Research has revealed that chimpanzees share an evolutionary trait only previously seen in humans, the ability to empathize with other chimpanzees by duplicating their pupil size. Scientists believe that the involuntary matching of another individual’s eyes reinforces social bonds and ultimately aids in a species’ survival.
As published in Plos One, scientists from the University of Amsterdam studied eight chimpanzees* and eighteen humans. Their research showed that both the chimpanzees’ and humans’ eyes mimicked the pupil dilation of the images researchers showed them. The pupil mimicry was strongest between members of their own species, supporting the theory of emotional contagion (the unconscious duplication of another’s emotional state).
Pupil Mimicry: An Evolutionary Advantage
According to the scientists, the research indicates that both chimpanzees and humans have used pupil mimicry as an evolutionary advantage.
“Through face-to-face interactions, humans and chimpanzees learn to recognize characteristics (such as emotional expressions and group membership) that signal safety, and to cooperate with those that seem trustworthy,” the scientists wrote. “According to the theory of emotional contagion, another’s state may be perceived through synchronization or mimicry. Mimicry is shared among the great apes, allows individuals to mirror other’s minds and has positive effects on the bond between individuals.”
The study, led by Mariska Kret, concluded that in chimpanzees, like humans, automatic pupil mimicry strengthens social bonds within groups by conveying empathy and understanding.
“Evolutionary theory implies that the propensity to mimic pupil-size should be especially adaptive within groups,” the study concludes. “In line with this assumption, pupil-mimicry is shared among humans and chimpanzees and is stronger during interactions with members of one’s own species than during interactions with members of the other species. Humans most likely evolved their communicative eyes with clear eye-white and fine musculature precisely because it benefits within-group interactions, survival, and prosperity.”
* Note: The Nonhuman Rights Project does not endorse experimentation on captive animals. However, we do quote the results of these experiments when they help make the case that the animals have a level of sentience, self-awareness, and, in some cases, a theory of mind, that demonstrates that we should not keep them in captivity in the first place.