The sight of another person yawning makes us open our mouths wide in imitation. Chimpanzees and lions can also catch yawns. It is likely that all animals yawn to regulate their inner body processes.
Andrew Gallup, an evolutionary biologist at the State University of New York Polytechnic Institute, says that the evolution of jawed fishes 400 million or so years ago probably caused us to yawn. In a paper published this month in Animal Behavior, he reports some evidence for how contagious yawns might have evolved to keep us safe. Science talked with Gallup about yawning and how useful it is. The interview has been edited for clarity and length.
No. Despite continued belief, research has explicitly tested that hypothesis and concluded that breathing and yawning are controlled by different mechanisms. In marine mammals, yawning occurs when the animal is submerged underwater and not breathing.
A: Yawning is a rather complex reaction. It is triggered under a variety of contexts. During periods of state change, it occurs following transitions of sleeping and waking. There is research that suggests that yawns are initiated with increases in cortical arousal. A growing body of research suggests that yawning is caused by rises in brain temperature. I've done a number of studies on this in humans, nonhuman mammals, and even birds.
The studies show that we can change the temperature of the brain and body to make yawns. In rats, we have shown that increases in brain temperature can cause yawning and decreases in brain temperature.
We have done a number of large-scale comparative studies, where we have recorded the yawn durations from over 100 species. There are strong positive relationships between how long an animal yawns and how large and complex their brain is, even when controlling for body size.
Spontaneous yawns are internal, physiologically driven. Contagious yawns have only been documented in highly social species. There is a wide variation in the response among individuals. Some people are very susceptible to yawns while others are not.
Some studies suggest that individual differences in empathy may be contributing to this response. If someone yawns and we respond the same way, that could be a sign of empathetic processing. Other studies did not show that relationship. I think the jury is still out.
Contagious yawning may have evolved to coincide with transitions and activity. It might have evolved to increase vigilance within a group. If yawning is an indicator of diminished arousal, then seeing another person yawn might increase the observer's vigilance to compensate for the low vigilance of the yawner. The entire group might be more alert because of the spread of the yawns.
I did a study last year that tested this. We showed people images of snakes, nonthreatening stimuli, and videos of people yawning and moving their mouths, and timed how fast they could pick them out. After seeing other people yawn, their ability to detect snakes rapidly improved. Frog detection was unaffected by the observation of yawning.
When I first started studying this subject, I was yawning a lot. I was yawning all the time while I was writing papers and reading literature. I became habituated to the effects over time. I still yawn during social interactions, but the stimuli I use in the lab no longer produce the same effect.
All Rights Reserved © 2024
