Exist sub-species?????

[Byron J. Adams]

Robin said:

>I don't understand the metaphysics of
>species concepts, but I find it hard to envision a "foolproof" method of
>defining species.  There are too many taxa with very low but very real
>genetic exchange. There is a lot of hybridization among members of the avian
>genus _Anas_, and even some with other duck genera.  Are all ducks a single
>species?

I agree with you that there is no foolproof methodology for discovering
species (epistemology).  Species are historical entities that have unique
evolutionary fates, so delimiting species actually requires that we recover
the past and predict the future.  Even if we all agreed on species
ontology, I don't think we can have a great deal of confidence in our
epistemology because: 1)  Accurately predicting the future lies outside the
field of evolutionary biology,  2)  We can only discover the species that
our epistemological methods are capable of recovering.  There may be
species out there that are _real_, but we don't know _how_ to find them.
Thus, every set of operations designed to help us delimit species will fail
at some level (Frost & Kluge, 1994; O'Hara, 1993).  However, some are more
prone to making systematic errors than others (i.e. your problem of the BSC
as inflicted upon ducks), and therefore more likely to screw up research
grounded in the comparative method (Adams, 1998; Frost & Hillis, 1990;
McDade 1995; Cracraft, 1989).

>
>Until I have a chance to read your references, Byron, can you explain these
>other methods of describing variation?  I've heard the declaration before,
>but I haven't found an alternative.

Ghiselin and Hull discuss the notion that species are real, and not
arbitrary (I forgot to mention Ghiselin's recent book on the subject
[1997]), but don't have much to say about "sub-species" pertinent to your
question.  The other methods of describing variability that I referred to
as being more descriptive and less arbitrary are those employed by
population biologists/geneticists.  I am not a pop gen person, but I think
their use of gene frequencies (for example) to describe intraspecific
variation carries more meaningful information than the term "sub-species"
(you seem to argue for this notion yourself, given your previous post about
"sub-species" and gene flow).  Gene frequencies (or the frequencies of
other quantitative traits for that matter), tell us exactly how much
variation exists.  The term "sub-species" only tells us "some kind of
intraspecific variation exists."

Byron

Cracraft, J.  1989.  Speciation and its ontology:  The empirical
consequences of alternative species concepts for understanding patterns and
process of differentiation.  Pp. 28-59 in D. Otte and J. A. Endler, eds.
Speciation and its consequences.  Sunderland, MA: Sinauer.

Frost, D. R., and D. M. Hillis.  1990.  Species in concept and practice:
Herpetological applications.  Herpetologica 46:87-104.

Frost, D. R., and A. G. Kluge.  1994.  A consideration of epistemology in
systematic biology, with special reference to species.  Cladistics
10:259-294.

Ghiselin, M.  1997.  Metaphysics and the origin of species.  SUNY press (I
think, I don't have it handy).

McDade, L. A.  1995.  Species concepts and problems in practice:  insight
from botanical monographs.  Systematic Botany 20:606-622.

O'Hara, R. J.  1993.  Systematic generalization, historical fate, and the
species problem.  Systematic Biology 42:231-246.