There’s been building evidence that a yawn’s ability to spread to others is somehow correlated with the ability to empathize — to pick up on others’ emotional states and imagine what they may be thinking or feeling.
Contagious yawning seems to increase starting around the age of 4 or 5 years, about the same time children start developing the ability to identify other people’s emotions, and it falls when those empathetic abilities also fall in old age.
by Amina Khan