On the relation between social dynamics and social learning

Anim.

Behuv.,

1995, 50, 144-1453

On the relation between social dynamics and social learning SABINE COUSSI-KORBEL* *Laboratoire

de Primatologie-Biologique fPsychology (Received final

& DOROTHY

Evolutive, CNRS Department, University

20 May 1994; initial acceptunce 15 March

acceptance 1995; MS.

M. FRAGASZYt URA 373, of Georgia

Universitt

de Rennes

I

12 September 1994; number: 466X)

Experimental studies on social learning in animals have commonly centred on the psychological processesresponsible for learning, and neglected social processesas potential inlluences on both the likelihood of social learning and the type of information that can be acquired socially. A model relating social learning to social dynamics among members of a group is presented. Three key hypotheses of the model are (1) behavioural coordination in time and/or space supports the process of social learning; (2) different kinds of coordination differentially support acquisition of different kinds of information; and (3) the various forms of behavioural coordination will be differentially affected by social dynamics. Severalpredictions relating inter-individual and group differences in social dynamics to social learning that follow from these hypotheses are presented,

Abstract.

,i 1995 The Association

Traditionally, social learning among animals has been studied experimentally by psychologists interested in demonstrating the phenomenon, and in identifying the psychological processes’responsible for learning (reviewed in Galef 1988; Heyes 1993; Laland et al. 1993). The typical experimental design has made use of a model and an observer, isolated from other conspecifics. In contrast, social learning has been considered by ethologists and ecologists in relation to its contributions to adaptive variations of behaviour within groups over time, and as a source of variations of behaviour across groups of the same species. At present, these two traditions of research on the same topic have little to say to one another. The understanding of social learning from ecological and comparative perspectives would be aided by experimental attention to social learning in groups rather than in individuals (Lepoivre & Pallaud 1985). Heartening developments in this direction are now occurring. For example, Lefebvre (in press) suggests focusing on the relations between competitive foraging strategies and social learning. Lefebvre’s research proCorrespondence:D. M. Fragaszy,PsychologyDepartment, University of Georgia, Athens, GA 30602-3013, U.S.A. (email: [email protected]). S. CoussiKorbel is at the Station Biologique, Laboratoire de Primatologie-Biologique Evolutive,Universitdde Rennes 1, 35380Paimpont,France. 0003-3472/95/121441+08

$12.00/O

for the Study of Animal

Behaviour

gramme includes observations of spontaneous interactions among free-ranging birds, as well as traditional experimental studies of observer/ demonstrator pairs. Patterns of social learning among the birds (Columbids) studied by Lefebvre and co-workers reflect in part the frequent formation of transient social groupings of relative strangers during foraging (Giraldeau & Lefebvre 1986). Many animals, however, live for long periods within the same social unit, and even birds that form transient flocks may also spend much time within stable social units, such as nesting colonies (Hausberger, in press). Within stable social groups, long-term social relationships develop, and dynamic social processes influence all aspects of life. Thus social learning takes place within a structured social context for many animals. It seemslikely that the specificsocial context in which a group-living animal finds itself influencesits opportunities for social learning, and perhaps also its propensity to learn certain things from certain individuals. This aspect of social learning has not received the formal attention it deserves. In this paper, we address the issue of social learning in relation to social dynamics among members of a group with stable membership. Two dimensions of variation in social learning are of interest to us: within group and between group, including between species.Both are relevant to the ecological and evolutionary significance of social

D 1995The Associationfor the Study of Animal Behaviour 1441

1442

Animal

Behaviour,

learning. To be able to discuss both of these dimensions of variation, we need a general framework to talk about social learning that is task- and species-independent. Therefore, we adopt a conceptual framework of social learning in terms of behavioural coordination between individuals, and in terms of the kind of information that may be acquired by an observer from a demonstrator. That is, we neglect for the moment the psychological mechanisms of learning (i.e. the distinctions between facilitation, enhancement, imitation, etc.). Differences across species in social learning have been proposed to reelect cognitive differences, most notably in comparisons of humans with other species(e.g. Tomasello et al. 1993). It is beyond the scope of this paper to evaluate the evidence that cognitive factors are responsible for individual and species differences in social learning between animals. We simply note that the obvious differences presented by humans compared with other species in attributional capacities, for example, are greater than those found in comparisons of other animal species.A presumed cognitive difference is merely a default explanation for speciesdifferences in social learning among non-human animals. Here, we wish to avoid the problem of identifying cognitive versus social sources of speciesdifferences in social learning. As long as tests of our model can make use of tasks that are easily within the capability of all individuals studied, and as long as fundamental differencesin social cognitive skills (e.g. attribution) are not involved, a cognitive explanation for species differences is unlikely. The same argument applies to individual differences within species. In the following sections of this paper, we (1) distinguish different forms of information that can be acquired from another individual’s activity; (2) elaborate our conception of behavioural coordination; (3) consider the type of coordination that supports obtaining each kind of information from the behaviour of a conspecific; (4) consider the relationship between social dynamics and behavioural coordination; and (5) present several testable predictions drawn from this approach which can address speciesdifferences in social learning. TRANSMISSION THROUGH

