Sounds of human languages can be affected by various factors of the natural environment. One such factor is the mean annual temperature. In new research, scientists from Nankai University and Kiel University analyzed the average sonority (loudness of speech sounds) of basic words of nearly three-quarters of the world’s languages, and confirmed a positive correlation between sonority and local temperature. Their findings suggest that lower temperatures, over the course of many centuries, lead to decreased sonority.
Global distribution of MSIs across 9,179 language varieties from the ASJP database. Color of dots represents the MSI of the language, with redder dots indicating higher and bluer dots indicating lower indices. The fill color of land areas represents the mean annual temperature. Image credit: Wang et al., doi: 10.1093/pnasnexus/pgad384.
Language evolution is a complex and never-ending process that can be affected by a multitude of internal and external factors. One such external factor is the natural environment.
A century ago, Edward Sapir investigated the correlation between language and environment, and emphasized the reflection of the environment in the vocabulary of a language.
He noted that the phonetic systems, however, are almost immune to environmental conditions, and characterized the development of the speech system as a quasimechanical process.
Regardless of the validity of Sapir’s point, the relationship between the phonetic system and the natural environment was generally ignored or even rejected in most subsequent linguistic studies.
“The natural environment can shape languages as they evolve through time,” said Nankai University researcher Qibin Ran and colleagues.
“Since we are surrounded by air when we speak and listen, the physical properties of the air can influence how easy speech is to produce and hear.”
“On the one hand, the dryness that comes with cold air represents a challenge for the production of voiced sounds, which involve vibration of the vocal cords, and, on the other hand, warm air tends to limit unvoiced sounds by absorbing their high frequency energy.”
“Such factors could favor higher sonority in warmer climates.”
“Sonority refers to the loudness of speech sounds, which is influenced by the openness of the vocal tract.”
The authors sought to verify this intuitively plausible relationship by leveraging the Automated Similarity Judgment Program (ASJP) database, which contains basic vocabularies for 5,293 languages.
They found that languages with high mean sonority indexes (MSI) are concentrated around the equator and the southern hemisphere.
Languages in Oceania have some of the highest MSIs.
However, there were some exceptions to the trend; Mesoamerica and Mainland Southeast Asia showed lower MSIs despite being tropical.
Overall, there was a positive correlation between MSI and mean annual temperature, averaged by language family.
However, when looking at relationships within families, the authors found no clear pattern.
“The fact that the relationship is only predictable at the language family level is an indication that temperature effects on sonority evolve slowly, shaping language’s sounds only on timescales of centuries or even millennia of linguistic evolution — longer than the average lifespan of an individual language,” the scientists said.
Their paper was published in the journal PNAS Nexus.
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Tianheng Wang et al. 2023. Temperature shapes language sonority: Revalidation from a large dataset. PNAS Nexus 2 (12): pgad384; doi: 10.1093/pnasnexus/pgad384
