科學家認爲，打哈欠是在通過生理的方式給大腦降溫。研究者發現，頭上放了熱水袋的參與者在看其他人打哈欠時，有41%的時候也會打哈欠，而頭上放了冷水袋的只有9%。當我們看到其他人打哈欠時，大腦內的鏡像神經元進入類似…
原標題：人爲啥會打哈欠?
Almost all animals with a spine yawn.
幾乎所有的有脊椎動物都會打哈欠。
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.
企鵝以此爲求偶儀式，餐後蛇藉此來整理下頜，荷蘭豬藉此表達憤怒。
So why exactly do humans yawn?
那麼人爲什麼要打哈欠呢？
And is yawning actually contagious?
哈欠有傳染性嗎？
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 still unknown, it may have to do with proper brain development.
其實，你第一次打哈欠應該是在胎兒時期。嬰兒會在3-6月開始打哈欠，儘管原因尚不明瞭，但這可能和大腦發育有關。
In adults, yawns were commonly thought to draw more oxygen into the lungs making you feel less tired, but new researches states that this may not be the case.
而成人打哈欠常被認爲是要向肺部充入更多氧氣，來緩解疲勞，不過，新研究卻另有其詞。
Scientists now believe that yawning has developed a way of physiologically cooling your brain.
科學家認爲，打哈欠是在通過生理的方式給大腦降溫。
Much like a computer, you brain work best at a certain temperature, and tries to avoid overheating.
和電腦一樣，人腦也有特定的最佳工作溫度，並且也會防止自身過熱。
And it turns out, yawning increases your heart rate, blood flow and the use of muscles in your face, which are all essential to cool your brain.
事實上，打哈欠可以提升心率、血液流速、並動用臉上的肌肉。它對大腦降溫來說都是必不可少的。
On top of that, deeply inhaling cold air can alter the temperature of the blood in our head.
更重要的是，深呼吸冷空氣可以調整大腦內血液溫度。
But, why is your brain hot in the first place?
不過，大腦原先怎麼會過熱呢？
Well, both exhaustion and sleep deprivation are known to increase overall brain temperature which explains why yawning occurs more in these states.
身心疲憊和睡眠缺乏都會導致大腦溫度升高，這就解釋了爲什麼這些情況下人更愛打哈欠。
Researchers have even found participants who place warm packs on their heads yawn 41% of the time while watching others yawn, as opposed to 9% with a cold pack on their head.
研究者發現，頭上放了熱水袋的參與者在看其他人打哈欠時，有41%的時候也會打哈欠，而頭上放了冷水袋的只有9%。
So if your head is already cold, you will yawn less.
因此，大腦越“冷靜“ 哈欠就越少。
But what about contagious or social yawning?
不過，受他人傳染的哈欠是怎麼回事？
Humans, primates and even dogs finding yawning contagious and it's most likely linked to empathy.
人類、靈長類甚至犬類都會被傳染打哈欠，這很可能與“共情“有關。
Contagious yawning begins in children around the age of 4-5,and this is when empathetic behavior, along with the ability to identifying emotions, begin to develop.
兒童在4-5歲的時候開始被哈欠傳染，同一時期，同情性行爲，以及辨識情緒的能力開始逐漸發育。
In fact, children with empathy related disorders, such as autism, yawn less and response to videos of people yawning comparing to other children.
事實上，患有與共情相關疾病的兒童，如自閉症，在觀看打哈欠視頻的時候，比其他孩子打哈欠更少。
Research also suggest that you are more likely to copy the yawn of someone socially or genetically close to you.
研究表明，當身邊有親人或者朋友打哈欠時，你更容易被傳染。
Even dogs are more likely to copy the yawns of their owner as opposed to the yawn of a stranger.
甚至狗相對於陌生人，更容易受主人哈欠的傳染。
Finally, mirror neurons also play a role.
最後，鏡像神經元對此也有功勞。
In our brain, mirror neuron fire when we perform a specific action view someone else doing the action, or even just hear someone talk about the action.
在我們大腦內，鏡像神經元會在我們看到他人做出特定動作時產生衝動，甚至僅在聽別人說到動作時也會。
They are important brain cells that are used for learning, self-awareness and relating to others.
它們是重要的腦神經細胞，作用於學習自我意識，以及於他人相處。
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.
當我們看到其他人打哈欠時，大腦內的鏡像神經元進入類似的活躍狀態，使得我們被傳染 打了哈欠。
So although yawning may occur in people who are literally hot-headed, contagious yawning allows us to be cool with the people around us.
因此，頭腦發熱的人可能會打哈欠，傳染性的哈欠也是讓我們與周圍的人冷靜相處。
