International Journal of Primatology

, Volume 27, Issue 5, pp 1311–1336 | Cite as

Is Postconflict Affiliation in Captive Nonhuman Primates an Artifact of Captivity?

Article

Researchers have conducted most studies on primate conflict management and resolution in captive settings. The few studies on groups of the same species in captivity and in the wild and the overall comparison across species of findings from studies in both settings have reported patterns of variation in the rates of various postconflict affinitive behaviors that may be setting related. In fact, some authors have claimed that the high rates of postconflict affiliation reported in captive studies could represent an artifact of captivity. I explored the claim and conclude that it is unjustified. I argue that the dichotomy captivity vs. wild is conceptually meaningless and scientists should abandon it as an explanatory variable, that differences across studies both in setting-related variables and in the methods used for assessing postconflict affiliation reduce the strength of comparisons within and across settings, that the empirical evidence thus far available neither allows adequate assessment nor supports any claim that links the rate of postconflict affiliation to captivity or wild conditions, and that studies conducted in both settings may be equally useful—and should be used—to test theoretically relevant hypotheses regarding the causes and predictors of variation in postconflict affiliation. Instead of asking the title question, I would ask which variables influence postconflict affiliation and then whether the variables are really associated only with one of the two settings.

Key Words:

captivity postconflict affiliation social behavior wild 

INTRODUCTION

The article that initiated the burgeoning area of research on conflict management and resolution was based on an observational study of social behavior in a colony of captive chimpanzees (Pan troglodytes: de Waal and van Roosmalen, 1979; de Waal 2000a). Since then, researchers have investigated >30 species of primates under a variety of conditions and in virtually all of them reported postconflict affiliation (Aureli and de Waal, 2000; de Waal, 2000b; Aureli et al., 2002; Judge, 2003). Aureli et al.(2002) listed ca. 44 studies on reconciliation in primates, of which only 9 (i.e., 20%) were in the wild. In fact, of the 30 primate species listed, researchers investigated only 4 in both settings—Macaca fascicularis, M. fuscata, Pan paniscus, and P. troglodytes—and 5 additional species only in the wild—Cercopithecus aethiops, Gorilla g. beringei, Macaca maurus, Papio anubis, and P. ursinus. Studies published during or after 2002 and reports from conferences increase the number of species studied up to 36: Papio hamadryas in captivity (Zaragoza and Colmenares, 1997; Romero-Benavente and Colmenares, 2003), Semnopithecus entellus in the wild (Sommer et al., 2002), Macaca assamensis in the wild (Cooper and Bernstein, 2002), Eulemur macaco in captivity (Roeder et al., 2002), Macaca radiata in the wild (Cooper et al., 2004), and Gorilla gorilla in captivity (Cordoni et al., 2004).

In their review of reconciliation research in primate and nonprimate species, Aureli et al.(2002) analyzed the question of whether the findings from studies in captivity might represent artifacts of the setting. They rejected this possibility by briefly examining several lines of empirical evidence. First, the relationship between the rate of a variety of patterns of social behavior in general and of reconciliation in particular and the size of the enclosure is complex and does not support the hypothesis that captivity causes a consistent elevation of the rates of aggression and reconciliation (de Waal et al., 2000; Judge, 2000). Second, authors had reported the occurrence of reconciliation in all the studies conducted in the wild at the time their review appeared. Finally, Aureli investigated the same species—Macaca fascicularis—in captivity and in the wild and found that reconciliation behavior occurred in both settings (Aureli and van Schaik, 1991; Aureli, 1992).

Sommer et al.(2002) recently analyzed data on aggression and postconflict affinity from 4 groups of hanuman langurs in the wild. Their data set is impressive; in effect, their study was based on 2000 h of observation of 37 individuals, and of 1365 agonistic and 4862 affinitive events. Their data analyses, deliberately chosen to depart from the conventional comparison of postconflict vs. matched-control observations, showed that the subjects hardly ever engaged in affinitive contacts after conflicts, i.e., 43 of 1365 or 3.15%, involving only 25 of 170 dyads or 14.7%. They interpreted the finding as evidence that wild langurs managed their conflicts via avoidance, not reconciliation. However, although they found no evidence for reconciliation, they did not provide evidence for avoidance (Sommer et al., 2002, p. 646). Sommer et al.(2002) went further and reinterpreted the findings on reconciliation reported from primates in the wild as indicating that, contrary to generally stated views, such a strategy was actually rare or absent among wild primates. They concluded (p. 647) that “ … it is likely that the majority of reports of reconciliation amongst primates are artificially inflated by the conditions of captivity.”

I address the claim by examining 3 major issues in turn. First, I argue that the dichotomy captivity vs. wild is conceptually meaningless and therefore must be abandoned as an explanatory variable. Second, in support of the view, I show that variation in the characteristics of the physical and social settings where scientists have conducted postconflict research, both in captivity and in the wild, and differences in a variety of methodological procedures adopted in the research area, are such that direct comparisons between studies within and across the two setting categories can lead to flawed interpretations and unwarranted generalizations. Third, I review empirical findings from a selected but rather comprehensive sample of postconflict affiliation studies and conclude that, even though the dichotomy held up, the information available thus far does not allow the claim that the occurrence and rate of postconflict affiliation is an artifact of captivity.

