Abstract
Hruschka proposes two aims in this book: “to…foreground the unique ways that friendships…have helped people deal with the struggles of daily life in a wide range of human societies” and “to document and account for the recurring yet diverse ideals and behaviors associated with friendship in human societies.” (pp. 2–3). In an account that incorporates evolutionary-based theoretical models, systematically analyzed cross-cultural data, experimental findings from predominantly western social contexts, and a small yet relevant neuroendocrine literature, Hruschka's book yields a comprehensive, current, and integrative scholarly view of human friendship. This book instantly serves as the go-to reference on the subject. The interdisciplinary theoretical and methodological coverage ensures that psychologists, anthropologists, sociologists, and others will find friendly material that does not privilege a single method or approach, but rather seeks to pull together the best work across the evolutionary and social sciences on human friendship. The length (219 pages of text) and accessible writing mean that a reader can dive into the work without drowning in jargon, also finding a spread of cross-cultural examples of friendship that are true to the breadth of the human experience. We discuss the outline of the book in chapter-by-chapter sequence, before providing some additional summary of the book's strengths and weaknesses.
Chapter 1 (An Outline of Friendship) characterizes the main features of human friendship. It considers behaviors, psychological processes, and physiological mechanisms entailed in friendship. As an example, Hruschka indicates how well norms of reciprocity do and don't characterize friendship; while many evolutionary and economic scholars have suggested that reciprocity characterizes non-kin cooperative behavior, friendships are less likely to balance exchange of favors. Further, a body of research suggests that closeness, love, and trust are frequently employed to describe friendship, with Hruschka touching on the ways that such emotions variably apply to friendships in different societies and with respect to other relationships including romantic partnerships. And to communicate friendship, this chapter recognizes that actions speak louder than words—that expressions of emotion such as Duchenne smiles and body postures, in addition to gift-giving, can serve as honest signals of friendship maintenance.
Chapter 2 (Friendships across Cultures) incorporates scattered depictions of friendship around the globe with a more systematic study of friendship that relies on a cross-cultural sample drawn from the Human Relations Area Files (HRAF). The cross-cultural scope of friendship presents both interesting challenges and compelling contrasts with western notions of friendship. In order to measure aspects of friendship, it must be defined, and Hruschka calls upon western views of friendship to initially study it cross-culturally. The result is that friendship in cross-cultural perspective exhibits features of western friendship (e.g., mutual aid) but also demonstrates features at odds with those in western contexts (e.g., friends don't necessarily engage in self-disclosure and don't necessarily enter such relationships voluntarily). As illustrations, some friendships are arranged or inherited from parents, and others entail commitment rituals, like blood-brotherhood practices among Lunda farmers in Zambia. A table and several figures capture some of the patterns in this cross-cultural survey of human friendship.
Chapters 3 (Friendship and Kinship) and 4 (Sex, Romance, and Friendship) contrast similarities and differences between friendship and kin-based relationships and romantic relationships, respectively. One thrust of these chapters is to discern how partially shared psychological processes and physiological mechanisms (e.g., love, closeness) could account for similarities in these types of relationships, with another thrust pointing toward the differences in psychological and physiological underpinnings (e.g., how kinship trumps friendship when faced with extremely costly behavior, and how sexual behavior is a more central feature of romantic relationships). The discussion of fictive kinship draws upon a longstanding tension between genetic and social kinship, with examples ranging from U.S. adoption to Binumarien New Guinean highlander help with sweet potato gardening to even a reassessment of the famous Yanomamo ax fight film. The coverage of romantic relationships leans heavily on Helen Fisher's model that lust, romantic love, and attachment represent distinct aspects of romantic partnerships, each with its own neuroendocrine underpinnings and typically characterizing different stages in the development of a relationship. Sure to interest undergraduate students is a discussion whether opposite-sex partners can be friends without sex; while “friends with benefits” may manifest among some populations, the wider cross-cultural literature indicates variable support for and against cross-sex friendships.
