Principios de Taxonomia

3.9 The Linnaean System is Based on Fundamental Assumptions that are Irreconcilablej61
resemblance. An example for a polythetic class from another field would be a disease
that is characterized by a number of symptoms. Not all symptoms have to appear
simultaneously; in each single patient, a single symptom can be absent, but the
patient still has this specific disease.
Thus, if a biological species can be defined at all by traits, then it can only occur in
the sense of statistically covarying traits (Hull, 1997). One particular Northern Pintail
(Anas acuta) is not a Northern Pintail because it necessarily has a pointed tail but
because it also has other traits and behavior patterns that delimit it from, for example,
the Mallard (Anas platyrhynchos). The common possession of several similar traits
justifies the classification of many individual organisms as the species Northern
Pintail and distinguishes the Northern Pintail from the Mallard.
However, although a polythetic class is clearly based on a similarity of traits, no
single trait is essential for class affiliation. Therefore, the polythetic class cannot be a
natural kind. No single factor determines whether a particular organism belongs to
this and no other class. No single trait is necessary and sufficient for class affiliation.
Class cohesion is not given due to natural laws. On its own, family resemblance
does not support a nomological generalization and is thus something entirely
different than the natural kind of a chemical element due to the number of protons
of its atoms.
3.9
The Linnaean System is Based on Fundamental Assumptions that are Irreconcilable
with a Contemporary Worldview of Science
From Aristotle to Linnaeus to certain modern authors, the idea of the biological
species has always been that of a class. Organismic diversity was grouped according
to trait similarities. The best-known representative of the viewpoint that the biological
species is a class is Linnaeus, who grouped the diversity of living beings into a system
by combining organisms with similar traits into taxa. Linnaeus had the conviction
that these taxa would really exist in the world, and he saw his task as that of
discovering them. Thus, Linnaeus was in no way a pure utilitarian or pragmatist
whose primary concern was to divide organismal diversity into manageable groups.
In contrast to modern pheneticists (Chapter 4), he was convinced he was discovering
reality. Linnaeus believed in the existence of groups. He perceived the biological
species as a real unit and not as a template created by humans into which the existing
diversity was allocated. With his viewpoint, Linnaeus followed Aristotle s traditional
conception. It is important to note that there is a fundamental difference between the
Linnaean species concept and today s phenetic species concept. Linnaeus believed in
the existence of species as natural kinds, while pheneticists consider their (likewise)
trait-oriented classification to be merely a pragmatic concept, not something truly
existing.
Linnaeus believed in traits as being essential because he believed that these traits
would be sufficient and necessary for a species membership in a class. The Linnaean
way of thinking assumed a divine act of creation with which the species were created