Haven’t you always wondered whether fleas that live on dogs jump higher than those that inhabit cats, or what the role of fellatio is in fruit bats copulation time? And what about that one question you had been pondering on for so long: is yawning contagious in red-footed tortoises? Now science has the answer.
Scientific questions can be improbable; but usually there is more to them than simply satisfying one’s curiosity. Anna Wilkinson (University of Vienna, Austria) and her collaborators looked at tortoises to better understand contagious yawning in humans. Their findings were published in the journal Current Zoology.
Yawning, as you might have noticed from personal experience, resembles an infectious disease in that it spreads from person to person. In our species, this universal sign of tiredness or boredom can be triggered by observing, hearing, or even thinking about yawning. However, it remains a mystery why we involuntarily open our mouths widely when we perceive someone else doing it.
There are several theories. One hypothesis suggests that contagious yawning is an instinctive behavior that is activated with the observation of another yawn. A second theory sees it as “non-conscious social mimicry, the tendency to adopt postures, gestures and mannerisms of an interaction partner,” as explained in the Current Zoology paper. Finally, a third hypothesis explains contagious yawning in terms of empathy: if someone yawns as a result of fatigue or boredom, we yawn back because we unconsciously understand and want to share those feelings.
The study with the red-footed tortoises aimed to eliminate some of these hypothesis. These animals are “the ideal subjects for examining this question” because there is no evidence that they mimic each other and they are unlikely to show empathy. Yet, they respond to visual stimuli. Hence, they might exhibit contagious yawning if they observe another tortoise extending its neck, tilting its head back, and opening its mouth widely — the three features of the species’ yawn.
The seven tortoises that took part in the study were not “experimentally naive,” the authors write, “but they had never previously been involved in a contagious yawning task.” So the scientists had to teach one of the subjects (Alexandra, “the demonstrator”) to yawn when presented with a little red square, which they waved near her head. “This training took 6 months,” they write, and “the resulting behavior appeared highly similar to a naturally occurring tortoise yawn.”
With the demonstrator yawning at scientists’ will, the study could begin. The experimental set-up was simple. The red squared was waved at Alexandra who yawned in response while the other tortoises observed. Wilkinson and colleagues could then measure “the number of yawns for each observer animal.”
After months of study, a great deal of waving of a red square, and plenty of yawning, the authors concluded that “tortoises do not yawn in a contagious manner.” Your curiosity has been satisfied and scientists understand a bit more about contagious yawning in humans. There is probably more to it than the simple response to a visual stimulus.
(And because you might still be wondering, dog fleas do jump higher than cat fleas, and oral sex increases the duration of copulation in fruit bats.)