Hybrids and genera
Chris J. Durden
drdn at mail.utexas.edu
Fri Nov 8 00:07:15 EST 2002
At 11:50 AM 11/7/2002 -0800, you wrote:
>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
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
>The very process
>of conceptualizing more or less inclusive groups of organisms as species,
>etc. imposes discrete boundaries among the entities identified, while the
>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
>- at the point when the waters first meet, or the point where they are
>mixed (two very separate places)? Are they one river, or three? A
>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
>its logical and empirical basis is at odds with the notion that taxa blend
>another. Rather, it is an epistemological artifice that treats groups of
>that are hypothesized to represent parts of lineages as though they were
>things with fixed character states in order to make powerful predictive
>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
>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
>(more inclusive ones), if one desires to do so, after they have been
>the basis of fixed character state differences. Others probably have a
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
> That's the great thing about semantic problems.
>- Andy Brower, Oregon State U.
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