crocodile tears

B. J. Tindall bti at DSMZ.DE
Tue Feb 8 12:00:19 CST 2000


Ken Kinman wrote:
>Brian,
>    I completely agree with your conclusion.  One of my biggest frustrations
>with the strict cladists is that many don't realize that they are replacing
>old assumptions with new ones.  Instead of minimizing arbitrariness, they
>are often substituting cladistic arbitrariness for eclectic arbitrariness.
>Therefore purely cladistic classifications generally gain very
>little---hardly enough to justify sacrificing stability and usefulness.

Having experimented with applying cladistic analysis to microorganisms I
came to the conclusion that it was a lot more tricky than I was being led
to believe, and that some of the conclusions which were being arrived at
were, in some cases actually the underlying assumptions. In the absence of
a good fossil record for microorganisms one is largely working with a set
of features from present day organisms (which already contradicts what some
people "conclude" based on "assumptions"). This is particularly true of
certain groups who often prove what they assumed in the first place (no
personal attack on anyone intended).

>     Unfortunately, the irritation the rest of us feel from purely cladistic
>"classification", spills over into an overreaction to (and attacks on)
>cladistic "analysis".  I think cladistic analysis can be misused (in my
>opinion, Woese is a prime example), but if it is used correctly it can be a
>very powerful analytical tool.  Therefore when it comes to cladistic
>"analysis", I encourage eclecticists not to throw the baby out with the
>bathwater.

I must confess that in botany and zoology I have the feeling that there is
probably a clear distinction between the phenetic approach and the
caldistic approach, but in microbiology I see trees based on similarities
being sold as "phylogenetic", and then cladistic terminology being applied
to signiature sequences derived from the same trees. I just get the feeling
that there is no clear idea about what system is being used. Unfortunately
the same problem seems to be spilling over into genomics. There would
appear to be cases where overall similarity may have something to say (as
in the case of rates of evolution of sequences over geoligical time) and
other cases where analysis of character states provides the information we
are looking for. I have even seen examples where branch lengths are being
applied to sequences trees derived from parsimony analysis, and interesting
marriage of phenetics and cladistics. Perhaps the next few years will see
more changes.
Brian Tindall

>                     ------Ken Kinman
>*****************************************************
>>From: "B. J. Tindall
>>I have been battling with this for some time now. It would seem that both
>>phenetic and cladistic methodology picked up on being "theory-free", but
>>then I seemed to have spent quite some time reading about the underlying
>>theory in order to understand how it works. I came to the conclusion that
>>what most people mean is not that it is "free of theory", but that the
>>minimum number of assumptions are being made, which is something different.
>>Brian Tindall
>>
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