阿姆斯特丹自由大学的心理学家罗扎·卡米洛格鲁领导的一项新研究表明，笑声其实只有两种基本类型：一种是人们觉得某事有趣时发出的笑声，另一种则只能通过挠痒痒这种身体行为引发。
The work started with the serious business of laugh collection. Dr Kamiloglu instructed research assistants to search YouTube, a video platform, for footage featuring spontaneous laughter. They collected a total of 887 videos that were then categorised based on the inciting comic incident, ranging from tickle attacks to Schadenfreude and verbal jokes.
这项研究始于严肃的“笑声收集”工作。卡米洛格鲁博士指示研究助理在视频平台YouTube上搜索包含自发笑声的视频片段。他们共收集了887个视频，然后根据引发笑声的事件对这些视频进行分类，事件类型从挠痒痒到幸灾乐祸再到言语玩笑，应有尽有。
Roughly 70% of these videos were then used to train a laughter-categorising machine-learning algorithm to connect different forms of laughter with the activities that caused them. The algorithm was then asked to deliver its verdict on the remaining 30%. After a quick listen, Dr Kamiloglu and her colleagues thought the different laughs would be too varied for any connections to be made. The algorithm disagreed.
这些视频中的大约70%被用于训练一个笑声分类机器学习算法，以将不同的笑声与引发它们的活动联系起来。然后，算法被要求对剩余的30%视频做出判断。在快速听过之后，卡米洛格鲁博士和她的同事们认为，不同的笑声变化太大，难以找到任何联系。但算法持不同意见。
Based on acoustic traits like loudness, rhythm and changes in frequency brought about by vocal-cord vibrations, the algorithm was able to correctly identify laughter produced by tickling 62.5% of the time. All other forms of laughter, whether they came from viewing stand-up comedy or watching someone pour salt into their tea instead of sugar, were nowhere near as easy to tell apart.
This suggested there was something unique about the post-tickling laugh. When Dr Kamiloglu ran the experiment again, this time asking human observers to categorise the laughs, a similar phenomenon presented itself: the observers correctly identified tickling laughter 61.2% of the time.
The findings, published this week in Biology Letters, are more than light entertainment. They could, instead, point scientists towards the evolutionary roots of laughter. After all, many mammals including dogs, squirrel monkeys, Barbary macaques and chimpanzees produce vocalisations during play that sound remarkably like laughter.
本周发表在《生物学快报》上的这些发现，远不止供人娱乐那么简单。它们可能为科学家指明笑声的进化根源。毕竟，许多哺乳动物，包括狗、松鼠猴、巴巴里猕猴和黑猩猩，在玩耍时发出的叫声听起来非常像笑声。
One of the first things that infants do early in life is laugh. Even babies born deaf spontaneously produce laughter. Humans are not the only animals that tickle either. Macaques and chimpanzees both engage in the activity too.
婴儿在生命早期做的第一件事就是笑。甚至天生耳聋的婴儿也会自发地发出笑声。而且，不止人类会挠痒痒。猕猴和黑猩猩也会进行这种行为。
All this suggests that laughter from tickling evolved over 10m years ago with the common ancestor that humans shared with these other primates. Dr Kamiloglu suspects that this early sort of laughter probably evolved to help primates build friendly relations, especially during play.
所有这些都表明，挠痒痒引发的笑声是在大约1000万年前，与人类和其他灵长类动物的共同祖先一起进化而来的。卡米洛格鲁博士怀疑，这种早期的笑声可能进化成有助于灵长类动物建立友好关系，尤其是在玩耍期间。
With this in mind, she is now keen to study how infectious different sorts of laughs are. If the tickling laugh is one that truly evolved to bring primates together, it ought to be particularly infectious—but nobody has yet tested if it is.
鉴于此，她现在很想研究不同种类的笑声感染力如何。如果挠痒痒引发的笑声确实是进化成让灵长类动物团结在一起的，那么它应该特别具有感染力——但还没有人测试过这一点。
As for all the other forms of laughter that only people produce, these probably evolved millions of years after tickling came along, when the human brain became complex enough to understand irony, slapstick and puns. But he who laughs last, it would seem, laughs longest.
至于人类独有的其他所有形式的笑声，它们可能是在挠痒痒行为出现数百万年后才进化出来的，当时人类的大脑已经足够复杂，能够理解讽刺、闹剧和双关语。但似乎笑到最后的人，笑得最久。
（红色标注词为重难点词汇）
重难点词汇：
chortle [ˈtʃɔːrtl] v. （因得意、满足等而）哈哈大笑
chuckle [ˈtʃʌkl] v. 轻声地笑；咯咯地笑
titter [ˈtɪtər] v. （因紧张、尴尬等而）窃笑；傻笑
hoot [huːt] v. 发出呼啸（或嘟囔、喊叫）声；n. 呼啸（或嘟囔、喊叫）声
giggle [ˈɡɪɡl] v. 咯咯地笑；傻笑
snigger [ˈsnɪɡər] v. 窃笑；傻笑（常含贬义）
howl [haʊl] v. 吼叫；嚎叫；n. 吼叫声；嚎叫声
guffaw [ˈɡʌfɔː] v. & n. 哄笑；大笑
spontaneous [spənˈteɪniəs] adj. 自发的；无意识的；自然的
Schadenfreude [ˈʃɑːdnˌfroɪdə] n. 幸灾乐祸
acoustic [əˈkuːstɪk] adj. 声学的；有关声音的；n. 声学；音响效果
来源：每日双语经济学人
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