Monkeys and Prosimians: Social LearningD. M. Fragaszy and J. Crast, University of Georgia, Athens, GA, USA

ã 2010 Elsevier Ltd. All rights reserved.

Introduction

In this chapter, we highlight examples of social influ-ences on learning observed in prosimians and monkeysand consider the role of socially mediated learning inthe biology of these animals. Learning is always theoutcome of interacting physical, social, and individualfactors and takes place over time. Thus, we cannot parselearning, either as a process or as an outcome, intoportions that are socially influenced and portions thatare not. Instead, we can document how social processesaffect behavior relevant to the learning process, andwe can seek evidence for social contributions to learningoutcomes.

To begin, we provide some background on the taxo-nomic groups of interest in this chapter: monkeys andprosimians. Primates are a remarkably diverse order. Bodysize alone spans three orders of magnitude, from tiny pro-simians weighing a few hundred grams to massive apesweighing more than 100 kg. Diet, morphology, matingsystems, locomotor style, life history, and every otheraspect of the biology of these animals is as diverse as bodysize, and this diversity is important when consideringthe contributions of the social context to learning in par-ticular species.

Phylogeny of Prosimians and Monkeys

As Fleagle (1999) discusses in greater detail, the orderPrimates includes two suborders: Prosimii, prosimians, andAnthropoidea, monkeys, apes, and humans (see Figure 1).The two suborders have evolved separately for at least55Million years. Two infraorders are classified withinAnthropoidea: the platyrrhines (New World monkeys)and catarrhines (Old World monkeys, apes, and humans).New and Old World monkeys diverged approximately40Millions of years ago (Mya), and apes and hominids(hominids include modern humans and their ancestors;superfamily Hominoidea) diverged from the Old Worldmonkeys (superfamily Cercopithecoidea) approximately20Mya. Given their lengthy independent evolution, vari-ation in the life histories, body sizes, social organizations,etc., within each suborder, infraorder, and superfamily inthe order Primates is to be expected.

The suborder Prosimii includes the infraorders Lemur-iformes (the lemurs of Madagascar), Lorisiformes (thelorises of Africa and Asia and the galagos of Africa), and

468

Tarsiiformes (tarsiers of Southeast Asia). All prosimianslive in tropical habitats in Africa and Asia and the vastmajority are arboreal and nocturnal. Prosimians are some-times referred to as ‘living fossils’ because they appear tohave some physical similarities to ancestral primates ofapproximately 50Mya. In general, prosimians rely to agreater extent than other primates on olfaction. Some aresolitary foragers; others travel and forage in groups rangingfrom small family units to larger social groups of as many as27 individuals. We know less about the lifestyles and behav-ior of prosimians than of monkeys.

In comparison with prosimians, species in the suborderAnthropoidea are characterized by a relatively largerbrain for their body mass, diurnal lifestyle, and a greaterreliance on vision than on olfaction. Anthropoid speciesgenerally exhibit greater manual dexterity than prosi-mians, and anthropoids are more likely to live in groups.NewWorld monkeys (infraorder Platyrrhini) are arborealand relatively small-bodied, ranging in size from approxi-mately 100 g (the pygmy marmoset [Cebuella pygmaea]) upto 10 kg (the muriqui [Brachyteles arachnoides] and spidermonkey [Genus Ateles]). Many genera live in small familygroups; others live in medium-to-large social groups(as many as 50–60 individuals). Within the New Worldmonkeys are the subfamilies Callitrichinae (marmosetsand tamarins), Atelinae (muriquis, woolly, howler, andspider monkeys), Pitheciinae (titis, sakis, bearded sakis,and uakaris), Cebinae (squirrel monkeys and capuchins),and Aotinae (owl monkeys, the only nocturnal anthro-poid). During the platyrrhine radiation in the Americas,the genera adapted to distinct niches, making a living indifferent parts of the forest canopy and resulting in greatdiversity in social organization, reproductive strategy,diet, and locomotor style.

Compared to NewWorldmonkeys, OldWorld monkeys(superfamily Cercopithecoidea) are mostly larger-bodied,ranging from around 1 kg to approximately 30 kg, and someare terrestrial. Old World monkeys include subfamiliesCercopithecinae (baboons, mandrills, drills, macaques,mangabeys, and guenons) and Colobinae (colobus monkeysand langurs), which differ particularly in their dietary adap-tations (see Fleagle for details).Most cercopithecoid specieslive in large polygamous social groupswith clear dominancehierarchies within and between matrilines (female kingroups), and some form multilevel societies during partsof the year. Of all primate superfamilies, cercopithecoidshave the widest geographic range, greatest number of spe-cies, and form some of the largest groups and biomass

All primates All monkeys

All apes

+Fleagle (1999) and others have recently eliminated the family callitrichidae and included marmosetsand tamarins in the family cebidae.

