You might want to get this over with now. Even reading about yawning is enough to set some people off. The late psychologist Robert Provine, who spent years studying the subject, pointed out that merely thinking about it can work. If you've just yawned, you're in good company.
The study behind "two out of three"
In 2014, Alex Bartholomew and Elizabeth Cirulli at Duke University showed 328 people a video of about three minutes and counted their yawns. Of those, 222 yawned at least once, or 67.7%, with individual counts ranging from none to 15.
Then they looked for what predicted it, and this is where it gets interesting. The popular idea had been that contagious yawning reflects empathy. You catch a yawn, the theory went, because you're attuned to other people. They found no such link with empathy, and none with tiredness either once age was taken into account.
The only thing that predicted it was age, with older people catching yawns less often. Even then, age accounted for only 8% of the variation. Most of the difference between one person and the next remains unexplained.
Figures we couldn't find
While researching this we came across a neat breakdown by age: 82%, 60% and 41%. It's the sort of statistic that's very tempting to repeat. We couldn't find it in the paper, or in Duke's press release, or in several news reports of the study. The paper treats age as a continuous variable and doesn't break it into those bands. We mention it here in case you run across it elsewhere.
Can you stop one?
Possibly. In a pair of small experiments published in 2007, Andrew and Gordon Gallup tested people watching yawning videos.
- Breathing through the nose. Out of 44 students, split into groups of 11, nobody who breathed through the nose yawned, compared with 45 to 54% in the other groups.
- Cold on the forehead. Out of 33 students, 9% yawned with a cold pack, just one person, against 41% with a warm or room-temperature one.
Those are very small groups, and they were designed to test a particular hypothesis, that yawning helps cool the brain. That idea is still disputed. We should also admit that we read these results in a reproduction of the abstract and methods, not the original article, and you should treat them with the same caution.
And once a yawn has started, stopping it is hard. Provine described yawning as a fixed action pattern: once it gets going, it tends to run to the end.
Why does it happen at all?
Nobody knows for certain. The two ideas you'll hear most are brain cooling and group synchrony, keeping a group's alertness in step. Neither has won. Both are hypotheses, and that's as far as the evidence goes.
The dogs
A 2008 study found that 21 of 29 dogs yawned after watching a person yawn. A 2009 attempt failed to reproduce that, and a later statistical re-analysis of six studies did support the effect. So the safest wording is "in some studies". Chimpanzees seem to catch yawns too, according to a 2013 study of 33 animals.
What we read
- Bartholomew & Cirulli, Individual Variation in Contagious Yawning Susceptibility, PLOS ONE, 2014
- Duke Health, Contagious yawning may not be linked to empathy
- Robert Provine, letter in APS Observer
- Gallup & Gallup, Evolutionary Psychology, 2007
- Reproduction of the Gallup study's abstract and methods, Baillement.com
- Provine on contagious yawning, Baillement.com
- Dogs and contagious yawning, re-analysis summary, Baillement.com
