The Anatolian branch of Indo-European is characterized by a split-ergative case-marking system in which neuters inflect ergatively and common-gender nouns inflect accusatively; its ergative case originated via the reanalysis of an unproductive neuter instrumental marker in null-subject transitive clauses. A development from instrumental to ergative also occurred in the prehistory of the Gorokan languages of Papua New Guinea, and it is suggested that this process is a general mechanism for the development of split ergativity of this type. The well-known NP hierarchy discovered by Silverstein receives a natural interpretation as a hierarchy of instrumentality.