Taxonomic 'Jargon'

[pierre deleporte]

At 15:49 06/11/2002 +0100, Michael Schmitt wrote:
>Maybe it is worth discussing the widely used terms "primitive"/"low" and
>"advanced"/"high" as applied to taxa (as long as we can distinguish a taxon
>as a monophyletic one from others, it must at least possess one
>autapomorphy amongst several or many plesiomorphies. Thus, what does
>"primitive" mean? I have the impression that "primitive" and "advanced" are
>used unconsciously in an anthropomorphic way: the more similar to humans an
>animal is in one respect or another, the more "advanced" it appears to us.
>E.g. the "highest" insects are social Hymenoptera since they are living in
>a social system that resembles a human (western) nation, or the "highest"
>molluscs are the cephalopods since they possess the largest brains, as we
>do amongst the vertebrates, and so on.

"Scala naturae" connotation apart (Barry's post), the terms "primitive" and 
"advanced" are admittedly acceptable for qualifying characters. 
Historically, they mean plesiomorphic / apomorphic (and these terms are 
better); functionally, they may mean more or less complex, or more or les 
fit, according to some theory of complexity or adaptation.
But these terms should be completely avoided for qualifying taxa: they are 
always an abusive extension to the whole taxon of what in fact qualifies 
only one or several characters in the mind of the author. Just try to 
question people about why they name a taxon "primitive", the answer always 
come as an argument concerning some characters of interest (and not all 
characters of the taxon).

>So, what do we mean when saying "these two taxa are
>related, while these other two are not".

At best, this is another case of abusive extension from a character of 
interest: the last may be homoplastic, i.e. without historical connection 
in diverse taxa, while all taxa are of course "related" some way. Only a 
notion of relative phylogenetic relatedness could make sense for taxa, 
corresponding to the nested hierarchy of clades.

best,  Pierre


Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
T?l?phone : 02 99 61 81 66
T?l?copie : 02 99 61 81 88