LABELING AND ASSESSING POSTCONFLICT AFFILIATION

Researchers have assessed postconflict affiliation in primates through a variety of behavioral measures, and workers have not always agreed about the labels and their behavioral content (Cords, 1993; Colmenares, 1996). Briefly stated, two major dimensions are noted. First is the nature of the affinitive behaviors exchanged soon after conflicts, which are divided into three major categories of increasing intensity of affinity: proximity; active affiliation not involving body contact, e.g., gestures, vocalizations, postures; and affiliative exchanges involving actual body contact, e.g., touching, embracing, genital contact, grooming. Second is the direction of the behavior, which is divided into two main categories: between opponents and between opponents and third parties. The former is generally labeled reconciliation (de Waal and van Roosmalen, 1979) and the latter category is labeled consolation if the third party is the initiator of the interaction and third-party or triadic affiliation if the opponent takes the initiative (de Waal and Aureli, 1996; Das, 2000). The list of labels to designate the different types of postconflict affiliative interactions is large, owing mainly to the fact that the authors often mix structural and functional labeling systems (Colmenares, 1996). I use the following labels: RC for reconciliation, i.e., friendly exchanges between former opponents, TA for triadic affiliation, i.e., affinitive interactions with third parties initiated by former opponents, and CS for consolation, i.e., affiliative behaviors directed by third parties toward former opponents (Table IV). When the identity of the initiator/recipient of the friendly interaction between former opponents and third parties is not reported I use the more general label third-party affiliation (TPA).

In the area of conflict management and resolution research, the label postconflict affiliation is not just a descriptive term to design the affinitive interactions that take place after a conflict. It is strictly applied to postconflict friendly exchanges that occur significantly more often after a conflict (postconflict period [PC]) than during a control observation (matched-control period [MC]) not preceded by aggression. De Waal and Yoshihara (1983) were the first to propose the method of pairing PC-observations with MC-observations, and it is now the standard procedure to assess the occurrence of any kind of postconflict affiliation (Aureli and de Waal, 2000; Aureli et al., 2002). Though there are various versions of the method (Aureli et al., 1989; Kappeler and van Schaik, 1992; Veenema, 2000), one of the most widely used is the original one, i.e., the affinitive behavior must occur only or earlier in the PC than in the corresponding MC. If this is the case, the PC-MC pair is attracted or earlier; if not, they are dispersed or later. Finally, PC-MC pairs in which affiliation does not occur in either sample or occurs at the same time in both samples are called neutral.
Fig. 1.

Different ways to conceptualize the dichotomy captivity vs. wild. Triangles represent observations in settings descriptively labeled wild and circles observations carried out in settings descriptively labeled captive. (A) The setting can be dichotomized; the labels have explanatory status; only a single dimension is considered, and within-category variation along this one dimension is ignored. (B) The setting can be dichotomized; the labels have explanatory status; although several dimensions along which the settings can vary are recognized and within-category variation is considered; however, the latter is assumed to be smaller than variation between categories. (C) The dichotomy has only descriptive value; the setting also encompasses multiple dimensions that vary along a continuum; however, between-category variation is not necessarily larger than within-category variation, and certainly is not for many significant variables (Table I).

Table I.

Setting dimensions and some variables describing their characteristics in studies conducted both in captivity and in the wild

Dimension

Variable

Captivity

Wild

Ecological setting

   
 

Predation pressure

Not applicable

Variable

 

Temperature

Variable

Variable

 

Amount of space

Variable

Not applicable

 

Complexity of space

Variable

Variable

 

Resource abundance

Variable

Variable

 

Resource distribution

Variable

Variable

Social setting

   
 

Group size

Variable

Variable

 

Group composition

Variable

Variable

 

Genealogical structure

Variable

Variable

 

Group structure

Variable

Variable

 

Social relationships

Variable

Variable

Activity budget

Time spent moving, resting, feeding, socializing, etc

Socializing increased

Foraging increased

Note. The list of variables is representative and not comprehensive.

De Waal and Yoshihara (1983) also proposed an index to assess differences in conciliatory tendency (CT) across individuals, dyads, or groups. One calculates the CT by dividing the number of attracted pairs between the total number of pairs (attracted+dispersed+neutral). Later, Veenema et al.(1994) proposed a measure that is independent of the baseline level of affiliation, which is calculated as the number of attracted pairs minus the number of dispersed pairs divided by the total number of pairs. The corrected conciliatory tendency (CCT) is now the most widely used method (Veenema, 2000). It is possible to adapt the method to measure triadic conciliatory tendencies (TCT), though so far its use has been much less frequent (Zaragoza and Colmenares, 1997; Call et al., 2002; Palagi et al., 2004).

IS THE DICHOTOMY CAPTIVITY VS. WILD MEANINGFUL?

Though researchers commonly used the dichotomy captivity vs. wild to describe the setting where observational studies of primate behavior and group structure are conducted, some workers have turned it into a variable with explanatory status (Fig. 1). However, are the two categories really unitary? Do they represent extremes of a unidimensional continuum? Is the dichotomy helpful at an explanatory level? In general, captive settings differ from wild settings in that the former are predator-free and humans feed and manage the subjects. However, even at a general level, differences across captive studies in the way the populations are managed can be high; e.g., the number of feeding sessions and the amount and dispersion of food provided can be highly variable. As regards the wild setting, variation across studies can also be important, with local human populations and scientists potentially influencing in many ways the ecological and social setting of the individuals in which they live or that are the subjects of their investigations, or both (Martin and Bateson, 1993; Lehner, 1996).

A close examination of the variables that define any given setting indicates that they typically encompass multiple dimensions rather than just one, all of which in turn may potentially vary along a continuum rather than dichotomously, with extensive overlap across categories (Fig. 1). Table I is a list of some of the dimensions and variables that are likely to vary widely both within and across the settings descriptively labeled captivity and wild. In many cases, the variables can and do influence one another. Thus, ecological factors influence both the time budgets that individuals allot to the performance of different activity categories, including walking, feeding, resting, and socializing, as well as a suite of demographic parameters, including group size and group composition, group growth rate and size of kin groups, and dispersal and intergroup transfer decisions (Dunbar, 1979, 1988, 1992). Demographic factors have a direct and often dramatic impact on group structure and the nature of social relationships among group members (Sambrook et al., 1995; Henzi et al., 1997, 2000; Hill, 2004).