All hominoids All hominids (including extinctforms and modern humans)All prosimians

*There is some disagreement among primatologists concerning where to place tarsiers. Many researcherssuggest that they more properly belong closer to the anthropoids and thus revise the primate classificationsto reflect this view. Here, for simplicity, we continue to use the traditional classifications.

All anthropoids

Order

Suborder

Infraorder

Superfamily

Family

Subfamily

Genus

Species

Primates

Prosimii*(all prosimians: lemurs,

lorises, galagos, and tarsiers)

Anthropoidea(monkeys, apes,

and humans)

Lemuriformes(all lemurs)

Lorisiformes(all lorises

and galagos)

Tarsiiformes*(the tarsiers)

Platyrrhini(all new world

monkeys)

Ceboidea(all new world

monkeys)

Cercopithecoidea(all old world

monkeys)

Cercopithecidae(all old world

monkeys)

Catarrhini(all old world monkeys,

apes, and humans)

Hominoidea(apes and humans)

Hominidae(humans)

Callitrichidae+

(marmosets andtamarins)

Atelidae(howlers, spidermonkeys, and

muriquis)

Cebidae(squirrel

monkeys, capuchins,owl monkeys, etc.)

Hylobatidae(gibbons and

siamangs)

Pongidae(the great apes)

Cercopithecinae(baboons, macaques,

guenons, etc.)

Colobinae(colobus species,

langurs)

Pongo Gorilla Pan Homo

Pygmaeus(orangutans)

(2 subspecies)

Gorilla(3 subspecies)

Troglodytes(chimpanzees)(3 subspecies)

paniscus(bonobos)

Sapiens

Figure 1 Primate taxonomic classification. This abbreviated taxonomy illustrates how primates are grouped into increasingly specific

categories.Only themoregeneral categories are shown, except for thegreat apes and humans. Reproduced fromTurnbaughWA,NelsonH,

Jurmain R, and Kilgore L (2002) Understanding Physical Anthropology and Archaeology, 8th edn., with permission fromWadsworth.

Monkeys and Prosimians: Social Learning 469

densities in the primate order. Despite this, Old Worldmonkeys have less diversity in diet and social organizationthan New World monkeys.

Phylogeny and Socially MediatedLearning

This brief review of primate phylogeny suggests somereasons why we might expect socially mediated learningto vary across primate taxa. First, group demographics andsocial dynamics within groups define the social context,and thus influence socially mediated learning within agroup. The number of groupmates, their age and sex, andthe nature of social relationships within the group varyenormously across species, and may vary considerablywithin species as well. Groups of monkeys of the samespecies may live in smallish groups (4–7 individuals) orquite large groups (more than 40 individuals) depending onthe local distribution of resources. Second, reliance onvarious sensory modalities (vision, olfaction, audition, andtouch) in social interaction and in general activity variesacross taxa. For example, species that are particularly atten-tive to smell (such as many prosimians) will be affected by

social partners in a way different from that of species thatare highly reliant on vision. Third, motor patterns andaction proclivities vary considerably across species. Forexample, leaf-eating monkeys are generally less likely tomanipulate objects spontaneously than species that feed onseeds and nuts. Finally, the variability in behavioral ecologyacross species means that individuals of different speciesare interested in different kinds of activities, locations,objects, and events. For example, leaf-eating monkeysmay be less likely to attend to sequences of actions duringfeeding than are seed- or nut-eating species; omnivorousspecies are less likely to attend to the odor of leaves eatenby another than are dietary specialists. Behavioral prioritiesand proclivities of each species constrain what an individ-ual is likely to learn in the first place, and thus the role ofsocial context in learning.

