A study reveals that as sanctuary-kept chimpanzees grow from infant to juvenile, they develop increased susceptibility to human yawn contagion, possibility due to their increasing ability to empathize. The study was published on October 16, 2013, in the open-access journal PLOS ONE by Elainie Madsen and colleagues from Lund University.
Scientists examined the extent to which two factors affected chimpanzees' susceptibility to yawn contagion: their age, and their emotional closeness to the person yawning. Thirty-three orphaned chimpanzees, 12 infants 1 to 4 years old, and 21 juveniles 5 to 8 years old, were included in the trials. A trial sequence consisted of 7 five-minute sessions: a baseline session, followed by three experimental sessions, where the human repeatedly either yawned, gaped or nose-wiped, and three post-experimental sessions, where social interactions continued without the inclusion of the key behaviors. Each chimpanzee separately observed an unfamiliar human and a familiar human preforming the sequence.