One assumption, uncritically accepted and untested for years, was that the crowding typically associated with captive settings should lead to increased levels of stress, conflict, and aggression among individuals (de Waal et al., 2000). However, empirical tests of the hypothesis provided evidence that the relationship between captivity and the social behavior of primates is far from simple; thus, strategies that individuals activate to cope with changes in density and amount of space available may vary widely across dyads within a group and are influenced by the duration of crowding (de Waal et al., 2000; Judge, 2000). In addition, whereas theoretically individuals in the wild may avoid one another after conflicts, resulting in increased interindividual distances and reduced group cohesion, in practice, other external forces such as predatory risk or intergroup competition that are absent or more relaxed in captive settings, may in fact produce interindividual distances comparable to the ones in captivity (Sommer et al., 2002; Isbell, 2004).

Researchers have widely documented that an individual’s social behavior is influenced by the group’s overall social organization and more directly by the nature of the particular network of individualized relationships in which the individual is embedded (Hinde, 1983; Dunbar, 1984, 1988; de Waal, 1987a; de Waal and Aureli, 1996; Cords, 1997). Though primatologists initially assessed postconflict affiliation as a group, or even a specific characteristic (Kappeler and van Schaik, 1992; de Waal, 1993), later work has correctly emphasized that variation in rates of postconflict affiliation is related to variation in the characteristics of dyadic relationships, e.g., value, compatibility and security, and that the characteristics will vary widely across dyads within a group, perhaps more so than across groups (van Schaik and Aureli, 2000; Cords and Aureli, 2000; de Waal, 2000b; Aureli et al., 2002; Judge, 2003). Accordingly, the more widely supported hypothesis is the so-called valuable relationship hypothesis (Kappeler and van Schaik, 1992; van Schaik and Aureli, 2000; Cords and Aureli, 2000; de Waal, 2000b; Aureli et al., 2002), in which the likelihood of reconciliation is related to the value that the adversaries attach to their relationship. Thus, relationship partners such as friends and allies, that strongly depend on one another to maximize their quality of life, e.g., levels of stress and access to desirable commodities and vital resources and their biological fitness, i.e., survival and reproduction, should be especially inclined to peacemaking after a conflict.
Table II.

Variables of physical and social settings from a sample of postconflict affiliation studies on species of Great Apes and Old World monkeys

Speciesa

Setting

Enclosure size

Group size

Sex ratio

Pan troglodytes1

C

375–7000 m2

20

3

P. troglodytes2

C

720 m2

19

9

P. troglodytes3

C

1909–4417 m2

5

1.5

P. troglodytes4

W

50–51

1.15

P. troglodytes5

W

31

3.67

P. paniscus6

C

84, 84, and 625

3, 3, and 6

.5, 1, and 1

P. paniscus7

W

17 (only FF)

?

P. paniscus8

C

5230 m2

11

1.67

Gorilla beringei9

W

31–33 and 16–17

5–2.75 and 3.5

Macaca mulatta10

C

100 m2

41

7.33

M. mulatta11

C

56–1444 m2

58–65

7.33–6

M. mulatta12

C

722 m2

67–94

14

M. mulatta13

C

1000 m2

19–21

6.5

M. tonkeana13

C

1000 m2

14–16

6

M. arctoides14

C

100 m2

21

12

M. arctoides15

C

625 m2

38

2.17

M. assamensis16

W

64

1

M. sylvanus17

C

5000 m2

31

4

M. nigra18

C

1800 m2

20

1.8

M. maurus19

W

20–31

2.5

M. fuscata20

C

50 and 60 m2

16 and 16

1 and 7

M. fuscata21

C

411 m2

36

1

M. fuscata22

C

300 m2

24

1.43

M. fuscata23

C

700 m2

82

1.69

M. fuscata24

W

187

7.83

M. fuscata25

W

227

1.69

M. silenus26

C

1500; 22; and 548 m2

8, 4, and 9

1.5, 3 and 1.33

M. nemestrina27

C

900 m2

34–39

?

M. nemestrina28

C

900 m2

48–53 and 59–65

13.5 and 5.33

M. fascicularis29

C

75 m2

26

9

M. fascicularis30

W

39–50

2

M. fascicularis31

C

310 and 75 m2

67 and 34–47

2.67 and 3

Cercopithecus aethiops32

W

17

6

C. aethiops33

C

120 m2

10

5

Rhinopithecus roxellanae34

C

43 m2

5 and 4

4 and 3

Colobus guereza35

C

40–44 and 97 m2

12 and 8

1 and 3

Trachypithecus obscurus36

C

140 m2

8 and 8

4 and 3

Semnopithecus entellus37

W

26, 10, 4 and 10

11, 0, 0 and 0

Erythrocebus patas38

C

940 m2

11

10

Cercocebus torquatus atys39

C

900 m2

85

4.63

Papio papio40

C

350 m2

33

1.5

P. anubis41

W

64–72

3

P. hamadryas42

C

936 m2

61–103 and 58–68

2.1 and 2.17

Theropithecus gelada43

C

?

(6 and 4)+1

5 and 3

Note. 1de Waal and van Roosmalen (1979);2 Preuschoft et al.(2002); 3Fuentes et al.(2002); 4Arnold and Whiten (2001); 5Wittig and Boesch (2003a, b); 6de Waal (1987b); 7Hohmann and Fruth (2000); 8Palagi et al.(2004); 9Watts (1995a, b); 10de Waal and Yoshihara (1983); 11Call et al.(1996); 12Matheson (1999); 13Demaria and Thierry (2001);14 de Waal and Ren (1988); 15Call et al. (1999, 2002); 16Cooper and Bernstein (2002); 17Aureli et al.(1994); 18Petit and Thierry (1994a); 19Matsumura (1996); 20Aureli et al.(1993); 21Chaffin et al.(1995); 22Petit et al.(1997); 23Schino et al.(1998); 24Koyama (2001); 25Kutsukake and Castles (2001); 26Abbeg et al.(1996); 27Judge (1991); 28Castles et al.(1996); 29Aureli et al.(1989), Aureli and van Schaik (1991); 30Aureli (1992); 31Das et al.(1997); 32Cheney and Seyfarth (1989); 33Daniel et al.(2003); 34Ren et al.(1991); 35Björnsdotter et al.(2000); 36Arnold and Barton (2001a,b); 37Sommer et al.(2002). 38York and Rowell (1988); 39Gust and Gordon (1993); 40Petit and Thierry (1994b); 41Castles and Whiten (1998); 42Zaragoza and Colmenares (1997), Romero-Benavente and Colmenares (2003); 43Swedell (1997)

aThe following publications include the study of more than one group: 6, 20, 26, 28, 31, 35, 36, 37, and 42.

