Contagious yawning in bonobos: evidence for the empathy and synchronization hypotheses.

Since '90s many studies have focussed on contagious yawning and its proximate factors in humans. The idea that yawning contagion in humans is predicated on an empathetic or a synchronization response was recently extended to other primate species. Here, we show for the first time that yawn contagion is also present in bonobos (Pan paniscus). During a period of five months, we collected data via all occurrences sampling on 16 adults (4 males and 12 females) hosted at Apenheul Primate Park (The Netherlands) and Wilhelma Zoo (Germany). Our analyses show that the frequency of contagion was higher among kin and when the trigger was a high ranking individual. These results support both the empathetic and synchronization hypotheses, which are not necessarily mutually exclusive. Kinship predicts yawn contagiousness, which is consistent with the idea that yawn contagion is mediated by emotional closeness. On the other hand, high ranking individuals have the main role in group decision-making and in regulating the group daily activities. In this view, the stronger yawn response elicited by high ranking individuals seems to support the synchronization hypothesis