Principios de Taxonomia

62j 3 Is the Biological Species a Class or is it an Individual?
in the beginning and have remained more or less unaltered. Linnaeus imagined the
species truly existed in the external world, independently from our mind (Ereshefsky,
1999). Because of the traits constancy, he did not encounter any difficulties in
assigning organisms to rigid classes. Linnaeus s taxonomic worldview had not yet
been tarnished by the findings of Darwin, who discovered that all traits were subject
to evolution. The theory of evolution implies that all traits are fleeting with the logical
consequence that a rigid allocation of organisms into classes is not possible. There
cannot be classes if all elements undergo continuous change.
Linnaeus s species concept was that of a natural kind, in which members are
characterized by essential traits. To Linnaeus, species were types in the platonic sense
and had an autonomous existence. Behind the sum of individual organisms,
Linnaeus imagined the species to formally exist in the external world and not only
in our mind (Ereshefsky, 1999). Linnaeus considered species and genera as units
existing in nature, and he based his binary nomenclature on this worldview. But only
species and genera were real to him. Higher taxonomic categories, such as families
and orders, were perceived as artificial constructs created by humans only for
pragmatic reasons, even by Linnaeus (Ereshefsky, 1999).
The Linnaean nomenclature is still in use all over the world. This is astonishing
because the Linnaean classification system was only possible under ideological
assumptions that are no longer scientifically accepted. Species essences cannot be
reconciled with the theory of evolution. It would be expected that the Linnaean
species concept would have been overthrown by Darwin s findings. The idea of the
species as a type cannot be reconciled with variation due to evolution. According to
Linnaeus s species concept, logic would force us to conclude that an individual
organism would immediately lose its species affiliation if it loses an essential trait.
Linnaeus assigned the organisms to groups according to the resemblance of their
traits. Individuals with significant similarities were combined to species, but
Linnaeus could not arbitrarily use all traits for his classification. He had to look for
criteria, and some traits were suitable, while others were not. Of course, according
to Linnaeus, the body size of an organism was not a property that could be used for
taxonomic classification, because it was immediately clear to him that body size can
vary. If body size was of taxonomical importance, then slightly larger and slightly
smaller organisms would not be allowed to belong to the same species. Linnaeus also
knew that the blossom coloration of many plants was not a reliable trait either because
it can depend on the plant s age and on the pH of the soil.
Linnaeus s criteria for the suitability or unsuitability of traits were based on
their stability. Linnaeus intuitively chose only a few from a large number of traits for
taxonomical classification, namely those that were not altered much by environmental
influences, such as weather, climate and location. (Here, alteration does not
mean evolution, but environmental change.) Linnaeus classified the stable traits as
taxonomically important and the variable traits as taxonomically unimportant, and he
saw the taxonomist s task as that of distinguishing between essential and nonessential
traits to use only essential traits for species classification.
He classified flowering plants according to the sexual system, that is, by male and
female sexual organ traits, which are closely linked to sexual compatibility. By doing