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　　As the human brain evolved, humans were able to laugh before they could speak, according to a new study．But here’s the punch line：Laughter and joy are not unique to humans, the study says．Ancestral forms of play and laughter existed in other animals long before humans began laughing．

　　“Human laughter has its roots in our animation past,” said Jaak Panksepp, a professor of psychobiology at Bowling Green State University in Ohio．Panksepp has studied rats and found that when they “play,” they often chirp(唧唧叫)－an early－stage form of laughter, according to the scientist．In an article to be published tomorrow in the journal Science, he makes the argument that animal laughter is the basis for human joy．

　　In studying laughter, scientists have focused mostly on related issues－h(huán)umor, personality, health benefits, social theory－rather than laughter itself．New research, however, shows that “circuits”(電路)for laughter exist in very ancient regions of the human brain．As humans have included language into play, we may have developed new connections to joyous parts of our brains that evolved before the cerebral cortex(大腦皮層), the outer layer associated with thought and memory．

　　There is plenty of evidence that many other mammals make play sounds, which are like human laughter．Indeed, animals are capable of many emotional feelings, just like humans, some scientists say．"The recognition by neuroscientists(神經(jīng)系統(tǒng)科學(xué)家)that the brain systems for pain, pleasure, and fear are the same in humans and other mammals underline our similarity to other species and is extremely important," said Tecumseh Fitch, a psychology lecturer at the University of St．Andrews in Scotland．In a 2003 study Panksepp and Bowling Green State University neurobiologist Jeff Burgdorf showed that if rats are tickled(呵癢)in a playful way, they readily chirp．Rats that were tickled developed a relationship with the researchers and became rapidly conditioned to seek tickles．Understanding the chirping of the rats may help scientists better understand human laughter．

　　Robert Provine, a psychology professor at the University of Maryland in Baltimore, agrees there is an evolutionary continuity of laughter．"Its origin is in tickling play," he says．Provine has studied chimpanzees and found a link between their laughter - like noises and human laughter．"Laughter is actually the sound of play, with the original’ pant – pant’(喘氣)- the heavy breathing of physical play - becoming the human ‘ha - ha,’” Provine said．By studying the shift from the panting of chimps to the human ha - ha, he discovered that breath control is the key to the appearance of both human laughter and speech．

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　　There's an old saying that laughter is the best medicine．No matter whether it's caused by a good joke, a cute child or pet, or a pie in the face of a comedian, the simple act of laughing offers medical benefits．Laughter has been shown to reduce stress and help people lose weight．It's a special tonic(滋補(bǔ)品)for older people, who are prone to loneliness and sad thoughts．

　　In fact, in more than 1,000 American communities, and a couple thousand more around the world, entire clubs have been formed so that people can get together and laugh! U．S．clubs have names like "Laugh-a-holics," "the Ha-Ha Spa," "Granite State Giggles(傻笑)," and "Judy's Joyful Laughter Club．"

　　The idea started in India, where laughing is an oral yoga(瑜珈)exercise using discipline, mind power and a good belly laugh．Laughter is certainly contagious(傳染性的)．Only a determined grouch(脾氣壞的人)could avoid at least smiling when others around him are laughing till it hurts．That's why members of laughing clubs don't just get together to howl with laughter themselves．They meet on street corners, in train stations, and other public places, laugh their fool heads off, and invite everyone around them to join in．

　　Laughing clubs have become so popular that one can even get training as a "certified laughing leader．" And the key qualification? You have to be really good at these, chortling, chuckling, howling, snickering, cackling, tittering, giggling and sniggling．