BSC

[Biology at]

The BSC does not need to be redefined as "biological species concept for
sexually reproducing organisms". This is a tautology, something like ?widow
woman?. The BSC already defines species based on ?sexual reproduction? and
?reproductive isolation?. While I agree with Gurcharan that the Evolutionary SC
is able to identify SOME asexually reproducing species, I think there is no
universally applicable concept for each and every borderline case. Templeton?s
Cohesion SC seems to cover most, if not all, problematical ?species? but it
remains a theoretical model that does not provide any tools or techniques to
measure demographic exchangeability in order to unequivocally distinguish
species.
 If an operational concept is wanted for identification purposes of asexual
species and other problematical cases, the best solution is probably the
combination of several testable and verifiable concepts (e.g., BSC, PSC +
Recognition SC). But isn?t this already a concept of its own: the Pluralistic SC
introduced by Mishler and others?
Stefan
___________________________________________________________
>Interesting to see what problems the "biological species concept" is
>producing. Just to throw the debate open a little more; the problems
>encountered in zoology and botany are those caused by not knowing where to
>draw the line with sexually breeding "species". Of course the definition is
>loaded in favour of sexual reproduction. One often hears that organisms
>which do not breed sexually do not have species, because they do not fit
>the "biological species concept". The problem is that asexually reproducing
>organsims seem to have been very successful in evolution, in fact a quick
>glance at molecular estimates of evolution would suggest that sexual
>reproduction is only reserved for a rather small section of organisms.
>Perhaps one must come to terms with the fact that the "biological species
>concept" is a "biological species concept for sexually reproducing
>organisms", and that there should be other concepts for dealing with the
>asexual organisms. After all if "speciation" is one of the first steps in
>the divergence of one "species" into two or more "species" which is part
>evolution, then asexual organisms also evolve and must be subject to the
>"asexual equivalent of (sexual) speciation".
>Brian Tindall

The problems of both sexually reproducing  and asexually reproducing
species are best addressed by "Evolutionary species concept" which describes
species as "single lineage of ancestor-descendent populations which
maintains its identity from other such lineages and which has its own
evolutionary tendencies  and biological fate". This concept takes care of
both sexually and asexually reproducing organisms. What is important that
species should be able to perpetuate itself through generations, and
maintain its identity from other species. In sexually reproducing species
reproductive isolation is essential, whereas in asexually reproducing
organisms continuing through generations is essential plus they should have
sufficient characters to distinguish (recognition systems).

Gurcharan Singh
************************************************************