Physiology, Theories and Contagiousness
First, let's look at what this bodily motion is: Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we're born: According to Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County, research has shown that 11-week-old fetuses yawn. And while yawning is commonly associated with relaxation and drowsiness, your heart rate can rise as much as 30 percent during a yawn.
Recent Theory: (The brain-cooling theory)
A more recent theory proposed by researchers is that since people yawn more in situations where their brains are likely to be warmer -- tested by having some subjects breathe through their noses or press hot or cold packs to their foreheads -- it's a way to cool down their brains. What does it matter if our brains are cold or hot? Cool brains can think more clearly; hence, yawning might have developed to keep us alert
Interestingly, while all vertebrates (including fish) yawn, only humans, chimps and possibly dogs find yawns contagious. And people don't find them contagious until they're about 4 years old. Recent studies show contagious yawning may be linked to one's capacity for empathy In one study, autistic and non-autistic children were shown videos of people yawning and people simply moving their mouths. Both groups of kids yawned the same amount when viewing the video of people moving their mouths. But the non-autistic kids yawned much more frequently than those with autism when watching people really yawning. Since autism is a disorder that affects a person's social interaction skills, including the ability to empathize with others, the autistic kids' lack of yawning when watching others do so could indicate they're less empathetic. The study also found the more severe a child's autism, the less likely he or she was to yawn. On a positive...
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