There's a pretty neat series of maps featured in Business Insider making the rounds on various social channels. They tell us about ourselves, showing how Americans speak differently from each other. My favorite is slide 17 because I have only ever owned sneakers and was absolutely confused when someone recently suggested that my concept of sneakers was really a generalization of "athletic shoes." (I still think they're sneakers. All of them.) It's a treasure trove of linguistic diversity revealing which everyday words in my lexicon vary (e.g., garage sale) and which seem fairly common (e.g., subway) to the overall American experience.

The maps are the work of NC State Ph. D. student Joshua Katz, who drew on a linguistic survey on the ways Americans pronounce words—you can view the original set of maps here. Regional variations in language are well-studied. Every speaker can be identified by region, social class and gender. Accents are incredibly revealing, which is why some people take great pains to hide theirs even while others use it to weave an identity. These identities reach beyond personal definition to explicitly include regional and social histories and cultural nuances.

However while accents can be hidden or faked, the sounds that we're able to make may not be so readily manipulated. A recent study published in PLOS One shares evidence that geography may play a part in shaping these sounds. Anthropologist Caleb Everett analyzed 567 language locations and found a commonality that crossed dialectical boundaries and language families: languages with ejective phonemes tend to occur at higher elevations throughout the world.

What are ejectives? They're a basic unit of sound—a type of phoneme—which when combined with other phonemes create words. Ejectives are unusual in that they're non-pulmonic. They're produced by the closing of the vocal cords. It is the vibration of the vocal cords that allow us to meld phonemes together to generate words. These sounds are essentially voiceless. They're hard to describe: it's almost as though you're trying to make the sound of a consonant while holding your breath. They're really better understood when you can hear them for yourself:

Fifteen percent of the habitable space in the world is at altitudes higher than 1500 m (approximately 1 mile) above sea level; these spaces are home to ten percent of the world's population. Everett divided the 567 languages he tapped for his study into two groups: those having ejectives (92) and those without (475). Among those languages with ejective phonemes, sixty-two percent are found at higher altitudes. The remaining languages with ejective components are disbursed, but the greatest concentrations are seen within 500 km (approximately 300 miles) of these linguistic peaks.

Everett believes the conditions at higher altitudes may encourage the production of ejective phonemes. These utterances require that the vocal cords are closed and raised. Everett holds that this is easier to accomplish at higher altitudes where atmospheric pressure is lower, which means that air pressure in the mouth and lungs is lower so it may be easier to force the vocal cords closed. Everett also proposes that the higher incidence of ejective phonemes at higher altitudes may represent a biological adaptation. With ever word uttered, we're generally exhaling during some portion of the utterance. This exhalation also releases water vapor, which Everett informs us is not a trivial matter. Apparently, we lose up 400 ml of water vapor though exhalations. At higher altitudes, this can lead to dehydration and severe forms of altitude sickness. Because ejective phonemes require the vocal cords to the closed, they're also not drawing on air contained within the lungs and therefore releasing water vapor—in this way, ejective phonemes could be a biological adaptation to an extreme living condition.

However, not everyone is quite sold on Everett's analysis. Over at Language Log, a blog run by the Research for Cognitive Science at the University of Pennsylvania, Dr. Mark Liberman raises some concerns over the statistical work done in this paper cautioning that this may be a causal effect. Liberman's primary concern appear to be that data can be molded to tell any story, but acknowledges that there is independent support for Everett's findings.

Given the amount of attention Katz's maps have received, we are definitely interested in exploring our linguistic differences. In the case of languages that are in isolated, as those with ejective phonemes, they will likely attract a fair amount of attention as we work to better understand ourselves and our differences. Do you have a accent or dialect story to share? Or are you an ejective speaker? How has your locality influences how you speak—both physiologically and acoustically?