OF INFORMATION BEHAVIOUR

A first requirement for the occurrence of social learning is a stimulus that both draws the learner’s

50, 6

attention and provides it with information. We conceive of information being provided from one animal to another through three forms of stimulation. (1) Affective stimuli, through affective displays (in several modalities; e.g. visual, olfactory, auditory). Also, stereotypical fixed action patterns that trigger the same patterns in others, and speciestypical behaviour that results in species-normal imprinting. (2) Physical stimuli reflecting previous activity (‘residual traces’: Sherry & Galef 1984), such as a scent or an object or surface that has been altered by previous activity (gnawed sections, etc.). (3) Activity stimuli, through movement and interaction with other animals or objects in the environment during ongoing activity. These forms of socially provided stimuli are not exclusive. Indeed, in many, if not most, situations, all three will be present. For example, in the common situation in which animals are feeding near one another, each animal may be moving, making sounds through its movements, providing scents through its mastication and other processing of foodstuffs, leaving bits of food nearby, and occasionally making vocalizations associated with feeding and contentment. The significance of the categorization of the forms of stimuli available for social learning for our purposes is that it allows us to consider the predominant form of information available in a given situation to a potential learner. This, in turn, allows a more precise consideration of the kinds of information that the learner can acquire in that situation. All of these forms of stimuli may contribute to social learning. Their distribution across speciesshould be related to the social, sensory, behavioural and cognitive characteristics of individuals in each species. COORDINATION

OF BEHAVIOUR

Behdvioural coordination is common to all forms of social learning. In principle, we may distinguish between two main forms of coordination: complementary (where behavioural asymmetry results) and isomorphic (where behavioural similarity results). Complementary coordination may occur, for example, in teacher/pupil, mother/infant, expert/scrounger or dominant/subordinate pairs, where one individual modulates its behaviour precisely to differ from another or to produce

Coussi-Korbel

& Frugaszy: Social Ieurning

change in the other. For example, Giraldeau & Lefebvre (1987) studied foraging in flocks of pigeons, Columba livia, housed in an aviary. In these flocks, when one individual used a specialized technique to obtain food, its foraging successes were accompanied by ‘scrounging’ in others. Scroungers developed consistent complementary behavioural patterns in this situation. This is an outcome similar to that seen in dominant/subordinate pairs of chimpanzees, Pun troglodytes, and mangabeys, Cercocebus f. torquuPUS,in which a more dominant individual exploits the activities of subordinates (e.g. Menzel 1973; Coussi-Korbel 1994). Although complementary coordination involves a social transmission of information, with the exception of teacher/pupil relationships, it inhibits rather than supports the transmission of a particular behaviour pattern, skill or habit between members of a group, at least as long as the particular social conditions supporting its occurrence are maintained (Giraldeau & Lefebvre 1986; Anderson et al. 1992). For example, Giraldeau & Lefebvre (1986) showed that scroungers did not learn to obtain food directly by opening a container as long as * scrounging was an effective option. More often, social learning involves isomorphic coordination of behaviour. An isomorphic coordination of behaviour patterns between two or more conspecific individuals occurs when one individual’s activity channels the attention of its conspecific to an activity or an element in the environment, such that behavioural similarity between the two individuals increases. Coordination of behaviour in this sense is necessarily sequential, rather than simultaneous. That is, A provides a model for B as opposed to instances where an external stimulus is responsible for behavioural similarity in A and B. The conspecific observer may acquire some general information from the conspecific demonstrator, such as the timing (through behavioural coordination in time) or the location (through behavioural coordination in space) of an activity and sometimes both (through behavioural coordination in time and in space). It may also learn more specific information about the event or situation through further observation of the demonstrator and/or through its own activities. Although behavioural coordination involves actions already in an individual’s behavioural repertoire, it could contribute to learning a new contingency when the socially

