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Object play in primates is viewed as generally having no immediate functional purpose, limited for the most part to immature individuals. At the proximate level, the occurrence of object play in immatures is regarded as being intrinsically self-rewarding, with the ultimate function of supporting motoneuronal development and the acquisition of skills necessary to prepare them for survival as adults. Stone handling (SH), a solitary object play behaviour occurs, and has been studied, in multiple free-ranging and captive troops of provisioned Japanese macaques, as well as rhesus and long-tailed macaques for over 35 years now. A review of our combined findings from these observations reveal that infants acquire SH in the first 3-4 months of life and exhibit increasingly more complex and varied behavioural patterns with age. The longitudinal data shows that many individuals maintain this activity throughout life, practicing it under relaxed ecological and social conditions. The ultimate function may be bimodal, promoting motor development in young and neural maintenance and regeneration in adult and aging individuals. [ABSTRACT FROM AUTHOR]

This study describes the stone handling (SH) behavior of captive rhesus macaques and compares it with that of a captive troop of Japanese macaques with reference to the relative contributions of phylogeny-driven behavioral propensities, environmental differences and socially facilitated learning to the formation of culture. These systematically collected data demonstrate for the first time that two closely related macaque species might share a common cultural behavior, SH. The rhesus troop displayed SH behavioral patterns that was already described in Japanese macaque troops. The one exception was a new pattern not yet seen in any Japanese macaque troop. Differences in the physical environment of the two study enclosures may be responsible for some of the variation in observed SH behavioral patterns in these two troops. These data support the idea that environmental factors can be important for the formation of cultural variation, when the key materials needed to perform the behavior are present in both habitats (stones). Our results are consistent with the prediction made by Huffman and Hirata [The biology of tradition: Models and evidence. Cambridge: Cambridge University Press. p 267–296] that an interactive triad of phylogenetic, environmental and social factors can be responsible for the formation of cultural variation in primates. Am. J. Primatol. 70:1124–1132, 2008. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

In this study we systematically investigate the mode of acquisition and the developmental process of stone handling, a form of solitary object play, in a captive troop of Japanese macaques (Macaca fuscata) housed in an outdoor enclosure at the Kyoto University Primate Research Institute, Japan. This study was conducted to evaluate two alternative hypotheses regarding the mode of acquisition of stone handling in infants: (1) environmental stimuli (availability of and exposure to stones) and (2) social stimuli (exposure to stone handling individuals). Early exposure to stones in the environment had no significant effect on when infants acquired the behavior. No significant correlations were recognized between the age of stone handling acquisition and number of stones encountered per hour from birth to acquisition, or the time spent in a specific area of the enclosure as a function of the number of available stones therein. However, being exposed to a stone handling model(s) was a social stimulus that had an effect on the age of acquisition, with a significant negative correlation between a mother's stone handling frequency and the age of acquisition by her infant. Infants of non-stone handling mothers acquired the behavior much later than others. Infant peers who acquired stone handling earlier played no significant role as stone handling models. Of the factors tested here, the timing of acquisition depended mainly on the level of proximity to a demonstrator and the frequency at which those available demonstrators performed the behavior. [ABSTRACT FROM AUTHOR]

Throwing is a major behavioral component of hominid evolution. Comparison of this behavior across a broad range of non-human primate species is needed to elucidate the phylogenetic constraints on throwing behavior. In this study of stone-throwing in Japanese macaques, we present a systematic multi-group comparison of the frequency and prevalence of this behavior as well as detailed descriptions and quantitative data on the form, context, and possible social transmission of stone-throwing. Stone-throws were mainly underarm, performed from a tripedal posture, and often accompanied by repeated vertical leaps. We found marked individual hand preferences for throwing, but no consistent group-level handedness. Our results support the hypotheses relating body posture, throwing style, and handedness in throwing by primates. Based on the analysis of the contexts that may elicit the behavior, we postulate that unaimed stone-throwing in Japanese macaques may serve to augment the effect of agonistic displays, and accordingly, can be regarded as spontaneous tool-use. Our findings are consistent with the comparative data using modern non-human primate species to model the structural processes and functional aspects of throwing evolution in early hominids. This study supports the view that tool-use evolves from initially non-functional behaviors, such as stone handling, which is a form of object play. Stone-throwing by Japanese macaques meets several criteria of a behavioral tradition, including group-specificity. This first report of a stone-tool-use tradition in Japanese macaques is of direct relevance to the question of the evolution of stone technology in hominids.

Stone handling (SH) in Japanese macaques, a form of solitary-object play, is newly acquired only by young individuals, and is the first example of a directly nonadaptive behavior that is maintained as a behavioral tradition within free-ranging provisioned social troops. We report here the first systematic investigation of this behavior in a stable captive social troop, the Takahama troop, which is housed in an outdoor enclosure of the Primate Research Institute (PRI), Kyoto University, Japan. This study was conducted to evaluate relevant competing hypotheses regarding the function of object play (e.g., misdirected foraging behavior and motor training) to explain the proximal causes and ultimate function(s) of SH. The "misdirected foraging behavior" hypothesis can be ruled out because of the lack of a clear temporal relationship between feeding and the occurrence of SH in any age class. Age-related differences in SH performance and behavioral patterns were observed, suggesting possible differences in the immediate cause and ultimate function between young and adults. Young individuals engaged in frequent bouts of short duration, involving locomotion and vigorous body actions throughout the day, which is typical for play by young in general. This pattern of behavior is consistent with the motor training hypothesis, which states that play occurs during the development of motor and perceptual skills and is thus potentially critical for neural and cognitive development. This practice is continued by those who acquire it at an early age, with adults engaging in significantly fewer but longer bouts that involve more stationary, complex manipulative patterns, almost exclusively in the late afternoon. We propose that for adults, at the proximate level SH is psychologically relaxing, but ultimately functions to maintain and regenerate neural pathways, and potentially helps to slow down the deterioration of cognitive function associated with advanced age in long-lived provisioned and captive macaques., ((c) 2006 Wiley-Liss, Inc.)