VARIATION IN SETTING-RELATED VARIABLES

Some of the characteristics of the settings wherein researchers have studied conflict management strategies of great apes and Old World monkeys are in Table II. I include three of the setting variables that generally have an impact on interindividual interactions and social relationships of primates. In captive settings, the size of the enclosures is extremely variable, e.g., 22–7000 m2 (Macaca silenus and Pan troglodytes, respectively). The wide range of variation in enclosure size occurs across studies both within and between species and genera (Table II). The size of the enclosure is not the only and, to some extent, the most important characteristic of the physical setting to consider when assessing the impact of captivity on postconflict affiliation. In many cases, the vertical or above-the-ground dimension is equally important, as well as the complexity of the enclosure as assessed by the availability of structures that allow individuals to be out of sight of other group members as they move along within the enclosure, like in the wild, and as a strategy of active avoidance when they want to behave furtively, e.g., mating by subordinates, or to escape from an ongoing aggressive interaction by running away across difficult routes or by breaking visual contact with aggressors, like in the wild. Unfortunately, this information is rarely reported in any detail in published studies and an adequate assessment of its effects is largely lacking.

The amount and type of food offered to captive groups, the way it is given, i.e., as a single patch or widely dispersed, and the number of times individuals are fed are rarely reported in captive studies; thus quantitative information on the variables is hard to come by. This is unfortunate because all of the variables influence social behavior, interindividual relationships and group structure (Wrangham, 1980; van Schaik, 1989) and therefore play a key role in the assessment and interpretation of postconflict affiliation (van Schaik and Aureli, 2000).

The characteristics of the social setting can be assessed via several parameters. Group size and the adult sex ratio are parameters easily quantified and therefore are generally reported in postconflict studies. The range of variation in the size of captive groups is very large, e.g., 3–103 (Pan paniscus and Papio h. hamadryas, respectively), as is also the case for groups studied in the wild, 4–72 (Semnopithecus e. entellus and P. h. anubis, respectively), and holds true across studies within and between species and genu (Table II). However, re: the social behavior among individuals within a group, perhaps the adult sex ratio, i.e., the ratio of sexually mature females to males, is more important than group size is because it strongly influences levels of competition for mates and social partners generally, of cooperation to out-compete rivals, and of partner choice and coercion among individuals (Dunbar, 1988; van Schaik, 1989; Hemelrijk and Luteijn, 1998; Janson and van Schaik, 2000). It was difficult to collate figures of adult sex ratio in Table II, because of differences across studies in the age range used to categorize the reproductive status of males mainly, and some may be incorrect. In fact, the socionomic sex ratio, i.e., the ratio of sexually mature females to males within reproductive units, would be a finer proxy for assessing intensity of competition within a group; however, it is available only exceptionally, e.g., for harem-forming species (Dunbar, 1984; Colmenares et al., 2002).

The adult sex ratio is highly variable within and across settings as well as across studies within and between species (Table II). For example, for chimpanzees, the range is 1.5–9 females per male in captivity vs. 1.15–3.67 in the wild; and for Japanese macaques .90–7 in captivity vs. 1.69–7.83 in the wild. Of the postconflict affiliation studies in Table II, in 16 (36%) captive groups and in 2 (13%) wild groups only 1 adult male was present. In some cases, the specific modal social system consists of one-male/multifemale units; in many others, however, the reproductive units typically contain multiple adult males, so that variation in the absolute number of males is most likely to make a difference in the patterns of social behavior observed at the group and dyadic levels. This is not a problem but an opportunity to study the effect of variation in levels of male and female competition on patterns of postconflict affiliation.

In addition to group size and adult sex ratio, several other parameters of the social setting influence social behavior and relationships and researchers should assess them adequately. The parameters include 1) the number and size of each group member’s network of friends and allies, 2) the history of relationships between group members, and 3) the level of stability of the dominance relationships and hierarchy within the group (Dunbar, 1988; Chapais, 1995; Henzi et al., 1997), and any of them may vary widely both in captivity as well as in the wild.
Table III.

Methods used in a sample of postconflict affiliation studies on species of Great Apes and Old World monkeys

Species

Settinga

Samplingb

Controlsc

Focal individuald

Behaviore

Pan troglodytes1

C

PC, PrC

VT

P (2 min), NC+C (5 min)

P. troglodytes2

C

PC, MC

GA

AG and VT

C (15 min)

P. troglodytes3

C

PC, MC

Both?

P, NC+C (10 min)

P. troglodytes4

W

PC, MC, BL

GA, D (≤10 m)

AG and VT

C (30 min)

P. troglodytes5

W

PC, BL

AG and VT

C (all-day)

P. paniscus6

C

PC, BL, PrC,

Both

C

P. paniscus7

W

PC, PrC

Both

Genital C

P. paniscus8

C

PC, MC

 

VT

C (30 min)

Gorilla beringei9

W

PC, MC, BL

GA

VT

C (10 and 30 min)

Macaca mulatta10

C

PC, MC

AG and VT

P, NC+C (10–20 min)

M. mulatta11

C

PC, MC

AG and VT

C (10 min)

M. mulatta12

C

PC, PA, BL

VT

C (60 min)

M. mulatta13

C

PC, MC

AG and VT

NC, C (10 min)

M. tonkeana13

C

PC, MC

AG and VT

NC, C (10 min)

M. arctoides14

C

PC, MC

D (≤5 m)