I-413

facilitated actions are exploratory or ha~c tile effect of producing novel outcomes when applied in new circumstances (Fragaszy et al. 1994). Note that behavioural coordination in tjnlc does not involve physical proximity across individuals. In the former. observation of a conspecific stimulates an individual to engage in sonl~’ activity (e.g. feeding) while relatively distant in space. Through monitoring the activities ot others, the observer is ‘brought up to date‘ ;md can synchronize its activities with those of others. Behavioural coordination in this manner aids group cohesion, and in that sense makes an important contribution to social life. even in species that do not exhibit more elaborated forms of coordination in space or space and time. Maintenance of group cohesion may contribute to detection and avoidance of predators, efficient exploitation of resources, or other commonly proposed advantages of group living. This argument has been made by Boinski (1987) for squirrel monkeys, Saimiri, and by several authors for flock foraging birds (Crook 196 1; Ward & Zahavi 1973: Krebs 1974; Emlen & Demong 1975; Clayton 1978). Behavioural coordination in space does not require proximity between individuals either. In this form of coordination, an individual approaches a place where another individual has been active, but does so only after the other has left. The first individual must tolerate the second individual approaching the place or object the first individual has vacated. In this case, naive individuals may learn about essential characteristics of the environment through information provided in the form of physical alterations of the environment which persist after the activity in question has ended. In both this and the first form of coordination, the observer is likely to acquire only general information about essential features of the environment from the demonstrator (such as the affective value of the site or activity). It must gain more specific information through its own activities (at a distant site, or at a later time). Only behavioural coordination in space and time involves physical proximity between individuals. In this strong form of behavioural coordination, an individual approaches the same site as another and engages in a similar activity simultaneously with the other at that site (e.g. both feed). This can involve using the same patterns of action as the conspecific demonstrator (e.g.

1444

Animal

Behaviour.

applying the same types of food-processing behaviour), or the observer may behave somewhat differently (for example, sniffing and inspecting a food, rather than consuming it). This form of coordination affords the observer its best opportunity to acquire detailed information from the demonstrator about action, substrate and outcome. This type of information is most related to the forms of social learning commonly described as ‘emulation’ (Tomasello et al. 1987) or imitation. To the extent that specific information about ongoing activities is most easily acquired when close by another, transmission of this type of information is most constrained by achievement of a specific kind of behavioural coordination, which is in turn dependent upon social dynamics. In any case, the extent of behavioural coordination between individuals can be a useful predictor of social learning. Learning (as an outcome) is distinguished by a relatively long-lasting change in behaviour; momentary adjustments in behaviour are not considered as evidence of learning. Coordination of behaviour involves behavioural modifications in the short term. Coordination is a behavioural process that supports social learning, but it is not itself evidence of the outcome of learning (that is, long-term behavioural change). We are interested in both process and outcome, but in this paper, we deal primarily with the process.

DIRECTED SOCIAL IDENTITY CAN MAKE

LEARNING: A DIFFERENCE

We make a distinction between social learning that occurs irrespective of the identity of the active individual (that is, Non-specific social learning) and social learning that occurs differentially as a function of the identity of the active individual (Directed social learning). In Non-specific social learning, one individual’s behaviour towards an object or event increases the likelihood that any other individual will display altered behaviour towards the same object or event. In Directed social learning, the identity of the active individual influences its salience for the observer. That is, particular individuals are more influential models for certain individuals than are others. To conclude that Directed social learning has occurred, as opposed to Non-specific social learning, one

50, 6

has to show that individual identity influences the transmission of information. Both Directed and Non-specific forms of social learning can involve all three forms (l-3 above) of socially provided stimulation. The difference between Non-specific and Directed social learning is not necessarily related to the form of information, the nature of the cognitive process that allows an individual to acquire information from the activity of another, or the complexity of what can be learned. Rather, it is the possibility of modulation of social learning as a function of pre-existing social relationships that varies between Non-specific and Directed social learning. The distinction between Non-specific and Directed social learning is important, biologically, because whereas the first form permits behavioural synchronization and homogeneity within groups, the second form permits these outcomes and several others as well. Directed social learning can (1) support within-group differentiations of behaviour, (2) increase the efficiency with which specific information is transmitted across members of a social group, as for example directional transmission from parents to offspring, and (3) a special case of (2) increase the efficiency of information transmission from an individual with unique information to others (i.e. from an ‘informed’ individual to ‘naive’ individuals). All of these characteristics add to the flexibility with which members of a social group can accommodate to changing environmental and social conditions. The opposite side of the coin is that, owing to its reliance on pre-existing social relationships, in Directed social learning, socially acquired information does not spread evenly, in time and/or in extent, through a group. These features are relevant to the ecological significance of social learning at the population level (Laland & Plotkin 1990; Laland et al. 1993). Non-specific social learning is more likely to support behavioural homogeneity within groups or populations; Directed social learning is more likely to support variability of behaviour within an individual through time or among members of a group at any moment in time. The clearest way to determine the occurrence of Directed social learning, and to evaluate its consequences for the transmission of information among members of a social group or population, is to manipulate experimentally the information

