Most people, when they see someone else yawn, quickly feel the urge to yawn as well. Between 40 and 60% of people automatically find yawning contagious and yawn themselves. The standard answers from scientists as to why people find yawning contagious used to be that, although it was clearly a real phenomena, there was no obvious reason for it. Research conducted in 2005 by Finnish scientists, however, may point to certain parts of the brain as being responsible.
When a person witnesses someone else yawning, he or she has a mostly unconscious urge to do the same. People may become conscious of the urge, but scientists suggest the beginning of the yearn to yawn is unconscious. This means that the signal must bypass the mirror neuron system, which is a process that would make this response a conscious and imitative act. Scientists have often, in the past, suggested that the mirror neuron system causes yawning.
Instead, researchers found that seeing someone else yawn seems to render the periamygdala sections of the brain inactive. This is a tiny part of the brain on either side of the head that helps interpret things like facial expressions. If it was working, the conscious response to yawning might be, “Oh, he’s tired.” By temporarily blocking such a reading, however, the response cannot at first be a conscious perception.
This does not explain specifically why people find yawing contagious, but it does suggest that there are brain sections responsible for a person’s perception of a yawn. In addition, the response does not begin with the mirror neuron system but instead bypasses it.
Other explanations include the idea that yawning may have evolved in early man as a way to signal or set up sleep schedules. A contagious yawn meant that perhaps more than one person was tired and people should sleep accordingly. Since tiredness might indicate a less energetic response to danger, yawning would mean people should find shelter and get out of danger. Those who yawned and paid attention to it may have been selected into the species because they got proper sleep and were more alert to danger.
The exact mechanism and reasons of why people yawn in response to others is still not clearly understood. The 2005 research may point the way to where to look for more clues about this interesting and automatic human behavior.