Something deep in the history of the German language pulled speech sounds toward hisses rather than pops. Words like that and ship end with a small popping sound in English, Dutch, and other Germanic languages—but in German, they end in softer s and f sounds—dass, Schiff. Centuries ago, before German was even German, this change was already underway, an example of one of the many small shifts that ends up separating a language from its close cousins and sending it off as its own distinct tongue.

How does change like this happen? One of the major reasons is speech efficiency. Speakers are constantly walking a tightrope between being understood and making speech as easy as possible—over time, this tension pulls languages in new directions. But if efficiency pushed German speakers in this direction, why not Dutch speakers, too? That is, if two languages share a given feature, why does that feature sometimes change in one language but not the other?

A paper published in Science today lays out an intriguing answer: technology might accidentally trigger a change. Changes like agriculture and food-preparation technology changed the arrangement of our teeth—and in turn, the authors suggest, this made certain speech sounds more likely. It's a daring suggestion, flying in the face of well-established linguistic thought. But the authors draw on multiple strands of evidence to support their proposal, which is part of a growing raft of ideas about how culture and environment could play a role in shaping language.

More labiodental fun for farmers

Humans have no clear policy for speech sounds. Click consonants are found in only a handful of languages in southern Africa, while the vowel a (as in mama) is universal. The rolled Rs of Spanish are somewhere in between. Why is this? The easy and obvious answer is that some sounds are easier to make in a human mouth, and the easy ones will be more common across the world's languages, while the hard ones (like clicks) will emerge and catch on only rarely.

Linguists have typically assumed that what makes sounds easy or difficult will be the same for all people. But evolutionary linguist Damián Blasí is interested in another kind of explanation: how people's environments could shape their speech, making certain features more likely to arise in some places and less likely in others. For instance, Blasí's previous work with colleagues Caleb Everett and Seán Roberts has found evidence that languages where rising and falling tones make a difference in meaning (like Chinese) are less likely to arise in arid climates—an idea that made a splash but also drew critiques and skepticism from other researchers.

Decades ago, linguist Charles Hockett pointed out that sounds like f and v are rare in languages spoken by hunter-gatherers. The reason for this, he suggested, was tooth wear: humans eating soft, modern food retain our childlike overlapping bites, but this wasn't always the case in our species' history—and as present-day hunter-gatherers show, isn't a universal today either.

Lips to teeth

Hockett thought that sounds made by pressing the lower lip against the upper teeth ("labiodental" sounds) would be easier with the overlapping bites and so more likely to arise in languages spoken by people eating the soft grains and dairy products produced by agriculture (not to mention the processed food of industrialized societies). In other words, eating mush your whole life makes it easier to say "Teeth was a 2007 movvvie about the fffictional condition vvvagina dentata."

Blasí and his colleagues used data from a range of sources to dig into Hockett's idea. First, they used computer simulations to explore how much muscular effort is involved in producing these sounds, compared to sounds made by pressing the lips together, like b, p, and m (called "bilabial" or two-lipped). We'll call these f-sounds and b-sounds to make things easier to follow.

The simulations showed that it was much less effortful to produce f-sounds with an overbite—and also that people with these overbites would be more likely to fudge a b-sound, pronouncing it as something easier to say. If you say the word symphony a few times quickly, you might notice that your m sound is more like a nasal-sounding v without properly closed lips—and you can possibly thank your agricultural diet and modern bite pattern for the lapse.

Labiodentals in the real world

Then, the researchers turned to global data on food and language, pointing to evidence that high levels of wear and tear on the teeth lead to important changes to the teeth and jaw: the teeth keep growing to make up for their lost height, they tip toward the tongue, and they take up different placement in the jaw. Softer food means less work for the jaw, leading to smaller jaws and more crowded teeth.

Because shared genetics, shared cultural history, and contact between groups of people could affect factors like cooking, language, and jaw development, the researchers accounted for those relationships when they looked at the data. Even after doing that, they found that hunter-gatherer groups had far fewer f-sounds than societies that produce their food through agriculture, suggesting that the sounds are less likely to arise in cultures that eat food leading to more wear and tear on the teeth. And when Blasí and colleagues looked into the history of the well-researched languages that make up Indo-European (the language family that includes English, its close cousins like Norwegian, and its distant relatives like Hindi), they found a similar signal of f-sounds accompanying innovations in food technology.

This evidence doesn't explain the sound shift in German—that happened much more recently, long after all the people involved were farming their food. The change also involved far more sounds than just those using the lips and teeth. But the theory does help to unravel one of the possible reasons why change might happen in one language and not another: environmental factors that differ between their speakers.

Beyond Indo-European

Although Blasí and his colleagues join multiple strands of evidence together to support their claim, there are still other avenues to explore that could strengthen, or weaken, their case. Exploring this relationship in languages other than Indo-European would be an important step, although it could be hampered by the availability of detailed data on language histories. A broader range of factors that could influence bite shape are also worth a look. And the role of industrialization and food utensils (as well as their impact on food, jaws, and teeth) could also be explored in conjunction with much more recent sound changes.

But this is yet another intriguing indication that the vast variation we see in the world's languages could be the result of more than just chance and speaker efficiency—that environment and even our own cultural innovations could contribute to shaping our language. This means that studying the history and evolution of language while ignoring humans' ecological and cultural context could be a dangerous game, missing important details that could load the linguistic dice in favor of one outcome or another.

Science, 2018. DOI: 10.1126/science.aav3218 (About DOIs).