Skip to main content Accessibility help
×
Home
  • Print publication year: 2016
  • Online publication date: May 2016

7 - Playing lemurs: why primates have been playing for a long time

from Part III - Why lemurs keep in touch

Summary

We do not stop playing because we get old. We get old because we stop playing

Stanley G. Hall, 1904

Playing, an everyday life activity: easy to spot, hard to define

After focusing for a long time on animal grief, trauma, violence, pain and suffering, comparative psychologists have been lately putting their efforts into dealing with happiness, laughter, joy and affection both in humans and other animals (the so-called ‘positive psychology’). Most of the ‘positive emotions’ which are under the psychologists’ magnifying glass are also indissolubly linked to play. Every day of our lives is punctuated by play and humour. We play during conversation with friends on the phone or on Skype, or when we post messages on Facebook – frequently inserting a smiling face like this :-) – etc. We play with our conspecifics and also with members of other species. Dogs, cats and even rats can be wonderful playmates. We play because it is pleasurable and rewarding. By social play and humour we experience emotions that can pass individuals’ boundaries and create a network of social and affective bonds (Power, 2000). Despite its pervasive nature, play is one of the most mysterious behaviours an ethologist can come across.

The difficulty with studying play behaviour starts with its theoretical definition. In his Confessions (Book 11, Chapter 14), St Augustine pondered the meaning of time, ‘Quid ergo est tempus? Si nemo ex me quaerit, scio: si quaerenti explicare velim, nescio’ [What is time? If no one asks me, I know. If I want to explain it, I no longer know]. Maybe the frustration experienced by St Augustine is the same as that experienced by most ethologists when dealing with the definition of play (Palagi and Paoli, 2007, 2008). We have no problems in recognising a playful interaction of our dogs, cats and children; however, as we go through the extensive literature dedicated to play we soon realise that there are as many definitions of play as there are the authors who studied it (for an extensive review see Burghardt, 2005). Play has been often defined via litotes, by not specifying what it is but by specifying what it is not. As play lacks certain characteristics that are typical of the serious and functional behaviours, play has been defined as a non-functional behaviour with no obvious immediate benefits (Martin and Caro, 1985; Bekoff and Allen, 1998).

Related content

Powered by UNSILO
Aldis, O. (1975). Play Fighting.New York: Academic Press.
Antonacci, D., Norscia, I. & Palagi, E. (2010).Stranger to familiar: wild strepsirrhines manage xenophobia by playing. PLos ONE, 5(10), e13218.
Bainum, C. K., Lounsbury, K. R. & Pollio, H. R. (1984). The development of laughing and smiling in nursery school children. Child Development, 55, 1946–1957.
Barlow, G. (1977). Modal action patterns. In: Thomas, S (ed.), How Animals Communicate. Bloomington: Indiana University Press, pp. 98–134.
Beach, F. A. (1945). Current concepts of play in animals. American Naturalist, 79, 523–541
Behncke, I. (2015). Play in the Peter Pan ape. Current Biology, 25, R24–R27.
Bekoff, M. (1972). The development of social interaction, play, and metacommunication in mammals: An ethological perspective. Quarterly Review of Biology, 47, 412–434.
Bekoff, M. (editor) (1974a). Social play in mammals. American Zoologist, 14, 265–436
Bekoff, M. (1974b). Social play and play-soliciting by infant canids. American Zoologist, 14, 323–340.
Bekoff, M. (1977a). Mammalian dispersal and the ontogeny of individual behavioral phenotypes. American Naturalist, 111, 715–732.
Bekoff, M. (1977b). Social communication in canids: Evidence for the evolution of a stereotyped mammalian display. Science, 197, 1097–1099.
Bekoff, M. (1995). Play signals as punctuation: The structure of social play in canids. Behaviour, 132, 419–429.
Bekoff, M. (2001). Social play behaviour: cooperation, fairness, trust, and the evolution of morality. Journal of Consciousness Studies, 8, 81–90.
Bekoff, M. (2004). Wild justice and fair play: cooperation, forgiveness, and morality in animals. Biology & Philosophy, 19, 489–520.
Bekoff, M. (2007). The Emotional Lives of Animals. Novato, CA: New World Library.
