London: Yawning for long has been considered contagious in adults -- but the phenomenon doesn`t catch on in babies, say researchers.
A new study in Britain has found that babies and young children are immune to "catching" yawns until they attain the age of five -- in fact, they almost never yawn back at someone who yawns at them.
The researchers from University of Stirling have found that infants and young children aren`t prone to the contagious aspect of yawning. Instead, they only ever yawn spontaneously, `The Daily Telegraph` reported.
Lead researcher Dr Jim Anderson said the findings will help to shed new light on how the human brain develops as people grow up and what makes them yawn.
"The exact reason why we yawn isn`t really understood very well at all, but there is no doubt that as adults it is highly contagious. People who score highly for empathy are significantly more likely to show contagious yawning.
"What we know from other research is that one part of the brain that continues to develop through out childhood is the frontal cortex and that the frontal lobes play a role in social decision making and the ability to empathise.
"That would tie in with the gradual development of contagious yawning during childhood," he was quoted as saying.
In the first part of the study, the researchers monitored the behaviour of 22 infants and toddlers while they were shown video footage of other children, adults and animals yawning. They`re also shown footage of their mothers yawning.
The researchers found that the children did not yawn in reaction to the footage.
In the second part of the study, the researchers also found that children do not start catching yawning until they reach the age of five years old when a small percentage start
Dr Anderson said: "With each age group up to the age of 11 years old, there is a higher proportion who will react to video footage of someone yawning. At the age of 11 years old, it reaches the same levels we would find in adults."
The exact reason why people yawn is still poorly understood. It is commonly thought to be a reaction to low levels of oxygen in the blood sparking a yawn to fill the lungs with air and so increase oxygen intake.
The scientific evidence for this, however, is poor and even breathing in extra oxygen makes no difference to yawning behaviour. But, there is now growing evidence that yawning may be a social cue that communicates a message.
Dr Anderson said: "I don`t think there is one primary function, but as adults we have a natural tendency to inhibit yawning because it is seen as being impolite. The contagious yawning might just that our brains see someone else doing it and so it becomes acceptable."
The findings have been published in the latest edition of the `Biology Letters` journal.