The what, why and how of primate taxonomy

Taxonomy has a well-defined role, which is much more than simply stamp-collecting and pigeon-holing. Species are the units of classification, biogeography and conservation; as such they must be defined as objectively as possible. The biological species concept, still widely used in biology, though predominantly by non-taxonomists and all too often misunderstood, is a process-based concept, which offers no criterion for the classification of allopatric populations beyond inference and hypothesis. The phylogenetic species concept - a pattern-based concept - is as nearly objective as we are likely to get. Amount of difference is not a criterion for recognizing species. It is not possible to insist on monophyly at the specific level, but it is mandatory for the higher categories ( genus, family, etc.). The rank we assign to a given supraspecific category should be determined by its time depth.