Nowadays, however, as I study and write about the expression of emotion in a variety of mammals, I have come to realise that this perspective is too limiting. If we make the biology of kinship the primary motivator for an animal’s behaviour, we might be slow to explore the nature of its other social relationships. Indeed, some scientists have begun to describe the close bonds between non-kin relatives as ‘friendships’, in species ranging from chimpanzees and elephants to domestic and farm animals. This is an encouraging trend. I think we can go further, especially by borrowing a new concept from anthropology that Marshall Sahlins calls mutuality of being.
Mutuality of being refers to a special type of relationship, one that overlaps with friendship but has its own distinct qualities. To qualify as friends, two animals must engage in positive social interactions beyond the context of mating and reproduction. In her pioneering field study Sex and Friendship in Baboons (1985), Barbara Smuts used grooming and proximity to decide which male and female baboons were friends. More broadly, the anthropologists Robert Seyfarth and Dorothy Cheney, professors at the University of Pennsylvania, define friendships as close, enduring social bonds, including those that form between males and between females. [...]
Among the Ku Waru people of New Guinea, for example, children become kin through an essential substance called kopong (grease) which originates in the soil. The Ku Waru call both father’s sperm and mother’s milk kopong, and it is through these two sources that conception of a child is said to occur. However, sweet potatoes and pork also contain kopong, and when people share these foods, the same fundamental connection emerges between them as does between parent and child: they become kin. The offspring of two Ku Waru brothers, Sahlins says, are ‘as much related because they were sustained by the same soil as because their fathers were born of the same parents’. The children of immigrants to the community become full kin with those who share no genes with them by carrying out socially inscribed practices around kopong. [...]
However, the social structures of chimpanzees have turned out to be much more complicated than originally thought. The primatologist John Mitani and his research team at the University of Michigan showed that male relationships among chimpanzees at Ngogo in Kibale National Park, Uganda, are not driven by genetic kinship. Using mitochondrial DNA analysis, Mitani demonstrated that these chimps’ matrilineal relatedness was not correlated with affiliation (as defined by measures of association, proximity, and grooming) nor with co-operation (which involved alliances, meat sharing and boundary patrols). Instead, non-related males routinely expressed close bonds through their everyday activities.