Bekoff, M. (2013). Why Dogs Hump and Bees Get Depressed. The Fascinating Science of Animal Intelligence, Emotions, Friendship, and Conservation. Novato, CA: New World Library.
Bekoff, M. & Allen, C. (1998). Intentional communication and social play: how and why animals negotiate and agree to play. In: Bekoff, M. & Byers, J. A. (eds), Animal Play: Evolutionary, Comparative, and Ecological Perspectives. Cambridge University Press, pp. 97–114.
Bekoff, M. & Byers, J. A. (1981). A critical reanalysis of the ontogeny and phylogeny of mammalian social and locomotor play: An ethological hornet's nest. In: Immelmann, K., Barlow, G., Main, M. & Petrinovich, L. (eds), Behavioral Development: The Bielefeld Interdisciplinary Project. Cambridge University Press, pp. 296–337.
Bekoff, M. & Byers, J. A. (1998). Animal Play: Evolutionary, Comparative and Ecological Approaches. New York: Cambridge University Press.
Bekoff, M. & Pierce, J. (2009). Wild Justice: The Moral Lives of Animals.Chicago: University of Chicago Press.
Bell, H. C., McCaffrey, D., Forgie, M. L., Kolb, B. & Pellis, S. M. (2009). The role of the medial prefrontal cortex in the play fighting of rats. Behavioral Neuroscience, 123, 1158–1168.
Bell, H. C., Pellis, S. M. & Kolb, B. (2010). Juvenile peer play experience and development of the orbitofrontal and medial prefrontal cortices. Behavioural Brain Research, 207, 7–13.
Berman, C. M. (1982). The ontogeny of social relationships with group companions among free-ranging infant rhesus monkeys: II. Differentiation and attractiveness. Animal Behaviour, 30, 163–170.
Berns, G. (2013). How Dogs Love Us: A Neuroscientist and his Adopted Dog Decode the Canine Brain. New York: New Harvest/Amazon.
Blurton Jones, N. (1971). Criteria for use in describing facial expressions of children. Human Biology, 43, 365–413.
Blurton Jones, N. (1972). Categories of child-child interactions. In: Blurton Jones, N. (ed.), Ethological Studies of Child Behaviour. London: Cambridge University Press, pp. 97–127.
Bout, N. & Thierry, B. (2005). Peaceful meaning for the silent bared-teeth displays of mandrills. International Journal of Primatology, 26(6), 1215–1228.
Brockman, D. K. (1999). Reproductive behavior of female Propithecus verreauxi at Beza Mahafaly, Madagascar. International Journal of Primatology, 20, 375–398.
Burghardt, G M. (2005). The Genesis of Animal Play: Testing the Limits. Cambridge, MA: MIT Press.
Call, J. & Tomasello, M. (2007). The Gestural Communication of Apes and Monkeys.Mahwah: Lawrence Erlbaum Associates.
Candland, D. G., French, D. K. & Johnson, C. N. (1978). Object play: test of a categorized model by the genesis of object play in Macaca fuscata. In: Smith, E. O (ed.), Social Play in Primates. New York: Academic Press, pp. 259–296.
Cattaneo, L. & Pavesi, G. (2014). The facial motor system. Neuroscience & Biobehavioral Reviews, 38, 135–159
Charles-Dominique, P. (1977). Ecology and Behaviour of Nocturnal Primates. Prosimians of Equatorial West Africa. New York: Columbia University Press.
Cheyne, J. A. (1976). Development of forms and functions of smiling in preschoolers. Child Development, 47, 820–823.
Ciani, F., Dall'Olio, S., Stanyon, R. & Palagi, E. (2012). Social tolerance in macaque societies: a comparison with different human cultures. Animal Behaviour, 84, 1313–1322.
Clay, Z. & de Waal, F. B. (2013). Bonobos respond to distress in others: consolation across the age spectrum. PLos ONE, 8(1), e55206.
Cordoni, G. & Palagi, E. (2011). Ontogenetic trajectories of chimpanzee social play: similarities with humans. PLoS ONE, 6(11), e27344.
Darwin, C. (1872). The Expression of the Emotions in Man and Animals. Chicago, IL: University of Chicago Press.
Davila-Ross, M., Owren, M. J., Zimmermann, E. (2009). Reconstructing the evolution of laughter in great apes and humans. Current Biology, 19, 1106–1111.
