Yawns could help keep us safe by making people nearby more vigilant to threats when someone is tired

• Researchers found seeing someone yawn makes people more vigilant to threats 
• Previous study found seeing yawns increased people’s ability to detect snakes.

The reason we yawn has long been something of a mystery.

But it might be because it helps us avoid harm, a study suggests.

Researchers found that seeing someone yawn makes people more vigilant to threats.

It’s thought that yawning evolved as a signal to the group that one of them is tired. An onlooker’s brain becomes more alert to threats in order to cover for the tired – and therefore more vulnerable – member of the group.

‘The group vigilance hypothesis proposes that seeing someone yawn should trigger neurocognitive changes to enhance the vigilance of the observer as a means of compensating for the reduced alertness of the yawner,’ the researchers from SUNY Polytechnic Institute said.

It’s thought that yawning evolved as a signal to the group that one of them is tired, making other people alert 

‘The tendency to be attuned to, and affected by, the yawns of others may have evolved due to the outcome this had on enhancing survival within groups.’

For the study, they investigated whether seeing others yawn improved the detection of lions – which were likely to have been a recurrent survival threat to humans during evolutionary history – compared to impalas, a type of antelope, which would not have posed a danger to our ancestors.

The researchers, whose findings are published in the journal Evolutionary Behavioural Sciences, tested 27 people.

First, they showed them videos of people either yawning or with neutral expressions. Then, in random order, they repeatedly showed them pictures of either a lion or an impala in a matrix of other distractor images and asked them to find the target animal.

‘Following exposure to people yawning, participants were faster at detecting lions and slower in their search of impala,’ said the researchers.

A previous study by the same university found that seeing people yawn increased people’s ability to detect snakes.

By replicating the study with a different animal, the team were able to show that the effect was not just specific to snakes, but across different contexts.

A previous study by the same university found that seeing people yawn increased people’s ability to detect snakes 

Dr Andrew Gallup, who was involved in both studies, said: ‘Replications are important to ensure that the original findings were not spurious or due to some chance events or statistical anomalies.

‘When we are able to replicate previous experiments, as we have done here, we gain confidence that the findings represent true effects.

‘In this case, we also wanted to replicate the previous study to ensure that the effects observed in the original study were not due to the specific type of stimulus used (i.e., snakes).

‘By performing a conceptual replication, we show that seeing other people yawn enhances threat detection, i.e., it improves vigilance, across different contexts.’

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