We all know that parrots can talk. Some people may have even seen elephants, seals, or whales mimicking speech sounds. So why can’t our closest primate relatives speak like us? Our new research suggests they have the right vocal anatomy but not the brainpower to use it.

我們都知道鸚鵡會(huì)說話。有些人甚至見過大象、海豹或鯨魚模仿人類聲音。那么為什么我們的靈長類近親不能像我們一樣說話呢?我們的新研究表明,他們擁有解剖學(xué)上的發(fā)聲器官,但是卻沒有使用這些發(fā)聲器官的腦力。

Scientists have been interested in understanding this phenomenon for centuries. Some have argued that nonhuman primates didn’t have the right-shaped body parts to make the same sounds as we do, and that human speech evolved after our speech organs changed. But comparative studies have shown that the form and function of the larynx and vocal tract is very similar across most primate species, including humans.

幾個(gè)世紀(jì)以來,科學(xué)家們一直對(duì)這一現(xiàn)象很感興趣。有些人認(rèn)為,非人類靈長類動(dòng)物沒有人類這樣合適的身體部位來發(fā)聲,而且人類的語言是在我們的語言器官改變后進(jìn)化的。但是比較研究表明,包括人類在內(nèi)的大多數(shù)靈長類動(dòng)物的喉和聲道的形式和功能非常相似。

This suggests that the primate vocal tract is “speech ready” but that most species don’t have the neural control to make the complex sounds that comprise human speech. When reviewing the evidence in 1871, Charles Darwin wrote, “the brain has no doubt been far more important.”

這意味著靈長類動(dòng)物的聲道已經(jīng)“準(zhǔn)備好說話了”,但大多數(shù)靈長類動(dòng)物沒有神經(jīng)控制來發(fā)出構(gòu)成人類語言的復(fù)雜聲音。查爾斯·達(dá)爾文在1871年回顧這些證據(jù)時(shí)寫道:“毫無疑問,大腦的作用要重要得多。”

Along with Jeroen Smaers from Stony Brook University in New York, I have been investigating the relationship between the number of different calls that each primate species can make and the architecture of their brains. For example, Golden pottos have only ever been recorded using two different sounds, while chimpanzees and bonobos use around 40.

我和紐約州立大學(xué)石溪分校的羅恩·斯邁爾共同研究了每種靈長類動(dòng)物能夠發(fā)出的不同叫聲的數(shù)量與它們大腦結(jié)構(gòu)之間的關(guān)系。舉個(gè)例子,我們只記錄到金熊猴使用了兩種不同的聲音,而黑猩猩和倭黑猩猩可以使用大約40種聲音。

Our recent study, published in Frontiers in Neuroscience, focused on two particular features of the brain. These were the cortical association areas that govern voluntary control over behavior, and the brainstem nuclei that are involved in the neural control of muscles responsible for vocal production. Cortical association areas are found within the neocortex and are key to the higher-order brain functions considered to be the foundation for the complex behavior of primates.

我們最近發(fā)表在《神經(jīng)科學(xué)前沿》雜志上的論文重點(diǎn)研究了大腦的兩個(gè)特殊特征。包括:控制行為自主控制的皮層聯(lián)絡(luò)區(qū),以及負(fù)責(zé)發(fā)聲的肌肉的神經(jīng)控制的腦干核團(tuán)。皮層聯(lián)絡(luò)區(qū)位于新大腦皮層,是大腦高階認(rèn)知的關(guān)鍵,是靈長類動(dòng)物復(fù)雜行為的基礎(chǔ)。

The results indicate a positive correlation between the relative size of the cortical association areas and the size of the vocal repertoire of primates. In simple terms, primates with bigger cortical association areas tended to make more sounds. But, interestingly, a primate’s vocal repertoire was not lixed to the overall size of its brain, just the relative size of these specific areas.

研究結(jié)果表明,靈長類動(dòng)物大腦皮層聯(lián)絡(luò)區(qū)的大小與聲波曲目的大小呈正相關(guān)。簡單地說,大腦皮層聯(lián)絡(luò)區(qū)越大的靈長類動(dòng)物往往能發(fā)出更多的聲音。但有趣的是,靈長類動(dòng)物的聲波曲目與大腦的整體大小無關(guān),而與這些特定區(qū)域的相對(duì)大小有關(guān)。

We also found that apes have particularly large cortical association areas, as well as a bigger hypoglossal nucleus than other primates. The hypoglossal nucleus is associated with the cranial nerve that controls the muscles of the tongue. This suggests that our closest primate relatives may have finer and more voluntary control over their tongues than other primate species.

我們還發(fā)現(xiàn)類人猿的大腦皮層聯(lián)絡(luò)區(qū)異乎尋常的大,舌下核也比其他靈長類動(dòng)物大。舌下核與控制舌頭肌肉的腦神經(jīng)相連。這表明,與其他靈長類物種相比,與我們親緣關(guān)系最近的靈長類物種可能更擅長自主地控制舌頭。

By understanding the nature of the relationship between vocal complexity and brain architecture, we hope to identify some of the key elements that underlie the evolution of complex vocal communication in our ancestors, ultimately leading to speech.

通過研究聲音的復(fù)雜性和大腦結(jié)構(gòu)之間關(guān)系的本質(zhì),我們希望確定一些關(guān)鍵因素,這些因素是我們祖先利用復(fù)雜的聲音交流并最終進(jìn)化為語言的基礎(chǔ)。