The transformation phase of the stone handling tradition is defined as the late period in which long-enduring practice and acquired familiarity with the behavior and the stones are gained through the integration of stone handling with other daily activities (Huffman & Quiatt 1986; Huffman & Hirata 2003). Longitudinal data over a 15-year period of continued observation at Arashiyama and Takasakiyama showed that the monkeys have almost doubled the size of their stone handling repertoire and largely diversified the contexts in which stone handling activity was practiced. [BOOK CHAPTER]

The late emergence of stone handling patterns not recorded before involved complex manipulative actions, such as combine with object, rub/put on fur, stone groom, and wash revealed an increased diversity in the combination of stones with other objects or substrates. The appearance of variants combining the use of hands and mouth (e.g., carry in mouth, move inside mouth, bite, and lick) suggested that stone handling had become more integrated with foraging and feeding activities, particularly in free-ranging troops where food provisioning strongly influenced the activity budget [REPORT]

In human material culture, the “ratchet effect” is referred to as the cumulative modifications and incremental improvements resulting in increasingly elaborate technologies (Tomasello, 1999). Our longitudinal data suggested that the long-term cultural transformation of stone handling might result in a generational ratchet effect, defined as an increase in the diversity and complexity of stone handling patterns compared to earlier generations of stone handlers. [BOOK CHAPTER]

Most of the 45 stone handling patterns currently observed in Japanese macaques are regarded as a non-instrumental manipulation of stones, with no obvious survival value. [REPORT]

However, we hypothesized that when practiced on a daily basis and by most members of a group, the functionless manipulation of stones could be considered as a behavioral precursor to the possible use of stones as tools. [REPORT]

The gradual transformation of the stone handling tradition, associated with a generational ‘ratchet effect’ could ultimately result in future stone-tool use, as stone-related behaviors become more deeply ingrained into the behavioral landscape of these monkeys at the population level. Although Japanese macaques are not frequent tool users [but see REPORT], the persistence of stone handling in food-related contexts may eventually turn into the instrumental use of stones as foraging tools by Japanese macaques [REPORT]

This prediction was eventually verified. In 2004, we witnessed the emergence of the first example of a possible adaptive transformation in the spontaneous practice of stone handling. Unlike all other stone handling patterns performed by Japanese macaques, unaimed stone-throwing exclusively observed in the captive Takahama troop during periods of disturbance and in conjunction with agonistic signals typical of this species could be regarded as a spontaneous tool-using behavior. [REPORT]

Based on the analysis of the contexts that may elicit the behavior, we inferred that stone-throwing might serve to augment the effect of agonistic displays. Among all the study groups, the Takahama troop exhibited the most diverse stone handling repertoire (44 patterns out of a total of 45) and showed the highest frequencies of occurrence in stone handling patterns. These findings suggest that, although stone handling was observed in the ten studied troops, its transformation into an adaptive behavior is more likely in troops where stone handling is a well established behavioral tradition showing diverse and complex patterns performed in various contexts [REPORT]

The study of stone-throwing also supports the view that tool-use evolves in stages from initially non-functional behaviors, such as object play, a categorization that perfectly suits the stone handling activity. Food provisioning and captivity have relaxed selective pressures on foraging and created favorable environmental conditions under which stone handling may simply serve the function of maintaining in some populations a set of behaviors that could evolve into tool-use provided particular environmental circumstances exist. As an unselected but eventually beneficial trait, the stone handling tradition would be an exaptation (cf. Gould & Vrba, 1982). [REPORT]