Chimps change pupil size to mimic other individuals
Pupil mimcry helps individuals to understand and empathise with one another.
Chimpanzees automatically adjust the size of their pupils to mimic other individuals they have contact with, according to new research published in the journal PLOS ONE.
Pupils display a wide variety of emotions including excitement, fear and interest. Humans are known to be able to detect and respond to these signals in others but researchers wanted to find out if chimps are also capable of pupillary synchronisation - meaning the pupils change size to mimic those of another individual.
Such synchronisation helps members of the same social groups to understand and empathise with one another. It is also important for generating greater mutual trust and effective co-operation.
Lead researcher Mariska Kret from the University of Amsterdam (UvA) and colleagues from Kyoto University in Japan used eye-tracking systems to study the pupil size of humans and chimpanzees while they watched short video clips of pupils dilating and contracting.
According to the findings, pupillary synchronisation, or pupil mimicry, was seen in both human and chimpanzee subjects, particularly when viewing their own species. Mimicry was found to be most pronounced in the three mothers than the other five chimps.
Humans are the only species with visible whites of the eye, or sclera, developed during the course of our evolution to facilitate the tracking of eye movements and other non-verbal communication.
Mariska Kret and colleagues say their research demonstrates that pupil mimicry is not uniquely human and is possible in species with no visible sclera.
With the help of a new research grant, Kret hopes to study the ways in which pupillary synchronisation affects day-to-day behaviour and the practical applications.
She explained: "We'll be focusing on the clinical practice (locked-in-patients, autism, social anxiety, care robots), and the business sector (negotiations, selection procedures)."
The BSAVA has opened submissions for the BSAVA Clinical Research Abstracts 2026.