AG and VT

P and C (10 min)

M. arctoides15

C

PC, MC

AG and VT

P and C (10 min)

M. assamensis16

W

PC, BL

D (≤25 m)

AG and VT

P and NC+C (10 min)

M. sylvanus17

C

PC, MC

VT

NC+ C (5–10 min)

M. nigra18

C

PC, MC

D (≤3 m)

VT

NC+C (10 min)

M. maurus19

W

PC, BL

D (≤3 m)

VT

NC+C (15 min)

M. fuscata20

C

PC, MC

VT

NC+C (5–10 min)

M. fuscata21

C

PC, MC, BL

AG and VT

P and C (10 min)

M. fuscata22

C

PC, MC

VT

NC+C (10 min)

M. fuscata23

C

PC, MC

D (≤3 m)

VT

NC+C (5 min)

M. fuscata24

W

PC, MC, BL

VT

NC+C (10 and 30 min)

M. fuscata25

W

PC, MC

D (≤50 m)

AG and VT?

NC+C (10 min)

M. silenus26

C

PC, MC

D (≤3 m)

VT

NC+C (10 min)

M. nemestrina27

C

PC, BL

AG and VT

NC+C (5 min)

M. nemestrina28

C

PC, MC, BL

AG and VT

NC+C (10 min)

M. fascicularis29

C

PC, MC

VT

NC+C (10 min)

M. fascicularis30

W

PC, BL

GA, in sight

VT

NC+C (15 min)

Macaca fascicularis31

C

PC, MC

AG

NC and C (5—10 min)

Cercopithecus aethiops32

W

PC, PrC

Both

C (30 min)

C. aethiops33

C

PC, MC

GA

Both

NC+C (10 min)

Rhinopithecus roxellanae34

C

PC, MC

VT

NC+C (10 min)

Colobus guereza35

C

PC, MC

AG and VT

P and NC+C (10 min)

Trachypithecus obscurus36

C

PC, MC

D (not in C)

AG and VT

NC+C (10 min)

Semnopithecus entellus37

W

PC, BL

Both

NC+C (3–15 min)

Erythrocebus patas38

C

PC, MC, BL

GA

Both

P+NC+C (10 min)

Cercocebus torquatus atys39

C

PC, MC

AG and VT

P+NC+C (10 min)

Papio papio40

C

PC, MC

D (≤3 m)

VT

NC+C (10 min)

P. anubis41

W

PC, MC

D (≤100 m)

AG and VT

NC+C (5–15 min)

Papio hamadryas42

C

PC, MC

Both, AG

NC+C (10 min)

Theropithecus gelada43

C

PC, MC

GA, D (≤3 m)

VT

NC+C (5 min)

Note. References 1–43 as for Table II.

aC = captivity, W = wild.

bPC = postconflict observations, MC = matched-control observations, PrC = preconflict observations, BL = baseline observations.

cD = interopponent distance; GA = general activity.

dBoth = both opponents were followed simultaneously, AG = the aggressor was focal subject, VT = the victim was focal subject. eP = proximity, NC = noncontact affiliation, C = contact affiliation. Figures in parentheses denote duration of PCs and the corresponding MCs.

DIFFERENCES IN METHODS

Table III is a summary of some of the methodological decisions that workers have adopted. Following de Waal and Yoshihara’s (1983) approach, almost every single study has relied on comparisons of the opponent’s behavior during postconflict periods and during matched-control observations. Two major trends pertaining to the way that authors match control observations with postconflict samples are evident. First, in the majority of captive studies, researchers collect control observations after the postconflict observations, on the next possible observation day and typically 5–7 d after the day of the conflict and postconflict. Though workers often attempt to match for ≥1 of the following variables: the time of day, season, general activity, distance between the opponents at the start of the control observation, and the absence of agonistic interactions before initiation of control observations, in practice, the number of control variables actually used and the way workers have measured them may vary widely across studies. Second, in some captive studies and in the majority of the few studies conducted in the wild, the control data have come from baseline observations. Investigators may have collected them before the conflict itself or another day, before or after the day they recorded the conflict and postconflict data. In the wild, there is greater emphasis on matching for the focal subject’s general activity and for the interopponent distance than for time of day.

With regard to the identity of the focal subject, i.e., aggressor or victim or both, overall, I followed victims more often than I followed aggressors (43 vs. 28). Nevertheless, in 26 of 45 studies, both opponents were focal subjects. The length of the PC and MC observation periods varied across studies (\(\bar x \pm {\rm SD} = 12.8 \pm 9.59\,{\rm min}\), n=51, range=3 min, all day); and they tended to be longer in wild settings than in captivity (wild: range=3 min, all day; captivity: range=5–60 min; Table III).

In many studies, authors do not clearly describe categories of behavior, i.e., proximity, noncontact affiliation, and contact affiliation, used to assess the occurrence of postconflict affiliation. In particular, whereas most studies seemed to be interested in comparing the rate of friendly contacts in PC vs. MC, in practice, however, the affiliation category actually involved both contact and noncontact exchanges (Table III).

In addition to the methods in Table III, several other methodological decisions are likely to influence the assessment of postconflict affiliation and vary across studies, including the 1) definition of conflict; 2) criterion to start (and restart) the postconflict observation period, e.g., the PC period is reset if an aggressive behavior occurs 30 s, 1 min, or 2 min after the beginning of the PC; 3) type of controls used to start a MC observation or to choose the control data from baseline observations, e.g., interopponent distance, general activity, and context; 4) definition of postconflict affiliation; and 5) way that the PC and MC data are scored, e.g., 30-s intervals, 1-min intervals).

