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When scientists set out to trace the roots of human laughter, some chimps and gorillas were just tickled to help.
That's how researchers made a variety of apes and some human babies laugh. After analyzing the sounds, they concluded that people and great apes inherited laughter from a shared ancestor that lived more than 10 million years ago.
Experts praised the work. It gives strong evidence that ape and human laughter are related through evolution, said Frans de Waal of the Yerkes National Primate Research Center at Emory University in Atlanta.
As far back as Charles Darwin, scientists have noted that apes make characteristic sounds during play or while being tickled, apparently to signal that they're interested in playing.
It's been suggested before that human laughter grew out of primate roots. But ape laughter doesn't sound like the human version. It may be rapid panting, or slower noisy breathing or a short series of grunts.
So what does that have to do with the human ha-ha? To investigate that, Marina Davila Ross of the University of Portsmouth in England and colleagues carried out a detailed analysis of the sounds evoked by tickling three human babies and 21 orangutans, gorillas, chimps and bonobos.
After measuring 11 traits in the sound from each species, they mapped out how these sounds appeared to be related to each other. The result looked like a family tree. Significantly, that tree matched the way the species themselves are related, the scientists reported online yesterday in the journal Current Biology.
They also concluded that while human laughter sounds much different from the ape versions, its distinctive features could well have arisen from shared ancestral traits.
Jaak Panksepp of Washington State University, who studies laughter-like responses in animals but didn't participate in the new work, called the paper exciting.
Panksepp's own work concludes that even rats produce a version of laughter in response to play and tickling, with chirps too high-pitched for people to hear.
Robert Provine, a neuroscientist at the University of Maryland, Baltimore County, who wrote the book, Laughter: A Scientific Investigation, said the new paper reveals some important insights, like ape sounds that hadn't been appreciated before.
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(Agencies)
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當科學家準備探究人類笑聲的起源時，被搔癢的大猩猩恰好幫了大忙。
科學家通過 “撓癢癢”這種方式來使不同種類的大猩猩和一些人類嬰兒發出笑聲。在分析了這些笑聲之后，研究人員得出結論，人和大猩猩的笑聲源自共同的祖先——他們生活在距今一千萬年前。
專家稱贊了這項研究成果。亞特蘭大市埃默里大學耶基斯國家靈長動物研究中心的弗蘭斯?德瓦爾稱，這強有力地證明了在進化史上，猿和人的笑聲密切相關。
早在查爾斯?達爾文時期，科學家就已經注意到，在玩耍或者被瘙癢后，猿類會發出特別的笑聲，這似乎表明它們很喜歡玩耍。
以前曾有觀點認為人類的笑聲是從靈長類祖先進化而來的。但猿的笑聲與人類的聽起來不同，它有可能是急促的喘息聲、較為緩慢且帶有噪音的呼吸聲或是短暫的呼嚕聲。
但這和人類的“哈哈”大笑有什么關系呢？為了研究這一點，英國樸茨茅斯大學的瑪麗娜?達維拉?羅斯和同事仔細分析了三個人類嬰兒和21個猩猩、大猩猩、黑猩猩、倭黑猩猩被搔癢后發出的聲音。
在分析了每類笑聲的11種特點后，研究人員繪制了笑聲如何相互關聯的圖譜，圖譜看起來像一個族譜。科學家在昨天發布于《當代生物學》網絡版上的報告中稱，這個族譜與各研究對象的內在關聯不謀而合。
他們還總結稱，盡管人類的笑聲與猿類大不相同，但其特質卻來源于共同的祖先。
華盛頓州立大學的雅克?潘克塞普專門研究動物的笑聲反應，但沒有直接參與這項新的研究。他稱研究報告令人興奮不已。
潘克塞普所做的研究成果也表明，即使老鼠在玩耍和被搔癢時也會笑，只是聲調過高人聽不到。
《笑的科學》一書的作者、馬里蘭大學巴爾的摩分校的神經學家羅伯特?普羅文稱，新的研究報告揭示了一些重要線索，比如猿類的笑聲，以前人們并沒有意識到這些。
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