M.A. Theses: Paul L. Vasey, 1991

Feeding Ecology and the Rise of Primate Intelligence: With Special Reference to the Orangutan

It is argued that the behaviours traditionally described as hominid "prime movers" in fact constitute part of a shared pongid/hominid behavioural repertoire and are a concomitant by-product and consequence of direct selection for higher order intelligence. Furthermore, in order to understand the origin of the behaviours deemed the "prime movers" of hominid evolution, an examination of pongid intelligence is necessary. Orangutans (Pongo pygmaeus) are the most phylogenetically conservative of all the pongids and, unlike the chimpanzee and the mountain gorilla, they have never radiated out of the climax tropical forest where pongid intelligence initially evolved. Consequently, it is argued that orangutans should be the great ape under consideration during any investigation of pongid intelligence.

Primatologists have long debated the relative importance of food acquisition problems versus social problems as selective mechanisms influencing the evolution of primate intelligence. Unlike all other anthropoid primates, wild orangutans are characterized by a unique semi-solitary adaptation with correspondingly infrequent social interaction. As such, literature pertaining to orangutan social intelligence has, to date, been scant and is unamenable to review. Therefore, this thesis provides a preliminary investigation into the role feeding ecology played as a selective mechanism favouring orangutan intelligence. In the process of doing so, it is demonstrated that the extreme complexity of orangutan feeding ecology necessitates that they constantly process large amounts of environmental information. This is demonstrated throughout all phases of the food acquisition process including: food recognition, searching/foraging and handling/processing. Over time, natural selection would have favoured the more intelligent orangutan individuals who were capable of processing the large amounts of complex information associated with feeding problems they encountered. As such, feeding ecology probably played a large role as a selective mechanism favouring the rise of orangutan intelligence.