The Evolutionary Origins of Friendship: A Cross-Species Comparison and Experimental Approach

Friendship is crucial for human health and well-being. People who are socially isolated have a greater risk of heart disease than heavy smokers, drinkers, and the obese, and halting social isolation’s ongoing rise is a growing priority for public health and political policy. But coming to grips with our need for friends and the consequences we face in their absence requires we not only look at how friendship is manifested in contemporary societies but to its origins in our evolutionary past. Yet, the evolutionary origins of friendship and the degree to which friendship’s components reflect human specializations are unclear. Studying nonhuman primates allows us to identify the causes and consequences of friendship in evolutionary time and the extent of its human uniqueness. Nevertheless, we know surprisingly little about the contexts that drove friendly social bonds to emerge, whether friendship-relevant cognitive abilities reflect primate universals, and the reasons why evolution allows social isolation to persist despite being detrimental. In this project, I will conduct a series of landmark studies to reveal critical insights into the evolutionary origins of friendship. I will generate an unparalleled cross-species dataset on the best-known taxa of group-living primates, the macaques, and will perform innovative social experiments on a unique macaque population. I have three key aims: (1) to test the environmental forces driving variation in social bonds across species; (2) to establish whether having information on the friendships of unrelated others is a uniquely human skill; and (3) to test whether social isolation is the result of competitive exclusion. Friendship may be one of the most important strategies humans have for surviving in large groups. Understanding friendship from an evolutionary perspective is therefore a critical component of understanding what it means to be human. The proposed project represents a major step forward in that endeavour.