The evolution of technical intelligence: perspectives from the Hylobatidae

Gibbons and siamangs (Hylobatidae), taxonomically apes, have been largely ignored in cognitive research. However, given their unique phylogenetic position, representing an intermediary divergence between monkeys and great apes, and diversity of extant genera, they are ideally placed to study the evolution of cognitive abilities in the hominoid line. This chapter presents a brief review of what is known about the use of objects as tools in the small apes. It also evaluates their understanding of the physical world through object manipulation and tool-use, predominantly based on studies conducted over the last 6 years on gibbons and siamangs housed at the Gibbon Conservation Center (GCC) in California. In a raking-in task, gibbons evidenced potentially insightful comprehension of object relationships when tool and goal were presented in direct alignment. Once the necessary relationships between tool and goal object were not physically situated in the task layout, gibbons performed poorly. This is unexpected given the taxonomic position of the Hylobatidae and their level of cortical development. However, given their unique socio-ecological adaptations, this may reflect differences in cognitive organisation rather than deficiencies.