It's something all humans do, regardless of race, culture, language, or creed: laugh. And, it turns out, some 10 million to 16 million years ago, the last common ancestor of humans and apes was laughing, too, most likely when tickled. That's the conclusion of an analysis of the recorded laughs of young orangutans, chimpanzees, and human children.
Charles Darwin and other researchers have long noted that apes and other mammalian species laugh or make similar sounds during social play. But no one had systematically compared laughter across a variety of primate species, particularly the great apes.
So zoologist Marina Davila Ross of the University of Portsmouth in the United Kingdom and colleagues recorded the laughs of young gorillas, chimpanzees, bonobos, orangutans, and one siamang at zoos and sanctuaries. Most ape toddlers, it turns out, love to be tickled: The animals erupted into laughter when their caretakers used twigs or their fingers to tickle feet, palms, necks, or armpits.
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The researchers then compared the acoustical properties of the recorded laughs with those of three human infants. They found that humans produce more sounds that are "voiced"--the characteristic "Ha! Ha!"--and that most human laughter is made when exhaling. "Human laughter is very distinctive," says Davila Ross. In contrast, laughing apes of all species sound more alike, with most making some type of short, noisy grunts (hear an orangutan laugh here ). But, to their surprise, gorillas and bonobos make longer, breathy laughs as well. And one bonobo made a "voiced" laugh, something akin to "Ha!," the team reports today in Current Biology. Davila Ross notes that other researchers have heard similar sounds from chimpanzees, too.
The findings challenge the notion that exhaled and voiced laughter are "a uniquely human trait," says Davila Ross. They also, she says, argue against the idea that human-type laughter requires a bipedal posture, as neuroscientist Robert Provine of the University of Maryland, Baltimore County, has argued.
Both Provine and Davila Ross say that, because humans and all living apes laugh, it's very likely that the distant 10-million- to 16-million-year-old progenitor of the ape lineage laughed, too. Based on the new analysis, "it probably had a laugh that was very noisy and unstructured" and was "similar to the laughter of living apes," says Davila Ross. Our laughter changed more dramatically, taking on its voiced and exhaled traits in the past 5 million years, after the human line diverged from chimpanzees and bonobos. But it's still simply an "exaggeration" of that ancestral laugh, she says. And, Davila Ross notes, there was one other thing we--humans and apes alike--probably retained from that long ago ancestor: our love of being tickled.