Coussi-Korbel

& Fragaszy: Social learning

possessed by different individuals in a social group. Studies by Menzel (1973, 1974) with a group of young chimpanzees and by De Groot (1980) with weaver birds, Quelea quelea, constitute pioneering efforts in this regard. In these studies, coordination was studied in terms of group movement patterns with respect to a hidden goal, and exploitation of a hidden goal, the identity and location of which only one individual knew. Both studies showed that naive individuals were more likely to follow the informed individual than a naive conspecific in all circumstances. For the chimpanzees, Menzel (1973) further noted the existenceof a ‘leadership hierarchy’. That is, the readiness of naive chimpanzees to follow a conspecific with privileged information about the environment was a function of preexisting social relationships, and was parelleled by the informed individual’s readiness to share the hidden food with its followers. In our terminology, the birds as well as the chimpanzees displayed Directed social learning since informed individuals were more effective models for a naive animal than its naive conspecifics. However, the chimpanzees performed a stronger form of Directed social learning than did the bit& because the identity of the informed animal additionally influenced its salience for the naive conspecific. We would therefore expect more variability of behaviour through time within the group among the chimpanzees than among the birds, because individual chimpanzees will vary in the salience they attach to specific others. In a more descriptive vein, but with similar aims, Cambefort (1981) studied the transmission of information about the location of hidden food in free-ranging baboons, Papio ursinus and vervet monkeys, Cercopithecus aethiops. Cambefort found group-specific patterns of information transmission. The information spread through certain pivotal individuals (the first to discover the food) in vervet monkeys. In baboons, the food was first discovered ‘almost instantaneously’ by juveniles, which then transmitted the information to other age classesthrough their feeding activities. In our terminology, baboons apparently exhibited Directed social learning because juveniles learned from other juveniles more readily than did adults. Vervet monkeys did not display Directed social learning; all individuals learned equally quickly from those that discovered the food.

1445

Most experimental studies of social learning have made use of test paradigms that prevent Directed social learning from being evident. Often a single subject is exposed to a single model, and the outcome of the exposure is monitored. To detect Directed social learning one must demonstrate that particular individuals acquire more information from certain individuals than from others. For example, demonstration of consistent orders of transmission, such as from parents to offspring or within an age class, is evidence of Directed social learning. Transmission in Nonspecific social learning would be expected to follow variable patterns of physical proximity among individuals and would not result in consistent patterns across time. Directed social learning is likely to occur in groups where social dynamics affect the salience of various individuals for each other, and the probability of behavioural coordination between specific individuals. Social dynamics may favour the occurrence of one or the other form of social learning. For example, ‘potato-washing’ among Japanese macaques, Macaca jiiscata, spread very slowly through the group in which this behaviour originated (see Nishida 1987 for a review). It has been argued that the slowness of the spread of potatowashing rules out imitative learning (Galef 1990; Visalberghi & Fragaszy 1990a, b). On the other hand, the patterned nature of the spread of potato-washing (first to a juvenile peer, then the innovator’s mother, then other juvenile peers, and later or not at all to non-related adults) fits our notion of Directed social learning, although the necessary experimental procedures are lacking from this field description to draw a strong conclusion on this point. Social dynamics among Japanese macaques (moderately hierarchical and with strong matrilineal relationships) would support Directed social learning. A METRIC

FOR SOCIAL

DYNAMICS

How can we characterize social dynamics within groups in a manner general enough to support comparisons across groups? The particular characteristics of social interaction that are most informative with regard to social functioning of dyads within groups, and of whole groups relative to other groups, will no doubt vary across species. Moreover, social dynamics and, more generally,

1446

Animal

Behaviour,

behavioural responsiveness may vary across groups within species, as is evident when comparing captive groups of the same species held in varying circumstances. It is beyond the scope of this paper to formulate a detailed framework suitable for characterizing all social groups along the several potentially relevant dimensions of social dynamics. However, differences in the frequency and degree of spatial proximity sought and tolerated between individuals are very evident across species, and can often be related to other well-studied aspects of social behaviour, such as dominance structures, group cohesion etc. (see, for example, Mason 1971, 1978; Thierry 1987; de Waal & Luttrell 1989). Within groups, striking asymmetry across dyads in social spacing is often evident, as for example in species in which matrilineal relationships are expressed in social spacing (e.g. rhesus macaques, M. mulatta). Frequent spatial proximity outside of kinship (‘friendships’) is also common within groups, even those typically exhibiting well-developed status relationships (Cheney & Seyfarth 1990; Butovskaya 1993). Given the evident correlation between spatial affinity (which includes both seeking and tolerating proximity) and other important aspects of social dynamics, and given the broad comparative purpose of our model, it seems best at this time to focus on the single variable of social spacing (proximity) as the clearest summary of social dynamics among individuals. In short, we propose characterizing dyads within a group, or a group among a set of groups (or species), as exhibiting a certain pattern of social dynamics largely on the basis of social spacing, as has Mason (1978). THE RELATIONSHIP SOCIAL DYNAMICS LEARNING