Davila-Ross, M., Allcock, B., Thomas, C. & Bard, K. A. (2011). Aping expressions? Chimpanzees produce distinct laugh types when responding to laughter of others. Emotion, 11, 1013–1020.
De Marco, A., Petit, O. & Visalberghi, E. (2008). The repertoire and social function of facial displays in Cebus capucinus. International Journal of Primatology, 29, 469–486.
de Waal, F. B. M. (2003). Darwin's legacy and the study of primate visual communication. Annals of the New York Academy of Sciences, 1000, 7–31.
Demuru, E. & Palagi, E. (2012). In bonobos yawn contagion is higher among kin and friends. PLoS ONE, 7(11), e49613. http://dx.doi.org/10.1371/journal.pone.0049613.
Demuru, E., Ferrari, P. F. & Palagi, E. (2015). Emotionality and intentionality in bonobo playful communication. Animal Cognition, 18, 333–344.
Doyle, G. A. (1974). Behavior of Prosimians. In: Schrier, A. M. & Stollnitz, F. (eds), Behavior of Nonhuman Primates: Modern Research Trends, vol. 5, pp. 155–353, New York: Academic Press, pp. 155–353.
Drea, C. M., Hawk, J. E. & Glickman, S. E. (1996). Aggression decreases as play emerges in infant spotted hyaenas: preparation for joining the clan. Animal Behaviour, 51, 1323–1336.
Dugatkin, L. A. & Bekoff, M. (2003). Play and the evolution of fairness: a game theory model. Behavioural Processes, 60, 209–214.
Eisenberg, J. F. (1976). Communication mechanisms and social integration in black spider monkey, Ateles fusciceps robustus, and related species. Smithsonian Contributions to Zoology, 213, 1–108.
Erhlich, A. (1977). Social and individual behaviors in captive greater galago. Behaviour, 63, 192–214.
Erhlich, A. &Musicant, A. (1975). Social and individual behaviors in captive slow lorises. Behaviour, 60, 195–200.
Fagen, R. (1981). Animal Play Behavior. New York: Oxford University Press, p. 684.
Fagen, R. (1993). Primate juveniles and primate play. In: Pereira, M. E. & Fairbanks, L. A. (eds), Juvenile Primates. Chicago: University of Chicago Press, pp. 182–196.
Fagen, R. & Fagen, F. (2004). Juvenile survival and benefits of play behaviour in brown bears, Ursus arctos. Evolutionary Ecology Research, 6, 89–102.
Feistner, A. T. & Ashbourne, C. J. (1994). Infant development in a captive-bred aye-aye (Daubentonia madagascariensis) over the first year of life. Folia Primatologica, 62, 74–92.
Field, T. M. (1982). Affective displays of high-risk infants during early interactions. Emotion and Early Interaction, 101–125.
Flack, J. & de Waal, F. B. M. (2004). Dominance style, social power, and conflict. In: Thierry, B., Singh, M. & Kaumanns, W. (eds), Macaque Societies: A Model for the Study of Social Organization. Cambridge University Press, pp. 157–185.
Flack, J. C., Jeannotte, L. A. & de Waal, F. (2004). Play signaling and the perception of social rules by juvenile chimpanzees (Pan troglodytes). Journal of Comparative Psychology, 118, 149–159.
Fouts, H. N., Hallam, R. A. & Purandare, S. (2013). Gender segregation in early-childhood social play among the Bofi foragers and Bofi farmers in Central Africa. American Journal of Play, 5, 333–356.
Fry, D. P. (1992). ‘Respect for the rights of others is peace’: Learning aggression versus nonaggression among the Zapotec. American Anthropologist, 94, 621–639.
Fry, D. P. (2005). Rough-and-tumble social play in humans. In: Pellegrini, A. D. & Smith, P. K. (eds), The Nature of Play: Great Apes and Humans. New York: The Guilford Press, pp. 54–85.
Furuichi, T. (2011). Female contributions to the peaceful nature of bonobo society. Evolutionary Anthropology: Issues, News, and Reviews, 20, 131–142.
Gabriel, D. N., Gould, L. & Kelley, E. A. (2014). Seasonal patterns of male affiliation in ring-tailed lemurs (Lemur catta) in diverse habitats across southern Madagascar. Behaviour, 151(7), 935–961.
