for National Geographic News
What happens if you tickle a gorilla? According to a new study, the ape laughs—which would mean we're not the only animals born with funny bones.
Their findings suggest we inherited our own ability to laugh from the last common ancestor from which humans and great apes evolved, which lived 10 to 16 million years ago.
Primatologist and psychologist Marina Davila Ross of the U.K.'s University of Portsmouth led a team that tickled the necks, feet, palms, and armpits of infant and juvenile apes as well as human babies. The team recorded more than 800 of the resulting giggles and guffaws.
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Hear Orangutan Laughter
Mapping the audible similarities and differences in laughs across the five species, the researchers created an acoustic family tree of human and great ape laughter.
The tree, they found, closely matched the standard genetics-based evolutionary tree of primates.
"So we concluded that these vocalizations all share the same common ancestry," Davila Ross explained.
But even the most casual listener can tell a human laugh from an ape laugh. Davila Ross points out that human laughter has distinct differences from ape laughter, most likely because humans have evolved much more rapidly than apes during the past five million years.
And at least one great mystery remains: What purpose does ape laughter serve?
"I'm very keen," Davila Ross said, "on learning how laughter is being used among great apes as compared to humans."
Is It Really Laughter?
It's previously been argued that chimps chuckle, but their method—"laughing" on both the exhale and inhale—had been deemed too different from the human, exhale-only laugh.
The tickle study, however, found evidence that most ape laughter, especially among gorillas and bonobos, shares key traits with human laughter.
Like humans, for example, gorillas and bonobos laughed only while exhaling—leading University of Wisconsin zoologist and psychologist Charles Snowdon, who was not involved in the study, to conclude that, "contrary to current views, the exhalation-only laughter is not uniquely human but is found in our ape ancestors."
Furthermore, gorillas' and bonobos' exhaling breaths during laughter lasted three to four times longer than during normal breathing.
This type of breath control, considered important in speech evolution, had also been thought to be unique to humans.
"Play Faces" to Chimp Chuckles?
Convinced by what he calls an "admirable" study, primatologist Frans de Waal said from now on he'd use "laughter" to describe what scientists have traditionally called a chimp's play face.
The combination of common facial expressions, breathing patterns, and sounds has led de Waal to the conclusion that our laughter has prehistoric, ape-based origins.
What's more, "the primate laugh is given in playful contexts, and as such has a strong similarity to the human laugh," added de Waal, who was not involved in the tickle study.
"Tickling and wrestling are the situations in which primates laugh—and I use the term 'laugh' now advisedly, because the evidence from this study is very strong that their display is evolutionarily related to the human laugh."
Next Up: Rat Laughter?
Primates have apparently packed a lot of laughter into the last 10 to 16 million years, but there's a chance the chuckle originated even earlier: Tickle-induced "laughter" has also been reported in rats.
The idea remains controversial, but it could suggest that our funny bone evolved much closer to the trunk of mammals' evolutionary tree.
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