Though it is clearly an oversimplification (Mason and Mendoza, 1993; Colmenares, 1996; Judge, 2003), for practical reasons, the vast majority of the studies of conflict management investigate only conflicts in which the conflicting parties display overt signs of aggression, e.g., threats, attacks, and actual physical contact. However, the studies may vary widely in the operational definition of aggressive conflict they adopt. For example, some define aggressive conflicts exclusively in terms of the actor’s behavior; others take also into account the recipient’s response, and yet others use such restrictive criteria as the requirement that the recipient must display submissive behavior. As regards the criterion to define what counts as evidence of affiliation (in either observation period, i.e., PC and MC), we find again that most studies tend to take into account only if any of the interactants—opponents or bystanders or both—display affinitive behavior; however, it would be important to consider if the recipient of friendly behavior by one of the participants responds with affiliation (de Waal, 1987a); in other words, one should make sure that the interaction is friendly, not just the behavior of one of the partners.

Finally, the categories of interopponent distance that have been used in captivity and in the wild have been highly arbitrary and variable (Table III), despite its potential implications (Call, 1999). This is also true of the length of the period preceding the matched control observation during which the investigator controls for the occurrence of aggression in the different studies.

IS THE CLAIM SUPPORTED BY THE DATA?

Table IV is a summary of some of the findings on presence/absence and rates of postconflict affiliation obtained in studies of great apes and Old World monkeys in captivity and in the wild. Differences in the number of agonistic dyads and PC-MC paired observations on which researchers have conducted analyses and from which they have drawn conclusions are very large indeed (overall: \(\bar x \pm {\rm SD} = 345.79 \pm 319.90\), range=33–1365, N=47; captivity: \(\bar x \pm {\rm SD} = 325.56 \pm 292.65\), range=33–1270, N=36; wild: \(\bar x \pm {\rm X} \pm {\rm SD} = 408.73 \pm 406.56\), range=48–1365, N=11). Most studies focused only on one type of postconflict affinitive behavior, i.e., reconciliation (Table IV), which is fairly inconvenient not only because the picture obtained is rather incomplete but also because we are left with only one measure to make any kind of comparison, e.g., across settings, species, dyads, regarding the importance of postconflict affiliation.

Researchers have analyzed third-party affiliation (TPA) in only 22 of 49 studies (16 in captivity and 6 in the wild). Unfortunately, in 7 of them, the authors did not distinguish which partner, i.e., one of the opponents or the bystander, initiated the friendly interaction. Researchers analyzed triadic affiliation (TA) in 15 studies, and in many of them (i.e., 7 of 15), the authors reported only whether their subjects showed TA or not. Where authors calculated and reported figures for triadic conciliatory tendencies, i.e., TCT, all of them from captive studies, the variation was important, from −0.21 to +71.9. It is often difficult to make comparisons across the studies, though, because the reports vary in the type of indices they provide. Thus, whereas some describe tendencies for the whole group (typically the adult individuals only), others present indices only for some age/sex classes or for aggressors and victims separately, or both (or even for pooled data). Researchers analyzed consolation (CS) in 12 of the studies in Table IV; CS occurs only in 4 studies involving 3 species—Pan troglodytes, P. paniscus, and Macaca arctoides—and indices are available only for 1 of the species, the study of captive P. paniscus by Palagi et al.(2004).

Reconciliation occurs in all the studies wherein investigators looked for it (Aureli et al., 2002), except in captive black lemurs (Eulemur macaco) (Roeder et al., 2002) and in the study by Sommer et al.(2002) on hanuman langurs in the wild. Though Kappeler (1993) also reported ring-tailed lemurs (Lemur catta) to be a nonconciliatory species, in later studies, also in captivity Rolland and Roeder (2000) and Palagi et al. (2005) found evidence for reconciliation in them. Interestingly, in the latter study, only 1 of the 2 captive groups of Lemur catta showed conciliatory behavior. Matsumura (1996) reported a CCT of 40% for wild M. maurus; however, when he controlled for the distance (<3 m) between the former opponents at the start of the selected paired MC sample, he found no evidence of reconciliation, i.e., the number of attracted pairs was not significantly higher than the number of dispersed pairs. In spite of the negative results when researchers adopted a more stringent criterion, Matsumura (1996) concluded that their findings supported the reconciliation hypothesis and further demonstrated that reconciliation also occurs in the wild. However, though several authors have incorporated a control measure for interopponent distance (Table III), the criterion of <3 m is likely too conservative, especially under field conditions. In fact, in the wild the criterion adopted is typically more relaxed, i.e., 10–100 m, or the opponents may have simply been within each other’s sight during the candidate MC observation.
Table IV.

Findings from a sample of postconflict affiliation studies on species of great apes and Old World monkeys

Species

Settinga

Sampleb

RCc

Initiatived

TAe

CSf

TPAg

Pan troglodytes1

C

350

Yes

AG=VT

Yes

P. troglodytes2

C

401

41.2

P. troglodytes3

C

224

13.9

No?

P. troglodytes4

W

120

12.3

AG<VT*

Yes

Yes?

P. troglodytes5

W

876

Yes

AG=VT

Yes

Yes

P. paniscus6

C

512

48.0*

AG>VT*

P. paniscus7

W

120

Yes

P. paniscus8

C

167

35.6

AG=VT

22.8

21.0

Gorilla beringei9

W

229

Yes: only dyads M-F

Yes

No

Macaca mulatta10

C

350

13.3ct

AG>VTns

Yes

No

M. mulatta11

C

1143

7.1–8.1

M. mulatta12

C

33

No

No

M. mulatta13

C

280

11.0: F–F dyads

AG>VTns

M. tonkeana13

C

260

47.9: F–F dyads

AG>VTns

M. arctoides14

C

400

51.3ct

AG<VTns

M. arctoides15

C

251

34.9

Yes

Yes

M. assamensis16

C

247

11.2

AG>VT*

M. sylvanus17

C

453

Yes

No

M. nigra18

C

89

40.5

AG>VTns

No

M. maurus19

W

45

40.0 and no

AG<VT

M. fuscata20

C

640

Yes

AG=VT

No

M. fuscata21

C

116

5.9ct

M. fuscata22

C

2688

Yes

M. fuscata23

C

1270

8.4

M. fuscata24

W

160

Yes

M. fuscata25

W

543

14.0

M. silenus26

C

57

43.8

  

