Re: The iguanodont paper

[evelyn sobielski <koreke77@yahoo.de>]

--- Mike Taylor <mike@indexdata.com> schrieb:

> 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".
> Kudos to Stefan
>  > Obenauer at Cologne Zoo for that one.
> 
> 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*.

If you do that with monophyletic taxa, you'll not end
up with a ludicrous and clearly pohylogenetically void
group by contrast, but at some point - usually when
you reach monotypy - no additional phylogenetic
information will be gained by further restricting that
taxon.

"Non-human primates" is a rather useful concept for
example.


Regards,

Eike


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