The Sources of Social Context

Social Organization

The social organization (i.e., the size, demographic com-position, and spatiotemporal coordination of individuals

470 Monkeys and Prosimians: Social Learning

within a group) and social relationships among individualsin a group provide the boundaries of the social context inwhich an individual can learn. As Coussi-Korbel and Fra-gaszy have proposed, conspecifics with which an individualhas a long-term social relationship and that are frequentlynearby are particularly important and enduring compo-nents of an individual’s experience. In theory, the moreclosely individuals coordinate their activity in space and/or time, the more likely an individual’s activity is toinfluence the activity of others. Individuals of species inwhich social partners spend more of their time apart thantogether are likely to experience less direct social influ-ences on learning specific actions than species that spendmost of their time in the company of conspecifics. Forexample, adults of many nocturnal prosimians form sleep-ing groups during the day but travel and forage alone atnight (e.g., dwarf and mouse lemurs [Genus Cheirogaleus andMicrocebus, respectively] and some galagos [Genus Galago]and tarsiers [Genus Tarsius]). These animals are thereforenot often in the company of others that might influencetheir behavior. However, all monkeys and some prosimianspecies, such as lemurs, sifakas, and indris, remain in cohe-sive groups and are near conspecifics virtually all the time.This intensely social lifestyle affects every aspect of expe-rience through every sensory modality. Interactions withconspecifics structure where and how an individual budgetsthe time that it devotes to different activities (e.g., travel vs.feeding), and conspecifics also influence how an individualresponds to events that occur nearby. For example, asCheney and Seyfarth have shown, monkeys attend toovert signals made by others concerning objects, events,or locations of affective value (i.e., desirable or objection-able) such as a recruitment call to a food site or an alarmcall to a predator, even if out of sight or some distance awayfrom the other group members.

Social Relationships

Individuals are more likely to be near others with whichthey share a mutually affiliative relationship (e.g., depen-dent offspring with a parent). If social influences onlearning are maximized when individuals are near oneanother, then a potential learner will be more influencedby those with which it shares positive affiliations than byothers: a phenomenon Coussi-Korbel and Fragaszy havelabeled Directed Social Learning. Over time, unevensocial influences on learning across individuals within agroup can lead to the generation of behavioral variationsamong subgroups. For example, young Japanese macaquesliving in Koshima, a small island in Japan, first began towash sweet potatoes in the sea when these were providedfor them on a sandy beach on the island. Initially, onlyjuveniles washed potatoes. In subsequent years, the juve-niles’ older siblings and mothers started to wash potatoes.Older individuals adopted the behavior more slowly than

juveniles; adult males most slowly or not at all. If socialinfluences contributed to the spread of the behavior, it didso unevenly across age and sex classes in accord with thepredictions of the Directed Social Learning model. How-ever, as Galef has indicated, a similar outcome couldreflect accumulation of individual experience withoutany social influence, so we cannot definitively claim thatsocial influence promoted the spread of the behavior.A similar caveat applies to several commonly cited exam-ples of traditions in non-human primates. Observing thedevelopment of behaviors by new practitioners, withthe requisite detail of social contexts and behavioralchange over time, is necessary to make strong claimsabout the contributions of social context to learning aspecific behavior. Such developmental studies are nowunderway with some species of monkeys.

Social influences within a group can be thought of aseither vertical (across generations) or horizontal (withingenerations; among juveniles, for example). Vertical andhorizontal social influences are common in primates. Ver-tical social influence is often discussed as promotingbehavioral continuity between generations, while hori-zontal social influence is more likely to promote adaptivebehavioral change; for example, in response to changingcircumstances. Vertical social influence promotes conti-nuity in commonplace and routine preferences and beha-viors that young primates acquire gradually whiletraveling with adults, such as habitual travel routes andsleeping sites. Vertical social influence can also promoterefinement of specific behaviors. For example, as Cheneyand Seyfarth have shown, young vervet monkeys (Cerco-pithecus aethiops) gradually narrow the range of animals towhich they give alarm vocalizations according to differ-ential adult responsiveness to their calls. Adults respondto juveniles’ calls in response to actual predators andignore calls in response to benign animals.

Perry’s studies of white-faced capuchins (Cebus capuci-nus) in Costa Rica provide examples of behaviors reflect-ing horizontal social influence. These monkeys sometimesdevelop idiosyncratic social behaviors (‘games’) that areplayed in pairs by close companions in a play context, butnot between parent and offspring. One of the gamesidentified by Perry and colleagues is the toy game, inwhich two monkeys take turns extracting an inanimateobject, like a twig or leaf, from each other’s mouth. In thetoy game, one monkey holds the object tightly in itsmouth without chewing it, and the other monkey attemptsto pry open the first monkey’s mouth and extract the item.Once retrieved, the monkeys then repeat the procedure orswitch roles. Although initially one individual instigates anew game, eventually several different pairs in the groupparticipate in the same game. Such behaviors are main-tained by a particular social context and often disappearwhen that context disappears (e.g., when the key initiatorof the behavior emigrates from the group).

