This paper investigates the ecological adaptation of language sound systems, focusing on the relationship between climate, voice quality, and the number of tones in Chinese languages. Using a large speech database (China’s Language Resources Protection Project), the authors examine the causal chain: humidity → voice quality → number of tones. Their analysis of 1,174,686 recordings from 997 language varieties reveals a significant negative correlation between humidity and voice quality (measured by jitter and shimmer) and a relationship between voice quality and the number of tones, particularly within Sino-Tibetan languages. The findings support the hypothesis that drier climates lead to poorer voice quality, which in turn is associated with a reduction in the number of tones.

Yuzhu Liang, Lining Wang, Søren Wichmann, Quansheng Xia, Shuai Wang, Jun Ding, Tianheng Wang, Qibin Ran