Chapters 5 (Friendship: Childhood to Adulthood) and 6 (The Development of Friendships) specify two developmental courses of friendship: the first over part of an individual's life course, and the second over the duration of a friendship itself. In Chapter 5, topics include the ages at which children begin to develop friendships, commentary upon imaginary and supernatural friends, the relevance of schools to the development of friendships (providing a pool of potential friends), the development of different attachment styles, and sex similarities and differences in friendship (a topic we return to below). In Chapter 6, Hruschka touches on subjects such as the contexts within which friendships originate (e.g., during separation from regular social networks), political and advertising attempts to manipulate friendship (please vote for me, my friend), how friends prevent being abused (e.g., through scaling up of rituals and investments from less to more costly forms over time), and how friends resolve their differences or walk away from each other when conflicts arise.
Chapter 7 (Friendship, Culture, and Ecology) aims to explain cross-cultural differences in friendship. This effort recognizes and applies four hypotheses intended to account for such differences: material and social uncertainty, geographic mobility, competition with kin institutions, and changes in the media. Among differences calling for explanation are self-disclosure (less commonly reported in some East Asian societies), provisioning of material support (lending money to friends extolled in some contexts, but avoided in others), and loyalty conflicts (e.g., whether preferences are granted to friends over kin, or vice versa). The expanding Internet world of “friends” also broadens the ecological scope of friendship. While there are some compelling connections made in this chapter, such as a positive international correlation between a measure of uncertainty and willingness to help a friend (under a logic that investing in friends may be more valuable when the local legal system is less reliable), few concrete conclusions are drawn.
Chapter 8 (Playing with Friends) investigates evolutionary and economically-based models for human unconditional willingness to invest in friendships. This account draws upon game theory, offering a concise and accessible account of its assumptions and utility for exploring the issue of unconditional investment. After describing the Prisoner's Dilemma, including the tit-for-tat strategy for playing it, Hruschka devotes more attention to a “Favor Game” that is designed to better model the nature of friendship, and which gives rise to a “raise-the-stakes” strategy in various iterations. The mathematical details are largely placed in an Appendix.
In the final chapter (Conclusion), Hruschka points toward friendly questions sure to draw ongoing scholarly interest. These questions are: Friendship's phylogenetic roots?, Friendship in the brain?, From deliberation to stimulus-response (and back again), Conflicts of allegiance, and Harnessing the power of friendship. These subjects point to how the continued integrative study of friendship will occur alongside the study of human romantic partnerships, kin-biased relationships, and other aspects of our social behavior, with likely some shared conceptual insights (e.g., that psychological processes once arisen can be co-opted into other relationships, and that knee-jerk altruism applies to various relationships).
Having covered the chapter-by-chapter breadth of Friendship, we now turn to additional discussion of the book's merits and limitations. A major strength of this book is its acceptance of methodological pluralism. The different methods employed by scholars of friendship each present strengths and weaknesses. As illustrations, Hruschka notes that the human cross-cultural surveys often rely on normative statements rather than quantified behavioral observations, and experiments offer more convincing tests of postulated relationships between variables, but at expense to ecological richness. As a means of clearly articulating the assumptions, strengths, and weaknesses of various methods, Boxes are scattered throughout the book, offering clear overviews of “Behavioral experiments”, “Vignette experiments”, “Behavioral observations”, “Meta-analysis”, and “Cross-Group analysis”, among other interdisciplinary methods. Further, in a welcomed methodological contribution, Hruschka provides measures of effect size whenever feasible. The inclusion of Cohen's D-statistic enables a reader to glean the magnitude of a statistically significant relationship.
