Can anybody please tell me what causes people to yawn.?
We yawn because we are tired. Like a smile, yawns probably serve more of a social function than a physiological one. The “lack of oxygen” theory is ridiculous and has been disproven. Yawning signals our fatigue to the other members of the tribe. It signals them that we may not be at our top performance, that our advice may be clouded and our help in group defense less than optimal. And yawns are indeed contagious. Biosociologically, yawns probably help to insure that tired members of the group all get their sleep at the same time to increase the numbers later available for hunting and defense.
