Scientific researchers don’t always get the most plum assignments—sifting through bird feces, for instance, wouldn’t be at the top of our list—but we think it would have been a blast to take part in one recent experiment: tickling baby apes.
Although making baby monkeys laugh seems like fun, the research actually had a scientific purpose. The researchers behind the study published yesterday in scientific journal Current Biology were measuring the laughter responses in six different types of apes to study the evolutionary history of the human laugh.
The scientists found striking similarities when comparing the young apes’ laughter to that of young human babies, proving that laughter has been evolving at least since the days when man and monkey’s last common ancestor walked the Earth.
“What we can say is that laughter goes back at least 10 to 16 million years,” Marina Davila Ross, a primatologist from University of Portsmouth told MSNBC. 
Though laughter may seem light-hearted, its social role is quite important, biologist Jared Tagliatela of Clayton State University told Wired.  “Laughter serves as an emotional contagion,” he said. “It serves as a way of getting everyone on the same page. Secondly, it serves as a way for individuals to inform their social partners about their intentions, as well as provide information and feedback about their own emotional state.”
In the wild, a chimp could use laughter to tell another primate that when he stole a piece of fruit, he wasn’t trying to start a fight—he was just starting a game. Likewise, when someone from your office makes a joke about your taste in music, a chuckle can help you recognize that your co-worker’s just teasing you—and is probably a closet ABBA fan himself.
The researchers found that laughter may not even be unique to humans and our primate relatives: According to tests performed throughout the years, rats, dogs, and possibly even cats can make vocalizations that may be equated to human laughter, though none bear such a striking resemblance to our noises as the apes’ laughs do.
Unfortunately, we don’t know how many zoos would let you walk in and tickle a few gorillas to recreate the researchers’ experiment—but if you’d like to check out a couple of apes’ laughs for yourself, take a look at these great video clips from the project.