A combination of comparative, longitudinal, and experimental approaches was taken to provide evidence for a stone handling tradition in Japanese macaques (Macaca fuscata) and in other macaque species [BOOK CHAPTER]

Our integrative approach to stone handling emphasizes both the product (via the comparative method to assess which differences are observed in the form of behaviors) and the mechanisms (via the longitudinal and experimental methods to determine which specific processes are involved in producing such differences) of the cultural phenomenon. Research on this behavior in both captive and free-ranging groups of monkeys has opened up new ways of addressing the complexities of learning in socially living animals through a deeper understanding of the dynamics of behavioral transmission.

We draw an overall picture of rich cultural diversity in a particular type of object-play behavior in macaques, and suggest that multiple factors should be jointly considered to identify the sources of behavioral variation in animals. We believe our comprehensive dataset can provide valuable empirical information to test predictions and fit models generated from theories about the role of cultural processes in human evolution. In order to understand the mechanisms associated with socially biased learning, future studies need to integrate this methodology with controlled experimentation on captive groups. This will allow us to more clearly address behavioral innovation and the underlying mechanism of diffusion within social groups.

Comparative method

We took a broad inter-troop comparative used a standardized observation procedure to systematically compare the context of occurrence, frequency and form of stone handling in 10 troops of Japanese macaques (nine troops of Macaca fuscata fuscata and one troop of Macaca fuscata yakui). More specifically, we compared four captive troops housed at the Kyoto University Primate Research Institute and Japan Monkey Centre, Inuyama, and six free-ranging provisioned troops living at four geographically isolated field sites in Japan, namely Arashiyama (Kyoto Prefecture), Koshima (Miyazaki Pref.), Shodoshima (Kagawa Pref.), and Takasakiyama (Oita Pref.). Recently, we extended our comparison to five additional field sites in Japan, namely Funakoshiyama (Hyogo Pref.), Katsuyama (Okayama Pref.), Minoo (Osaka Pref.), Miyajima (Hiroshima Pref.), and Tsubaki (Wakayama Pref.). (Leca, Gunst, & Huffman, 2007; see also our study sites in Japan)
We also extended our comparison of stone handling to two other macaque species, namely rhesus macaques, Macaca mulatta (one captive group housed at Kyoto University Primate Research Institute) and long-tailed macaques, Macaca fascicularis (one free-ranging provisioned troop in the Sacred Monkey Forest Sanctuary, Padangtegal, Ubud, Bali, Indonesia).

Longitudinal method

At Arashiyama, Kyoto, we collected longitudinal data on the appearance, early diffusion, and long-term maintenance of stone handling within a free-ranging provisioned group of Japanese macaques and across generations at several points in time over a 30-year period [BOOK CHAPTER] (see also Figure).

Additionally, in the semi-controlled conditions of an outdoor enclosure at the Kyoto University Primate Research Institute, Huffman & Nahallage (2007) focused on 14 mother-infants dyads for 24 months spanning two breeding seasons over a three-year period, and evaluated the influence of early exposure to environmental and social stimuli in the acquisition of stone handling during the first six months of life.

Experimental method

We conducted field experiments at Arashiyama to test the effect of stone handling artefacts (e.g., piles of stones left on the ground by previous stone handlers: see photo) on the subsequent performance of stone handling. Within experimental areas, we set stones according to two specific spatial arrangements, several sets of 12 stones that we gathered into a small pile, and several sets of 12 stones that we randomly scattered on the ground [REPORT]