Principios de Taxonomia

7.12 The Phylocode j213
Thus, if the ant genus Formica contains almost 300 species worldwide, but the bird
genus Aythya (diving ducks) only includes 12 species, then via this comparison, the
impression is conveyed that there is an objective difference between ants and ducks
with regard to biodiversity, as if the ant genera were richer in species. However, this
comparison reflects nothing more than that myrmecologists attribute species to
genera more generously than do ornithologists. The genus category in different
animal or plant groups does not stand on the same hierarchical level. The statement
that within a particular hectare of rain forest, there are 200 genera of insects, but only
20 genera of birds thus becomes meaningless.
Yet Linnaean nomenclature is also impractical. New species are continually
discovered, and existing genera therefore progressively become too large. It is
impractical to work with genera that contain hundreds of species. For example, the
butterfly genus Papilio (Swallowtails) established by Linnaeus in 1758 would contain
approximately 325 species today if it had not been successively subdivided into newly
established genera in post-Linnaean times (http://www.insects-online.de/frames/
papilio.htm). Today, a distinction is made between nine genera of the former genus
Papilio, such that each genus only contains 35 species on average.
Additionally, new insights regarding kinship relations appear continually, and
certain species therefore must be withdrawn from one genus and categorized into
another. It proves hindering that the designation of a species also contains the genus
name because with every reclassification into a new genus, the name of the species
has to be changed. Every name change creates communication difficulties. Among
lepidopterologists (experts on butterflies), this has led, for example, to the situation
that in daily practice, the currently valid genus names often are not known by field
biologists and are no longer used; instead, only the species names are mentioned in
everyday communications.
For these reasons, the advocates of the phylocode consider binary nomenclature
and the Linnaean taxon hierarchy to be out-dated (Cantino et al., 1999). The
Linnaean system does not do justice to the monophyletic principle of classification
because hierarchical ranks do not exist in a cladistical system. Furthermore, the
Linnaean names are not especially practical, as they are too short lived.
As an alternative, the phylocode has been proposed with the aim of replacing
Linnaean taxonomy (http://phylonames.org/; Wilson, 1999). The principle of the
phylocode is a taxonomic nomenclature that names the system of living beings by
consistently using monophyletic clades. The phylocode separates the entire phylogenetic
tree of life into comprehensive and less comprehensive monophyla and
assigns them names that no longer contain a taxonomic ranking (Cantino et al.,
1999). The phylocode assigns taxonomic names according to phylogenetic connections
without consideration of hierarchical levels, such as genus, family, order and
class. Instead, a taxon name is only assigned to bifurcating clades according to the
principle of monophyly, whereby it is crucial to combine all branches that trace back
to a most recent common ancestor. Although at lower levels, there are clearly clades
containing only a few bifurcations, whereas at higher levels, there are superordinate
clades consisting of many bifurcations, no hierarchical levels between clades are
acknowledged. The increments between clades are continuous, rather than stepwise.