"We hold these truths to be self-evident, that not all yawns are created equal, that although they are endowed by Mother Nature with certain un-alienable causes, that among these are Sleepiness, Ex-citement, and the Pursuit of Emp-athy."

Reading this im-provised Declar-ation of Yawning probably did little to unlock the mysteries surrounding this phenomenon, but ten bucks says you yawned while reading it. Here is Dr. Nina's What You Need to Know about yawning:

What are some possible explanations for why we do this? The next time you yawn during a meeting or while the teacher is giving a lesson in the classroom, realize that your body is probably trying to stretch out its lungs or become more alert. Our breathing tends to be shallow when we are tired, sleepy, bored, or just waking up. The deep breath that accompanies a yawn can fill up your lungs and prevent tiny airways from collapsing. Addition-ally, moving your ligaments and muscles may also make you feel more awake.

On the other end of the spectrum, yawning also occurs in response to stressful situations. The next time you see athletes or live entertainers before a game or performance, pay close attention. Similar to deep breathing techniques, yawning can increase blood flow to the brain and help prepare for increased activity or focus.

Seeing someone laugh, often makes you laugh. Seeing someone cry can bring tears to your own eyes. Similarly, yawning is contagious. It is believed to reflect empathy and social bonding.

In fact, contagious yawning is more likely when you are close to someone - family or friends - as compared to strangers.

Although simple and reflexive, yawning is suggestive that you are seeing things from another person's point of view and are responding to that person's emotions.

Additionally, yawning is also believed to diffuse stress after a period of being on high alert and spread a feeling of calm through a group.

When do we do it the most? In general, we tend to yawn approximately 10 times per hour. This number may increase in the morning and at night.

With the temperatures dropping, brace yourself for an increase in the number of yawns you dish out. This may be because yawning also serves to cool the brain. Like a radiator, the warm blood is removed from the brain when cooler blood from the lungs is introduced.

At what age do we start yawning? Yawning begins even before you are born! As early as 11 weeks after conception, fetuses begin yawning. However, contagious yawning typically does not begin until 4 years of age.

Are humans the only ones in the animal kingdom that yawn? Nope. As those of you with pets probably know, yawning is not unique to humans. In fact, spontaneous yawning occurs in all vertebrates, including fish, snakes, and lizards. Contagious yawning, which is believed to reflect empathy and social bonding, however, is limited to dogs and chimpanzees. So the next time you yawn in front of your pet dog or chimpanzee, see if they reciprocate.

Are there any conditions to worry about? Contagious yawning is reflective of empathy and social bonding. Therefore, it is not surprising that people with schizophrenia and autism, conditions with impaired emotional development, yawn less. In fact, the more severe autism is, the less frequently the person yawns. On the other hand, excessive yawning may be seen in people with multiple sclerosis, Lou Gehrig's disease, Parkinson's disease, and following radiation therapy. The reasons for this are not clear. That said, don't go running to the doctor if you've been yawning a lot - you might just be tired.

How many times do you think you yawned while reading this? I know, I yawned a lot while writing it. Just thinking about it is enough to trigger your brain to dish one out. The next time you yawn around others see for yourself how contagious it is. Just make sure to cover your mouth to avoid inhaling flies.

Dr Nina Radcliff, of Galloway Township, is a physician anesthesiologist, television medical contributor and textbook author. Email questions on general medical topics to her at drninaradcliff@aol.com