Principios de Taxonomia

22j 2 Why is there a Species Problem?
Sparrows (Passer domesticus) existing on Earth, including their ancestors and descendants
are, or were, subject to evolution. They mutate and are selected. What, then,
is the House Sparrow taxon? Taxa themselves cannot be vague or variable. Classes in
an Aristotelian sense are fixed concepts and cannot therefore be vague or subject to
evolution (Mahner and Bunge, 1997). The class concept species House Sparrow
cannot mutate and be subjected to alteration; if this did take place, the concept would
become a new class. The taxon as a class is to be understood as a human-constructed
template that is temporarily imposed on the reality of organismic diversity. There will
always be non-assignable organisms. The vagueness lies in the fact that the
assignment of existing organisms to a predefined class is precarious, or even
impossible in boundary cases. However, the vagueness of assigning particular
objects to a class does not lie in the fact that the taxonomic class itself is vague.
A taxonomic class is always a theoretical construct. In reality, there are no traits
that, as a necessary and sufficient criterion, bind particular organisms together in a
group while excluding others. Of course, you can find a particular identification trait
that distinguishes a House Sparrow (Passer domesticus) from a Field Sparrow (Passer
montanus). Where is the problem in that? All Field Sparrows have a black spot on the
cheek that House Sparrows do not have, so they look different. But do all Field
Sparrows really have that spot or is it only the vast majority of them?
In attempting to find a set of organisms that belong to a single species due to
being characterized by a particular essential trait, you will always encounter some
organisms that do not exhibit this trait but still belong to this species. This is a farreaching
declarative statement, as it brings the fact that species are not defined by
traits to light. Trait equivalence cannot be an essential requirement for species
membership. The possession of a trait can never be understood in a way that means
that every organism that presents this trait must absolutely belong to this and no
other species, or conversely, that every organism with differences with regard to this
trait must absolutely belong to a different species. In other words, species are not
natural kinds in the philosophical sense (see Chapter 3). If you attempted to
define a species by means of essential traits, you would have to exclude any
organism that displays a different trait from the species just for this reason, yet
this is not done.
The creation of a class is an attempt to match objects of empirical knowledge with
an explanatory template. This template is human constructed, although several
criteria used as components of the template are taken from evolutionary or other
natural characteristics. Taxa in the sense of Linnaeus cannot be subject to evolution.
The idea of a biological class in the Aristotelian and Linnaean sense as existing in
reality and the reality of organisms being subject to evolution, in a state of constant
change with regard to their traits, are incompatible with each other. If taxonomy and
evolution must be united, this can only be done through the concept of the humanconstructed
class. The fixed type in the Platonic sense, which Linnaeus realized in
nature and described in his taxonomy, does not exist and was abandoned by Darwin.
Taxonomists prefer to set aside these and similar implications (Neumann, 2009).
They often act as if they are describing a virtual world with respect to taxa that exists
independent from our mind in the outside world. However, although the Darwinian