Hennig's enkaptic system.

Hennig's phylogenetic system is characterized by an asymmetry between (sexually reproducing) species that form tokogenetic systems, versus monophyletic taxa that form a phylogenetic system. This was claimed to reflect a conflict between two hierarchies, i.e. the hierarchy of species-lineages splitting and splitting again as opposed to the phylogenetic hierarchy of groups within groups. Some cladists have sought the unification of the phylogenetic system by abandoning the species concept. In contrast, contemporary commentators (Klaus Günther, Walter Zimmermann) characterized Hennig's system as an enkaptic hierarchy. This paper explores the concept of enkapsis, and the way Hennig used it as a basis for the unification of his phylogenetic system.  © The Willi Hennig Society 2009.