FWD>certainty/un

[Richard Jensen]

On Wed, 2 Aug 1995, Meredith Lane wrote:

> If we leave off trying to reconstruct phylogeny, we will be back
> _exactly_ to the spot that Sokal and Sneath and that crew stood upon in
> the 60s when they invented phenetics. Their assumption was that evolution
> happens, but we can't _possibly_ ever figure out how, so let's not try.

I don't believe that Sokal, Sneath, and others ever said let's not try.
What they objected to was the misguided attempt to interpret phenetic
analyses (especially phenograms) as indicators of evolutionary
relationships.  In their books they devote considerable space to
numerical cladistic methods.  There was, and still is, a fundamental
philosophical difference of opininon on hwat a classification should
represent, and how we should construct classifications.  Gilmour
naturalness is a not unreasonable criterion and phenetic classifications
can be very natural.  In fact, phenetic classifications can be more
stable and can have higher predictivity than cladistic classifications.
It depends on the data used to construct the classification.  A lot of
hay was made by those who used special data sets to demonstrate the
fallibility of both methods - it is easy to come up with a data set that
will demonstrate superiority by either approach.
One concern about cladistic approaches is that they have an extra layer
of hypotheses between the data and the classification - generally,
polarity is hypothesized for each character, a step not necessary for a
phenetic analysis.

> Their methods of comparison of overall
similarity are good in a
> statistical sense, but not very satisfying biologically (in my opinion).
> I think that is why the systematic world swung away from phenetics toward
> cladistics rather rapidly.
>
I will repeat a point I have made before.  One reason for the swing was
the apparent mathematical simplicity of numerical cladistics.  In fact,
no math is really necessary.  However, eigen analysis cannot be intuited
very easily from the data and certainly is not something that is easily
done by hand (excpet in trivial cases).

Dick Jensen