42

47.6

  

74

41.9

M. nemestrina27

C

614

30.0ct

AG<VT*

Yes

M. nemestrina28

C

174

20.4

AG>VTns

  

223

41.9

AG<VT*

   

M. fascicularis29

C

526

21.0ct

AG<VT*

Yes

No

M. fascicularis30

W

156

15.0ct

 

Yes

no

M. fascicularis31

C

301

−0.21−0.11

Cercopithecus aethiops32

W

289

7ct

17 ct

C. aethiops33

C

57

14.0

Rhinopithecus roxellanae34

C

196

43.0 (pooled)

Colobus guereza35

C

132

45.0

AG<VT

   

Trachypithecus obscurus36

C

93

51.3

AG>VT

AG:43.1ct

No

  

173

41.3

AG<VT

VT:71.9ct

  

Semnopithecus entellus entellus37

W

1365

No

AG<VT

?

Erythrocebus patas38

C

100

52.0

AG>VT

Cercocebus torquatus atys39

C

307

13.0

AG<VT

Papio papio40

C

580

22.2

AG>VTns

P. anubis41

W

590

15.6

AG>VTns

No

P. hamadryas42

C

790

19.0

AG<VTns

AG:21,VT:16

No

  

664

19.2

AG: 17

No

Theropithecus gelada43

C

47

47.0 (pooled)

Note. References 1–43 as for Table II.

aC = captivity, W = wild.

bNumber of PC-MC pairs; †total number of agonistic interactions.

cRC = reconciliation; figures denote CCTs, unless otherwise stated. CT = conciliatory tendency. CCT = corrected conciliatory tendency. *Percentage of PCs with affiliation within 10 min.

dAG = aggressor, VT = victim; *statistically significant difference; NS = not significant. Otherwise no statistical analysis was reported.

eTA = triadic affiliation; figures represent TCTs.

fCS = consolation. gTPA = third-party affiliation.

Though the evidence for reconciliation appears strong and widespread, quantitative comparisons across studies and therefore across different levels of variables of theoretical interest, e.g., settings, species, dyads, may sometimes be difficult to make for several reasons. First, the indices provided for assessing conciliatory tendencies can be different, for example, CT vs. CCT or simply the proportion of conflicts that were followed by affiliation within a given time window (de Waal and van Roosmalen, 1979; de Waal, 1987b), and investigators have not yet empirically established how large the differences between the various indices can be.

Second, the number, if any, and type of controls used and the actual measures of each of them can also vary. For example, for chimpanzees, Arnold and Whiten (2001) controlled for interopponent distance (<10 m) and general activity, the latter assessed in terms of such activity categories as resting, feeding and traveling (on trees as well as on the ground). Preuschoft et al.(2002) controlled only for general activity, which they assessed in a quite different way: number of nonagonistic interactions for each MC relative to number of nonagonistic interactions in all PC periods. Finally, Fuentes et al.(2002) and Wittig and Boesch (2003a,b) did not use any of the aforementioned controls.

Finally, the studies often provide average values of CT or CTT for different units of analysis, for example, whole groups or particular age/sex classes of dyads (Table IV), and the consequences can be potentially important. For example, in a study of wild mountain gorillas, Watts (1995a) found that reconciliation occurred only between the unit leader male and his females, as expected according to the relationship value hypothesis; had he averaged over the different classes of dyads the picture that emerged would have been greatly distorted. In two different studies of hamadryas baboons conducted in the same captive setting (but 5 years apart, 1995 vs. 2000), we found that whereas the average CCT for the whole group (only adult individuals) was almost the same, i.e., 19 and 19.2, respectively (Table IV), the average CCT for different classes of dyads was quite different, i.e., male-male dyads = 36% vs. 22%, male-female dyads = 50% vs. 38.22%, and female-female dyads = 13% vs. 18%, respectively.

Given all the differences across studies in so many significant variables, one should not take results from direct comparisons based on the figures provided at face value, but treat them with caution. Researchers have studied 5 of the species in Table IV in both settings: Pan troglodytes, P. paniscus, Macaca fuscata, M. fascicularis, and Cercopithecus aethiops; in all of them reconciliation occurs, and the differences in the average conciliatory tendencies reported are neither dramatic nor consistent, and investigators do not always obtain the highest rates in captive settings. For example, in 4 studies on chimpanzees based on controlled PC-MC comparisons, 2 in captivity (Fuentes et al., 2002; Preuschoft et al., 2002) and 2 in the wild (Arnold and Whiten, 2001; Wittig and Boesch, 2003a,b), differences in average CTT, when reported, were larger within than across settings, i.e., captive settings: 41.1 vs. 13.9, wild setting: 12.3. Among Japanese macaques, the tendencies were CT=5.9 and CTT=8.4 for 2 captive studies and CTT=14.0 for 1 (of 2) study conducted in the wild.

DISCUSSION

The claim that the rate and form of postconflict affiliation represents an artifact of captivity may mean several things. A soft version of the artifact charge could be that captivity increases the likelihood of postconflict affiliation simply because captivity leads to a general increase of aggressive interactions between group members and a reduced opportunity for victims to avoid their attackers if they want to (Sommer et al., 2002). One can readily reject the version. First, captivity does not necessarily lead to increased rates of aggression (Judge, 2000). Second, the version appears to interpret postconflict affiliation initiated by victims as the outcome of tendencies to repulse that are thwarted by space limitations in captivity. However, in many cases, the size and complexity of the captive settings clearly allow victims to choose their postconflict strategy (Table II), that is, to approach and make peace with the former opponent or to withdraw. Further, in the wild, victims also at times approach rather than avoid their opponents (Table IV). Finally, according to the relational model (de Waal, 1996, 2000b), friendly reunions with former opponents are driven motivationally by attraction not by thwarted repulsion, which fits the evidence that in many species aggressors often take the initiative in postconflict affinitive interactions (Aureli, 1997; Das, 2000); sometimes they are even more active in initiating reconciliation than their victims are (Table IV).

