Life can be funny, and not just for humans.
Studies by various groups suggest monkeys, dogs and even rats love a good laugh. People, meanwhile, have been laughing since before they could talk.
"Indeed, neural circuits for laughter exist in very ancient regions of the brain, and ancestral forms of play and laughter existed in other animals eons before we humans came along with our 'ha-ha-has' and verbal repartee," says Jaak Panksepp, a neuroscientist at Bowling Green State University.
When chimps play and chase each other, they pant in a manner that is strikingly like human laughter, Panksepp writes in the April 1 issue of the journal Science. Dogs have a similar response.
Rats chirp while they play, again in a way that resembles our giggles. Panksepp found in a previous study that when rats are playfully tickled, they chirp and bond socially with their human tickler. And they seem to like it, seeking to be tickled more. Apparently joyful rats also preferred to hang out with other chirpers.
Laughter in humans starts young, another clue that it's a deep-seated brain function.
"Young children, whose semantic sense of humor is marginal, laugh and shriek abundantly in the midst of their other rough-and-tumble activities," Panksepp notes.
Importantly, various recent studies on the topic suggest that laughter in animals typically involves similar play chasing. Could be that verbal jokes tickle ancient, playful circuits in our brains.
More study is needed to figure out whether animals are really laughing. The results could explain why humans like to joke around. And Panksepp speculates it might even lead to the development of treatments for laughter's dark side: depression.
Meanwhile, there's the question of what's so darn funny in the animal world.
"Although no one has investigated the possibility of rat humor, if it exists, it is likely to be heavily laced with slapstick," Panksepp figures. "Even if adult rodents have no well-developed cognitive sense of humor, young rats have a marvelous sense of fun."
Science has traditionally deemed animals incapable of joy and woe.
Panksepp's response: "Although some still regard laughter as a uniquely human trait, honed in the Pleistocene, the joke's on them."
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