Hybrids and genera

[Chris J. Durden]

At 11:50 AM 11/7/2002 -0800, you wrote:
>Howdy Lepers,
>
>Let's also not forget that the ability to interbreed is a symplesiomorphy 
>- a shared
>primitive feature, that is not relevant to the empirical discovery of 
>species and
>other taxa.

Yes the inability to interbreed may certainly be a recently acquired 
character that prevents closely related species from interbreeding, but it 
also may be due to gross physiological incompatibility accumulated over a 
long time in lineages that have not recently interbred.


>Also, taxonomy could never fully "reflect phylogeny," because if we had 
>access to the
>complete history of phylogeny, there would be only one taxon ("life"), 
>with a bunch
>of polymorphic features that have changed in frequency over time.

I disagree. In the fossil record I see clear evidence of punctuated 
equilibria as the norm. Our taxonomy at the species level is labelling 
these equilibria.

>The very process
>of conceptualizing more or less inclusive groups of organisms as species, 
>genera,
>etc. imposes discrete boundaries among the entities identified, while the 
>process of
>lineage splitting has no single ontological point at which the lineages become
>divided.  Kind of like, when do the Rio Negro and the Rio Solimo~es become 
>the Amazon
>- at the point when the waters first meet, or the point where they are 
>completely
>mixed (two very separate places)?  Are they one river, or three?  A 
>taxonomist would
>say three, a lineage-minded person would say one.

Sorry. I would have to run the rivers upstream to find an analogy with the 
tree of life.


>Taxonomy is not intended to provide an accurate map of the evolutionary 
>process, and
>its logical and empirical basis is at odds with the notion that taxa blend 
>into one
>another.  Rather, it is an epistemological artifice that treats groups of 
>organisms
>that are hypothesized to represent parts of lineages as though they were 
>static
>things with fixed character states in order to make powerful predictive 
>statements
>about relationships among them.

I really disagree with this at the species level.

>   Sort of a calculus of biodiversity.
>
>Last, I disagree with the implication that there is an "objective biological
>definition" of species.  Given that there are multiple, competing 
>definitions in the
>current literature, it is quite clear that the definition of species is a 
>semantic
>rather than an empirical or logical problem.

No. I think that there are several valid species concepts each of which may 
operate under local conditions. A linear gradualist could not be concerned 
with species concepts as there would be no switch from one species to the 
next. A punctual systematist on the other hand will place the species 
boundary at the punctuation. Unfortunately punctual systematists are too 
often perceived as racists and that is not politically correct. 
Unfortunately I see the possibility of more than science at work here.

> From my perspective, species are really
>no different than genera or families, which also "can be thought of as 
>lineages"
>(more inclusive ones), if one desires to do so, after they have been 
>recognized on
>the basis of fixed character state differences.  Others probably have a 
>different
>perspective.

Yes. I am not ready to accept neatly punctuated genera. I think they are 
more the statistical refuse of irregular extinction. I do not think the 
problem is semantic but one of familiarity with the fossil record, versus 
neo-Darwinian theory that insists on gradual and constant change rather 
than the stability of fine tuned selective interaction with a finite 
complex habitat..
..................Chris Durden

>  That's the great thing about semantic problems.
>
>- Andy Brower, Oregon State U.



 
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