > > is a proof in which you start by assuming to be true what you
 > > want to prove is false, then show that a contradiction ensues.
 > > 
 > > What we have in the Caerulommatanimalia case is more like a
 > > straw-man argument: you extrapolate and exaggerate your
 > > opponent's position into one which is clearly false, and deduce
 > > (incorrectly) that his original position was also false.
 > If my intention would have been proof, yes. But that is not so - it
 > was to demonstrate that if the concept of non-monophyletic
 > (polyphyletic in this case, as all blue-eyed life ultimately could
 > be traced back to some eyeless - and hence non-blue-eyed - common
 > ancestor) taxa, if it is to have any value at all, *cannot be
 > applied rigorously*.

It's still a straw-man argument, and those are always better avoided.
As soon we start using them in favour of our own pet ideas, we open
ourselves up to anti-cladists saying things like "A nice way to
explain the uselessness of cladistics to laypeople by reductio ad
absurdum: consider an analysis using a single character "has stripes"
that recovers tigers closer to zebras than to lions."

When you push any idea to a ridiculous extreme, you end up with --
guess what? -- a ridiculous extreme.  That doesn't prove anything
... execept that you've pushed an idea to a ridiculous extreme.

So if we want to attack an idea, whether that idea of paraphyletic
taxa, cladistics, creationism or evolution, we need to attack it on
the basis of what is _actually_ says, not of what we'd find it amusing
if it _did_ say.

This has been a public service announcement :-)  Please excuse the
didactic tone, this is a bit of a hobby-horse for me.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor    <mike@indexdata.com>    http://www.miketaylor.org.uk
)_v__/\  "Why does man kill?  He kills for food.  And not only food:
         frequently there must be a beverage" -- Woody Allen, "Without