species as individuals

John Grehan jrg13 at psu.edu
Thu Jun 10 02:14:36 EDT 1999

>I would argue that species are probably rarely actually treatable as

James K. Adams

Species  can be treated as individuals in all cases if the approach involves
delineation of membership according to a diagnosis of biological and
geographic characters rather than some definition of essential
character that is not contingent upon a particualr place or time.

What probably really *does* respresent  evolutionary
>individuals are *populations*.  I don't truly believe that a
>widespread species has enough gene flow so that if major climatic
>change takes place all populations will respond all in the same
>fashion, as a single unit.

As I understand the concept of phylogenetic or evolutionary individual, the
relevant feature is shared history and absence of essence. Thus
there is no necessary implication of the members acting in
concert (which would be essentialism). If one allows species to be
polytipic this
would certainly not be necessary.

 It is different *populations* of a
>species that are potentially under different selective pressures, and
>only if the species is represented by one population only will the
>*species* respond as an individual.

Again, here the concept of individual is linked to a concerted response.
My conception of "individual" is shared history. Thus, over the
geographic range of a widespread species, there may be differentiation
involving natural selection or biased gene conversion that does not
involve the entire species. With that process there is a change in the
characters of some members of the species and not others. At that point
(or more properly a series of points in space and time) one individual
(as a lineage) becomes two or more. It would seem that Lepidotpera
provide inumerable examples of the difficulty of applying distinct
taxonomic categories to a process that is continuous. So molecular
genetics or not, the process will continue to confound some attempts
to categorize. Individuals escape complete enclosure.

Just a perspective.

John Grehan

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