Tone and Humidity.

A startling theory (description from the FAQ):

Everett, Blasi & Roberts (2015) review literature on how inhaling dry air affects phonation, suggesting that lexical tone is harder to produce and perceive in dry environments. This leads to a prediction that languages should adapt to this pressure, so that lexical tone should not be found in dry climates, and the paper presents statistical evidence in favour of this prediction.

It’s reminiscent of this bit of japery, but this is serious, and the FAQ answers some obvious questions, e.g., re exceptions:

There are certainly exceptions to the prediction. But we’re not expecting a hard and fast rule, just a statistical tendency. We were aware of such exceptions before even embarking on the analysis of the database. Our account is not simply deterministic, but suggestive of gradual pressures operating at the same time as other pressures known to impact the evolution of sound systems. Occasionally such influences may even be at odds. We note in the SI, however, that even in a language family like Tibeto-Burman, in which there are exceptions, the overall pattern holds in the predicted direction. Tibeto-Burman languages spoken in more desiccated regions are less likely to employ complex tone.

Thanks, Yoram!


  1. Just an FYI: Caleb Everett is Dan Everett’s (he of the Pirahã fame) son.

  2. I have not read the article and I would not be qualified to offer an informed opinion. But it seems plausible to me that sound would travel differently in dry and humid air. And, that this would have some effect on perception of sounds. And, over time, this could effect the phonology of languages.

  3. Sure, it seems plausible to me too. But I’m just some patzer, and we all know what plausibility is worth.

  4. Trond Engen says:

    Doesn’t seem plausible to me, but I’m definitely nobody.

    If the mechanism is real, I’d expect tonal languages spoken in dry climates to have greater difference between tones than equally complex tonal languages spoken in wet climates.

  5. It’s easy to knock this down with counter-examples but the real test is if they used a valid sample to analyze. The Apachean languages are all tonal, and in the case of Navajo there are functionally four tones. It can get dryer than the Southwest, but not by much. Speaking of four tones, Mandarin has four and northern China is a dust bowl in the winter. Ditto for Tibetan. Where you find the best sample is in Africa, where you have tonal languages in areas ranging from coastal forests to Sahelian savannahs. The same is true of east Africa.

    Maybe you get more tones in wetter climates – Cantonese versus Mandarin – but Khmer has none at all. the Hmongic languages, at higher elevations, are all tonal. In fact they top everyone when it comes to having tones.

  6. The study focused on complex tones as an indicator for the effect they claim, so Navajo and many Bantu languages are binned with the not-so-tonal languages. The authors say that using tonal vs. non-tonal gives similar results.

    I wonder, do speakers of Thai, Cantonese or Trique who live in Phoenix or Riverside have a hard time understanding each other? Do people who sing outdoors in L.A., Madrid or Jaipur find it extra difficult to produce clear tones during the summer? Someone must have noted something by now.

  7. Jongseong Park says:

    Trond Engen: If the mechanism is real, I’d expect tonal languages spoken in dry climates to have greater difference between tones than equally complex tonal languages spoken in wet climates.

    Their thesis seems to be that lexical tone is harder both to perceive and to produce in drier climates, which I would guess to mean that producing greater difference between tones would also be harder.

    One way to enrich the data could be to investigate dialects that belong to the same language, like Mandarin, whose dialects are spoken over a wide swathe of China with a significant range of climates. But I don’t think Mandarin dialects display significant variation in the complexity of the tonal systems, with most having four tones just like Standard Mandarin.

    I’m all for taking a crack at investigating those numerous claims about the influence of climate on language, such as the influence of humidity on different kinds of phonation and classes of sounds like fricatives. We hear these old nuggets like the Australian accent of English arising from having to speak with the mouth closed to keep out the dust. We’re not meant to take these claims seriously, but imagine we actually investigated how various environmental factors affect openness and tongue root position in the vowel inventory. We’re probably not going to find anything conclusive, but it would be a fun exercise.

  8. Trond Engen says:

    Differences would be harder to percieve, so greater effort would have to be made for the same level of tonal complexity to be transmitted. So a language magically brought into a dryer environment might either reduce transmitted complexity or increase the effort. Either way, for any given level of tonal complexity, more articulatory effort should be involved.

  9. Just to go back to Everett et al., the claim for the mechanism of dry air impacting tone production comes from a paper by Hemler et al., The effect of relative humidity of inhaled air on acoustic parameters of voice in normal subjects. I have only seen the abstract. What Hemler et al. find is that test subjects, saying a prolonged “aaa…” in dry air, have more jitter in their voice compared to doing the same in normal and humid air. Presumably that is due to dehydration of the surface of the vocal cords. By inference, more jitter (fluctuation in pitch) should make tone harder to perceive.

    One may ask, how dry is “dry air” in the experiment? Does the effect kick in at 10% humidity? 2%? 30%? Is the jitter noticeable over the duration of a single vowel? Is the pitch variation significant compared to that due to tone? Is it perceptible by human ears? Do speakers of tonal languages have trouble perceiving lexical tone of speakers with high jitter from other causes, like age?

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