Correlations among measures of playfulness and skillfulness in captive common marmosets (Callithrix jacchus jacchus).

Infant sensorimotor and social skills, playfulness, and nonplayful behaviors were measured in common marmosets from 6 to 22 weeks old. Different measures of skill showed a low concordance, implying that skill is a multiple rather than unitary attribute. Significant correlations were found between the amount of social play infants performed from 11 to 13 weeks of age and their performance at 14 weeks in (1) competitive food tests with their mothers, and in (2) their ability to negotiate an obstacle for a food reward. Significant correlations were also found between these skills and nonplayful behaviors, however. Comparable analyses at other ages revealed few significant correlations, suggesting that the association between social play and skills is restricted to the age when infants are rapidly becoming independent of their caregivers both for locomotion and food. Age-specific correlations occurred between changes in levels of skills and both playful and nonplay behaviors. Our results are consistent with the hypothesis that social play promotes the development of skills, but alternative explanations are possible.