Animals cannot synthesize polyunsaturated fatty acids (PUFAs), but PUFAs are an important source material for eicosanoids, and thus must be consumed as essential fatty acids. Furthermore, blood cholesterol levels are dependent on the types of fatty acids consumed. However, the composition of fatty acids in food consumed by wild Japanese macaques has not yet been reported. In this study, the fatty acid composition of 58 species/parts of plants were analyzed by capillary gas chromatography. A total of 11 types of fatty acid were found. A UPGMA (Unweighted Pair Group Method with Arithmetic mean) dendrogram by PCA (Principal Component Analysis)was drawn from all 8 principal component scores. Leaves, petals, and fruits and seeds diverged into three groups. The fruit of Hazenoki (Rhus succedanea) diverged from other samples due to its extremely high palmitic acid content. Fruits and seeds in Group 1 contained high C18 monoenoic acid levels, but low α -linolenic acid (C18:3, n-3) levels. Group 1 was divided into two sub-groups based on the composition of linoleic acid (C18:2, n-6). All leaves and petals included in Group2 had higher α -linolenic acid (C18:3, n-3) and lower C18 monoenoic acid than fruits and seeds in the same group. From these results, it appears that Japanese macaques consume more α -linolenic acid (C18:3, n-3) and that the ratio of (n-6)/(n-3) decreases in seasons when they take more leaves. Furthermore, blood cholesterol levels might have been kept low, as myristic acid (C14:0) was scarce, and a high linoleic acid (C18:2, n-6) content is included in the fruits and seeds of Group 1.

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‘ The metaphor of transmission’ (cognition-transmission model), which is a root metaphor of contemporary primatology, was reconsidered and deconstructed by referring to other academic domains such as anthropology, communication study, psychology and cognitive science. Instead, I introduced another epistemological standpoint, action-practice model, based on the ‘ situated action’ approach, in order to expand the perspective of contemporary ‘ cultural primatology’ and to understand the relationship comprehensively between primate culture and sociality.
From this standpoint, I analyzed social interactions along ant-fishing among wild chimpanzees at Mahale, Tanzania. Some situated characters of their social practice, such as attitude depending on others’ actions, moderate exploring proposition to others, and direct reaction to such propositions, were considered to be important to realize such social situation of ant-fishing as a cultural practice of chimpanzees.

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The male-female affinitive relationships among non-kin which persist beyond the estrus period have been known in some primates, mainly savanna baboons, Japanese macaques and rhesus macaques. I call this friendship, and review the benefits of friendships for each sex. For females, proximity and alliance of male friends disrupts antagonism by opponents, more or less, in all three species. On the other hand for the males, the effect of enhanced reproductive success seems to be negative. It is necessary to fully consider male benefits via infants in savanna baboons. Since it is highly possible that baboon males take care of a female friend's infant that he sired in the past, such friendships, especially in infanticidal baboons, would evolve through kin-selection rather than reciprocal altruism. When it comes to reciprocal exchange of benefits between a male and female, it seems that females play a positive role in the maintenance of friendships, as overall benefits seem to be female-biased. Socio-ecology can offer explanations for the ultimate cause of friendships. However, its explanatory power is not enough to explain the following observations: two non-troop males visit a group of Japanese macaques in coastal forest, Yakushima on separate days during a mating season. They received grooming one-sidedly by a female and soon left the group without copulating. These two cases seemed to be interactions between old friends, but the reciprocity cannot be formed. As the reunion with an old female friend of a male after immigration rarely occurs, mal-adaptive behavior would not be a problem. Socio-ecology does not explain such rarely occurring events. However, we can not ignore such cases just because they rarely happen. It is one aspect of the Japanese macaque society that monkeys “renews” old friendship.

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This paper aims to consider why the sphere of social phenomena is significant in the study of primates, including humans, and what aspects of the phenomena we should focus on in order to understand its significance. Although the process of making relations with others may easily become undecided, it may not be retained. We humans cope with such undecidability by paying attention to the motivation of activity easily shared by participants, or adequate readiness for regulating each other's interaction. This does not mean that the social sphere is independent of other spheres, but these characters are common to the activities of making relations with the natural environment for surviving. The social sphere should be placed in the larger range of phenomena produced by the activities of making relations with the outer world in general. An individual animal tries to decide his act of making relation with an object depending on the meaning of the object, while he tries to identify the meaning depending on his act of making relation with the object. Here, the undecidable circle is formed. The same situation is found in the case of making relations with others. That is to say, one tries to decide his act to the other depending on the other's act while the latter decides his act depending on the former's act, so that the undecidable circle is also formed here. The undecidability in the process of making relations with objects is usually perfectly hidden. However, the other's selection in the process of making relation with the object is always apparent in the social sphere. The other not only makes the undecidability apparent by making a different selection from my own, but also teaches a new way of coping with it by sharing the motivation with him or regulating the process of interaction with him.

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