Another strength of the book is its explicit attention to cross-cultural aspects of friendship. The cross-cultural scope demonstrates similarities and differences in the processes and nature of friendship across societies, helping guard against assumptions that patterns of friendship studied in WEIRD societies can be generalized across all other societies (Henrich, Heine, and Norenzayan, 2010). The Chapter 2 synthesis of this cross-cultural literature represents a unique resource in this respect. The scattered Boxes (e.g., Ethiopians living in Addis Ababa commenting on the importance of honoring requests of friends to maintain one's reputation) and in-text cultural accounts further illustrate the variation in friendship around the globe.
Our major concern with the book rests in its general restriction of “evolution” to game-theoretic modeling, largely shunning phylogenetic accounts of friendship. While in the Conclusion Hruschka acknowledges the need for more research adopting a phylogenetic view on friendship, such work is confined to a few nonhuman primate examples (e.g., a Box asking whether non-human animals can be friends) and implicit assumptions that neuroendocrine research on rodent models (e.g., experimental alteration of oxytocin and vasopressin systems) can inform human physiological mechanisms of friendship. We feel that this narrow approach unnecessarily avoids conceptual and empirical continuities in an understanding of primate social behavior. Most importantly, such a narrower view avoids applying a straightforward socioecological model to friendship, one that would likely illustrate age- and sex-specific functions of non-kin social bonds in other primates and in humans alike. To illustrate, if female reproductive success is limited by resources such as food and predator avoidance, but males by reproductive access to females, these patterns help structure the age- and sex-specific benefits associated with forming bonds that bear some similarities to friendship. Features of what look like male friendships, whether in chimpanzees or humans, are likely related to status concerns, with benefits for acquiring mates and ultimately reproductive success. Features of what look like female friendships, whether in capuchin monkeys or women, may be more closely tied to offspring care than men's relationships. We urge greater application of these theoretical and empirical approaches, building on a socioecological model (Wrangham, 1979), in order to enhance our understanding of the similarities and differences in human and nonhuman animal features of friendship (see Silk, 2002), along with greater elucidation of the limited fossil, archaeological, genetic, physiological, and ethnographic evidence that can be used to reconstruct a hominin phylogenetic trajectory to friendship. In applying such a view, we also suspect a more sophisticated understanding of sex differences in friendship will emerge than presented in the book; Hruschka points out that the psychological processes and network sizes of friends are quite similar in female and male friendships, but we suspect there are also sex-specific functions in friendship across development that have been left out in an emphasis on similarities.
As for more minor quibbles with content and organization of the book, we imagine that future work focusing more on friendship dissolution will uncover both more evidence of the fitness-relevant content of friendships (e.g., buttressing the sense in the book that friends can aid each other in economic, marital, and reproductive contexts), and a sense that dissolution does involve some greater degree of a reciprocal logic than Friendship highlights (e.g., that a devoted friend may dissolve that friendship when the costs to maintaining it become too high). The 108 pages of notes and references aid the scholar reading this book, but may overdo the documentation that a lay reader or undergraduate student would require. As far as writing style, with clear prose and structure, the book moves efficiently, in some places a bit dry, but altogether employing a style that is accessible and that should keep a scholar interested in the subject wanting to read more, but which may lose in patches the interest of some wider lay audience or undergraduate student readers. We feel that this book could comfortably be assigned in upper-level undergraduate or graduate courses in Anthropology, Psychology, and other disciplines for which the subject matter is relevant and could benefit from a rigorous, integrative approach.
In summary, Friendship represents a welcomed contribution to our study of this relationship, but also the wider arena of human social relationships. Hruschka notes that anthropologists have long obsessed with kinship, but largely ignored friendship. More recent scholarship has highlighted motherhood (Hrdy, 1999), fatherhood (Gray and Anderson, 2010), grandparenting (Coall and Hertwig, 2010), even human-non-human animal relationships (Gray and Young, 2011; Shipman, 2010), but the study of friendship now has its proper voice. Hruschka's integrative, scholarly book on friendship provides a wonderful synthesis, and helps lay the groundwork for continued investigation of this relationship.