The nature of cladistics [...]

pierre deleporte pierre.deleporte at UNIV-RENNES1.FR
Fri Nov 19 15:21:35 CST 2004


A 10:32 18/11/2004 -0800, Barry Roth wrote:
>No less of a personage than Willi Hennig recognized this difference between
>"tokogenetic" and "phylogenetic" processes.

So, it appears that Hennig also was fascinated by sexual organisms (is 
there any difference in strictly clonal organisms?).

Anyway, from the moment when two populations are separated (possible baby 
species, maybe "neospecies"), there seems to be no more "process" affecting 
them both together, only independent populational processes inside each 
population (each natural system). Thus, what is a "phylogenetic process" at 
all, beyond the splitting of the ancestral population? A phylogeny 
connecting different species is not a natural system. Maybe one could talk 
of a local community of populations belonging to different species as a 
system of some sort, but this is not the standard phylogenetic standpoint.

A phylogeny is a history and a possible classification, hence a concept, an 
"invention" (hopefully a scientifically useful one). Can there be 
"processes" affecting a phylogeny?
Only real biological systems are affected by evolutionary processes, 
concepts are not. "Phylogenetic" processes must be populational processes, 
and also cellular, individual and social processes (e.g. mutation, 
ontogenetic development and selection processes).

Curtis Clark Wrote :
 >"Species are the lower limit of phylogenetic study. We discover
 >paraphyletic species. We invent paraphyletic higher taxa."

We obviously also "invent" monophyletic higher taxa. No higher taxon is 
standing by itself as a consistent, observable "thing" out there.
But more than this, it appears that we even "invent" paraphyletic species, 
because we usually group under the term "species" (be it holo- or para-) a 
lot of individuals, from different disconnected populations, dead and alive 
(and guessing about the dead is quite important for the concept of 
paraphyletic species, as illustrated in Ken's recent 'Branta' posts). 
Hence, "species" is still not a real thing. We can "empirically discover" 
(i.e. "observe") only individuals dead or alive, social groups of living 
individuals, populations of living individuals, and ecological communities 
of populations of living individuals...

But we "invent" (conceive of) all classifications of all kinds at all 
supra-populational levels (and a population of effectively interacting 
individuals may be quite a tiny part of a species).

Just a tentative materialist and rational apprehension of taxa... They are 
definitely not material things (hence much less "natural things" = things 
existing in nature), but there is no shame in conceptually defining them 
some useful way for some specific purpose.

This likely goes right against some "systematic legends" (or at the very 
least, some detrimental imprecision of language) rather deeply rooted in 
our culture. A famous one is "clades as individuals" (are we supposed to go 
and check them out there? or breed some?), while "species as observable 
real systems" is hardly less confusing.

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




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