Principios de Taxonomia

70j 4 What are Traits in Taxonomy?
because it matches with both parent species in regard to half of all traits (T€opfer,
2007) (Chapter 6). This statement is scientifically worthless because the concept
half results from a purely subjective selection of traits.
There are no fixed rules for trait-based taxon membership (Christoffersen, 1995).
The selection is based on intuition, not on rules. This awareness opens the door for
different taxonomists to use different traits to execute taxonomic classification.
However, the choice of different traits for taxonomic classification might lead to
different taxon entities. A flashback on the history of taxonomy shows that in different
epochs different traits were used for taxonomic classification, creating taxa that are
today no longer acknowledged as such. For example, bats were included in the taxon
of birds from the antique naturalist Plinius to the Swiss biologist and bird painter
Konrad Gessner in the sixteenth century because the property of having wings had
been considered as an essential trait for being a member of the birds. Another
example is the screamers of South America (genus Anhima). These were formerly
considered to belong to the Galliformes (the order of pheasants, hens and quails)
because they do not possess webbed feet. In fact, they belong to the Anseriformes (the
order of ducks, geese and swans) because it has been discovered that the property of
having webbed feet is not an essential trait for being a member of the Anseriformes
(Chen, 2002).
The realization that, for many taxonomical purposes, traits are subjectively selected
should not be misunderstood to indicate that the selection was arbitrary. They are not.
Trait selection is subjective but not arbitrary because there is a distinction between
taxonomically useful and less useful traits. Linnaeus already distinguished between
the more variable and more constant traits and only chose the latter for his
taxonomical classification (Chapter 3). Ernst Mayr also realized this. However, he
justified his approach to the rating of traits by saying that with experienced
taxonomists it was founded on considerable knowledge and experience (Mayr,
1982). Thus, he did not bring a rule into the world because he completely appealed to
intuition. Mayr viewed this approach as a testament to taxonomy being fundamentally
different than physics and other natural sciences. In doing so, he did not
consider that with this analysis he labeled taxonomy and other disciplines of
organismal biology as soft science, potentially harming organismal biology (Chapter
2). This is not to be taken lightly because in the last half century a trench has
developed between the biological disciplines labeled as classical and the biological
disciplines labeled as molecular, although these vocabularies do not resolve the
underlying problem (Roush, 1997; Pigliucci, 2002).
In the 1930s, the well-known geneticist Alfred Sturtevant tried to develop a method
with which somebody without any experience at all, even a non-biologist, would be
able to divide species into natural groups. The essential element of such an
approach would be the development of procedures with which the degree of
resemblance could be quantified so that subjective taxonomy would be transformed
into an objective, numerical taxonomy (Mayr, 1982). However, Sturtevant failed and
did not realize his intention.
In recent times, numerical, computer-based phenetics has attempted this (Sneath
and Sokal, 1973). Phenetics classifies organisms by only their trait similarities.