Subtitles section Play video Print subtitles Almost all animals with a spine yawn. Penguins do it as a mating ritual, snakes do it to realign their jaws after a meal and guinea pigs do it to display anger. So, why exactly do humans yawn? And is yawning actually contagious? If you haven't already checked out our YAWN-O-METER video, click here, or use the link in the description to see how long you can last before yawning. If you're anything like us, you may have even yawned at the title of this video. The truth is, the first time you yawned was likely as a fetus. Babies begin to yawn during the second trimester, and though the reason why is still unknown, it may have to do with proper brain development. In adults, yawns were commonly thought to draw more oxygen into the lungs making you feel less tired, but new research states that this may not be the case. Scientists now believe that yawning has developed as a way of physiologically cooling your brain. Much like a computer, your brain works best at a certain temperature, and tries to avoid "overheating". And it turns out yawning increases your heart rate, blood flow and the use of muscles in your face which are all essential to cooling the brain. On top of that, deeply inhaling cold air can alter the temperature of the blood in our head. But why is your brain hot in the first place? Well, both exhaustion and sleep deprivation are known to increase overall brain temperature, which explains why yawning occurs more in these states. Researchers have even found participants who place warm packs on their head yawn 41% of the time while watching others yawn, as opposed to 9% of the time with a cold pack on their head. So if your head is already cold, you'll yawn less. But what about contagious or social yawning? Humans, primates and even dogs find yawning contagious, and it's most likely linked to empathy. Contagious yawning begins in children around the age of 4-5, and this is when empathetic behavior, along with the ability to identify emotions, begins to develop. In fact, children with empathy-related disorders, such as autism, yawn less in response to videos of people yawning compared to other children. Research also suggests that you are more likely to copy the yawn of someone socially or genetically close to you. Even dogs are more likely to copy the yawns of their owner as opposed to the yawn of a stranger. Finally, mirror neurons also play a role. In our brain, mirror neurons fire when we perform a specific action, view someone else doing the action or even just hear someone talk about the action. They are important brain cells that are used for learning, self-awareness and relating to others. When we view someone else yawn, the mirror neurons in our brain become activated in a similar way, and as a result, we copy the yawn. So, although yawning may occur in people who are literally 'hot-headed', contagious yawning allows us to be cool with the people around us. If you haven't already checked out our Yawn-O-Meter, go try it out and let us know in the comments how long you were able to last. And subscribe for more weekly science videos!