polarized and unpolarized

[Pierre Deleporte]

At 17:02 09/01/2002 +1000, Larissa Vasilyeva wrote:

>2. He   [Pierre Deleporte]   wrote that different states are given a 
>different weight, but, actually, states of the same character are of equal 
>weight since 'weight' of a character means its position in a hierarchy.

In fact I wrote:
"In phylogenetic inference, ordering characters is a coding procedure 
consisting in giving a different weight to changes between different states 
of a character".

The key word is "changes". I was speaking of weight of transitions between 
character states, i.e. weight of "steps" for parsimony analysis, but 
neither "weight of characters" nor "weight of character states" properly.

>  (If two genera differ in some character, and one genus possesses a 
> primitive state of this character, while another genus has an advanced 
> state, one can trace a phylogenetic line but both states are equal in 
> level, consequently in weight).

I did not mean this at all, but  "weighting changes" (steps). Character 
ordering, in cladistic jargon, consist in giving increasing weight to steps 
between character states more distant in the "order" (=unpolarized sequence 
of states).
"Unordered" characters mean that for such characters all changes (= steps) 
between any two states are given equal weight for calculating tree length.

Talking of "character weighting" instead of "character steps weighting" may 
be misleading.

Best wishes,
Pierre


Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
Téléphone : 02 99 61 81 66
Télécopie : 02 99 61 81 88