Principios de Taxonomia

90j 4 What are Traits in Taxonomy?
Only a few genes are adapted to the local environmental conditions; therefore, the
phenotypic uniformity of the traits of the individuals within a species is not based on
genome uniformity. Instead, only a tiny fraction of the genome gives a species its
species-specific appearance (Coyne and Orr, 1999). Very few genes are involved in the
adaptation of a species to its ecological environment and very few genes are involved
in correct partner choice. Only the few genes for local adaptation and partner choice
constitute the similarity of the individuals within a species. The primary difference
between species is not due to the overall genetic difference that arises very slowly and
accidentally over the course of long isolation times. The majority of the genome is not
involved in maintaining the identity of a species. However, this portion of the genome
contains precisely those sequences that are used as a barcode. These sequences are
the ones that are subject to the molecular clock, and they become increasingly
different over the course of time. Differences with regard to the barcode do not
provide information about a species-specific adaptation to a specific ecosystem,
which maintains the distinctive uniform appearance of the individuals of a species.
The species concept of the barcoders is based on some outdated assumptions that
date back to the beliefs of the twentieth century. This concept is based on the belief
that speciation always occurs under the conditions of geographic separation and,
therefore, usually requires a long time, during which the genome would have
sufficient time to diverge. Recent discoveries on speciation processes, however,
reveal more and more examples of sympatric speciation, and sympatric speciation
has been shown to be a relatively fast process in several cases (Dieckmann et al.,
2005). Sympatric speciation refers to sexual selection and/or adaptive habitat niching
that separates two groups of organisms into different species at the same location.
The erection of crossing barriers in the case of sympatric speciation is subject to a
high selective pressure to prevent the remixing of the separating populations.
Sympatric speciation is the opposite of the allopatric paradigm of speciation because
in sympatric speciation, selection is the driving force, whereas allopatric speciation
occurs by pure coincidence and proceeds contingently without selection pressure as
the driving force of speciation. Allopatric speciation is solely the result of genetic drift
and, therefore, it is a slow process (Lande, 1980). Sympatric speciation, in contrast,
can immediately split a gene pool, an action which can occur in a few generations.
After only a few generations, the time of separation of the newly originated species is
not sufficient for the evolution of barcode differences between the new species.
Another main criticism against barcoding concerns the confusion of two different
ontological intentions. A diagnosis is not the same as a definition (see Section It is
one thing to identify a species but another to define what a species is in Chapter 2). It
is one task to check whether an arbitrarily chosen organism is a member of a specific
species but another task to call a newly discovered group of organisms a new species
(Sterelny and Griffiths, 1999). The mixing of the criteria used to diagnose an already
established species with the aim of defining a new species is a misconception that
apparently cannot be eradicated from taxonomy. The ontological status of a real
species and the teleological approach, saying by which criteria a species can be
recognized (identification traits), are two utterly different intentions with which to
approach nature (Mayden, 1997; Sterelny and Griffiths, 1999). Identifying an already