Principios de Taxonomia

4.10 The DNA Barcoding Approach – is Taxonomy Nothing more than Phylogenetic Distance?j91
known species by its barcode is a method of diagnosis, not a method for deciding
whether a group of organisms is a species (de Queiroz, 1999; Hull, 1968). The
biologist who identifies a species already presupposes its existence and only pursues
the epistemic goal of how to best recognize it. Barcoding may be a useful tool for the
identification of species, but it cannot be a tool for the discovery of new species.
The sudden success of barcoding is surprising because nothing about it is
scientifically new. The use of DNA for species identification is as old as the technical
ability to sequence the DNA. What is new are the broad claims, the pompous
promises and the public relations. The advocates of barcoding pronounce that
whereas conventional species identification requires experienced and professional
taxonomists, barcode species identification can be performed by trained technicians,
or even machines, because the short DNA sequences can be read routinely by
automatic scanners. Even the task of the field collection of animals, for example,
insects, may be organized with an industrial-scale collection program having the
capacity to deliver large numbers of specimens for analysis. Current sequencing
protocols permit the recovery of barcode sequences in minutes. The use of on-board
barcode reference libraries will facilitate fast species identification in the field (Hebert
and Gregory, 2005).
In 2004, the Consortium for the Barcode of Life (CBOL) was founded. This
consortium now includes more than 120 organizations from 45 nations (www.
barcodinglife.org). The declared goal of the consortium is to build, over the next 20
years, a barcode library for all eukaryotic life. It is expected that the compiled
registration of all species of birds and fishes will require some 0.5 million barcode
records. For the estimated 10 million animal species of the entire animal and plant
kingdom, a comprehensive barcode library will contain approximately 100 million
records. This complete barcode library will be constructed within less than two
decades.
The resistance against the many assurances of this method has predominantly
grown in the circles of the more classically oriented taxonomists (Ebach and
Holdrege, 2005). However, also molecularly oriented taxonomists and biophilosophers
argue against barcoding. One of the most destructive critics against the
barcoding taxonomy has been challenged by the well-known taxonomists Kipling
Will, Brent Mishler and Quentin Wheeler (Will, Mishler, and Wheeler, 2005). They
accuse the Herbert school of returning to an ancient, typological, single-charactersystem
approach. This point of critique is overreacted because it ignores the
fundamental difference between DNA traits and phenotypic traits in taxonomic
classification. DNA traits directly reflect phylogenetic relationships. In most cases,
DNA comparisons are blind to morphological convergence (parallel evolution) and,
therefore, cannot mislead a taxonomic classification that intends to be based on
kinship (Sibley, 1997). Phenotypic traits, in contrast, are controlled by selective
pressure and, therefore, are in many cases the subject of convergent evolution. They
often do not reflect kinship. This distinction makes barcoding taxonomy incomparably
superior to typological taxonomy.
The four objections of J. W. H. Ferguson, however, introducing this section, are still
valid (Ferguson, 2002). They are all arguments against the reliability of the barcoding