Why do we yawn and Why is yawning contagious?

Regulates Internal Temperature

Just like the CPU of a computer, the brain generates intense heat out of all body organs. Unfortunately, much of the brain’s functions are temperature-sensitive, with high temperatures associated with cell damage. This makes thermoregulation — maintaining optimal brain temperature within a certain range through cooling mechanisms — key to our survival. On a less severe note, the hotter your brain, the drowsier you feel, which explains why we tend to sleep so much during a fever