As the human brain evolved, humans were able to laugh before they could speak, according to a new study.

But here's the punch line: Laughter and joy are not unique to humans, the study says. Ancestral forms of play and laughter existed in other animals long before humans began cracking up.

"Human laughter has robust roots in our animalian past," said Jaak Panksepp, a professor of psychobiology at Bowling Green State University in Ohio. Panksepp has studied rats and found that when they "play," they often chirp—a primitive form of laughter, according to the scientist. In an article to be published tomorrow in the journal Science, he makes the argument that animal laughter is the basis for human joy.

In studying laughter, scientists have focused mostly on related issues—humor, personality, health benefits, social theory—rather than laughter itself.

New research, however, shows that "circuits" for laughter exist in very ancient regions of the human brain.

As humans have incorporated language into play, we may have developed new connections to joyous parts of our brains that evolved before the cerebral cortex, the outer layer associated with thought and memory.

Researchers say that the capacity to laugh emerges early in child development, as anyone who has tickled a baby knows.

There is ample evidence that many other mammals make play sounds, including tickle-induced panting, which resembles human laughter. Indeed, animals are capable of many emotional feelings, just like humans, some scientists say.

"The recognition by neuroscientists that the brain mechanisms underlying pain, pleasure, fear, and lust are the same in humans and other mammals underscores our similarity to other species and is extremely important," said Tecumseh Fitch, a psychology lecturer at the University of St. Andrews in Scotland.

In a 2003 study Panksepp and Bowling Green State University neurobiologist Jeff Burgdorf demonstrated that if rats are tickled in a playful way, they readily chirp. Rats that were tickled bonded with the researchers and became rapidly conditioned to seek tickles.

Understanding the chirping of the rats may help scientists better understand human laughter.

Robert Provine, a psychology professor at the University of Maryland in Baltimore, agrees there is an evolutionary continuity of laughter. Its origin is in tickling and rough-and-tumble play, he says.

Provine, the author of Laughter: A Scientific Investigation, and other scientists have studied chimpanzees and found a link between their laughter-like noises and human laughter.

"Laughter is literally the sound of play, with the primal 'pant-pant'—the labored breathing of physical play—becoming the human 'ha-ha,'" Provine said.

By studying the transition between the panting of chimps and the human ha-ha, scientists discovered that breath control is the key to the emergence of both human laughter and speech. 

一项最新的研究结果显示，由于大脑的进化，人类在能够说话之前就已经学会笑了。研究结果同时表明，笑和喜悦并不只是人类所特有的，早在人类会笑之前，其它一些动物就已经拥有原始形态的笑声了。

据美国《国家地理》杂志3月31日报道，美国俄亥俄州保令·格林州立大学( Bowling Green State University)的神经生物学家杰克·潘克塞普表示：“人类笑的历史深深植根于我们的动物史。”

潘克塞普曾对老鼠进行了相关研究，他发现，当老鼠“玩耍”的时候，他们经常发出一种唧唧喳喳很尖的声音，而这则是笑的一种原始形态。他的一篇相关文章将发表在4月1日的《科学》杂志上。潘克塞普在文章中提出的论点是，认为动物的笑是人类快乐的基础。

在以前的研究中，科学家们曾把工作的重心大部分集中在和笑相关问题上，如幽默感、个性、以及健康的好处等，而非笑本身。

而最新的研究结果则显示，笑的“循环线路”存在于人类大脑非常古老的区域中。当人类把语言与玩耍结合在了一起时，我们或许已经和大脑的快乐部分建立了新的关系，这个部分的进化要早于和人们思考及记忆密切相关的大脑皮层的进化。对此，研究人员表示，笑的能力在孩子发育阶段早早地就显现出来，这一点是任何一个曾经胳肢过小婴儿的人都知道的。

有很多证据可以表明，其他一些哺乳动物也可以发出类似笑的声音，其中包括很类似于人类笑声的由挠痒痒引起的喘息声。一些科学家说，事实上，动物和人类一样是具有多种情感和情绪的。

苏格兰圣·安德鲁斯大学的心理学讲师菲奇表示：“神经科学家公认的，人类和其它哺乳动物间支撑痛苦、压力、恐惧及性的大脑机制都是相同的这一理论强调了人类与其它物种的相似之处，而这一点是非常重要的。”

早在2003年的一项研究中，潘克塞普和保令·格林州立大学的神经生物学家杰夫·伯格多弗就曾证明，如果人们以一种十分有趣的方式胳肢老鼠，它们就会发出一种唧喳的声音。而弄清老鼠的这种叫声，则可能会帮助科学家们更好地了解人类笑的历史。

美国马里兰大学的心理学教授罗伯特·布鲁文赞同笑也具有进化连续性的这一说法。他说，笑的起源来自于挠痒痒以及杂乱无章的游戏。布鲁文教授和其他一些科学家还对黑猩猩进行了相关的研究，他们发现黑猩猩的笑（声音类似于噪音）与人类的笑存在着某种联系。他说：“确切地讲，笑是一种游戏的声音，从最初的喘气的呼呼声（吃力的呼吸声）发展到人类的“哈哈”笑的声音。”

通过研究从大猩猩喘气的呼呼声到人类“哈哈”的笑声两者之间的转化，科学家发现，呼吸控制是人类语音和笑声出现的关键所在。很多科学家相信，在大脑中玩耍和笑声的来源是本能的。如果这样的话，其它动物很多本能的行为则可以帮助研究人员更好地理解意识及其它的人类条件。科学家们也同时希望能够发现控制人们喜悦情绪的基因。