Infant State in Apes and Humans
What are the inborn capacities of chimpanzees? How do chimpanzees compare to humans? These questions typify the long-standing interest in "what makes us human." As a developmental psychologist, I am interested in describing the developmental process, and as a comparative psychologist, I am interested in comparing development in chimpanzees with development in humans. In this talk, I will present data on comparative development of infant states, that is, states of arousal, state regulation, emotion states, and engagement states in chimpanzee and human infants. For example, within the first 30 days, chimpanzee raised in a human nursery develop the ability to maintain a quiet and alert state for minutes when out of physical contact (significantly longer than human infants from Providence RI). Chimpanzees raised by their chimpanzee mothers, however, are significantly less able to regulate their attentive state when out of physical contact compared to human infants and to nursery-raised chimpanzees . Thus, state regulation systems in chimpanzees are sensitive to caregiving variables and these effects are manifest very early in development. Within the first 3 months, rearing effects are dramatic in the preferred modality of engagement states in chimpanzees. In some chimpanzee groups positive face-to-face interactions (visually-based mutual gaze) emerge from 6-8 weeks of age, whereas in other groups, close physical contact (tactile-based cradling) is the preferred modality for mutual engagement. This interchangeability in the modality of engagement state is found also among humans, exclusive dyadic attention is valued in Euro-American settings, whereas physical contact and shared attention, among various people and activities, is valued in interdependent cultures. Comparative developmental studies are valuable for understanding hominid evolution, and essential for delineating those characteristics that are uniquely human.