Tired? Me too. No, don’t yawn. You’ll set me off…..
As infectious yawning is only found in apes and humans, it has attracted some research dollars. Consensus seems to be settling on contagious yawning as a form of social bonding. But our hunter-gatherer ancestry means there might be more to it than simple social cohesion.
Yawning in company frequently co-incides with active mirror neurons located in the more primitive parts of the brain. Mirror neurons cause us to smile or laugh when others do, expressing a basic commonality which reinforces social bonds. Studies with less neurotypical groups, such as those on the autistic spectrum for whom social cues are less apparent, show a significant reduction in yawning following others1. And interestingly yawning is rare in children under the age of 4, suggesting that while a primitive part of the brain may be involved, the behaviour requires a certain level of social development.
While it may be true that yawning is associated with tiredness when we’re alone, this seems to have little influence when catching a yawn from others. So while imitation may be the sincerest form of flattery as the old saying goes, and collective yawning re-enforces social bonds, perhaps the infectious yawn has one additional element which has contributed to human survival?
Apes and early humans survived by living in close social groups with high levels of mutual dependency. Bedding down for the night would always mean some risk. Perhaps a yawn signals members of the group are getting tired, so others unwittingly copy this behaviour and then turn their attention to sleep. The contagious yawn is then a sign it is time for the whole group to prepare for rest, which includes working out where members will sleep with regard to risk from predators, exposure to the weather, and expressing the group’s social order etc.
A related study might explain why teenagers are frequently hopeless until late morning and conversely the elderly rise early2. For social animals having a range of times when group members are awake and acting as sentries will increase the groups’ odds of survival. And perhaps the contagious yawn prepares the group for the time when it is most vulnerable?
1. Yawning less common in children with ASD https://today.uconn.edu/2010/09/when-yawning-isnt-contagious
2. A study of the Hadza people in Tanzania shows age based sleep patterns https://today.duke.edu/2017/07/live-grandparents-helped-human-ancestors-get-safer-night’s sleep