Units of phylocladistic and non-Linnaean classification - With a discussion of species, LITUs and complementarity – Niels Bohr Institute - University of Copenhagen

Niels Bohr Institute > Calendar > 2009 > Lecture on philosophy ...

Units of phylocladistic and non-Linnaean classification - With a discussion of species, LITUs and complementarity

The traditional Linnaean system and its present rules of nomenclature are in direct conflict with modern phylogenetic systematics based on cladistic methods and here called 'phylocladistics'. Especially the absolute ranks (formal categories of which Species, Genus and Family are obligatory) are at odds with modern phylogenetic thinking, and should be abandonned completely. The basal units of the system, the terminal taxa - traditionally called 'species' - are discussed, and a replacement is suggested called LITU (Least Inclusive Taxonomic Unit). The role of the many different species concepts is discussed, and it is suggested that most of them are different aspects of the most general species concept, the 'evolutionary species concept' as based on a general lineage concept.


The several species definitions are seen as different operational criteria of being a species, and it is argued - following a suggestion by de Queiroz - that these many aspects of species have a 'complementary' relation to each other, probably in analogy with complementarity as employed in the 'Copenhagen interpretation' of quantum physics by Niels Bohr. The latter complementarity is associated with the wave-like versus particle-like aspect of the behaviour of electrons under different observational conditions, and the two aspects are mutually exclusive, but both necessary and sufficient for a complete description of the experimental observations. Bohr was convinced that complementary descriptions were valid in all sciences, in fact, a central feature of all human communication, and he most often used biology and psychology as examples.


The possibility of using complementarity viewpoints in biology is explored, particularly concerning 'species' and phylogeny. It is suggested that there is transition from a more imprecise and 'vague' use of complementarity in daily language (more than two aspects, not mutually exclusive, no claim of 'completeness') via some also less restrictive employments in biology (no completeness, some overlapping aspects), to some other situations in biology approaching the conditions in physics, and finally to the very restrictive situation in quantum mechanics with well defined experimental set up and measurements demanding dualistic, mutually exclusive complementarity for a complete description. So Bohr was at least partly right, and this complementarity viewpoint should be scrutinized more closely in biology and other sciences.

A hierarchic, non-Linnaean, phylogenetic system based on cladistic methodology, a 'phylocladistic' system, is suggested with taxa free of formal rank categories, but in stead attributed ages, with LITUs with a single name as terminal taxa, as anagenetic stages and sometimes as ancestors, and with many novel, but simple conventions for a precise transformation from a phylogenetic tree. Such system is based mainly, but not exclusively, on taxa being monophyletic clades, and is therefore called a 'cladification' as opposed to a 'classification' of classes. The status of LITUs, species and clades as individuals and/or 'natural kinds' is discussed.



You are welcome to contact Niels Bonde for additional background material.