How to chop up a tree

Over the past 50 years it has been pointed out with increasing frequency that our traditional Linnaean system of classification and nomenclature is incompatible with a phylogenetic system which recognises only monophyletic groups. Dividing up an evolutionary tree into mutually exclusive families, genera, and species which are all monophyletic is a logical impossibility. Darwin had emphasised that evolution is descent with modification. The rise of cladistic thinking in the last 40 years has promoted an obsession with monophyletic taxa, with classification based solely on descent at the expense of modification. Despite strong psychological pressures on a generation of biologists who have been brought up on the dogma of monophyly, the Hennigian view of classification is now increasingly seen as illogical and out­of­date. Some are therefore supporting the PhyloCode , which is based on a logical position but is impractical for general purpose classification and communication since it recognises no ranks and abandons binomials. Others still cling to the nonsensical concept of recognising families, genera, species, etc., and all being monophyletic. Linnaean classification is the optimal tool for cataloguing biodiversity and will inevitably be maintained, but this requires recognition of paraphyletic taxa and some rethinking of the practice and purposes of biological classification. Those who want a classification to recognise only monophyletic taxa should adopt an appropriate nomenclatural system such as is offered by the PhyloCode . To do otherwise will tend to lead to bad taxonomy.