Principios de Taxonomia

202j 7 The Cohesion of Organisms Through Genealogical Lineage (Cladistics)
capacity of Hennig s theory. In taxonomy, the incompatibility of a purely pragmatic
goal with consistent theoretical thinking cannot be expressed more clearly. The
author of this book has the opposite opinion. He sees a greater degree of scientific
merit in mental consistency.
However, the classification of organisms according to consistent monophyletic
principles would clearly lead to a system that is significantly more difficult to manage
than the current system, and the system of the kingdom of animals and plants would
have to be completely rearranged in a new way. This would be highly inconvenient.
However, in taxonomy logical consistency and manageability are incompatible (Hull,
1997), which is the reason that two different taxonomies are probably needed
(Chapter 2).
The mixture of trait-oriented classification principles with cladistic classification
principles in many individual cases leads to the designation of biological taxa that,
although comfortably manageable, cannot be theoretically justified. In such a case, it
does not help to appeal to the claim that evolution consists of both trait alterations and
bifurcations as a justification (Mayr, 1982). The blending of trait-oriented classification
principles with cladistic classification principles leads to artificial groupings
that reflect nothing other than human convenience. This cannot be called science. A
taxonomy based on the assessment of traits, as defended by Mayr to justify paraphyly
(Mayr and Ashlock, 1991), cannot be false in principle; therefore, it is not falsifiable
and accordingly is not a scientific proposition (Hull and Ruse, 2007).
7.7
Monophyly and Paraphyly on Different Hierarchical Levels
The principle of monophyly or paraphyly can be applied to phylogenetic trees at all
hierarchical levels of biological organization, including taxon trees, organismal trees,
cell trees or genome trees. A taxon group, an organism group, a cell group or an allele
group can be monophyletic or paraphyletic. However, the different hierarchical levels
should never be mixed with each other or combined into a common system.
Researchers should always explicitly clarified what is meant if a phylogenetic tree
is presented. Phylogenetic correlations at the DNA level (gene trees) do not necessarily
allow reliable conclusions to de drawn regarding the same phylogenetic
correlations at the taxon level (species trees).
The problem lies in the fact that phylogenetic trees at different hierarchical levels
are not congruent with each other. Each of the different hierarchical levels, whether
taxa, organisms, cells or genomes, has its own phylogenetic tree. It can be faulty to
make an inference from the phylogenetic tree of a gene sequence regarding the
phylogenetic tree of the respective species. Likewise, it can be faulty to make an
inference from the phylogenetic tree of a cell genealogy with respect to the
phylogenetic tree of the organisms emerging from it (Lee and Skinner, 2008).
There is a simple reason for this situation, which is demonstrated in Figure 7.8.
From the mother object a, the two daughter objects b and c descend. From b and c, the
F2 descendants d, e, f and g arise. This scheme of a descent pattern can be applied to