BETWEEN AND SOCIAL

In our conceptual framework, social learning by an individual is supported by its behavioural coordination with other individuals. The forms of behavioural coordination likely to be achived by certain dyads depend upon the social dynamics among members of that group. In this way, social dynamics influence the likelihood of social learning, and to the extent that what is learned is affected by what forms of coordination occur, social dynamics influence what is learned socially. For example, more specific information about actions (e.g. their form, orientation or timing) can

50, 6

be given by means of ongoing behaviour than through affective or residual trace information. To the extent that information about ongoing activities is most easily acquired when close by another, the closer the proximity and the longer and more frequently such proximity is attained between individuals, the more likely they will acquire more specific information from each other. It also seems likely that the more proximity is tolerated, the more likely that an observer may augment socially acquired information with information gained through its own activities at the same place or with the same object at the same time, or soon after, it has seen another individual at that place. We think this general scenario of the relations among social learning and tolerance is likely to be the case among diurnal primates, for example. We predict that more extensive and more frequent behavioural coordination in time and space will be achieved among groups exhibiting an egalitarian or tolerant style of social dynamics. This style of social dynamics can support both isomorphic coordination (where behavioural similarity results) and complementary coordination (where behavioural asymmetry results). Among groups exhibiting a despotic or less tolerant style of social dynamics, behavioural coordination in space but not in time, or behavioural coordination in time while relatively distant in space should predominate. When coordination does occur jointly in time and space, it is more likely to be complementary (e.g. exploitative) in a despotic group than in an egalitarian group. The frequency of the other forms of coordination should depend on the extent to which group members have access to particular places and objects, and/or on the extent to which they are able to focus attention on events. Moreover, in species exhibiting a despotic style of social dynamics, coordination should occur at unequal rates across dyads in the group. There is one additional manner in which we see social dynamics affecting social learning, and that is through its influence on attention (particularly visual attention). We assume that visual attention to others sets the stage for behavioural coordination. Thus, to the extent that social dynamics direct an individual’s visual attention to particular others, they will affect the likelihood that an individual will acquire information from the behaviour of those others. Affiliative and status relationships affect the likelihood of each

Coussi-Korbel

& Fragaszy:

individual attending visually to each other individual in the group (Chance & Jolly 1970). A recent study by Nicol & Pope (1994) suggests the influence of previously developed social relationships on visual attention to others in a social learning context. In Nicol & Pope’s study, the social transmission of key-pecking in small flocks of adult laying hens, Gallus gallus domesticus, was affected by the pre-existing social relationship between observers and demonstrator. Observers that were exposed to socially dominant demonstrators learnt more quickly than those that were exposed to socially subordinate or unfamiliar demonstrators. Demands for attention to others can also limit attention to other events, and this can lead to differential ability to focus on any particular other individual as a source of information about the non-social environment. Demands for frequent visual monitoring of the social environment can vary across individuals within a group in accord with their current age, sex or social status (Alberts 1994) and across species. Squirrel monkeys, Saimiri sciureus, and tamarins, Saguinus labiatus, afford an example of how visual regard can vary across species and within groups in ways relecant to opportunities for social learning. Squirrel monkeys live in large groups which, in captivity at least, exhibit modestly hierarchical organization, whereas tamarins typically live in family groups. In a variety of captive settings, squirrel monkeys interrupted their foraging activities to monitor their group mates more often than did tamarins. Tamarins looked proportionally more frequently at non-social targets when they interrupted foraging (Caine & Marra 1988). Moreover, the degree to which individual squirrel monkeys visually scanned the social environment was related to their social status. Lower-ranking individuals monitored others more often than did higherranking individuals. Even when space was increased, and when an external distraction (a potentially frightening novel object) was present, the differences between the species in the extent of social monitoring remained (Caine & Marra 1988). We would predict that acquisition of information from any particular other individual would be lessened to the extent that the observer cannot maintain its focus on that individual, owing to competing attentional demands. For example, compared with tamarins, squirrel

Social learning

1447

monkeys would be less likely to focus attention upon another for more than brief moments, and thereby less likely than tamarins to acquire information from another about the non-social environment. In addition to influencing the probability and form of attention and behavioural coordination, social dynamics influence whether an individual acts on information that it has acquired through observation of others in its social group. This can affect the course of social learning, and it can also affect our ability to detect that the observer has learned something. For this reason, if one is interested in evaluating whether social learning has occurred, it is important to provide each subject with equal access to the relevant materials under non-competitive circumstances (Visalberghi & Frdgaszy 1990b).

