Hybrids and genera

Andrew Brower browera at science.oregonstate.edu
Thu Nov 7 14:50:40 EST 2002

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.

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.  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.

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.  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.  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.  That's the great thing about semantic problems.

- Andy Brower, Oregon State U.

Jeff Oliver wrote:

> Let's not forget that 'genera' are concepts, and don't really have any objective
> biological definition (no 'Biological Genus Concept' or 'Phylogenetic Genus
> Concept').  'Species', despite all the different definitions given in the
> literature, can be thought of as lineages.  If taxonomy is to reflect phylogeny,
> then taxa with contemporary gene flow should definitely be considered congeneric,
> and potentially conspecific (depending on levels of gene flow).  Of course,
> determining contemporary gene flow is another ball of wax...
> Jeff Oliver
> University of Arizona
> jcoliver at email.arizona.edu
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