Gervais, M. & Wilson, D. S. (2005). The evolution and functions of laughter and humor: A synthetic approach. The Quarterly Review of Biology, 80(4), 395–430.
Goodall, J. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, MA: Belknap Press of Harvard University Press.
Graham, K. L. (2011). Coevolutionary relationship between striatum size and social play. American Journal of Primatology, 71, 1–9.
Gray, P. (2009). Play as a foundation for hunter-gatherer social existence. American Journal of Play, 1, 476–522.
Gray, P. (2012). The value of a play-filled childhood in development of the hunter-gatherer individual. In: Narvaez, D., Panksepp, J., Shore, A. & Gleason, T. (eds), Evolution, Early Experience and Human Development: From Research to Practice and Policy.New York: Oxford University Press.
Groos, K. (1896). Die Spiele der Tiere. Jena ed.
Hall, S. G. (1904). Adolescence: Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, Religion and Education. New York: Appleton.
Harlow, H. F. & Harlow, M. K. (1965). The affectional systems. In: Schrier, A. M., Harlow, H. F., & Stollnitz, F. (eds), Behavior of Nonhuman Primates (vol. 2). New York: Academic Press, pp. 287–334.
Henry, J. D. & Herrero, S. M. (1974). Social play in the American black bear: its similarity to canid social play and an examination of its identifying characteristics. American Zoologist, 14, 371–389.
Horowitz, A. (2008). Attention to attention in domestic dog (Canis familiaris) dyadic play. Animal Cognition, 12, 107–118.
Horowitz, A. (2009). Disambiguating the ‘guilty look’: salient prompts to familiar dog behavior. Behavioural Processes, 81, 447–452.
Jolly, A. (1966). Lemur Behavior: a Madagascar field study. Chicago: University of Chicago Press.
Jolly, A. (1985). The Evolution of Primate Behavior, 2nd ed. New York: Macmillan.
Jolly, A. (2003). Lemur catta, ring-tailed lemur, Maky. In: Goodman, S. M. & Benstead, J. P. (eds), The Natural History of Madagascar. Chicago, MA: The University of Chicago Press: pp. 1329–1331.
June, G., Devlin, H. C. & Moskowitz, J. (2014). Seeing both sides: An introduction to the light and dark sides of positive emotion. In: Gruber, J. & Moskowitz, J. (eds), Positive Emotion: The Light Sides and Dark Sides.New York, NY: Oxford University Press.
Kano, T. (1984). Distribution of pygmy chimpanzees (Pan paniscus) in the central Zaire basin. Folia Primatologica, 43(1), 36–52.
Kuczaj, S. A. & Horback, K. M. (2013). Play and Emotion. In: Watanabe, S. & Kuczaj, S. (eds), Emotions of Animals and Humans: Comparative Perspectives.New York: Springer, pp. 87–111.
Lawler, R. R. (2007). Fitness and extra-group reproduction in male Verreaux's sifaka: an analysis of reproductive success from 1989–1999. American Journal of Physical Anthropology, 132, 267–277.
Lazar, J. W. & Beckhorn, G. D. (1974). Social play or the development of social behavior in ferrets (Mustela putorius)?American Zoologist, 14(1), 405–414.
Lewis, M. (2000). The emergence of human emotions. Handbook of Emotions, 2, 265–280.
MacKinnon, J. (1974). The behaviour and ecology of wild orangutans (Pongo pygmaeus). Animal Behaviour, 22, 3–74.
Mancini, G., Ferrari, P. F. & Palagi, E. (2013a). In play we trust. Rapid facial mimicry predicts the duration of playful interactions in geladas. PLoS ONE, 8(6) e66481. http://dx.doi.org/10.1371/journal.pone.0066481.
Mancini, G., Ferrari, P. F. & Palagi, E. (2013b). Rapid facial mimicry in geladas. Scientific Reports, 3, 1527–1533.
Marshall, L. J. (1976). The !Kung of Nyae Nyae. Cambridge, MA: Harvard University Press.
Martin, P. & Caro, T. M. (1985). On the functions of play and its role in behavioral development. Advances in the Study of Behavior, 15, 59–103.
McGrew, W. C. (1972). Interpersonal spacing of preschool children. The Development of Competence in Early Chilhood, 72–96.
Messinger, D. S., Mattson, W. I., Mahoor, M. H. & Cohn, J. F. (2012). The eyes have it: Making positive expressions more positive and negative expressions more negative. Emotion, 12, 430–436.
