Fragility of traditions: The disturbance hypothesis for the loss of local traditions in orangutans

Chimpanzees and orangutans have increasingly well documented local traditions involving learned skillful behaviors, often involving tools, which vary from place to place and are maintained by social transmission. These local traditions are most likely the antecedents of human culture. The complexity of local traditions is thought largely to be a function of the cumulative frequency of opportunities for social learning, and hence of the extent of tolerant gregarious foraging. Data on orangutans and chimpanzees are consistent with this hypothesis. This reliance on continued social transmission makes local traditions vulnerable to interruptions of transmission. I examine the disturbance hypothesis, which suggests that local extinction, hunting pressure, selective logging, and habitat loss in general affect the key parameters of the transmission process-innovation, diffusion, horizontal transmission-and hence will significantly impoverish the repertoire of complex skills for subsistence. Given current trends in orangutan habitats, serious erosion of local traditions is taking place. I also speculate that disturbance in the past has led to a significant loss of orangutan traditions.