Yawning is contagious for perhaps half of all adults, but the reason why is unknown. While the common perception is that contagious yawning relates to human empathy and other social factors, Psychology Today reports a 2014 Duke University study that contradicts this notion.
Despite contradicting the correlation between contagious yawning and empathy, the Duke study offers little clarity in contributing factors. It does note that age plays a role because people tend to yawn contagiously less as they get older. Studies also show that children typically start to yawn contagiously at age 4 and that children with autism are less susceptible to contagious yawning.