Mutschler, T. & Tan, C. L. (2003). Hapalemur, bamboo or gentle lemurs. In: Goodman, S. M. & Benstead, J. (eds), The Natural History of Madagascar. Chicago: The University of Chicago Press, pp. 1324–1329.
Nakamichi, M. & Koyama, N. (1997). Social relationships among ring-tailed lemurs (Lemur catta) in two free-ranging troops at Berenty Reserve, Madagascar. International Journal of Primatology, 18, 73–93.
Narvaez, D. & Gleason, T. (2012). Developmental optimization. In: Narvaez, D., Panksepp, J., Shore, A. & Gleason, T.), Evolution, Early Experience and Human Development: From Research to Practice and Policy. New York: Oxford University Press.
Nesse, R. M. (2004). Natural selection and the elusiveness of happiness. Philosophical Transactions of the Royal Society, B., 359, 1333–1347.
Newell, T. G. (1971). Social encounters in two prosimian species: Galago crassicaudatus and Nycticebus coucang. Psychon Soc, 2, 128–130
Norbeck, E. (1974). Anthropological views of play. American Zoologist, 14, 267–273.
Norscia, I. & Palagi, E. (2011). When play is a family business: adult play, hierarchy, and possible stress reduction in common marmosets. Primates, 52(2), 101–104.
Norscia, I., Antonacci, D. & Palagi, E. (2009). Mating first, mating more: biological market fluctuation in a wild prosimian. PLoS ONE, 4(3), e4679.
Pages, E. (1980). Ethoecology of Microcebus coquereli during the dry season. In: Charles-Dominique, P., Cooper, H. M., Hladik, A., et al. (eds), Nocturnal Malagasy Primates: Ecology, Physiology, and Behaviour. New York: Academic Press, pp. 97–116.
Palagi, E. (2006). Social play in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): implications for natural social systems and interindividual relationships. American Journal of Physical Anthropology, 129, 418–426.
Palagi, E. (2007). Play at work: revisiting data focusing on chimpanzees (Pan troglodytes). Journal of Anthropological Sciences, 85, 63–81.
Palagi, E. (2008). Sharing the motivation to play: the use of signals in adult bonobos. Animal Behaviour, 75, 887–896.
Palagi, E. (2009). Adult play fighting and potential role of tail signals in ringtailed lemurs (Lemur catta). Journal of Comparative Psychology, 123, 1–9.
Palagi, E. (2011). Playing at every age: modalities and potential functions in non-human primates. In: Pellegrini, A. D. (ed.), The Oxford Handbook of the Development of Play. Oxford: Oxford University Press, pp. 70–82.
Palagi, E. & Cordoni, G. (2012). The right time to happen: play developmental divergence in the two Pan species. PLoS ONE, 7(12), e52767.
Palagi, E. & Mancini, G. (2011). Playing with the face: Playful facial ‘chattering’ and signal modulation in a monkey species (Theropithecus gelada). Journal of Comparative Psychology, 125(1), 11–21.
Palagi, E. & Norscia, I. (2013). Bonobos protect and console friends and kin. PLoS ONE, 8(11), e79290. http://dx.doi.org/10.1371/journal.pone.
Palagi, E. & Norscia, I. (2015). The season for peace: reconciliation in a despotic species (Lemur catta). PLoS ONE 10(11), e0142150. http://dx.doi.org/10.1371/journal.pone.0142150.
Palagi, E. & Paoli, T. (2007). Play in adult bonobos (Pan paniscus): modality and potential meaning. American Journal of Physical Anthropology, 134, 219–225.
Palagi, E. & Paoli, T. (2008). Social play in Bonobos: Not only an immature matter. In: Furuichi, T. & Thomson, J. (eds), The Bonobos. Developments in Primatology: Progress and Prospects. pp. 55–74
Palagi, E., Gregorace, A. & Borgognini-Tarli, S. (2002). Development of olfactory behavior in captive ring-tailed lemurs (Lemur catta). International Journal of Primatology, 23, 587–599.
Palagi, E., Telara, S. & Borgognini-Tarli, S. (2003). Sniffing behaviour in Lemur catta: seasonality, sex, and rank. International Journal of Primatology, 24, 335–350.
