Why do we yawn?

Almost all animals with a spine yawn. Penguins yawn as a mating ritual, snakes yawn to realign their jaws after a big meal, and guinea pigs do it to display anger. But why do humans yawn?

Babies begin to yawn even in the womb, during the second trimester, and it is likely to help with brain development. In adults, scientists have hypothesized that yawning helps to cool the brain down by increasing your heart rate, blood flow, and the use of muscles in your face. But is there any correlation with yawning and your tiredness?

Turns out that your brain temperature increases with exhaustion and tiredness, so it makes sense that you yawn more when you're tired to cool down your brain!