Changes in the environment have shaped the development of our brain and the human body.
A recent study however suggests that our different languages have also evolved through adaptations to the local environment. Researchers at the University of New Mexico and Laboratoire Dynamique du Langage-CNRS in France undertook a study looking at the relationship between the sound structures of a worldwide sample of human languages and climatic and ecological factors such as temperature, precipitation, vegetation and geomorphology.
The results of the study indicate a correlation between ecological factors and the ratio of sonorant segments created by uninterrupted airflow in the languages examined. This supports the hypothesis that environmental adaptation of the acoustics in language played a part in the evolution of languages.
“We find that the number of distinct consonants and the degree to which consonants cluster together in syllables correlate with mean annual precipitation, mean annual temperature, the degree of tree cover and the geographic elevation and ‘mountain-ness’ (‘rugosity’) of the area in which they are traditionally spoken,” he said. “Both the number of distinct consonants and their distribution in syllabic structures are lower where tree cover and temperature are higher.”
Tree cover and higher temperature both make higher frequency transmission less reliable which is speculated to explain why languages in tropical areas tend to have more vowels. Also by using simpler syllable structures, the vowels occur more often in the stream of spoken language.
“Maddieson said that their findings offer support for an application of the Acoustic Adaptation Hypothesis — which argues that species adapt their acoustic signals to optimize sound transmission in the environment they live in — to human languages. The hypothesis was first proposed by E.S. Morton in 1975 in relation to the calls of 177 bird species. Morton suggested that birds in forested areas tend to sing at lower frequencies than birds living in open areas in order to enhance the effectiveness of transmission of the signal in the specific environment they live in. More recent work has shown that birds of the same species adapt their calls to make them more effective against the background of modern urban noise pollution.”
In order to further examine the relevance of the Acoustic Adaptation Hypothesis and its impact on the evolution of human languages, the researchers compared phonological data on languages from the Lyon-Albuquerque Phonological Systems Database with the International Steering Committee for Global Mapping’s data on climate and ecology.
“The transmission of sound waves consists of the propagation of small pressure differences through space in a medium such as air. For the most faithful propagation of sound waves, the medium needs to be uniform, otherwise some distortions will occur,” Maddieson explained. “In an area with dense vegetation, the paths of transmission are not uniform. Some sound waves are reflected backwards by the vegetation, while others are diverted sideways, leading to signal degradation and ineffective transmission. Additionally, sound signals containing very rapid changes, or high frequencies — such as the consonants /p, t, k/ — are more affected by dense vegetation than sound signals with steady-state or low-frequency characters, such as vowels.”
This was proposed as the reason why languages in geographical locations with greater tree cover tend to have less consonants. Environments where higher frequencies are transmitted poorly tends to favour will use more sounds with low frequencies. Vegetation is not the only ecological factor that impacts sound transmission though. Warm dry air tends to create ripples in the air that disrupts the coherence of high-frequency sound transmission, and rough terrain can distort high-frequency sounds as well. Other factors such as temperature, wind and rain also have an impact on the evolution of human language and these factors account for almost a quarter of the variation in a language’s consonant density.
“The researchers’ next step is to study a large sample of spoken language recordings rather than summary data on inventories and syllable structures to see if ecological factors could predict the proportion of sonorant segments per unit time in spoken languages.”