Monkeys and Prosimians: Social Learning 471

For many species of primates, the most influentialsocial partner from birth until independence is themother, and in some species that share parental care, themother and father (e.g., callitrichids, owl monkeys, and titimonkeys). Infants of most primate species are carried bythe mother and thus are influenced by her activity as theytravel together throughout the day. Even when able totravel independently, infants typically remain near theirmother to nurse, rest, and feed, and this period of depen-dency is often considered important for skill learning byinfants. Aye-ayes (Daubentonia madagascariensis), a noctur-nal prosimian species, provide a striking example (seeFigure 2). A significant part of the aye-aye’s foragingactivity involves extracting larvae from woody substrates,using a method called tap-foraging. In tap foraging, aye-ayes tap the substrate with a finger to locate a hollowcavity, gnaw the wood in the right place, and insert aspecially adapted, long and skinny digit to probe thecavity and to extract the larva. Krakauer demonstratedseveral ways in which immature aye-ayes’ proficiency intap foraging is influenced by close proximity with theirmother while she engages in the behavior. In general, theaye-aye mother allows her infant to remain nearby whileshe tap-forages. Over time, the infant begins to take overthe site where the mother is working and extract thelarvae itself. Infants of a naturally nontap-foraging motherattempted tap-foraging less often than other infants andnever succeeded at extracting a larva.

Processes Mediating Learning in a SocialContext

Facilitation and Enhancement

One common and powerful form of social influence onlearning in primates is increased probability of performing

Figure 2 Mother and infant aye-aye foraging jointly. Aye-ayes

(Daubentonia madagascariensis, lemurids) locate hidden prey bytapping on woody substrates. Infants begin to practice this

technique at the same sites as their mothers. Photo by David

Haring/Duke Lemur Center.

a behavior when a conspecific is seen performing thatbehavior. Such socially facilitated behaviors are already inan individual’s repertoire, for example, vocalizing orgrooming. Another powerful social influence on behavioris increased interest in an object or in an area whereanother has recently been active or where others’ previousactivity has left artifacts (e.g., scents or physical alterations)(see Figure 3). Such increased interest in areas or objectswhere others have been active has been termed, respec-tively, local and stimulus enhancement; hereafter, enhance-ment. The bulk of empirical studies of social influences onlearning in monkeys and prosimians have concerned thesetwo phenomena.

Social facilitation is particularly common in primatesin the context of feeding. For example, individuals arelikely to begin eating, even if satiated, if nearby groupmembers are eating. Social facilitation can lead to expo-sure to a new food item, or support exploratory activitiesthat indirectly aid learning a foraging skill, as when youngmonkeys learn to locate hidden prey through repeatedbouts of searching begun while or shortly after seeingothers forage for hidden prey. This simple mechanismcan support individuals developing the same dietary pre-ferences as their groupmates, as individuals eating at thesame time usually eat in the same place, and thereforeoften eat the same things. More generally, social facilita-tion results in temporal coordination of group activity.

Enhancement may occur through multiple senses andover an extended time period. For example, an indivi-dual’s attention may be drawn to a foraging site throughobservation of another feeding, hearing the other’s actions(such as breaking a stick), eating food items derived from

Figure 3 Infant Japanese macaques (Macaca fuscata,

cercopithecines) attend closely to their mother’s activity with

stones. In groups of Japanese macaques provisioned with food,

many individuals engage in stone-handling, and this behavior hasbeen characterized as a tradition. Photo by Jean-Baptiste Leca/

Primate Research Institute, Kyoto University and Iwatayama

Monkey Park.

472 Monkeys and Prosimians: Social Learning

another’s activity at the site, smelling another’s mouth,and encountering artifacts (including scents) of past for-aging activity, as well as through joint contact with mate-rials another is handling. Any and all of these experiencesincrease the probability that an individual will investigatethe site that another is exploiting or has exploited. Typi-cally, young primates show strong interest in sites whereothers, especially adults, are foraging (see Figure 4). Tothe extent to which juveniles’ proximity is tolerated byadults, young primates may approach and eat droppedfood or even take bits of food from another’s hand ormouth. However, even when young monkeys do notacquire food as a result of approaching, they are stillintensely interested in sites where others forage.

