"Laugh and the world will laugh with you."2） That legendary line by Ella Wheeler Wilcox still holds true. Just like yawning， laughing is also highly contagious， but laughing is one contagious disease that we love and we gladly spread it to others. In fact， even the sound of someone laughing can make you let out a gut-busting3） chuckle4）.

How many times has it happened that you laughed your heart out5） at a movie theatre， but when you watched the movie alone again on TV， you didn&apos；t find it that funny， or at least didn&apos；t laugh nearly as loud？ It&apos；s because you were watching the movie by yourself， but that isn&apos；t the same thing that happens when we experience humor in larger groups. So what makes laughing so contagious？ Why do we end up laughing with other people even if we don&apos；t find the joke all that funny？

Why Do We Laugh？

People may laugh for various reasons， such as if they like a joke， if they see their friend take an awkward tumble6）， or if they experience anything else that might tickle their funny bone7）.

Studies have shown that laughing has been passed on to humans from our ancient primate8） ancestor. For our ancestors， laughter was a process of strengthening the bond between them. People laugh when they feel free and are comfortable with one another， so laughter definitely increases bonding between people， just as it did for our ancestors.

Why Is It Contagious？

The way a person reacts to a sound is dependent on the brain&apos；s premotor cortical9） region. This region is responsible for how the muscles in the face react to the corresponding sounds. University College of London conducted a study on certain volunteers where they played different sounds to them and measured their brain&apos；s reaction to the sound.

It was seen that responses were higher for positive sounds， such as laughing or the sound of triumph， and were much lower for negative sounds like screaming or retching10）. This suggests that humans are more susceptible11） to the sound of laughter as compared to negative sounds. This explains the reason for our involuntary12） smile when we see other people laughing.

There is a famous case of the contagious nature of laughing known as the Tanganyika laughter epidemic13）. In 1962， three girls studying in a boarding school14） in a village in Tanganyika （now Tanzania） began to laugh， and soon it spread to the whole school. Eventually， it affected about 95 of the 159 pupils.

This natural response that we have to laughter is the reason why pre-recorded laughter is frequently put on sitcoms15）， as this increases the chance of inducing laughter from the audience. Laughter therapy also works on the same principle： when you see many people laughing， you involuntarily end up laughing too！

It is often said that laughter is the best medicine， as it has many benefits for human health. In that case， I just have one thing to say： laugh and make the whole world laugh with you.

為什么笑會傳染？為什么聽到別人笑，你也會不由自主地揚起嘴角？為什么明明很生氣，可對方含著笑向你賠禮道歉的時候，你就再也生不起氣來？笑真是個奇妙的東西，好好的就能連成一片。至于其背后的一部分原因，科學家們已經有所發(fā)現，你想知道嗎？

“你歡笑，這世界陪你一起歡笑。”埃拉·惠勒·威爾科克斯這一膾炙人口的詩句仍然在理。就像打呵欠一樣，笑也有很強的傳染性，但笑這種“傳染病”人見人愛，還樂意傳染給別人。事實上，甚至是別人的笑聲也能讓你開懷一笑。

有多少次，你曾遇到下面的情況？你在電影院會捧腹大笑，可當你獨自在電視上再看這部電影時，你卻不覺得那么好笑了，或者至少笑得沒那么歡了。這是因為此時你是獨自一人看這部電影，而當我們在人數較多的人群之中體驗幽默時，情況就不一樣了。那么，是什么讓笑這么容易傳染？為什么我們即便不覺得某個笑話那么好笑，可最終還是會和其他人一起笑呢？

為什么我們要笑？

人們發(fā)笑可能有很多不同的原因，比如說可能是喜歡一個笑話，可能是看到朋友跌倒出糗，或者遇到了其他什么可能會戳中笑點的事情。

研究表明，笑是人類從我們那古老的靈長類動物祖先那里遺傳來的。對我們的祖先來說，笑是強化彼此情感關系的一種方法。當人們彼此相處感到無拘無束、輕松愉快時，他們就會笑。所以，笑無疑會增進人們之間的感情，就像其對我們祖先的作用那樣。

為什么笑會傳染？

人對聲音的反應取決于大腦的前運動皮層區(qū)。這個區(qū)域負責決定臉部的肌肉如何對相應的聲音做出反應。倫敦大學學院做過一項研究，研究人員給一些志愿者播放了不同的聲音，并測量了他們的大腦對這些聲音的反應。

研究發(fā)現，志愿者對積極的聲音（比如笑聲或是獲勝的歡呼聲）反應較強，而對消極的聲音（像尖叫聲或嘔吐聲）反應較弱。這表明，與聽到各種消極聲音相比，人類更容易受到笑聲的影響。這就解釋了為什么當我們看到別人笑時，我們也會不由自主地笑起來。

有個著名的事例可以說明笑的傳染本質，這個事例被稱作坦噶尼喀大笑病。1962年，在坦噶尼喀（現稱坦桑尼亞）某村一所寄宿學校就讀的三個女孩笑了起來，她們的笑很快傳染到了整個學校。最終，159名小學生中約有95名學生都受到影響笑了起來。

因為我們會對笑產生這種自然反應，所以情景喜劇里常常加入預先錄制的笑聲，以便更多地引發(fā)觀眾的笑聲。笑聲療法也是同樣的道理：當你看到很多人笑的時候，你最終也會不由自主地笑起來！

常言道，笑是最好的良藥，因為笑能給人們的健康帶來諸多益處。既然如此，我只有一句話想說：笑吧，讓全世界陪你一起歡笑。

1. contagious [k?n?te?d??s] adj.（感情、態(tài)度等）感染性的

2. 這句話出自美國作家、詩人埃拉·惠勒·威爾科克斯（Ella Wheeler Wilcox， 1850～1919）的詩歌《孤獨》（Solitude），詩歌的前兩句為：Laugh， and the world laughs with you； /Weep， and you weep alone.

3. gut-busting： 讓人捧腹大笑的

4. chuckle [?t??kl] n. 輕輕的笑

5. laugh one&apos；s heart out： 捧腹大笑；縱聲大笑

6. tumble [?t?mbl] n. 跌倒；摔跤

7. funny bone： 幽默感

8. primate [?pra?me?t] adj. 靈長類（動物）的

9. premotor cortical： 大腦前運動皮層的

10. retch [ret?] vi .作嘔；惡心

11. susceptible [s??sept?bl] adj. 易受……影響的

12. involuntary [?n?v?l?ntri] adj. 不由自主的

13. Tanganyika laughter epidemic： 坦噶尼喀大笑病。1962年1月30日，新興國家坦噶尼喀（現在是坦桑尼亞的大陸部分）有三個女孩子因為一個笑話大笑出聲，傳染了整個學校，影響了全校一半以上的學生，并在當地傳染開來。這些學生突然爆發(fā)出笑聲，笑到流淚、昏倒、出疹子。有專家認為這與壓力有關，但具體原因不詳。

14. boarding school： 寄宿學校

15. sitcom [?s?tk?m] n. 情景喜劇