The reason humans and other animals yawn has long been a mystery. Now, a team of scientists led by the State University of New York (SUNY) has argued that yawning might have evolved to make us more vigilant to threats.
According to the experts, yawning has evolved as a signal to the group that one of its members is tired. When noticing this signal, other group members become more alert to cover for the tired – and thus 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 authors explained.
“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.”
To test this hypothesis, the researchers investigated whether seeing other people yawn could improve the detection of lions – which were most probably a common threat to the survival of humans during evolutionary history – compared to impalas, a species of antelope that would not have posed a significant danger to our ancestors.
The experts enrolled 27 participants who were first showed videos of people either yawning or with neutral facial expressions.
Afterwards, in a random order, the researchers repeatedly showed the participants pictures of either a lion or an impala alongside a variety of other distracting 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,” the authors reported.
These findings are consistent with those from a previous study conducted by the same university in which the researchers discovered that seeing someone yawn increases the ability to detect snakes.
By replicating the experiments with a different animal, the scientists were able to provide evidence that this effect was not specific to snakes, but occurs similarly across different contexts.
“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,” said Andrew Gallup, a professor of Biopsychology and Evolutionary Behavioral Sciences at SUNY, who was involved in both studies.
“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.”
The study is published in the journal Evolutionary Behavioral Sciences.
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