Although most adult monkeys and prosimians do notovertly share food, enhancement of interest in foragingsites appears to be actively promoted in callitrichids. Forexample, Rapaport and Brown have found that adultgolden lion tamarins (Leontopithecus rosalia; see Figure 5),which live in cohesive family groups that are led by acooperatively breeding pair, emit food-offering vocaliza-tions that draw their dependent offspring to a site con-taining live prey or large/tough-skinned fruit. Instead oftaking the food for themselves, an adult waits until a juvenilereaches the site and allows the juvenile to extract the fooditem. This form of provisioning (or, as Rapaport and Brownrefer to it, opportunity teaching) peaks around weaning(3–4 months) and continues untill infants are about a yearold. Adults selectively provision infants with items that aredifficult to process.

Callitrichids rely to varying degrees on extractive for-aging for hidden foods, and participating in foraging with

Figure 4 Infant and juvenile bearded capuchins (Cebus

libidinosus, cebids) watch an adult crack a palm nut using a stonehammer, a common behavior in many wild groups of this

species. Young monkeys regularly attend closely to proficient

crackers and collect bits of broken nut from sites where adults

crack. This tolerant social context is thought to promoteinvestigation of appropriate sites and materials by the

youngsters, and thus to aid them in learning to crack nuts. Photo

by Barth Wright/EthoCebus Project.

adults apparently helps youngsters learn to search inappropriate places and to perform appropriate actions.Research has shown more overt instances of adults activelyproviding social supports for youngsters learning to foragein callitrichids than in other monkeys, such as cercopithecinesand colobines, which live in larger groups and show lessshared parental care. Brown and Rapaport suggest that thedegree of parental assistance in foraging seen in callitrichidsis matched only by apes.

Motor Imitation

Motor imitation (i.e., performing a specific action afterobserving another perform the same action) is thought tocontribute importantly to learning in humans. Currently,we have no evidence that prosimians or monkeys imitatenovel actions spontaneously, as do humans. Nevertheless,recent experimental evidence indicates that marmosetsand tamarins (callitrichids) will use the same part of thebody to move an object that they have witnessed a con-specific use to solve a foraging problem. Currently, calli-trichids provide the best evidence of imitation of familiaractions in monkeys. It is interesting that callitrichids haveaptitude in this domain (as well as in opportunity teach-ing), whereas cercopithecoid monkeys do not, becausecallitrichids are phylogenetically more distant from homi-nids than cercopithecoid monkeys (see Figure 1), whiletrue imitation is present in hominids.

Figure 5 Adult golden lion tamarin (Leontopithecus rosalia,callitrichids), carrying twins. Parents in this species call their

dependent offspring to places where a hidden food item can be

procured, a phenomenon called ‘opportunity teaching’. Photo by

Jessie Cohen/National Zoo, Smithsonian Institution.

Monkeys and Prosimians: Social Learning 473

Learning a Decision Rule through Observation

Psychologists have long been interested in whether indi-viduals can learn arbitrary decision rules from watchingothers select objects from a set. Typically, a subjectobserves a skilled partner and a short time later workson an identical problem. Monkeys have considerablygreater success on this kind of task than in reproducingnovel actions after watching others perform them. Forexample, Subiaul trained two rhesus macaques (Macaca

mulatta, cercopithecines) to touch in fixed order each offour pictures appearing simultaneously on a touch-screenmonitor. Each monkey trained alone and became anexpert at a particular sequence of four pictures, andthen each monkey learned the other monkeys’ sequencesas well as other new sequences. Both the monkeys morequickly learned the series that they had watched theirsocial partner perform than series that they had notwatched the other monkey perform. As each monkeywas already skilled at touching pictures in a particularsequence, what each monkey learned from watching theother was the order in which to touch a new set ofpictures. Subiaul labels this type of learning ‘cognitiveimitation,’ because the observer adopts a rule demon-strated by another, rather than a particular action. Subiaulargues that monkeys can adopt novel decision rules, butnot match novel actions, from watching others becausematching novel actions depends upon ‘derived neuralspecializations mediating the planning and coordinationof fine and gross motor movements’ that some hominids(see Whiten, this volume), but not monkeys and prosi-mians, possess.

