Healthcare professionals and researchers have observed human fetuses yawning as early as 11 weeks after conception. Many researchers regard the desire to yawn as a primal human instinct. Experts are not entirely sure why humans yawn, but one common explanation is that yawning stretches and lubricates the lungs. Yawning also increases a person’s heart rate.
More about yawning:
One study showed that people yawn more often during the colder winter months than they do during the summer. The researchers speculated that yawning might be a way for people to cool their brains — something that yawning in high temperatures would not accomplish, because the air that is breathed in would be warmer.
Yawning can be contagious, but some research shows that it is less so in children who are less than 6 years old.
In 2005, a US judge fined a juror for contempt of court after the juror yawned loudly in the courtroom.