EXAMPLES OF THE RELATION BETWEEN SOCIAL DYNAMICS AND BEHAVIOURAL COORDINATION Comparisons of heterosexual pairs of squirrel and titi monkeys illustrate the relation between social dynamics and behavioural coordination at the species level. Heterosexual pairs of titi monkeys. Cullicebus moloch, a monogamous species, look at one another more often and for longer periods than do heterosexual pairs of squirrel monkeys, which in nature live in large mixed-sex groups (Mason 1971; Phillips & Mason 1976). Titi monkeys develop strong affiliative relationships between pair mates, whereas squirrel monkey pair mates do not. Titi monkeys display stronger coordination of behaviour with the pair mate in time and space in many circumstances, such as feeding. exploring novel objects, and moving through a novel space. Social relations between pair mates are mutual and overwhelmingly affiliativc in titis. but relatively aloof and asymmetrical in pairs of squirrel monkeys, with the male occasionally exerting control over contested resources, and the female often simply avoiding confrontation with the male (e.g. Mason 1971, 1978; Fragaszy & Mason 1978; Mendoza & Mason 1989). In our terminology, the larger degree of behavioural coordination among pair mates in titis, which follows from the social dynamics within the pair. corresponds to a greater likelihood of social learning in this species than in pairs of squirrel

Animal

1448 Table I. Potential

Behaviour,

SO, 6

behavioural coordination. Table II indicates four different features of behavioural coordination and Outcome social learning, which we predict will vary in accord with the type of social dynamics character1. Facilitation of learning by naive individuals about istic of the group, and three hypothetical types of essential characteristics of their environment social dynamics, from highly egalitarian to highly 2. Extensive or rapid change in the affective response despotic. Egalitarian societies show even distrito an event or stimulus 3. Maintenance of social cohesion via synchronization butions of aggression and affiliation across dyads of activities among group members and symmetrical distributions between members 4. Rapid acquisition of new skills or information by of a dyad. Despotic societies are characterized by naive individuals a high degree of asymmetry in the direction of 5. Homogenization of behaviour within groups initiated aggression and the frequency of affiliative interactions among dyads. That is, certain dyads exhibit primarily agonistic interactions, others monkeys. We predict, for example, that accept- exhibit primarily affiliative interactions, and ance of a novel food would be more affected by its within dyads, the direction of agonistic interconcurrent acceptance by its pair mate in titis than actions is predictable. Intermediate societies diswould be the case for squirrel monkeys. play the asymmetries present in despotic societies, A second example of relations between social but less intensively and perhaps not across all dynamics and behavioural coordination between unrelated dyads. individuals is available from studies by Aisner & In egalitarian societies,proximity is rather simiTerkel (1992) on the social transmission of pine lar among all members of the group. Tolerant cone opening in black rats, Rattus rat&s. These egalitarian societies are characterized by frequent rats live in the Jerusalem pine forests in Israel; close proximity among their members. Family their primary source of nourishment is the seeds groups of titi monkeys are good examples of contained within the pine cones. The rats obtain tolerant egalitarian societies (e.g. during feeding: the seedsby means of a complex feeding behav- Fragaszy & Mason 1983). We would expect all iour. The only way in which rat pups acquire three forms of behavioural coordination to occur the necessary feeding technique is to observe an frequently in tolerant egalitarian societies, resultexperienced individual and to interact with the ing in an even transmission of socially acquired experienced individual while it is feeding on the information through the whole group or popusame pine cone. Behavioural coordination in time lation, and a predominance of Non-specific social and space between experienced and naive animals learning. is, however, only possible between mother and In societies exhibiting an intermediate style of offspring pairs during the short period that the social dynamics, subgroups will be present within pups remain with their mother. When the young- which spatial tolerance will be greater. Behavsters grow older, their experienced mothers do not ioural coordination in time and space occurs more tolerate the close proximity of their offspring. often within these subgroups, while the two other Naive animals do not learn the technique when forms of behavioural coordination (time only, or they are forced to stay some distance away while space only) may occur equally often among all observing an experienced animal, even when they members of the group. Groups of capuchin monhave unlimited accessto cones during observation. keys, C&us apella, are good examples of societies with intermediate characteristics: dominance relations are present, but manifested only ocA MODEL OF THE RELATION casionally; aggressive interactions are infrequent; BETWEEN SOCIAL LEARNING AND tolerance of others is prominent (O’Brien & SOCIAL DYNAMICS Robinson 1993; Fragaszy et al. 1994; A. Skolnick, H. Devermann & I. Bernstein, unpublished data). Table I lists several likely outcomes of social Stumptail macaques, M. arctoides, are also an learning, and Table II presents a summary of our example of an egalitarian to intermediate society model of the relation between social learning (Thierry 1987; de Waal & Luttrell 1989; outcomes and social dynamics, mediated through Butovskaya 1993). In such a society, we expect outcomes

