Human languages may have evolved to suit the natural habitats in which they were originally spoken according to a study of the different sounds used in vocal communication around the world.

Languages that originated in the dense forests of tropical regions are more likely to use low-frequency sounds and vowels compared to languages that evolved in more open habitats where high-pitched sounds and consonants are more easily understood, scientists said.

A study involving the analysis of 628 languages from different regions of the world has found evidence to support a controversial theory of “acoustic adaptation” which hypothesises that the natural landscape can influence the kinds of sounds used by animals when communicating with one another.

The researchers believe they have found the first hard evidence to support the idea that human languages have evolved in a way that optimises the transmission of vocal sounds depending on the natural environment in which the speakers have lived – such as tropical forests, mountains or open savannahs.

The study has also identified other geographic factors, such as average levels of rainfall and temperature, which can influence the propagation of the sound waves through the air that form the basis of communicating human speech, the scientists said.

“We believe that some part of the characteristics of the sound patterns in languages is shaped by the ecological or climatic features of the area where it was originally spoken,” said Ian Maddieson, an adjunct professor of linguistics at the University of New Mexico, who led the study.

A vowel-rich language that typifies a tropical, forested habitat is Hawaiian (Getty Images)

The study concentrated on smaller languages spoken by less than 5 million people that are indigenous to a particular region of the world – which ruled out English, Chinese and Spanish.

By cross referencing linguistic sounds – such as consonants and vowels – against the geographical and climatic factors of the language region, the scientists were able to show that there is a correlation between how a language is spoken and the type of landscape in which it evolved.

“We believe this work is by far the most extensive and careful work on a possible link between specific aspects of human language’s sound patterns and environmental factors,” Professor Maddieson said.

“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’ of the area in which they are traditionally spoken,” he said.

“Both the number of distinct consonants and their distribution in syllabic structure are lower where the tree cover and temperature are higher,” he added.

Words rich in consonants – such as “strict” in English – are more easily understood in more open landscapes in temperate climates, while those that are rich in vowels – such as “banana” – are more easily heard in tropical regions with dense vegetation, Professor Maddieson said.

A vowel-rich language that typifies a tropical, forested habitat is Hawaiian, while consonant-heavy Georgian is a good example of a language that has evolved in a more open, mountainous region with little dense vegetation, he suggested.

“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 distortions will occur,” he said.

“That could explain why languages in areas with greater tree cover tend to be less ‘consonant-heavy’. Environments in which higher frequencies are less faithfully transmitted may favour greater use of sounds characterised by low frequencies, that is more sonorous sounds,” he explained.

The study was presented at the annual meeting of the Acoustical Society of America in Jacksonville, Florida.

The theory: Acoustic adaptation

The idea that the acoustic background of a landscape affects how human languages develop comes from studies, mainly of birds, where vocal communication appears to vary according to the habitat.

Birds that live in dense, tropical forests tend to emit low-frequency, tone-like calls, while those inhabiting open spaces typically have high-frequency songs.