Ornithology, Evolution, and Philosophy 123

324 10 Systematics and Classification
logenetic analysis and phylogenetic classification; the term “cladistic” was coined
by Mayr). Taxa are based on the joint possession of derived characters (synapomorphies):
“Hennig deserves great credit for having fully developed the principles
of cladistic analysis, especially the clear recognition of the importance of synapomorphies
for the construction of branching sequences.” This step of the analysis
is important for the cladist, the evolutionary systematist, and the historical biogeographer.
There is no argument over the value of cladistic analysis and the final
product, the cladistic diagram or branching pattern for evolutionary studies. Arguments
arise over the construction of a classification from the cladogram (Mayr
1974g). Hennig (l.c.) proposed simply to translate the cladogram into a hierarchical
classification reflecting only the recency of common descent (“branching point”),
whereas evolutionary classification as recommended by Mayr, Simpson and others
reflects common descent and evolutionary divergence. Mayr’s objections to
cladistic classifications may be summarized as follows (Mayr and Bock 2002h):
(1) Relationship means to the cladist only kinship in a strictly genealogical sense
rather than inferred amount of shared genotype or gene content;
(2) Monophyly was, since Haeckel, a distinctly “retrospective” term referring to
the nearest relatives inferred to have descended from the same stem species.
Hennig added the following qualification: “[…] and which includes all species
descended from this stem species.” Monophyly became a “prospective” criterion
and groups which do not include all its descendent species became “paraphyletic.”
Ashlock (1972) discussed how different Hennigian phylogeny is
from Haeckelian phylogeny universally employed by traditional taxonomists.
The term monophyly refers to Haeckelian phylogeny and Ashlock introduced
the term holophyly for Hennigian phylogeny.
(3) The neglect of the dual nature of evolutionary change: All phylogenetic splits
have equal weight for the cladist, just as all characters have equal weight for the
pheneticist. Autapomorphies or anagenetic invasion of new adaptive zones,
the existence of minor or major “grades,” and mosaic evolution are all ignored
in the construction of a Hennigian ordering system. The cladist acts as if he
assumed that all lineages diverge in an equivalent manner and that genealogical
distance corresponds to genetic distance. The reptiles, a “paraphyletic” group,
represent a well-defined “grade” between the amphibian level and that of the
derivates of reptiles: birds and mammals.
(4) A purely formalistic species definition: A cladistic species is simply the distance
between two branching points on a phylogenetic tree of related species. This
is both unbiological and unrealistic. If one “branch” has not changed, it is
the stem species which has continued and from which another species has
branched (or “budded”) off. Also, a simple dichotomy into two daughter
species is not the rule, as shown by superspecies often consisting of more than
two allospecies.
(5) Themodeoforiginofhighertaxa:Theevolutionofanewhighertaxonis
correlated with the invasion of new adaptive zones by existing species and
has nothing to do with a splitting event (speciation). It is the later process