title: Playful expressions of one-year-old chimpanzee infants in social and solitary play contexts.
abstract: Knowledge of the context and development of playful expressions in chimpanzees is limited because research has tended to focus on social play, on older subjects, and on the communicative signaling function of expressions. Here we explore the rate of playful facial and body expressions in solitary and social play, changes from 12- to 15-months of age, and the extent to which social partners match expressions, which may illuminate a route through which context influences expression. Naturalistic observations of seven chimpanzee infants (Pan troglodytes) were conducted at Chester Zoo, UK (n = 4), and Primate Research Institute, Japan (n = 3), and at two ages, 12 months and 15 months. No group or age differences were found in the rate of infant playful expressions. However, modalities of playful expression varied with type of play: in social play, the rate of play faces was high, whereas in solitary play, the rate of body expressions was high. Among the most frequent types of play, mild contact social play had the highest rates of play faces and multi-modal expressions (often play faces with hitting). Social partners matched both infant play faces and infant body expressions, but play faces were matched at a significantly higher rate that increased with age. Matched expression rates were highest when playing with peers despite infant expressiveness being highest when playing with older chimpanzees. Given that playful expressions emerge early in life and continue to occur in solitary contexts through the second year of life, we suggest that the play face and certain body behaviors are emotional expressions of joy, and that such expressions develop additional social functions through interactions with peers and older social partners.
authors.affiliation: Department of Psychology, University of Winchester Winchester, UK ; Department of Psychology, Centre for Comparative and Evolutionary Psychology, University of Portsmouth Portsmouth, UK.
authors.forename: Kirsty M
authors.initials: KM
authors.lastname: Ross
authors.affiliation: Department of Psychology, Centre for Comparative and Evolutionary Psychology, University of Portsmouth Portsmouth, UK.
authors.forename: Kim A
authors.initials: KA
authors.lastname: Bard
authors.affiliation: Department of Behavioral and Brain Sciences, Primate Research Institute, Kyoto University Kyoto, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Matsuzawa
keywords: chimpanzee; communication; development; emotion; infancy; play face
references.citation: J Comp Psychol. 2004 Jun;118(2):149-59
references.pmid: 15250802
references.citation: Am J Primatol. 1997;41(3):213-28
references.pmid: 9057966
references.citation: Psychol Forsch. 1964 Jun 2;27:337-65
references.pmid: 14233517
references.citation: Adv Child Dev Behav. 2007;35:327-66
references.pmid: 17682330
references.citation: Pers Soc Psychol Rev. 2005;9(4):278-311
references.pmid: 16223353
references.citation: Brain Res Bull. 2002 Feb-Mar 1;57(3-4):561-4
references.pmid: 11923029
references.citation: Infant Behav Dev. 2013 Jun;36(3):289-97
references.pmid: 23545077
references.citation: Emotion. 2011 Oct;11(5):1013-20
references.pmid: 21355640
references.citation: PLoS One. 2012;7(12):e52767
references.pmid: 23300765
references.citation: Nature. 1999 Jun 17;399(6737):682-5
references.pmid: 10385119
references.citation: Annu Rev Psychol. 2003;54:329-49
references.pmid: 12415074
references.citation: Emotion. 2002 Jun;2(2):179-93
references.pmid: 12899190
references.citation: Behaviour. 1974;49(3):227-67
references.pmid: 4597405
references.citation: Am J Primatol. 2012 Feb;74(2):102-13
references.pmid: 22025273
references.citation: Am J Primatol. 2014 Jan;76(1):14-29
references.pmid: 24038115
references.citation: Anim Cogn. 2011 Sep;14(5):745-67
references.pmid: 21533821
references.citation: Proc Biol Sci. 2005 Feb 7;272(1560):253-8
references.pmid: 15705549
references.citation: Neurosci Biobehav Rev. 2011 Oct;35(9):1791-804
references.pmid: 21872619
references.citation: Biol Lett. 2008 Feb 23;4(1):27-30
references.pmid: 18077238
references.citation: Dev Psychol. 2005 Jul;41(4):616-24
references.pmid: 16060808
references.citation: Am J Primatol. 2013 Sep;75(9):891-903
references.pmid: 23564649
references.citation: Am J Phys Anthropol. 2006 Mar;129(3):418-26
references.pmid: 16323189
references.citation: Ann N Y Acad Sci. 2003 Dec;1000:56-78
references.pmid: 14766620
references.citation: Child Dev. 2014 Mar-Apr;85(2):675-84
references.pmid: 23802842
references.citation: Am J Primatol. 2004 Dec;64(4):377-96
references.pmid: 15580580
references.citation: Anim Cogn. 2013 May;16(3):471-81
references.pmid: 23263709
references.citation: J Comp Psychol. 2011 Feb;125(1):11-21
references.pmid: 21244137
references.citation: Primates. 2009 Oct;50(4):333-41
references.pmid: 19562436
references.citation: Annu Rev Psychol. 2003;54:145-73
references.pmid: 12359915
references.citation: Philos Trans R Soc Lond B Biol Sci. 2009 Dec 12;364(1535):3475-84
references.pmid: 19884142
references.citation: PLoS One. 2011;6(11):e27344
references.pmid: 22110630
references.citation: Dev Sci. 2014 Sep;17(5):682-96
references.pmid: 24410843