Yawning is contagious—unless you're a baby. Children are immune to the phenomenon until the age of five, a new study shows. Dogs and chimpanzees also "catch" yawns, even from people, but human youngsters only yawn spontaneously, psychologists found after studying 22 children. They showed each videos of other children, adults, animals, and even their mothers yawning to determine the results, published in the Biological Letters journal.
The tendency to find yawns contagious starts at five and increases as children age, a researcher tells the Telegraph. Previous studies have shown "catching" yawns is an empathetic response, and researchers note that the ability to empathize develops throughout childhood, which could explain the findings. Click for more on why yawning is contagious, or more on why we yawn at all.