A two-year longitudinal study of deferred imitation of object manipulationin a juvenile chimpanzee (Pan troglodytes) and orangutan (Pongo pygmaeus)

Changes in deferred imitation of novel actions on objects were assessed ove r a 2-year period in two enculturated, juvenile great apes (one chimpanzee, Pan troglodytes, and one orangutan, Pongo pygmaeus). Both apes displayed d eferred imitation, and both displayed improvements in deferred imitation ov er the 2-year period, although the magnitude of improvement was greater for the chimpanzee. This is, to our knowledge, the first experimental demonstr ation of longitudinal improvements of deferred imitation in great apes. The results were interpreted as reflecting maturationally paced cognitive diff erences consistent with other cognitive accomplishments in these species, a nd as demonstrating the influence that a species-atypical rearing environme nt can have on cognitive abilities in juvenile great apes. (C) 2000 John Wi ley & Sons, Inc. Dev Psychobiol 37: 229-237, 2000.