Why do we yawn?

There is some controversy as to why we yawn and scientists haven't agreed on a single explanation just yet. Some say that yawning may be a means to keep the brain cool. A parallel new theory is that yawning is used for regulation of body temperature. One more suggestion is that yawns are caused by the same chemicals or neurotransmitters in the brain that affect emotions, mood, appetite, and other phenomena. Yet another hypothesis is that yawns are caused by a lack of oxygen in the bloodstream, and that yawn reflex incorporates a "rush of oxygen" to the brain.Most people agree that when hen you are bored, you yawn. Scientists have confirmed this observation by comparing the number of yawns in 17-19 year old students who watched music videos to the number of yawns in students who watched an uninteresting color test bar pattern.