It might be the bane of the dreary lecture theatre, but research has revealed that the contagious yawn could be a sign of evolution's highest mental states.
Psychologists have found a strong correlation between an individual's empathy and the compulsion to follow suit when they witness another person yawning.
Preliminary results from a separate study suggest that chimpanzees similarly find it impossible to resist the urge.
There are many theories as to why animals yawn - from raising brain oxygen levels to clearing meat from the tonsils. It has been documented in many species - there are even reports that tadpoles do it.
But the latest research suggests that the "contagious" yawn is restricted to humans and the great apes.
For some people, simply thinking or reading about someone yawning is enough to trigger a response and set them off yawning.
The study by Steven Platek, who is assistant professor of psychology at Drexel University in Philadelphia, found that people who were better at inferring someone else's state of mind were more likely to yawn when shown video footage of a person yawning.
By comparison, people who have schizotypal personality traits - such as odd behaviour or having no close friends - were found to be almost immune to the effect of seeing other people yawn. Professor Platek's study is published in the journal Cognitive Brain Research .
James Anderson, reader in psychology at Stirling University, said that Professor Platek's work indicated that the same trait may be found in chimpanzees.
In laboratory tests, some of the apes were observed to yawn more after watching a video recording of a yawning chimp.
"We know that chimpanzees are capable of quite advanced self-awareness, and there is evidence that they show empathy with others," Dr Anderson said.
Professor Platek said: "Contagious yawning might be some primitive form of empathy that may be expressed as emotional contagion in humans and great apes."
This could have evolved to enable groups to synchronise their social behaviour. Alternatively, it could be the by-product of empathic processes in the brain.
Some interpretations of the contagious yawn were not so advanced.
Professor Platek noted that one of his students was using it to his own advantage - to pick up women in bars.
If a woman yawned in response to his yawn, he would know that she was paying attention to him - he would then walk over and buy her a drink.