But how could the experimenters be sure that if tortoise B
yawned after tortoise A, it was a genuine example of mimicry?
Each time they
yawned they were instructed to record the time of day and the activity in which they were engaged at the time.
I participated in a study [published in Frontiers in Evolutionary Neuroscience in September 2010] that confirmed this dynamic after we observed changes in the brain temperature of rats before and after the animals
yawned. The cooling effect of yawning is thought to result from enhanced blood flow to the brain caused by stretching of the jaw, as well as countercurrent heat exchange with the ambient air that accompanies the deep inhalation.
The first I should like to mention is a paper called Dogs Catch Human Yawns (by R M Joly-Mascheroni et al in Biology Letters, 2008) which reported an experiment in which 29 dogs watched a human yawning at them and the experiments counted how many of them
yawned back.
In another set of tests, rats
yawned more as the temperature rose and their brains heated up, Gallup and colleagues reported in the February Ethology.
During and immediately after the yawning videos, the chimps
yawned more than twice as often as they
yawned after watching nonyawning chimps.
The participants then watched a three-minute video of people yawning, and recorded the number of times they
yawned while watching the video.
If stress were the main factor, then the dogs would probably have
yawned during a modified version of the test, in which the person caught the dog's eye and then silently made a face, but didn't yawn.
A trial sequence consisted of 7 five-minute sessions: a baseline session, followed by three experimental sessions, where the human repeatedly either
yawned, gaped or nose-wiped, and three post-experimental sessions, where social interactions continued without the inclusion of the key behaviours.