Palagi, E., Telara, S. & Borgognini-Tarli, S. (2004a). Reproductive strategies in Lemur catta: balance among sending, receiving, and counter-marking scent. International Journal of Primatology, 25, 1019–1031.
Palagi, E., Cordoni, G. & Borgognini-Tarli, S. M. (2004b). Immediate and delayed benefits of play behaviour: new evidence from chimpanzees (Pan troglodytes). Ethology, 110, 949–962.
Palagi, E., Paoli, T. & Tarli, S. B. (2006). Short-term benefits of play behavior and conflict prevention in Pan paniscus. International Journal of Primatology, 27, 1257–1270.
Palagi, E., Antonacci, D. & Cordoni, G. (2007). Fine-tuning of social play in juvenile lowland gorillas (Gorilla gorilla gorilla). Developmental Psychobiology, 49, 433–445.
Palagi, E., Norscia, I. & Spada, G. (2014). Relaxed open mouth as a playful signal in wild ring-tailed lemurs. American Journal of Primatology, 76, 1074–1083.
Palagi, E., Burghardt, G. M., Smuts, B., et al. (2015). Rough-and-tumble play as a window on animal communication. Biological Reviews, http://dx.doi.org/10.1111/brv.12172.
Pasztor, T. J., Smith, L. K., MacDonald, N. K., Michener, G. R. & Pellis, S. M. (2001). Sexual and aggressive play fighting of sibling Richardson's ground squirrels. Aggressive Behavior, 27(4), 323–337.
Pellegrini, A. D. & Smith, P. K. (1998). Physical activity play. Child Development, 69, 577–598.
Pellis, S. M. (1981). A description of social play by the Australian magpie Gymnorhina tibicen based on Eshkol-Wachman notation. Bird Behaviour, 3, 61–79.
Pellis, S. M. (1988). Agonistic versus amicable targets of attack and defense: Consequences for the origin, function and descriptive classification of play-fighting. Aggressive Behavior, 14, 85–104.
Pellis, S. M. (2002). Keeping in touch: Play fighting and social knowledge. In: Bekoff, M., Allen, C. & Burghardt, G. M. (eds), The Cognitive Animal: Empirical and Theoretical Perspectives on Animal Cognition. Cambridge, MA: MIT Press, pp. 421–427.
Pellis, S. M. & Iwaniuk, A. N. (1999). The problem of adult play: A comparative analysis of play and courtship in primates. Ethology, 105, 783–806.
Pellis, S. M. & Iwaniuk, A. N. (2000). Adult-adult play in primates: Comparative analyses of its origin, distribution and evolution. Ethology, 106, 1083–1104.
Pellis, S. M. & Pellis, V. C. (1987). Play-fighting differs from serious fighting in both target of attack and tactics of fighting in the laboratory rat Rattus norvegicus. Aggressive Behavior, 13, 227–242.
Pellis, S. M. & Pellis, V. C. (1997). Targets, tactics, and the openmouth face during play fighting in three species of primates. Aggressive Behavior, 23, 41–57.
Pellis, S. M. & Pellis, V. C. (2006). Play and the development of social engagement: A comparative perspective. In: Marshall, P. J. & Fox, N. A. (eds), The Development of Social Engagement: Neurobiological Perspectives. Oxford: Oxford University Press, pp. 247–274.
Pellis, S. M. & Pellis, V. C. (2007). Rough-and-tumble play and the development of the social brain. Current Directions in Psychological Science, 16, 95–98.
Pellis, S. M. & Pellis, V. C. (2009). The Playful Brain: Venturing to the Limits of Neuroscience. Oxford: Oneworld Publications.
Pellis, S. M. & Pellis, V. (2010). Social play, social grooming, and the regulation of social relationships. In: Kalueff, A. V, La Porte, J. L & Bergner, C. L (eds), Neurobiology of Grooming Behaviour. Cambridge University Press, pp. 66–87.
Pellis, S. M. & Pellis, V. C. (2011). To whom the play signal is directed: a study of headshaking in black-handed spider monkeys (Ateles geoffroyi). Journal of Comparative Psychology, 125, 1–10.
Pellis, S. M., Pellis, V. C. & Whishaw, I. Q. (1992). The role of the cortex in play fighting by rats: Developmental and evolutionary implications. Brain, Behavior & Evolution, 39, 270–284.
