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Unfortunately not. the jury is still out on the exact reason or reasons why we and other animals yawn. Im sure you have looked at this before, but wiki has a nice article on the suggested reasons http://en.wikipedia.org/wiki/Yawn#Proposed_causes
its because u get bored
due to having lack of oxygen in rbc when the amount of co2 increases hope so
there is no exact reason YET but the most famous and credible reason as of now is the lack of oxygen in the body. Notice that a person yawns when he or she feels really sleepy or tired or perhaps a little dizzy. This is due to the lack of oxygen in the brain. So, the main reaction of the person is to yawn which makes the person concern open his/her mouth really big thus sucking in large amounts of oxygen that would compensate for the lack of it. :D
*makes the person concerned
is it a good thing or a bad thing???
I guess it's a good thing then because if the reason above is true, then it's a way of the body to recuperate from lack of oxygen which is a bad thing for the body. :/
it is really when u tired..................................scientifically their is no explanation
No definite answer, juries out on it. It happens with the expansion and contraction of the diaphram under the lungs though
its funny the things scientist cant explain
Though there is merit on the theory that the Autonomic nervous system with the medulla oblongata and the pons regions slow down the breathing rate and we see a drop in O2, this could trigger an automatic 'gasping' reflex that is the yawn