{"id":18879,"date":"2019-12-11T00:23:16","date_gmt":"2019-12-11T00:23:16","guid":{"rendered":"https:\/\/www.lifeandnews.com\/articles\/?p=18879"},"modified":"2019-12-14T05:21:20","modified_gmt":"2019-12-14T05:21:20","slug":"examining-how-primates-make-vowel-sounds-pushes-timeline-for-speech-evolution-back-by-27-million-years","status":"publish","type":"post","link":"https:\/\/www.lifeandnews.com\/articles\/examining-how-primates-make-vowel-sounds-pushes-timeline-for-speech-evolution-back-by-27-million-years\/","title":{"rendered":"Examining how primates make vowel sounds pushes timeline for speech evolution back by 27 million years"},"content":{"rendered":"

Thomas R. Sawallis<\/a>, University of Alabama<\/a><\/em> and Louis-Jean Bo\u00eb<\/a>, Universit\u00e9 Grenoble Alpes<\/a><\/em><\/p>\n

Sound doesn\u2019t fossilize. Language doesn\u2019t either.<\/p>\n

Even when writing systems have developed<\/a>, they\u2019ve represented full-fledged and functional languages. Rather than preserving the first baby steps toward language, they\u2019re fully formed, made up of words, sentences and grammar carried from one person to another by speech sounds, like any of the perhaps 6,000 languages spoken today<\/a>.<\/p>\n

So if you believe, as we linguists do, that language is the foundational distinction between humans and other intelligent animals, how can we study its emergence in our ancestors?<\/p>\n

Happily, researchers do know a lot about language \u2013 words, sentences and grammar \u2013 and speech \u2013 the vocal sounds that carry language to the next person\u2019s ear \u2013 in living people. So we should be able to compare language with less complex animal communication.<\/p>\n

And that\u2019s what we and our colleagues have spent decades investigating<\/a>: How do apes and monkeys use their mouth and throat to produce the vowel sounds in speech? Spoken language in humans is an intricately woven string of syllables with consonants appended to the syllables\u2019 core vowels, so mastering vowels was a key to speech emergence. We believe that our multidisciplinary findings push back the date for that crucial step in language evolution by as much as 27 million years.<\/p>\n

The sounds of speech<\/h2>\n

Say \u201cbut.\u201d Now say \u201cbet,\u201d \u201cbat,\u201d \u201cbought,\u201d \u201cboot.\u201d<\/p>\n

The words all begin and end the same. It\u2019s the differences among the vowel sounds that keep them distinct in speech.<\/p>\n

Now drop the consonants and say the vowels. You can hear the different vowels have characteristic sound qualities. You can also feel that they require different characteristic positions of your jaw, tongue and lips.<\/p>\n

So the configuration of the vocal tract \u2013 the resonating tube of the throat and mouth, from the vocal folds to the lips \u2013 determines the sound. That in turn means that the sound carries information about the vocal tract configuration that made it. This relationship is the core understanding of speech science.<\/p>\n

After over a half-century of investigation and of developing both anatomical and acoustical modeling technology, speech scientists can generally model a vocal tract and calculate what sound it will make, or run the other way, analyzing a sound to calculate what vocal tract shape made it.<\/p>\n

So model a few primate vocal tracts, record a few calls, and you pretty much know how human language evolved? Sorry, not so fast.<\/p>\n

Modern human anatomy is unique<\/h2>\n

If you compare the human vocal tract with other primates\u2019, there\u2019s a big difference. Take a baboon as an example.<\/p>\n

\"\"<\/a>
The vocal tract of a baboon has the same components \u2013 including the larynx, circled in green \u2013 as that of a person, but with different proportions.<\/span>
\nLaboratory of Cognitive Psychology (CNRS & Aix-Marseille University) and GIPSA-lab (CNRS & University Grenoble-Alpes)<\/span>, CC BY-ND<\/a><\/span><\/figcaption><\/figure>\n

From the baboon\u2019s larynx and vocal folds, which is high up and close to their chin line, there\u2019s just a short step up through the cavity called the pharynx, then a long way out the horizontal oral cavity. In comparison, for adult male humans, it\u2019s about as far up the pharynx as it is then out through the lips. Also, the baboon tongue is long and flat, while a human\u2019s is short in the mouth, then curves down into the throat.<\/p>\n

So over the course of evolution, the larynx in the human line has moved lower in our throats, opening up a much larger pharyngeal cavity than found in other primates.<\/p>\n

About 50 years ago, researchers seized on that observation to formulate what they called the laryngeal descent theory of vowel production. In a key study<\/a>, researchers developed a model from a plaster cast of a macaque vocal tract. They manipulated the mouth of an anesthetized macaque to see how much the vocal tract shape could vary, and fed those values into their model. Then finally they calculated the vowel sound produced by particular configurations. It was a powerful and groundbreaking study, still copied today with technological updates.<\/p>\n

So what did they find?<\/p>\n

They got a schwa \u2013 that vowel sound you hear in the word \u201cbut\u201d \u2013 and some very close acoustic neighbors. Nothing where multiple vowels were distinct enough to keep words apart in a human language. They attributed it to the lack of a human-like low larynx and large pharynx.<\/p>\n

As the theory developed, it claimed that producing the full human vowel inventory required a vocal tract with about equally long oral and pharyngeal cavities. That occurred only with the arrival of anatomically modern humans, about 200,000 years ago, and only adults among modern humans, since babies are born with a high larynx that lowers with age.<\/p>\n

This theory seemed to explain two phenomena. First, from the 1930s on, several (failed) experiments had raised chimpanzees in human homes<\/a> to try to encourage human-like behavior, particularly language and speech. If laryngeal descent is necessary for human vowels, and vowels in turn for language, then chimpanzees would never talk.<\/p>\n

Second, archaeological evidence of \u201cmodern\u201d human behavior<\/a>, such as jewelry, burial goods, cave painting, agriculture and settlements, seemed to start only after anatomically modern humans appeared, with their descended larynxes. The idea was that language provided increased cooperation which enabled these behaviors.<\/p>\n

Rethinking the theory with new evidence<\/h2>\n

So if laryngeal descent theory says kids and apes and our earlier human ancestors couldn\u2019t produce contrasting vowels, just schwa, then what explains, for instance, Jane Goodall\u2019s observations of clearly contrasting vowel qualities in the vocalizations of chimpanzees<\/a>?<\/p>\n