Aspects of physical and cognitive development in the infant orang-utan ( Pongo pyqmaeus ) during the first fifteen months of life

Abstract

Several aspects of Orang-utan development were Followed from 7-63 weeks. Housing care and feeding are described. Deciduous, dentition and weight data are recorded, and compared with human and chimpanzee data. Physical development was in advance of Homo sapiens. Motor development was studied by (i) intercoordination of discrete limb/body movements. Ever-more complex behaviour stemmed from accretion or intercoordination of previously seen behaviour, or arose de novo, (ii) General motor development showed a gradual mastery of more complex actions, (iii) Gessel testing of motor development and comparison with other Hominoidea revealed this Orang-utan to be in advance of the human infant. Development was more similar to Gorilla than Chimpanzee, yet was in many respects more extended than the chimp. This is explained by the small Gorilla and Orang subject number, and variability within Primate species. Piagetian cognitive development was tested using a battery of sensorimotor tests. The Orang-utan was in advance of the human infant, except in the Stage VI Stick test, which was never achieved. An alternative to Piaget's explanation of certain sensorimotor behaviour is advanced. There was, generally, a shorter (though complete) sensorimotor period in the Orang. Contrary to human data, there was no synchronicity in achievement of the same stage over different tests. This is explained by the species' different ecological/evolutionary histories. A phylogenetic scale of Piagetian accomplishment is suggested. Visually directed grasping was achieved at 3 1/2 months, before H. sapiens, and after the chimpanzee. Several new grasping behaviours are described, many of Piaget's observations are confirmed, and several are not. Development of hand to mouth, visual following and visual-auditory coordination are charted.