Why do humans speak so many languages?

The ecosystem and climate people lived in might have contributed to the evolution of a language, say scientists.

There are as many as 7,000 different languages spoken worldwide. How did we get so many? Environment may have played a role. 

Scientists have long known that voices carry differently in dense forests and open plains and in humid air and dry air. Now, researchers say that the ecosystem and climate in which languages developed might have actually helped shape how they sound.

“What we’re suggesting is that at least some characteristics of different languages were shaped by the climatic and ecological environment in which they were being used,” says phonetician and linguist Ian Maddieson, who presented his research along with colleague Christophe Coupé on Wednesday at the 170th Meeting of the Acoustical Society of America.

“In the clear environment, you can use speech sounds that have very rapid changes and very high-frequency components, but these would be disrupted in transmission if it’s in the more difficult kinds of environment, such as a forested area,” Dr. Maddieson tells The Christian Science Monitor in an interview. In an environment with more disruption, he says, languages tend to have more steady sounds, particularly vowels. 

“The basic theory we have is that you’ll have a more kind of consonant-rich language in some environments compared to a more vowel-rich language in others, simply because of the effectiveness of transmission of different types of sounds in different environments,” Maddieson says. 

But trees aren’t the only environmental disruption for sound. Maddieson and Dr. Coupé looked at other variables, including elevation, terrain, temperature, and precipitation. 

The researchers found languages with more consonants were associated with rugged terrain and higher elevation. Less consonant-heavy languages tended to match regions with higher tree-cover, warmer temperatures, and more precipitation. 

To determine the relationship between these environmental factors and language development, the researchers compared the sound properties of languages from around the world with the regions in which they originated. To do this, they compared sound and language data with information from the International Steering Committee for Global Mapping, which provides ecosystem and climate data from around the world. 

The scientists evaluated and compared the languages using an index of consonant heaviness, the number of consonants in a language, and how those consonants cluster around syllables.

The researchers excluded English, Mandarin Chinese, and Spanish, and other global languages whose present-day sounds are unlikely to retain links with the environments in which they first developed. 

After looking at over 600 indigenous languages from all over the globe, the researchers concluded that tree-cover and temperature best predicted the consonant heaviness of a region’s language. 

What if a group of people were to move, bringing their language along with them?

“If people moved to a certain area, then the way that they are going to be hearing sounds in their language will be shifted a little bit by the change in environment,” Maddieson says. “They’ll hear things a little differently, they’ll adapt their language to the way that they’re hearing it.”

But that won’t happen overnight. 

“This would be a slow process over a lengthy period of time,” he says. “We’re not talking about changes that would happen within a generation or even two or three generations, but over a long period of time.”

Transmission of sound may not be language’s only environmental hangup 

Caleb Everett, an anthropological linguist at the University of Miami, has also investigated an environmental link to the evolution of language. In February, Dr. Everett and his colleagues found that languages with complex tones are unlikely to evolve in dry climates.

“In really dry contexts the human vocal cords operate a little less efficiently,” Everett tells the Monitor, in what should not be a surprise to singers.

After looking at data about how the human larynx works, Everett checked his prediction across databases of languages. He confirmed that languages with complex tone, requiring precise manipulations of pitch, were associated with more humid regions. 

In a 2013 study, Everett examined the link between altitude and ejective consonants, produced by compressing a pocket of air in the throat rather than the lungs, a sound we don’t have in English. 

At the time, he surmised that one explanation could be that the reduced atmospheric pressure made it easier to hold such air pockets in the throat. 

The environment may not be the only factor in language evolution

“There’s no reason to think that there are not a lot of other factors that are involved,” says Maddieson. 

Those factors might be social. For example, the way you interact with other people might influence how language might be needed to communicate. Or perhaps the frequency of these interactions might play a role. 

Or perhaps social influences are linked to environmental ones. A 2004 study linked sonority – a measure of loudness and vowel-heaviness — to warmer climates. These researchers suggested that it wasn’t the temperature that lead to increased sonority, it was the intermediate step: how much time people spent indoors.

People spending a lot of time indoors wouldn’t have to project their voices over far distances, they suggested, while those outdoors might have needed to shout across fields or up mountains.

Birds’ songs adapt too

Maddieson’s suggestion that humans will adapt the sounds they use to better communicate in their environment is not new to biology. 

Acoustic adaptation hypothesis was first proposed in birds in 1975, but may still be occurring today.

Research suggests that birds living in or around cites alter their sounds to better communicate over urban noise. A 2003 study found that some of these birds sing at a higher pitch than their country counterparts. 

Language: A distinctly human mode of communication 

Although both birds and humans display evidence for acoustic adaptation hypothesis, Maddieson and Everett both maintain that human communication stands out.

“Ultimately language is probably the most distinguishing characteristic of Homo sapiens,” says Everett. But, “here we are considering this possibility that like other species, our language is ecologically adaptive in ways we never even recognized and in ways that are totally subconscious.”

Still, humans’ complex communication systems are unique, asserts Maddieson. “One of the things that is different about human language compared to communication systems of virtually all other animals we know anything about is that we have so many different languages. This is a very important factor in human existence.”

“We are the only species that has anything like this rich communication system,” he says. “So it’s an extremely important thing to understand about what makes us different from other creatures.”

Maddieson and Coupé will submit a written version of their presentation to the Proceedings of Meetings on Acoustics. In the future, they hope to expand their research by making recordings of languages around the world and analyzing their sounds.