Ha Ha! The Intriguing Origins of Laughter

May 7, 2006 — -- On Sunday the whole world was laughing -- literally.

The first Sunday in May marks International Laughter Day, a holiday established in 1998. Now, eight years later, cities all around the world have planned their own special celebrations to mark the day of smiles.

No one doubts that laughing makes us feel good, but why do we laugh? After all, it's not exactly a trait we share with other animal species.

"It's a signal that it's safe to relax," said psychologist Steve Wilson, who is co-founder of the World Laughter Tour.

Laughter activates reward centers in the brain, Wilson said, causing a pleasant release of tension within the body. The ability to laugh is innate, and we're hardwired to laugh about a month or so after birth.

Anthropologists believe that laughter dates back millions of years -- we were laughing long before we were verbally communicating. Whether you speak Chinese, English or Swahili, a laugh or smile has virtually the same meaning all over the world, researchers said.

"At it's base, humor is connection between people that goes far beyond language," said Dr. Clifford Kuhn, a psychiatrist at the University of Louisiana Medical Center.

Yes. And most people have experienced what Americans call a case of the giggles.

"We laugh 30 times as much when we're with other people than we do when we are alone," said Robert R. Provine, a professor of psychology and neuroscience at the University of Maryland Baltimore County. "Laughing is not a solo activity."

Unbelievably, an epidemic of contagious laughter struck the African country of Tanzania in the 1960s. A school temporarily closed down after three schoolgirls set off about two-thirds of the other students into uncontrollable hysterical laughter.

While there were no real consequences, it just goes to show the contagious element of laughing.

Many studies have found that laughter does a number of positive physical things such as reduce stress, lower blood pressure, boost the immune system and protect the heart.