Evolutionary Anthropology 85

NEWS

Females, Food, Family, and Friendship

or much of the last twenty ances, female philopatry, well-differ- student in the late 1970s, I was ad- years, females have occupied entiated female relationships, and vised by a well-respected primatolo- Fcenter stage in theoretical and male dispersal. On the other hand, gist not to study the sources of varia- empirical analyses of primate social when within-group contest competi- tion in reproductive success among organization. Richard Wrangham1 tion is weak and between-group con- female bonnet macaques because I was one of the first to give females top test competition is strong, we expect wouldn’t find any. But I did, and so billing, when he suggested that social- to see egalitarian dominance relation- have many primatologists since ity has evolved in primates because it ships among females, group-level co- then.10–13 enhances females’ access to resources. alitions against other groups, female If female reproductive success var- Female nutritional needs drive the philopatry, and poorly differentiated ies, then we can ask how the form and plot because female fitness is largely female relationships.4 features of females’ social relation- determined by their access to re- Socioecological models shine the ships contribute to variability in their sources, while male fitness is mainly spotlight on females, and primatolo- fitness.14 Widespread (but not univer- affected by their access to receptive gists have spent much of the last sal) evidence that female dominance females. This means that females dis- twenty years collecting data on female rank influences reproductive perfor- tribute themselves in space according life histories, feeding behavior, and mance provides the first clue that so- to how their food is distributed, and social relationships. Some of this cial relationships do have adaptive males go where females are. Many work was designed explicitly to test value for females. The strong bonds have criticized Wrangham’s plot line, predictions derived from socioeco- among maternal kin, nepotistic coali- arguing that predation provides the logical models, and featured pairwise tions, and matrilineal dynasties that primary selective factor favoring soci- comparisons of carefully selected spe- we see among baboons, macaques, 2 ality in primates and that sociality cies. For example, Mitchell, Boinski, and vervets provide further evidence creates dramatic tension by produc- and van Schaik5 compared the behav- that social relationships have fitness ing substantial intragroup competi- ior of closely related species of squir- consequences for females. tion for resources. rel monkeys that live in different hab- Socioecological analyses sketch the Although we probably will never be itats but rely on different kinds or rough outlines of female behavior, certain why sociality first evolved resources; Isbell and her colleagues6,7 documenting the fraction of reversals among primates, there is wide agree- are studying two sympatric guenons in dominance matrices, the existence ment about the rest of the story: Re- that focus on different types of re- of coalitions during within- and be- source competition among females sources; and Koenig and his col- tween-group conflicts, the extent of drives the evolution of primate social leagues8 compared Hanuman langurs differentiation in female grooming organization. Resource competition occupying different types of habitats networks, and dispersal patterns. In- can take different forms—there can be in India. These comparisons mainly fit formation about the detailed struc- scramble or contest competition, and predictions derived from socioeco- ture and quality of female social rela- both can occur within or between logical models9 and have confirmed tionships comes from a different groups. Many researchers have ex- females’ place as lead characters in branch of primatology. This body of plored the dimensions of this space, the story of how sociality evolved work focuses explicitly on relation- generating models that bear reassur- among primates. ships, taking as given that animals live ing similarities to one another.2–4 For One of the primary messages of so- in social groups. This research tradi- example, when within-group contest cioecological models is that social re- tion blends Robert Hinde’s emphasis competition is strong and between- lationships among females have adap- on the dialectic between social inter- group contest competition is weak, we tive value. This idea seems completely actions, social relationships, and so- expect to see strong female domi- obvious to most of us now, but we cial interaction and Hans Kummer’s nance hierarchies, matrilineal alli- should remember that it was not part insight that natural selection guides of the received wisdom when Wrang- investment in social relationships that ham published his paper on primate have adaptive value for individuals. social organization in 1980. At that Research on the dynamics of social Evolutionary Anthropology 11:85–87 (2002) time it was widely assumed that there relationships spans proximate and ul- DOI 10.1002/evan.10011 Published online in Wiley InterScience was little systematic variation in fe- timate levels of analysis. For example, (www.interscience.wiley.com). male reproductive success. As a Ph.D. de Waal and his colleagues15 have ar- 86 Evolutionary Anthropology NEWS gued that peaceful interactions after sium will be published in a forthcom- group encounters, but rarely form co- conflict (reconciliation) mend social ing issue of Behaviour). alitions in within-group contests. relationships that have been frayed by Several of the papers presented in However, females have quite well-dif- conflict, while I have suggested that the symposium were explicitly rooted ferentiated social relationships and reconciliation provides a timely signal in socioecological models. Lynn Isbell stable linear dominance hierarchies. that conflict has ended.16 Dunbar17 and Truman Young (Davis) compared Karen Strier (Wisconsin) discussed has emphasized the role of social and contrasted socioecological mod- social relationships among male grooming in creating and maintaining els, delineating commonalities be- muriquis, a species that contradicts social