Evolutionary Anthropology 22:213–225 (2013) ARTICLE A Practical Guide to the Study of Social Relationships JOAN SILK, DOROTHY CHENEY, AND ROBERT SEYFARTH Behavioral ecologists have devoted considerable effort to identifying the sour- raised several related questions: How ces of variation in individual reproductive success.1–5 Much of this work has are relationships among individuals focused on the characteristics of individuals, such as their sex and rank. How- patterned? What are the proximate ever, many animals live in stable social groups and the fitness of individuals mechanisms that mediate the impact depends at least in part on the outcome of their interactions with other group of social interactions on individuals? members. For example, in many primate species, high dominance rank enhan- What are the long-term adaptive conse- ces access to resources and reproductive success.4,5 The ability to acquire and quences of social relationships for indi- maintain high rank often depends on the availability and effectiveness of coali- viduals? What do primates know about tionary support.6 Allies may be cultivated and coalitions may be reinforced by their own relationships and the rela- affiliative interactions such as grooming, food sharing, and tolerance.7,8 These tionships of others? findings suggest that if we want to understand the selective pressures that The absence of an established toolkit shape the social behavior of primates, it will be profitable to broaden our focus for describing the properties of social from the characteristics of individuals to the properties of the relationships that relationships complicates efforts to they form with others. The goal of this paper is to discuss a set of methods that answer the first question, and this can be used to quantify the properties of social relationships. inevitably affects our ability to answer the others. Thus, our primary goal is to present a set of procedures for quanti- Although primatologists have long on individuals for several reasons. fying the properties of social relation- emphasized the importance of social First, we are used to thinking about ships. Our efforts are strongly relationships, in most studies of how natural selection shapes behav- influenced by Jeanne Altmann’s influ- social behavior the individual, not ioral traits, and natural selection ential efforts to provide a rigorous the dyad, is the unit of analysis. acts on individuals, not dyads. Sec- foundation for behavioral data collec- Researchers have focused primarily ond, dyadic data present a statistical tion. We also discuss experimental headache because dyads are not methods that have been developed for independent. Although powerful new probing primates’ perception of their relationships, as well as noninvasive Joan Silk is Professor of Anthropology in statistical procedures enable us to the School of Human Evolution and deal with this problem, not all of us procedures that have begun to illumi- Social Change at Arizona State Univer- are up to speed on these methods. nate the proximate physiological mech- sity. For most of her career, she has anisms linking behavior to adaptive studied the evolution of social behavior Third, behavioral data are not always outcomes. We then explore the associa- and reproductive performance of female dense enough to support dyadic macaques and baboons. Email: tion between the structure of social [email protected] analyses; in these cases, researchers relationships and fitness outcomes. We Dorothy Cheney and Robert Seyfarth may prefer to combine information are, respectively, Professor of Biology end with a discussion of questions that across individuals within specified and Psychology at the University of may direct future work. Pennsylvania. They have pioneered the categories such as close kin and use of naturalistic experiments to investi- peers. Moreover, there is no estab- gate vocal communication and social CONCEPTUAL FOUNDATIONS cognition in vervet monkeys and lished consensus about how measure baboons. the properties of social relationships. Current interest in social relation- The goal of this paper is to provide a ships builds on conceptual founda- Key words: observational methods; behavioral practical guide to the study of social tions established by Robert Hinde, analysis; methods; dyadic relationships; social relationships. We begin with a brief who pioneered the study of relation- bonds discussion of the conceptual founda- ships in primates.9,10 Hinde considered tions for the study of relationships that relationships to be the outcome of a VC 2013 Wiley Periodicals, Inc. was originally developed by Robert contingent series of interactions DOI: 10.1002/evan.21367 Hinde and subsequently expanded by between two individuals. and empha- Published online in Wiley Online Library (wileyonlinelibrary.com). Hans Kummer. Hinde and Kummer sized the importance of constructing 214 Silk et al. ARTICLE descriptions of relationships from ob- tions of relationships from observa- dyads in which one partner becomes servational data on social interactions. tions of social interactions. Such attractive to the other for a limited In studies of mother-infant relation- descriptions would include informa- period (for example, a female in ships among rhesus macaques, Hinde tion about the content, quality, and estrus), and such relationships might and his colleagues showed how temporal sequence of interactions.10 be characterized as opportunistic or changes in the behavior of both Researchers have spent thousands of instrumental. mother and infant influenced the hours conducting focal observa- Some researchers have used the amount of time they spent in close tions15 that generate high-quality rate of affiliative behavior or the proximity during the infant’s matura- data about who does what to whom, absence of agonistic behavior as a tion.11–13 Hinde’s work showed that in how often, for how long, and in proxy for relationship quality.18 In many cases the behavior of an individ- what sequence. However, we do not general, dyads with high rates of ual was best predicted by the proper- have a well-developed consensus affiliation and/or low rates of aggres- ties of its relationship with others, not about how to quantify the character- sion are categorized as having good, by its own properties. For example, the istics of dyadic relationships.16 strong, or intense social relation- behavioral consequences of a brief sep- Any two animals that recognize ships. Rates of affiliation may be an aration of mother and infant were one another as individuals and meet important component of social rela- best predicted by the characteristics of repeatedly have some kind of rela- tionships, but they may not fully the relationship before separation tionship; the empirical task is to capture their complex dynamics. occurred rather than by individual describe its characteristics. We sug- Our multi-dimensional view of attributes such as the infant’s age, sex, gest that relationships or social social relationships is similar in or the mother’s experience. Infants bonds occupy a multidimensional some ways to Cords and Aureli’s19 who showed the greatest distress were space, and that we can use behav- proposition that relationships can be those who, before the separation, had ioral data to map the contours characterized by three components: been relatively more active than their within that space. There are various compatibility, security, and value. mothers in maintaining physical con- dimensions along which relation- They defined compatibility as the tact. Jeanne Altmann’s classic mono- ships may differ.17 For example, two degree of tolerance within a dyad, it graph, Baboon Mothers and Infants, individuals may rarely interact or is therefore similar to what we have took Hinde’s approach to the field.10 interact often (frequency); they may termed the tenor of social relation- Hans Kummer integrated Hinde’s interact in a limited number or in a ships. Secure relationships are those conceptual formulation with the func- diverse range of behavioral contexts that are predictable and consistent tional perspectives of behavioral ecol- (diversity); their directional interac- over time, and thus partially overlap ogy. Kummer14 proposed that tions may be highly one-sided or with the dimension that we have relationships are long-term invest- evenly balanced (symmetry); their labeled consistency. Cords and Aureli ments that generate benefits for the interactions may range from mostly define relationship value in terms of members of the dyad. Kummer rea- hostile to mainly friendly (tenor); the benefits that individuals derive soned that the value of relationships they may be tense or relaxed when from their relationships. Our scheme would depend on the intrinsic qualities they are together (tension); they may has no direct analog for relationship of the members of the dyad, such as behave toward one another in a con- value, partly because the value of rank and sex; their tendency to act in sistent or inconsistent manner (pre- social interactions is so difficult to ways that increased or decreased each dictability); and they may interact at quantify. other’s fitness; and their availability to high rates for short periods or con- The procedures that we describe one another, which would affect their sistently at high rates over long peri- below provide a starting point for ability to act on their behavioral ten- ods (stability). This is a preliminary, efforts to quantify the dimensions of dencies. He proposed