Are species real?

[pierre deleporte]

>On Sat, 15 Apr 2006 16:17:48 -0500, Steve Manning <sdmanning at ASUB.EDU>
>wrote:
>
> >But isn't it the ABSENCE of gene flow (or absence of "gamete flow") ... 
> that maintains the integrity of a group as a species (or, for that matter, of a
> >higher order taxon such as a genus)?  Of course, not all such groups
> >(populations) are separate species but they can become separate species if
> >they eventually lose the capacity to exchange genes between groups.
> >What else did you have in mind that are types of relations that maintain
> >the integrity of species?

Thomas Lammers answered:

>Inertia.
>A population at Hardy-Weinberg equilibrium tends to stay at H-W equilibrium
>until some force (like natural selection or genetic drift) acts upon it ...

This definition of "species" implies a criterion of genetic distance, in 
order to specify when the H-W equilibrium will be sufficiently modified to 
allow the naming of "a different species".
Looks like a phylogenetic notion, with a phenetic delineation criterion, 
defining a class of organisms (those with the property of common ancestry, 
but standing inside the allowed phenetic range), not a material system.
This is not a charge of mine: if considered along phylogenetic lineages, 
defining species (if needed) requires a delineation criterion - "obvious 
gaps" are not always available, as underlined by others.

------------------------------------

Otherwise, Jan Metlevski answered:

>I mean various relations between organisms that belong to the SAME
>GENERATION. There are no gene flows when we consider only organisms of the
>same generation, however there still are discrete natural entities of 
>organisms.
>Relations between members of the same species make this species to be a real
>object.

If you mean material systems, I can think of social groups or colonies, not 
"species" under any classical definition. The property of potentially (not 
effectively) physically interacting is a property of similar organisms you 
can class together, not a feature exhibited by members of a real material 
biological system. Species, as concepts, can of course be called "natural 
entities" if they conform to some criteria for a "natural classification".

>Relations between close related species make this group of species to be not
>only a number of species that share some characters, but a real object.

If you mean material systems (i.e. you take "relation" as meaning some 
effective physical interaction) I can think of nothing, with the extra 
difficulty that this definition of "a real object" requires an a priori 
definition of "species"... which is the question at stake.

If you don't mean material systems, but classifications (i.e. you take 
"relation" as meaning some similarity), then these species and groups of 
species are "real" as concepts in your mind, anyway you define them. Of 
course your criteria for classifying may make sense in biology (phylogeny, 
hence phylogenetic classification, makes sense in evolutionary biology).

------------------

Suggestion for debates on systematics (= organizing our knowledge in some 
consistent classificatory system): if the term "relation" is used at all, 
always specify whether this term "relation" is to be understood as 
effective interaction in a physically consistent material system (e.g. 
social interactions in social groups, or predator-prey interactions in 
ecosystems, or mating interactions in a reproductive community...), or as 
some notion of similarity between objects being attributed similar 
properties for classificatory needs (e.g. being potentially able at 
socially interacting, preying on one another, or mating together... / 
social classifications, ecological classifications, biological species 
concept classifications...).

Please note that, literally, the "biological species concept" is a concept 
(a thinking process in some brain), not a material system out there. This 
should vail the more for the "phylogenetic lineage concept". Not all 
scientifically meaningful concepts correspond to material systems / objects 
/ individuals...

Best,
Pierre


Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
Téléphone : 02 99 61 81 63
Télécopie : 02 99 61 81 88