A stronger version of the artifact claim might entail that captivity pushes an individual’s behavior beyond the reaction norm of the species. The behavior of captive individuals would then be abnormal and, perhaps, maladaptive, and its study would be of hardly any value to understand the natural behavior of the species, which can be expressed only in the natural habitat. To analyze the hidden and overt assumptions behind such a view of naturalness, which has sometimes called into question the validity of findings in captive settings, unless and until confirmed by field data, is beyond the scope of my article. The range of natural variation of a specific behavior and habitat is not known and may never be. Thus, our priority should be to identify relevant (independent or predictor) process-related variables that account for variation in the social behavior in either setting and then to test the corresponding hypotheses under the observational and experimental conditions at hand. Every setting can and should contribute to this endeavor (de Waal, 1994). The processes driving an individual’s rate of postconflict affiliation in either setting will only be hinted at if we are able to unveil the range of behavioral variation of the species, which will be possible only if we observe it under the widest possible range of conditions. In this regard, setting conditions that may deviate very much from hypothetical natural conditions of a given species can in fact shed unique light on their adaptability potential and, even more important, on the unobservable, but equally natural, psychological processes that support the behavior of individuals in either setting.

Presently, a wealth of evidence shows that the rate and type of postconflict affinitive behavior are strongly determined by the nature of the relationship between the opponents and between them and third parties, including such characteristics as the value and security of the relationship and the compatibility between the partners (Kappeler and van Schaik, 1992; Cords and Thurnheer, 1993; van Schaik and Aureli, 2000; Cords and Aureli, 2000; de Waal, 2000b; Aureli et al., 2002). In turn, social processes, e.g., the history of interactions between the individuals within the groups, the stability and size of alliance networks, and the style of dominance relationships and the group’s demographic structure, e.g., sex ratios, and its effects on levels of competition and cooperation, greatly influence the distribution of the relationship characteristics over the dyads of individuals in a group (Baker and Smuts, 1994; Chaffin et al., 1995; Watts, 1995a,b; Castles et al., 1996; Aureli et al., 1997; Thierry, 2000; Arnold and Whiten, 2001; Preuschoft et al., 2002). Further, the variables are as likely to vary within as across settings.

The emphasis in previous approaches to the analysis of the captivity artifact charge has been on showing that postconflict affiliation, especially reconciliation, also occurs in the wild (Aureli, 1992; Matsumura, 1996; Arnold and Whiten, 2001; Aureli et al., 2002). The approach I have adopted here is somewhat different though complementary. First, I started by arguing that the dichotomy captivity vs. wild is meaningless because the number of variables that vary within and across the 2 settings can be enormous, with ranges of variation potentially exhibiting considerable overlap (Fig. 1; Table I). Because the categories are not unitary, one cannot invoke them to explain variation in postconflict affiliation. Second, I have presented evidence that, in fact, the characteristics of the physical and social settings of postconflict affiliation studies in captivity as well as in the wild are highly variable and overlapping (Table II; Fig. 1C). Third, I have also identified several differences across studies in the methodological procedures applied to the collection and analysis of postconflict affinitive interactions (Table III). Finally, I have reviewed the nature of the empirical evidence available and have noted that, even at this level, one cannot support the claim that captivity artificially inflates the rates of postconflict affiliation (Table IV).

Progress in the area of conflict management and resolution research requires not only further empirical tests of established theoretical predictions but also a critical examination of untested (and sometimes hidden) assumptions, and of a number of conceptual and methodological issues. Such a critical attitude has always helped to revitalize research in the area since it began in 1979 (de Waal and Yoshihara, 1983; Aureli et al., 1989, 2002; Kappeler and van Schaik, 1992; Cords, 1993; Veenema et al., 1994; de Waal, 1996; Silk, 1996, 2002; Aureli, 1997; Call, 1999; Call et al., 1999). The critical approach of Sommer et al.(2002) and their challenge of established procedures also represent important contributions in this respect. Nevertheless, I think that one cannot support their specific claim that postconflict affiliation may be partly an artifact of captivity. In fact, I propose that researchers abandon altogether the dichotomy captivity vs. wild as a variable with explanatory status. A great many ecological, demographic, and social variables influence the occurrence and intensity of peacemaking and other social behaviors in nonhuman primates, but variation in very few of them, if any, can be consistently associated with only one of the two settings. Even if postconflict affiliation occurs only (or more often) in one of the two categories of setting, we still would have to find out why. In this respect, one would need to account for either its occurrence or absence, and in searching for the underlying causes we would gain valuable information about the psychological processes that drive the expression of natural conflict resolution strategies under a variety of circumstances.

Notes

ACKNOWLEDGMENTS

Project grants PB92-0144, PB95-0373, PB98-0773, and BSO2002-00161, from the Ministry of Education, Science and Technology, Spain have continuously funded my research on conflict management and resolution in nonhuman primates and children. I thank the Directorate of the Madrid Zoo for permission to conduct the long-term research project on the colony of hamadryas baboons and for their collaboration. I prepared portions of the paper while I was a guest scientist in the Max-Planck Institute for Evolutionary Anthropology, at Leipzig, Germany. I thank Josep Call and Michael Tomasello for the use of the facilities in their department and for their hospitality, and the Ministry of Education and Science, Spain, for funding my stay through a Salvador de Madariaga scholarship (PR2004-0015). I thank Nicola Koyama and Elisabetta Palagi for inviting me to participate in the IPS Symposium in which I presented a draft version of the paper, and the Facultad de Psicología of the Universidad Complutense de Madrid for a travel grant to attend. Finally, I thank 2 anonymous reviewers for their constructive and helpful comments.

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© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Departamento de Psicobiología, Facultad de PsicologíaUniversidad Complutense de MadridMadridSpain

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