bonds. There is also a growing tween the models and pointing out nearly all of our generalizations about interest in how social relationships their differences. Sue Boinski (Flor- primate social relationships: Males are calibrated: What do animals know ida) presented new data on a third form closer ties than females do; about their own relationships and the species of squirrel monkeys from bonds are strong, but grooming is relationships of others? How do they Surinam. At first glance, Surinamese rare; males rarely fight and freely regulate the exchange of cooperative squirrel monkeys seem to challenge share access to resources, even recep- interactions that sustain social bonds? socioecological models because re- tive females. Louise Barrett and Peter And how do they navigate the uncer- source competition among them is in- Henzi (Capetown) raised questions tainties and conflicts of interest that tense, but female bonds are quite about the essential nature of social arise in social life? weak. However, these monkeys rely relationships among female baboons, Other work on social relationships on foods that occur in small, dense suggesting that females often use addresses the evolutionary forces that clumps that feed only one, making co- grooming for strategic purposes such structure social interactions and operation in resource defense unprof- as gaining access to newborn infants, shape social relationships. Many pri- itable. Ronald Noe¨ (Strassburg) de- not for building long-term social mates behave as if they had been tu- scribed the ecology and social bonds. They speculate that monkeys tored in the principles underlying kin are simply not smart enough to man- selection, showing nepotistic biases in age the accounting problems that most forms of cooperative behavior, Much of the work on the long-term reciprocity in multiple cur- including grooming, alliance forma- rencies would present. tion, and food sharing.18 Others pro- dynamics of social Several of the papers considered vide good evidence for reciprocity, relationships focuses on proximate factors that influence the trading favors in the same currency or females for the same development of social relationships. swapping one form of altruism for an- Thus, Felippo Aureli and Colleen other.19–22 reason that Willy Sutton Schaffer (Liverpool) addressed the Much of the work on the dynamics robbed banks—that’s role of emotion, particularly anxiety, of social relationships focuses on fe- in regulating social interactions that males for the same reason that Willy where the money is. shape social bonds. Jeanne Altmann Sutton robbed banks—that’s where (Princeton) considered the role of de- the money is. For reasons that socio- mography in defining individuals’ so- ecological models make clear, social cial options and shaping their adap- relationships, particularly social tive outcomes. behavior of three sympatric colobine bonds that extend beyond dominance Finally, Anja Widdig and her col- species in the Taı¨ Forest, and sug- relationships, are generally a more leagues presented a remarkable set of gested that they may represent differ- profitable long-term investment for fe- data indicating that monkeys can rec- ent peaks in the adaptive landscape. males than for males. ognize paternal kin. Using genetic But not all data fit neatly into socio- A group of primatologists gathered data to identify paternal kin and be- at the recent meetings of the Interna- ecological models. Anne Pusey (Min- havioral data to assess social relation- tional Primatological Society in Ad- nesota) presented data from long- ships, Widdig and her colleagues elaide, Australia, to consider what we term studies of chimpanzees at showed that female rhesus macaques have learned over the last twenty Gombe that contravene the notion on Cayo Santiago display strong affin- years about the form and function of that female dispersal is typically asso- ities for paternal kin. The monkeys primate social relationships. The sym- ciated with an absence of feeding seem to rely on two kinds of cues to posium, entitled “What are Friends competition among females. Her recognize paternal kin. First, they For? The Adaptive Value of Social analyses reveal that immigrant fe- show marked preferences for age- Bonds,” was intended to provide a fo- males face stiff competition from res- mates. Similarity in age is likely to be rum for presenting new data on the ident females, and that such competi- a good proxy for kinship when one nature of social relationships among tion is directly reflected in females’ male monopolizes mating activity,23 primates, mainly females, and to ex- reproductive performance. Marina and this holds true on Cayo Santiago. plore the evolutionary forces that Cords’ (Columbia) analysis of blue But females also prefer paternal kin shape these relationships and gener- monkeys suggests that they do not fit over unrelated females when they in- ate adaptive consequences. (Most of neatly into socioecological categories teract with nonpeers. This suggests the papers presented at the sympo- either. Females cooperate in inter- that monkeys may be able to recog- NEWS Evolutionary Anthropology 87 nize paternal kin from phenotypic relationships across individuals con- 11 Borries C, Sommer V, Srivastava A. 1991. cues alone. These results are consis- tributes to variation in fitness among Dominance, age, and reproductive success in free-ranging female Hanuman langurs (Presbytis tent with an independent dataset from individuals in primate groups. A lot of entellus). Int J Primatol 12:231–257. Amboseli;24 if widely replicated, they work still needs to be done to under- 12 Pusey A, Williams J, Goodall J. 1997. The will radically change our interpreta- stand the connections among females, influence of dominance rank on the reproductive success of female chimpanzees. Science 277: tions of the evolutionary basis of so- food, family, and friendship in nonhu- 828–831. cial behavior in primate groups. man primates. 13 Van Noordwijk MA, van Schaik CP. 1999. The The diversity of the papers pre- effects of dominance rank and group size on sented at this symposium reflects the female reproductive success in wild long-tailed REFERENCES macaques, Macaca fasicularis. 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