Fact. There are many theories about why we yawn, and one is that we do it when we're bored or tired. Many people also believe yawning helps bring more oxygen into our bodies, although this theory was disproved in 1987. Still another theory is that yawning began with our ancestors, who did it to show their teeth, which was a symbol of power and strength. Scientists still aren't set on one reason as to why we yawn, but we do know that yawning is contagious.