Pellis, S. M., Pellis, V. C. & McKenna, M. M. (1993). Some subordinates are more equal than others: Play fighting amongst adult subordinate male rats. Aggressive Behavior, 19, 385–393.
Pellis, S. M., Pasztor, T. J., Pellis, V. C. & Dewsbury, D. A. (2000). The organization of play fighting in the grasshopper mouse (Onychomys leucogaster): Mixing predatory and sociosexual targets and tactics. Aggressive Behavior, 26, 319–334.
Pellis, S. M., Hastings, E., Shimizu, T., et al. (2006). The effects of orbital frontal cortex damage on the modulation of defensive responses by rats in playful and non-playful social contexts. Behavioral Neuroscience, 120, 72–84.
Pellis, S. M., Pellis, V. C. & Bell, H. C. (2010a). The function of play in the development of the social brain. American Journal of Play, 2, 278–296.
Pellis, S. M., Pellis, V. C. & Reinhart, C. J. (2010b). The evolution of social play. In: Worthman, C., Plotsky, P., Schechter, D. & Cummings, C. (eds), Formative Experiences: The Interaction of Caregiving, Culture, and Developmental Psychobiology.Cambridge University Press, pp. 404–431.
Pellis, S. M., Pellis, V. C., Reinhart, C. J. & Thierry, B. (2011). The use of the bared-teeth display during play fighting in Tonkean macaques (Macaca tonkeana): Sometimes it is all about oneself. Journal of Comparative Psychology, 125(4), 393–403.
Pereira, M. E. & Kappeler, P. M. (1997). Divergent systems of agonistic behaviour in lemurid primates. Behaviour, 134(3), 225–274.
Pessoa, L. (2009). Nature ReviewsNeuroscience, 9, 148–158
Petit, O., Bertrand, F. & Thierry, B. (2008). Social play in crested and Japanese macaques: Testing the covariation hypothesis. Developmental Psychobiology, 50, 399–407.
Petrů, M., Špinka, M., Charvátová, V. & Lhota, S. (2009). Revisiting play elements and self-handicapping in play: a comparative ethogram of five Old World monkey species. Journal of Comparative Psychology, 123, 250–263.
Pierce, J. & Bekoff, M. (2012). Wild justice redux: What we know about social justice in animals and why it matters. Social Justice Research (special issue edited by Sarah Brosnan), 25, 122–139.
Power, T. G. (2000). Play and Exploration in Children and Humans. Mahwah, NJ: Lawrence Erlbaum Associates.
Preuschoft, S. & van Hooff, J. A. (1997). The social function of ‘smile’ and ‘laughter’: Variations across primate species and societies. In: Segerstrale, U & Mobias, P (eds), Nonverbal Communication: Where Nature Meets Culture. New Jersey: Erlbaum, pp. 252–281.
Provine, R. R. (1996). Laughter. American Scientist, 84, 38–45.
Provine, R. R. (2004). Laughing, tickling, and the evolution of speech and self. Current Directions in Psycological Sciences, 13, 215–218.
Provine, R. P. & Fischer, K. R. (1989). Laughing, smiling, and talking: Relation to sleeping and social context in humans. Ethology, 83, 295–305.
Reinhart, C. J., Pellis, V. C., Thierry, B., et al. (2010). Targets and tactics of play fighting: Competitive versus cooperative styles of play in Japanese and Tonkean macaques. Journal of Comparative Psychology, 23, 166–200.
Richard, A. F. (1992). Aggressive competition between males, female-controlled polygyny and sexual monomorphism in a Malagasy primate, Propithecus verreauxi. Journal of Human Evolution, 22, 395–406.
Ross, K. M., Bard, K. A. & Matsuzawa, T. (2014). Playful expressions of one-year-old chimpanzee infants in social and solitary play contexts. Frontiers in Psychology, 5, 741. http://dx.doi.org/10.3389/fpsyg.2014.00741.
Sclafani, V., Norscia, I., Antonacci, D. & Palagi, E. (2012). Scratching around mating: factors affecting anxiety in wild Lemur catta. Primates, 53, 247–254.
Silk, J. B. (1997). The function of peaceful postconflict contacts among primates. Primates, 38, 265–279.
Smith, P. K. (1982). Does play matter? Functional and evolutionary aspects of animal and human play. The Behavioural and Brain Sciences, 5, 139–184.
