Emotional engagements predict and enhance social cognition in young chimpanzees

Abstract

Social cognition in infancy is evident in coordinated triadic engagements, that is, infants attending jointly with social partners and objects. Current evolutionary theories of primate social cognition tend to highlight species differences in cognition based on human-unique cooperative motives. We consider a developmental model in which engagement experiences produce differential outcomes. We conducted a 10-year-long study in which two groups of laboratory-raised chimpanzee infants were given quantifiably different engagement experiences. Joint attention, cooperativeness, affect, and different levels of cognition were measured in 5- to 12-month-old chimpanzees, and compared to outcomes derived from a normative human database. We found that joint attention skills significantly improved across development for all infants, but by 12 months, the humans significantly surpassed the chimpanzees. We found that cooperativeness was stable in the humans, but by 12 months, the chimpanzee group given enriched engagement experiences significantly surpassed the humans. Past engagement experiences and concurrent affect were significant unique predictors of both joint attention and cooperativeness in 5- to 12-month-old chimpanzees. When engagement experiences and concurrent affect were statistically controlled, joint attention and cooperation were not associated. We explain differential social cognition outcomes in terms of the significant influences of previous engagement experiences and affect, in addition to cognition. Our study highlights developmental processes that underpin the emergence of social cognition in support of evolutionary continuity.

Figure 1

Infants' experiences of engagement with caregivers' encouragement of species-typical skills. The columns are the rates (minutes per hour based on an 8-hour day) during which infant chimpanzees experienced their caregiver support, encouragement, or nurturing of species-typical development (i.e. a summation of caregiver time spent nurturing motor skills, nurturing social skills, nurturing communicative skills, and nurturing general autonomy). The open columns are the average rates for caregivers of responsive care chimpanzees (at 4 months, n = 13, at 6 months, n = 16, at 9 months, n = 17, at 12 months, n = 16), with 99% confidence intervals. Solid columns are the rates for chimpanzee mothers (based on a total of 8 hours of observation), and the 0s indicate the average rates for caregivers of standard care chimpanzees. At 6 and 12 months of age, RC infants experienced these nurturing interactions significantly more often than mother-raised infants (ps <.01). At 9 months, RC infants experienced nurturing as much as mother-raised infants (p > .05), and at 4 months, mother-raised infants experienced more nurturing than RC infants (p < .01).

Figure 2

Joint Attention Developmental Trajectories. The average number of joint attention items passed (JA Success indicated by symbols), developmental trajectories (slope of change with age, shown in solid lines) and 99% confidence intervals (dashed lines) are shown for 28 Standard Care (in blue) and 17 Responsive Care (in red) chimpanzees, and for human norms (in black) tested from 5 months to 12 months of age.

Figure 3

Cooperativeness Developmental Trajectories. Cooperativeness mean scores (symbols), developmental trajectory (solid lines) and 99% confidence intervals (dashed lines) are shown for 28 standard care chimpanzees (in blue), 17 responsive care chimpanzees (in red), and 42–57 human infants (in black) tested from 5 months to 12 months of age.