On Wed, 21 Jun 1995, Eugene Hunn wrote:
> Joe, David, et al.
>
> I'n not a professional in these matters but my impression is that the
> actual contrast in taxonomic assignments between proponents of these
> alternative species concepts is miniscule with respect to the totality of
> taxonomic categories recognized. The major disagreement seems one of
> semantics: what level of the taxonomic tree is to be called the "species"?
> The terminal contrast level or some level above that of terminal contrast
> at which "gene pool isolation" seems to be well established. There seems
> little real difference of judgment as to the actual SHAPE of the tree.
> Examples such as that of the orioles seem to me minor differences of
> interpretation or weighting of various subsets of the characteristic
> contrasts between branches of the tree.

But the BSC says Bullock's is more closely related to Baltimore than to
other orioles, while a phylogenetic approach to the problem (e.g., the
PSC; but *not just* the PSC) finds that Baltimore is actually more closely
related to Altamira, i.e., that the BSC is dead wrong about this. The
*shapes* of the resulting trees are thus very different. It is not a matter
of quibbling over levels, over whether this branch is a "subspecies" or a
"species," but an argument about what the *branches* are, i.e., is
Bullock's + Baltimore a branch, or is Altamira + Baltimore a branch?
These are mutually exclusive options. It not simply a matter of
differentially weighting evidence, but rather of very different approaches,
and use of different evidence, to address the fundamental question of
how we recognize taxa. The BSC is *based on* hybridization. Hybridization
is *irrelevant* to a phylogeneticist. The BSC, as Joe has noted, does not
attempt to diagnose phylogenetic relationships among species, that is,
the BSC is non-phylogenetic. The PSC (along some other species concepts)
is *based on* phylogenetic principles (despite Cracraft's version of the PSC
being operationally non-phylogenetic; please check out Donoghue's
verison of the PSC for an explicitly phylogenetic one).

> Differences of opinion that one
> might expect to find among proponents of a common theory of
> classification, rather than evidence of contrasting "paradigms." The
> ultimate goal of constructing a taxonomy to reflect as accurately as
> possible the actual phylogenetic history of life seems common to both
> sides of this fence. The assertion that reliance on "gross similarity"
> judgments as an index of phylogenetic "distance" is fundamentally flawed
> seems quite an exaggeration to me, as "gross similarity" judgements, i.e.,
> "classical taxonomics," if done well, do more than count characters (ala
> numerical taxonomy) but rather "intuitively" weigh the power of particular
> types of phenotypic characters as predictors of the whole pattern of
> variation, that is, they involve intuitive judgements of the "information"
> each character entails. I seem to recall reading studies that show that
> taxonomic judgments do not differ significantly among proponents of
> competing theories.

I tried to contrast cladistic vs. overall similarity approaches in a
response today (hopefully) to Dennis's message.

David Wright
dwright at u.washington.edu