Question

why do human yawn???reason?

Answer 1

One is that when we are bored or tired, we just don't breathe as deeply as we usually do.
As this theory goes, our bodies take in less oxygen because our breathing has slowed.

Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood.

hope it helps you
thanks

Answer 2

Yawning is a psychological which is message transmitted by our brain. Before starting any activity we yawn. Why?? Because our brain and body gets ready before starting something fresh .