Why Bonobo Yawning Is Contagious
November 15, 2012

Scientists Study Why Bonobo Ape Yawning Is Contagious

Brett Smith for redOrbit.com — Your Universe Online

Yawning is contagious among many species and two biologists from the University of Pisa in Italy have found that the social relationships of bonobos can determine if yawns spread from ape to ape.

According to the scientists´ report in the open access journal PLOS ONE, if several bonobos are socially related, there is a greater chance that a yawn by one adult ape will cause the other adults to also yawn, especially when the first to yawn was a senior member of the group. They also found the propensity for yawning was higher when the animals were most relaxed.

A previous study of non-human primate yawning focused on yawn interactions between familiar chimpanzees and between unfamiliar chimpanzees, the Italian scientists wrote in their report. Unlike their newer study, the previous study did not take into account social closeness among a group of apes.

In the study, the researchers, Elisa Demuru and Elisabetta Palagi, observed 12 captive bonobos for 3 months at the Apenheul Primate Park in the Netherlands. Observation sessions lasted 6 hours and took place in both the morning and in the evening. A total of 1,125 yawns were recorded from the adult apes during the observation period.

Besides studying the contagious element of yawning, the researchers also looked into a potential empathetic component to the behavior. Empathy involves the sharing of emotional states and many recent studies suggest yawning could be a form of empathy.

In support of the empathy hypothesis, the researchers noted bonded male-female pairs were seen ℠infecting´ each other with yawns at a higher rate. However, the two scientists were unable to make any strong correlation between empathy and yawning based on their observations and analysis.

"Though we are still far from a clear demonstration of a link between yawn contagion and empathy, the importance of social bonds in shaping this phenomenon in bonobos suggests that a basic form of empathy may play a role in modulating yawning behavior,” the authors wrote.

Yawning among humans is very contagious, with previous research showing that seeing, hearing, reading, or thinking about another individual yawning can stimulate a yawn in the observer. About 50 percent of humans will yawn within several minutes of seeing another person yawn.

Previous research by Palagi and her colleague Ivan Norscia emphasized the empathy component among humans. A 2011 study by the pair suggested only social bonding affected the likelihood of a yawn contagion spreading. They dismissed other possible connections including age, country of origin, and sex. They were also able to demonstrate the yawning was passed more quickly among related individuals than among acquaintances or strangers.

Many studies also support the yawning-as-empathy hypothesis as well.  A 2007 study found children with autism, who have a lower capacity for empathy, are less likely to be infected by a yawning contagion than other children of the same age.

One theory suggest yawning is an evolutionary mechanism that keeps the brain cool and raises alertness among a social group that may have had to keep vigilant in a predatory and dangerous environment.