Weather and environmental factors have had a huge influence on human evolution. It’s responsible for everything from our skin color to the texture of our hair. Scientists once believed that the environment’s influence on humans stopped at physical features, but a recent study has revealed it stretches even further and even influenced the development of spoken languages.

Tonal languages are described as languages where pitch is used as part of the speech. These language types are found throughout the world, with Mandarin and Cantonese being the two most widely spoken and easily recognized tonal languages. There are even examples of tone specific words in non-tonal languages, which is how the English word “record” can be either a noun or a verb depending on which syllable is stressed.

Caleb Everett, an anthropological linguistic professor at the University of Miami, found a common characteristic in countries with a complex tonal language as their native tongue: high humidity. To further investigate this observation, Everett and his colleagues mapped the distribution of more than 3,700 tonal and non-tonal languages and confirmed that tonal languages do tend to be spoken in warm, humid areas. According to Everett, this is not merely coincidental.

“Extensive research on human physiology suggests that really dry air makes it hard for us to use our vocal cords very precisely,” Everett explained, as reported by Scientific American.

Your voice is formed by vocal cords, and these need to be fully hydrated to work at top efficiency. The humidity, or lack thereof, in air can affect our physical ability to make certain sounds. For example, Singing For A Living suggests that singers who must perform in areas with dry climates, such as Los Angeles, be extra vigilant and ensure that they are drinking enough water.

Without optimal hydration it may be difficult for you to correctly emphasize slight tonal differences. For this reason, Everett believes that tonal languages became most popular in areas with high levels of humidity. Of course, this is simply a theory and in no way means that tonal languages are impossible to speak in drier climates.

"Obviously, speakers of Cantonese, for instance, can communicate in Siberia and other dry places,” Everett explained.

What the study does do, however, is offer an interesting perspective into how the land we live on shapes who we are.

Source: Everett C, Blasi DE, Roberts SG. Climate, vocal folds, and tonal languages: Connecting the physiological and geographic dots. PNAS. 2015.