The ecological drivers of variation in global language diversity

Background
There are about 7000 languages spoken on earth (Gavin et al., 2013). However, these languages are not evenly spread across the globe. The number of different languages spoken in a specific geographical area, referred to as language diversity, appears to be linked to environmental factors and to biodiversity. Areas closer to the equator, which have a warmer climate, usually have higher language diversity than colder areas farther away from the equator.

How does the environment affect language diversity? Researchers over the years have proposed two hypotheses to explain this correlation. The first, called the ecological risk hypothesis, states that language diversity is linked to whether collaboration among a large group of people is critical for survival. Under this hypothesis, language diversity is higher in a favorable environment. In an area with a long growing season, people have an easier time getting food and other natural resources, and therefore do not need to collaborate to survive. With this lowered need for collaboration comes a lowered need for communication, and people tend to speak different languages. In harsher climates, survival may depend on collaboration among large groups of people, and thus, fewer distinct languages are spoken.

The second hypothesis, isolation theory, proposes that language diversity is linked to geographical isolation. According to this hypothesis, language diversity is higher in areas where people are separated into smaller groups by rivers, mountains and other natural barriers.

Several studies have been conducted on a region-by-region basis to tease apart the effects of geography and ecology on language diversity. However, these two hypotheses had not been examined on a global level. In this preprint, the authors conduct a comprehensive global analysis of the links between language diversity, geography and ecology to identify the drivers of language diversity.

Interesting findings
To test whether ecology or geography best explains the link between language diversity and the environment, the authors examined the correlation between language diversity and several environmental, climactic, population and biodiversity parameters. For this work, 6,425 languages were analyzed. Results showed that language diversity was highest near the equator, and reduced in a gradient as one moved away from the equator (preprint Figure 1).

The authors then examined which aspects of climate were associated with language diversity. They found that seasonal rainfall patterns and high temperature were most closely linked to high language diversity. These observations support the ecological risk hypothesis. Results also showed that bird and mammal diversity, but not amphibian or plant diversity, is linked to language diversity. However, the authors explained that the association between bird and mammal diversity and language diversity is because animal and language diversity are driven by the same factors: warm temperatures and lots of rainfall that lead to an increase in resources. Such a favorable ecosystem supports a larger number of unique species.

Does landscape have any influence on language diversity? The authors did find that the presence of larger rivers was significantly linked to higher language diversity. However, based on their analyses, this correlation is because rivers are a source of water and therefore a natural resource, and not because rivers may act as a barrier separating various groups of people. Bigger rivers mean more water, a better environment, and therefore more languages spoken. The authors also found links between altitude and landscape roughness and language diversity, though those links were not unanimously significant when examined by all the methods of analysis used.

Interestingly, though climate and ecology faithfully predicted diversity in most cases, there were some areas of higher or lower-than-predicted language diversity. Areas of lower-than-expected diversity, such as in the lower Amazon Basin of South America, may be due to underreporting of languages spoken. Higher-than-expected language diversity, on the other hand, may be driven by factors not captured by the parameters measured in this study.

Hua and colleagues conclude that on a global scale, patterns of language diversity can largely be explained by the ecological risk hypothesis. Favorable climates allow people to thrive in smaller groups, each with their own language. The link between language and species diversity is incidental, with both factors being dependent on a favorable environment.

What I like about this preprint
The authors did a thorough job of data analysis by using multiple parameters. This approach uncovered results that would not have been obtained by a less extensive approach.

Follow-up question
As the world becomes more industrialized and we become less dependent on climate alone for survival, will the link between ecology and language diversity disappear?

References
• Gavin, M. C., Botero, C. A., Bowern, C., Colwell, R.K., Dunn, M., Dunn, R.R., Gray, R.D., Kirby, K.R., Mccarter, J., Powell, A., Rangel, T.F., Stepp, J.R., Trautwein, M., Verdolin, J.L., And Yanega, G. (2013). Toward a Mechanistic Understanding of Linguistic Diversity. BioScience 63, 524−535.

 

doi: https://doi.org/10.1242/prelights.5488

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