Principios de Taxonomia

7.6 Why are Paraphyla used Despite their Inconsistency?j201
A through D, the two grandchildren A and D both possess the common trait of having
blond hair, while B and C are dark-haired. According to the principle of close kinship,
the four grandchildren must be assigned to the two groups A þ B and C þ D (the
respective brothers). Applying, by contrast, the principle of trait similarity, however,
the four grandchildren must be assigned to the two groups A þ D (the blond ones)
and B þ C (the dark-haired ones). Nobody would group the organisms in a family
tree in this way, but paraphyletic taxonomy is conducted in this manner.
The principle of a consistent monophyletic grouping was an inherent part of the
fundamental theory of the cladistic system of the German zoologist Willi Hennig
(1966). The charm of the cladistic system is its clear and consistent logic. Hennig
meant to keep subjective criteria out of biological systematics and to model taxonomy
according to criteria that correspond to nomological status and not human wishes for
feasibility. Hennig meant to specify a grouping that is based only on descent and
kinship and is logically conclusive. This outstanding merit of Hennig appears to be
underestimated till recent days.
It is not easy to understand why Ernst Mayr, in contrast, so often defended
paraphyly (Mayr and Ashlock, 1991) because Mayr, on the other hand, was a decisive
advocate of objective science against subjective typology. In retrospect, it is unknowable
why Mayr justified the principles of a paraphyletic classification. Because Mayr
refused typology in systematics, it is mysterious why he was a firm advocate of
paraphyletic systematics. The retention of reptiles as a distinct class was justified by
Mayr by claiming that reptiles look entirely different from birds and, therefore, are
intuitively perceived as an enclosed group and that birds are immediately conceived
as a group separate from this one, even by laypeople in the field of taxonomy (Mayr
and Ashlock, 1991).
Mayr defended paraphyly and distinguished it energetically from pure cladistics.
He even went as far as to accuse Hennig of having a one-sided perspective because
Hennig would ignore the relevance of trait alteration in evolution. Mayr lamented
that Hennig s principle of monophyly had caused painful upheavals in taxonomy
(Mayr, 1982). This is doubtless true, but unavoidable, if the consistence of reasoning
is to be given priority over convenience and pragmatism.
Considering both trait differences and kinship relationships at the same time,
Mayr rejected the three-kingdom system of living beings introduced by Carl Woese,
in which all living beings are classified into bacteria (older name: eubacteria), archaea
(older name: archaebacteria) and eukaryotes (Woese, 1990). Mayr – in contrast –
defended the two-kingdom system, that is, the classification of all organisms into only
prokaryotes and eukaryotes, regardless of the nearly nonexistent kinship of the
bacteria with the archaea (Mayr, 1998). The only reason to classify bacteria and
archaea into a common group is their phenotypically similar appearance, as both
types of organisms are extremely small, have no cell nucleus and do not undergo
mitosis. However, these criteria are subjective human estimates that are not
scientifically founded.
Mayr accused the cladisticist Willi Hennig of turning classification into an
intellectual exercise instead of a means of rediscovering information (Mayr,
1982). This was meant derogatively. This opinion did not appreciate the intellectual