[in Japanese]

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We analyzed the maternal style in Japanese macaques (Macaca fuscata) toward their yearlings and the effects of maternal style on the yearlings' social interactions with other group members. We observed 11 yearlings (11-14 months old at the starting point of observations) from the Arashiyama E group of provisioned free-ranging Japanese macaques. We assessed maternal style, performing principal component analysis of data for 5 categories of maternal behaviors toward their yearlings. We found that variability in maternal style toward yearlings occurred primarily along 2 dimensions, "protectiveness" and "rejection." These 2 dimensions were the same as those for maternal style toward infants (0-3 months old; Maestripieri, 2006). Yearlings with highly protective mothers received less grooming from other group members. On the other hand, we found no effects of either maternal protectiveness or rejection on social play with peers. These findings suggest that maternal protectiveness has a stronger effect on the yearlings' interactions initiated by other group members, such as receiving grooming, rather than interactions initiated by yearlings themselves, such as social play with peers.

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[in Japanese]

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Bonobo tool-using behavior is rare, limited in variety and relatively simple in form. The tools of bonobos are almost always made of a crude branch with little processing and are used neither for getting food nor as a weapon but for improving "the quality of life" (rain hat, social communication etc.). The paucity is said to be influenced by the abundance and richness of the food resources, relieving them of the need to develop food processing tools. I agree with this explanation and propose another possibility. The chimpanzees' curiosity, high activity and aggressiveness to strangers and strange objects accelerated their development of tool-using behavior. In contrast, the mild and shy disposition of bonobos might have influenced the types of tools they developed.

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