Washington, Jan 24 (IANS): Finding a correlation between climate and the evolution of language, researchers say that languages with complex tones are much more likely to occur in the world's humid regions.

Similarly, languages with simple tone occur more frequently in desiccated regions, whether frigid areas or dry deserts.

To discover an association between the environment and vocal sounds, researchers found that many languages of the world use tone or pitch to give meaning to their words.

"In my estimation, it changes a bit our understanding of how languages evolve," said Everett, associate professor in the department of anthropology at University of Miami College of Arts and Sciences, and lead investigator.

"It does not imply that languages are completely determined by climate, but that climate can, over the long haul, be one of the factors that helps shape languages," Everett noted.

The team examined more than 3,700 languages and found 629 languages with complex tones.

They provide extensive evidence that sound systems of human languages are adaptive and can be influenced by climate.

One explanation is that inhaling dry air causes laryngeal dehydration and decreases vocal fold elasticity.

It is probably more difficult to achieve complex tones in arid climates - particularly very cold ones-- when contrasted to warmer and more humid climates.

The findings are supported by data relating to over half of the world's languages and to previous extensive experimental research on the properties of the human larynx that affect tonality.

Most were found in tropical regions, throughout Africa and Southeast Asia, but also in some humid regions of North America, Amazonia and New Guinea.

The findings are published in the Proceedings of the National Academy of Sciences.