of social

learning

Highly

II. Hypothetical

egalitarian

relationships

between

frequency

of complementary

*Outcomes

numbered

(C) and isomorphic I=C

I

dynamics

(I) coordination

time

High

probability:

1, 2, 3

the acquisition of ongoing behaviour for the acquisition ongoing behaviour, stimuli

and among

of

From parent to offspring selective transmission peers

dynamics

and social

of social

Intermediate

Style

learning

Space+

of social

Evenly through the whole group 0: population

features

Space only Time only

dlf‘erent

to type of information that can be acquired Directed social learning for detailed information from Non-specific social learning general information from residual traces and affective

as in Table

Probability of outcomes* High probability: 1, 2, 3, 4, 5

Type of social learning in relation Non-specific-social learning for all types of information

Relative I>C

Type of coordination Space only Evenly through the whole Time only group or population Space+ time

Table

From parent to offspring selective transmission peers

despotic

High probability: Low probability:

1, 2 4, 5

Directed social learning’for all types of information Reduced opportunities for the acquisition of detailed information from ongoing behaviour Reduced opportunities to act on socially acquired information

ICC

Space only Time only Space+ time

Highly

and among

F 3-. 2

2 2 %

2 09 E 9

E 2”. h 0 sh R

1450

Animal

Behaviour,

transmission of detailed information about ongoing behaviour to occur more often between certain individuals as a function of pre-existing social relationships, to the extent that coordination jointly in time and in space must be achieved to acquire this information. That is, specific behavioural skills are likely to be passed through Directed social learning, rather than Non-specific social learning, in societies exhibiting an intermediate style of social dynamics. Other types of information which can be learned through behavioural coordination in space or in time should spread evenly through the group or population (through Non-specific social learning), in accord with the individuals’ propensities to pursue the relevant forms of coordination. Finally, in highly despotic societies, only a few dyads present in the group exhibit frequent tolerated proximity. Rhesus macaques are a good example here (de Waal & Luttrell 1989). In despotic societies, social constraints and asymmetrical affiliative relationships make Non-specific social learning, and the concomitant even and/or rapid spread of socially acquired information through a group or population, unlikely. In these societies, shared access to places and objects is most reliably evident between parent and young offspring. Directed social learning thus can occur etfectively only among certain dyads. Moreover, Non-specific social learning would be restricted to those forms of information that do not require extensive coordination in space and time. Even with the less restrictive forms of coordination, Directed social learning may predominate, as individuals’ attention may be directed asymmetrically to specific others in the group (as in hamadryas baboons, Papio hamudryas; Kummer 1971). Table II also indicates some potential outcomes of the social transmission of information in each type of social dynamics. Note that there is some overlap in outcomes, but that a rapid expansion of the behavioural repertoire (that is, appearance of a new skill, such as exploiting a new food source through an instrumental action) of a whole group or population can be achieved through social learning only if the social dynamics of that group or population permit the transmission of such information through Non-specific social learning. This set of circumstances is not likely to be common in nature. Social learning may broaden the behavioural repertoire of groups in many species, but it is not likely to do so very quickly.

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The model leads to several predictions about variations within and between groups in social learning. First, the extent of spatial proximity under ordinary conditions should correlate positively across dyads in a group with the frequency of joint coordination in time and space when activities of interest to others occur. To test this hypothesis, one must compare dyads within a group independently on the two variables of spatial proximity (under routine conditions) and coordination (during a specific perturbation or challenge). An extension of this hypothesis is that, within despotic groups, one or more subgroups will be present within which greater tolerance during normative conditions is associated with greater tolerance during challenging conditions (i.e. when ongoing behaviour of another individual is especially interesting to the observer). This prediction is relevant to the occurrence of Directed social learning. Second, the degree of similarity to the demonstrator’s behaviour achieved by an observer is likely to be correlated with degree of proximity achieved by the observer during the demonstrator’s relevant ongoing behaviour. This prediction depends on the assumption that the closer the proximity between partners, the more detailed information can be acquired. Hausberger (in press) provides support for this prediction. Within groups of starlings, Sturnus vulgaris, the number of shared variants of song in any dyad reflects the time spent in proximity by these dyads compared to others in the same group. In some species, such as many primates, individual testing might be necessary to assess the observer’s performance, because social dynamics within a group can influence individual performance (Fragaszy & Visalberghi 1990; Visalberghi 1990; Visalberghi & Fragaszy 1990b). A third prediction applies to between-group comparisons. We predict that transmission of information from ongoing behaviour (as through joint coordination in time and space) will be greater in more egalitarian groups (exhibiting more homogeneous patterns of proximity) than more despotic groups (exhibiting more heterogeneous patterns of proximity). First, social dynamics can affect the information a demonstrator provides. Individuals can inhibit behaviour or alter their behaviour as a function of social constraints (as, for example, an informed

