One good yawn is worth another but psychologists are still baffled; Symptom of self-awareness doesn't tell us why we do it.
ONE of the most enduring and elusive mysteries of the human body is why yawning is so contagious.
No one yet has yet been able to pinpoint categorically why some people spontaneously break into yawns when they see another person yawning.
One of the world's foremost experts believes contagious yawning is triggered by a mechanism in the brain that can detect a yawning face and set off a chain reaction.
'Yawning is extremely contagious,' says Professor Robert Provine, of the University of Maryland. 'Seeing a person yawn triggers yawns. Reading about yawning causes yawns. Sitting alone in a room thinking about yawning triggers yawning. Once the neurological machinery in our head gets under way it's hard to stop a yawn.'
A group of US researchers believes that contagious yawning speaks volumes about the people susceptible to it.
Psychologists believe that rather than just being a coincidence or a neurological knee-jerk reaction contagious yawning is common among the self-aware or empathetic people.
Between 40% and 60% of people who watch videos of others yawning or hear talk about yawning end up joining in, something that psychologist Steven Platek, of Drexel University in Philadelphia, describes as a 'hokey phenomenon', but he believes such behaviour is indicative of someone who is empathetic or self-aware.
Platek and colleagues from the State University of New York have also discovered that those who are impervious to contracting yawns also struggle to put themselves in other people's shoes.
It is thought that people identify with another person's state of mind while they yawn, which triggers the unconscious impersonation, helping to explain why people with schizophrenia who have difficulty doing this rarely catch yawns.
Some psychologists even believe that contagious yawning may have helped our early ancestors to co-ordinate times of activity or rest.
Professor Provine said, 'When you see someone yawn you're initiating a chain reaction of biology, so whatever changes in our body are brought about by yawning are synchronised in everyone that's doing it.'
Despite the new insight into why yawning is contagious the US research has still not shed any light on exactly why we yawn. The most common perception that yawning is a reaction to a lack of oxygen has been widely disproved, as experiments have shown that people given more oxygen or carbon dioxide are just as likely to yawn.
Ronald Baenninger, who has studied yawning in Philadelphia, believes that yawning can help keep the brain aroused when sleep is unwanted, such as early in the morning and when we struggle to awake longer at night.
He says fake yawning can trigger the same bodily response but warns that if you do a fake yawn it is likely to turn into a real one.
Humans do it, mammals and reptiles do it, and penguins do it as part of their mating ritual
THE average yawn is six seconds long.
All humans yawn, most mammals yawn and some birds and reptiles yawn.
The earliest occurrence of yawning in humans happens at about 11 weeks after conception, while the baby is still in the womb.
The hypothalamus part of the brain is thought to play a role in yawning.
Experiments with teenagers watching MTV and a colour test card have show that yawning is indicative of boredom.
Blind people have been known to yawn more after hearing an audio tape of people yawning.
A person's heart rate can rise as much as 30% during a yawn.
Children up to the age of five yawn, but not contagiously. They become increasingly susceptible between the ages of five and 11. Adelie penguins yawn as part of their mating ritual.