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 behaviours.
Researchers found that yawning, but not nose-wiping, was contagious for juvenile chimpanzees, while infants found neither yawning nor nose-wiping contagious.
Chimpanzees appear to develop susceptibility to interspecies contagious yawning as they grow from infant to juvenile, possibly due to their developing ability to empathize with the person yawning. Emotional closeness with the yawning human did not affect contagion.
According to researchers, the results of the study reflect a general developmental pattern, shared by humans and other animals. Given that contagious yawning may be an empathetic response, the results can also be taken to mean that empathy develops slowly over the first years of a chimpanzee's life.
The study is published in journal PLOS ONE.
--ANI (Posted on 18-10-2013)