Coussi-Korhel

& Frugaszy: Social leurning

individual of low rank avoiding the site of hidden food when a high-ranking companion is near by; Coussi-Korbel 1994). Second, social dynamics can affect the frequency and degree of joint coordination in time and space, which we predict best supports the transmission of this kind of information. Studies of social learning outcomes comparing groups with different social dynamics are needed for a proper test of the prediction. A fourth prediction is that social dynamics will influence behavioural coordination only, or most, in the case of ongoing behaviour, and less in the case of the other two classesof information. This is more problematic to test for residual trace information than for affective information, becauseaccessto residual trace information might vary within a group depending on the extent of direct competition over accessto it. For example, if the site of another individual’s activity attracts interest, certain individuals among those attracted to the site may pre-empt the approach of others. In natural environments, direct competition over, and potential monopolization of, residual trace information is less likely than in captive environments (where space is more limited). Affective information is lesslikely to be subject to monopolization in any environment, as it is transient. Of course, the type or quantity of information that can be acquired by an individual from the behaviour of others might depend upon cognitive and sensory abilities, as well as social dynamics, all other things being equal. This is relevant to both within- and between-group comparisons, but it is most obvious in cross-speciescomparisons. We do not mean to imply that social dynamics are the only basis for variation across individuals in social learning. Clearly, sorting out the contributions of multiple factors in any particular case will require convergent evidence. In any case, for an unbiased comparison of social learning across groups or individuals, one must provide opportunities to obtain information which are within the sensory and cognitive capacities of all individuals to be studied, and one must provide a probable and accessiblemeans for any possessor of this information to express its knowledge in behaviour. Variations of tasks that have clear ecological validity and abiding salience for the individuals under study (such as naturalistic foraging tasks) are more useful for this purpose than presentation of novel tasks, the mastery of which is inherently improbable. Novel tasks requiring

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improbable actions may be needed to provide unequivocal evidence of imitation (Visalberghi & Fragaszy 1990a), but they are not needed or desirable for an analysis of social learning generally. CONCLUSIONS

Advances in our conception of social learning as a biologically significant phenomenon require consideration of more factors than the psychological mechanisms of learning (i.e. the distinctions between facilitation, enhancement, imitation, etc.). The field is in some danger of drowning in semantic arguments over these issues (e.g. Galef 1988; Whiten & Ham 1992). The model presented here looks at social learning from the perspective of information acquired, rather than the psychological process responsible for its acquisition. Therefore, it is independent of process-driven arguments, with their thicket of semantic distinctions. It generates a spectrum of testable hypotheses concerning the relation between social dynamics and social learning. It might contribute to resolving the apparent paradox that some of the most striking examples of social learning are found in speciesthat are phylogenetically distant from humans (e.g. birds and rats) rather than in primates. We agree with Laland et al. (1993) and Box (1994) that the assumption of more extensive or more sophisticated social learning in mammals in general, and non-human primates in particular, because of their phylogenetic proximity to ourselves, is unwarranted. Social learning is more likely to vary in biologically meaningful ways as a function of social characteristics and social setting, and the kinds of information that might be transmitted socially, than as a function of phylogeny per se. The contribution of sociality to social learning, and to its variation within and across groups, deserves our attention. ACKNOWLEDGMENTS

The preparation of the manuscript was supported by the University of Rennes I through the programme ‘Invitation d’un chercheurlenseignant etranger’ and by the Public Health Service of the United States, through a Research Scientist Development Award to D.M.F., and by a joint grant from the Centre National de la Recherche

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Behaviour,

Scientifique and the Ministere de 1’Education de la Jeunesse et des Sports, France and by the University of Rennes I to S.C.-K. We thank Heather McKiggan, Hilary Box and Elisabetta Visalberghi for commenting on a previous version of the manuscript.

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