Joyful expressions in infancy
: cross-species comparisons

  • Kirsty Mhairi Ross

Student thesis: Doctoral Thesis


Joyful expressions of one-year-old infants were studied in naturalistic contexts in infants’ home environments. Chimpanzee infants (n = 7) and human infants from the Cameroon Nso community (n = 8) were studied in their own right and in comparison. Similar methodologies and the development of a single coding scheme allowed direct comparisons between the groups. The research aims to contribute to knowledge about 1) emotion socialisation; 2) the whole-body expression of emotions in infancy; 3) the evolutionary heritage of emotions; and 4) the functions of joyful emotions.

Playful behaviours were analysed for play type, infant joy (facial, motor, and vocal1), play partners and their engagement, and matching of infant joy by play partners. The first study (Chapter 4) describes the play contexts of chimpanzee infants from two settings (Chester Zoo, UK, and Primate Research Institute (PRI), Japan), as there was little published quantitative data specific to one-year-old
chimpanzees. Play contexts were similar across settings though the proportion of time spent in the different types of social play varied with more rough-and-tumble play at Chester Zoo (larger group, juveniles present) and more tickling by mothers at PRI. The second study (Chapter 5) describes the joyful expressions of chimpanzee infants. Facial and motor joy occurred at similar rates overall though the rate of facial joy was skewed towards social contact and tickling play to a greater degree than motor joy. Mothers elicited a particularly high rate of infant joy (often during tickling) but peers matched a greater proportion of infant joy (often during contact play). The third study (Chapter 6) describes the joyful. Vocal joy was analysed for human sample only expressions of human infants. Facial, motor, and vocal joy occurred at similar
rates overall though rates of facial joy and vocal joy were skewed towards social communicative and rhythmic play to a greater degree than was motor joy. Play partners matched a greater proportion of infant joy during social communicative and rhythmic play and social object exchange than during other types of social play. The fourth study (Chapter 7) compares the joyful expressions of chimpanzee infants and human infants. The rate of facial joy was equivalent in both groups despite differences in the contexts of play, underlining the importance of joy to infant development in both species. Differences were evident in the rate of motor joy (higher in the human sample) and in matching of infant joy (marginally higher in the human sample, variation by play partners).

The general discussion highlights key findings in relation to the socialisation of joy (e.g. the high rates of joy during play contexts which support social cohesion, the different roles of mothers and peers/older children in eliciting and responding to infant joy) and the whole body expression of joy (the distinctive patterns of facial, motor and vocal joy across social and solitary play contexts). Findings are discussed in relation to theories about the functions of joy.
Date of AwardNov 2010
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorKim A. Bard (Supervisor), Vasu Reddy (Supervisor) & Anne Patricia Hillstrom (Supervisor)

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