Researchers have long assumed that mother-infant mutual gaze, or the act of a mother looking into her baby's eyes and the baby staring back at her, was unique to human development.
However, a study in the July issue of Developmental Psychology (Vol. 41, No. 4) suggests that certain groups of chimpanzees also use the mother-infant mutual gaze, depending on their social norms.
"Developmental outcomes are not fixed as a function of our shared evolutionary history, but rather the fact that humans and chimpanzees have the ability to flexibly adapt to their environments," says lead researcher Kim A. Bard, PhD, a psychology professor at the University of Portsmouth in England.
In the study, researchers videotaped eight mother-infant chimpanzee pairs at Yerkes National Primate Research Center at Emory University in Atlanta and three mother-infant chimpanzee pairs at the Primate Research Institute (PRI) at Kyoto University in Japan when the mothers were in their living areas with no humans present.
The researchers then selected one hour from when each infant was 1, 2 and 3 months old. For each hour, researchers noted whether the mother was paying attention to her infant and if so, whether she focused on the infant's body or face. The researchers also noted whether the context was positive and involved physical contact or motor stimulation.
Bard and her colleagues found that while chimpanzees in both groups showed mutual gaze at 1, 2 and 3 months old, the chimpanzees at PRI displayed mutual gaze nearly twice as often as those at Yerkes. Furthermore, like humans, the chimpanzee mothers at PRI actively encouraged mutual gaze by tilting or holding up their infants' chins with their fingers while looking into their eyes.
The study suggests that mother-infant mutual gaze in chimpanzees, as in humans, varies across cultures as a result of group norms.
"Our theory is that there is a biological basis of intuitive parenting skills in humans and chimpanzees," Bard says. "But there is flexibility in how those skills are exhibited."
In the future, Bard and her colleagues aim to investigate whether the amount of mutual gaze chimpanzee infants receive affects their attention later in life.