Biological Significance of SociallyMediated Learning

Socially mediated learning probably serves biologicalfunctions in primates similar to those it serves in othertaxa. Social partners provide a context for learning innon-human primates, both highlighting relevant featuresof the environment through enhancement and promotingbehaviors that are generally appropriate for a particularplace and time through social facilitation. In the shortterm, social mediation of learning reduces risk duringthe acquisition of useful skills and knowledge, and socialmediation may be especially beneficial to acquiring cer-tain foraging skills. Differentiated relationships with spe-cific others produce a mosaic of learning opportunitiesacross individuals within a group, thus promoting behav-ioral variation within a group.

Social mediation of learning can also have longer-termconsequences when it results in traditions (i.e., relativelyenduring behaviors acquired in part by socially mediatedlearning and practiced by at least two members of a

group). Behavioral traditions hold strong interest for evo-lutionary biologists because traditions generate and main-tain behavioral variation over time outside of, or perhapseven ahead of, changes in the genetics of a population. Inthis indirect manner, socially mediated learning contri-butes to evolution, and social learning becomes central tothe contemporary debate about the relationship betweentraditions in non-human animals and the phenomenon ofculture (for discussion see Perry, this volume, or Caldwelland Whiten, 2007).

Summary

Monkeys and prosimians have varied social lives, whichinfluence how and what individuals learn. In general,monkeys and prosimians are interested in conspecificsand attend to what they are doing. The motivation tosynchronize behavior with others (social facilitation) pro-motes behavioral coordination within a group. Interest inwhere another is acting (enhancement) draws attention toboth places and objects. Such processes channel an indi-vidual’s activity sufficiently that monkeys and prosimianstend to acquire preferences and behavioral patterns simi-lar to those of their groupmates. Monkeys match thespecific actions of others only in very limited circum-stances. The influence of older on younger individualspromotes the maintenance of behaviors across genera-tions (traditions), and enduring traditions may have animpact on natural selection.

See also: Apes: Social Learning; Culture; Imitation:

Cognitive Implications.

Further Reading

Brown GR, Almond REA, and van Bergen Y (2004) Begging, stealing,and offering: Food transfer in non-human primates. Advances in theStudy of Behavior 34: 265–295.

Caldwell CA and Whiten A (2007) Social learning in monkeys andapes: Cultural animals? In: Campbell C, Fuentes A, MacKinnon KC,Panger M, and Bearder SK (eds.) Primates in Perspective. New York,NY: Oxford University Press.

Cheney DL and Seyfarth RM (1990) How Monkeys See theWorld: Inside the Mind of Another Species. Chicago:University of Chicago Press.

Cheney DL, Seyfarth RM, Smuts BB, and Wrangham RW (1986) Thestudy of primate societies. In: Smuts BB, Cheney DL, Seyfarth RM,Wrangham RW, and Struhsaker TT (eds.) Primate Societies.Chicago: The University of Chicago Press.

Coussi-Korbel S and Fragaszy DM (1995) On the relationbetween social dynamics and social learning. Animal behaviour50: 1441–1453.

Fleagle JG (1999) Primate Adaptation and Evolution, 2nd ed. San Diego,CA: Academic Press.

Fragaszy DM and Perry S (2003) Towards a biology of traditions.In: Fragaszy DM and Perry S (eds.) The Biology of Traditions.Cambridge, UK: Cambridge University Press.

Fragaszy D and Visalberghi E (2004) Socially-biased learning inmonkeys. Learning and Behavior 32: 24–35.

474 Monkeys and Prosimians: Social Learning

Galef BG Jr. (1992) The question of animal culture. Human Nature3: 157–178.

Huffman MA (1996) Acquisition of innovative cultural behaviors in non-human primates: A case study of stone handling, a sociallytransmitted behavior in Japanese macaques. In: Heyes CM andGalef BG Jr. (eds.) Social Learning in Animals: The Roots of Culture.San Diego, CA: Academic Press, Inc.

Kappeler PM (1997) Determinants of primate social organization:Comparative evidence and new insights from Malagasy lemurs.Biological Reviews 72: 111–151.

Perry S, Baker M, Fedigan L, et al. (2003) Social conventions in wildwhite-faced capuchin monkeys – Evidence for traditions in aneotropical primate. Current Anthropology 44(2): 241–268.

Rapaport LG and Brown GR (2008) Social influences on foragingbehavior in young non-human primates: Learning what, where andhow to eat. Evolutionary Anthropology 17: 189–201.

Subiaul F (2007) The imitation faculty in monkeys: Evaluating itsfeatures, distribution and evolution. Journal of AnthropologicalSciences 85: 35–62.

Relevant Websites

http://pin.primate.wisc.edu – Primate Info Net.