I believe its because yawning helps people become more "alert" so if one person yawns, it may send an unconscious message to other people in the area, so that they yawn and become more alert themselves. It's kind of hard to understand unless you think of humans as animals who are trying to survive.
There is some work done on this with baboons. They yawn for the same reason as us but also to display their canines. It is a social signal. If you want to dig deep you go into animal behaviour articles, technical.
i was watching this show called "luther" (csi type thing but its mostly in london)
and he faked yawned to catch this sneaky lady in her game. the way he initiated the case with a yawn and he asked her why didn't she yawn back and most people with a warm heart with yawn back out of sympathy .
A yawn is a sign of a lack of oxygen to the brain. It is very visually contagious. That's because biologically, we all lack oxygen to the brain, as the day progresses. Whenever we see someone, especially a friend or family member, it seems almost impossible to stop from yawning. Boredom factors in, as well.
2 months ago
Last edited at 11:47AM on 10/15/2013
I think it is lack of stimulation to the mind or maybe lack of oxygen. If I am sleepy while driving within a reasonable time, all it takes is to stop get out and walk around for a couple of minutes and then I feel renewed and ready for the road again. The same with speakers. One of my instructors in school says that after 15 or 20 minutes of listening to the same voice is enough. After a break of five minuets or so, you are ready to listen again. I have found this to be true.