Soma, T. & Koyama, N. (2013). Eviction and troop reconstruction in a single matriline of ring-tailed lemurs (Lemur catta): what happened when ‘grandmother’ died? In: Masters, J., Gamba, M. & Génin, F. (eds), Leaping Ahead – Advances in Prosimian Biology. New York: Springer, pp. 137–146.
Špinka, M., Newberry, R. C. & Bekoff, M. (2001). Mammalian play: training for the unexpected. Quarterly Review of Biology, 76, 141–168.
Srofe, L. A. & Waters, E. (1976). The ontogenesis of smiling and laughter: A perspective on the organization of development in infancy. Psychological Review, 83(3), 173–189.
Sussman, R. W. & Richard, A. F. (1974). The role of aggression among diurnal prosimians. In: Holloway, R. L. (ed.), Primate Aggression, Territoriality, and Xenophobia. San Francisco: Academic Press, pp. 50–76.
Sutton-Smith, B. & Roberts, J. M. (1970). Cross-cultural and psychological study of games. In: Lüschen (ed., G.), Cross-Cultural Analysis of Sport and Games. Champaign, Illinois: Stipes, pp. 100–108.
Swaddling, J. (2002). The Ancient Olympic Games. Austin: Texas University Press.
Tan, J. & Hare, B. (2013). Bonobos share with strangers. PLoS ONE, 8, e51922. http://dx.doi.org/10.1371/journal.pone.0051922.
Tanner, J. E. & Byrne, R. W. (1993). Concealing facial evidence of mood: evidence for perspective-taking in a captive gorilla?Primates, 34, 451–456.
Thierry, B. (2000). Covariation of conflict management patterns across macaque species. In: Aureli, F. & de Waal, F. B. M. (eds), Natural Conflict Resolution, Berkeley, CA: University of California Press, pp. 106–128.
Thierry, B. (2007). Unity in diversity: Lessons from macaque societies. Evolutionary Anthropology, 16, 224–238.
Thierry, B., Demaria, C., Preuschoft, S. & Desportes, C. (1989). Structural convergence between silent bared-teeth display and relaxed open-mouth display in the Tonkean macaque (Macaca tonkeana). Folia Primatologica, 52, 178–184.
Thompson, K. V. (1998). Self assessment in juvenile play. In: Bekoff, M. & Byers, J. A. (eds), Animal Play – Evolutionary, Comparative and Ecological Perspectives. Cambridge University Press, pp. 183–204.
Tinbergen, N. (1951). The Study of Instinct.New York: Oxford University Press.
Tinbergen, N. (1952). ‘Derived’ activities, their causation, biological significance and emancipation during evolution. The Quarterly Review of Biology, 27, 1–32.
Tinbergen, N. (1963). On aims and methods of ethology. Zeitschrift für Tierpsychologie, 20, 410–433.
van Hooff, J. A. R. A. M. & Preuschoft, S. (2003). Laughter and smiling: the intertwining of nature and culture. In: de Waal, F. B. M. & Tyack, P. L. (eds), Animal Social Complexity. Cambridge, MA: Harvard University Press, pp. 260–287.
Vettin, J. & Todt, D. (2005). Human laughter, social play, and play vocalizations of non-human primates: An evolutionary approach. Behaviour, 142(2), 217–240.
Voland, E. (1977). Social play behavior of the common marmoset (Callithrix jacchus Erxl., 1777) in captivity. Primates, 18, 883–901.
Wendland, J. R., Lesch, K-P., Newman, T. K., et al. (2006). Differential variability of serotonin transporter and monoamine oxidase A genes in macaque species displaying contrasting levels of aggression-related behavior. Behavior Genetics, 36, 163–172.
Wilson, E. O. (2002). Sociobiology: the new synthesis. Cambridge, MA: Harvard University Press.
Wilson, D. E. & Reeder, D. M. (eds), (2005). Mammal Species of the World: a taxonomic and geographic reference (vol. 12). JHU Press.
Wrangham, R. W. (1999). Evolution of coalitionary killing. American Journal of Physical Anthropology, (Suppl 29), 1–30.
Wrangham, R. W. & Glowacki, L. (2012). Intergroup aggression in chimpanzees and war in nomadic hunter-gatherers: evaluating the chimpanzee model. Human Nature, 23, 5–29.