This paper examines the enormous variation in linguistic diversity among Pacific Islands by testing its relationship with various environmental variables put forth in several common theories of language richness. The researchers identify variables relating to land area and island isolation as accounting for about half of variation in linguistic diversity, suggesting that the other half is a result of complex social factors.

The researchers utilize a GIS approach in order to examine the relationship between global linguistic distribution and various cultural and environmental factors. The resulting positive association between political complexity and both latitude and language range leads the researchers to propose that large, politically complex entities exert a homogenizing pressure on language. However, the causal link may also be in the other direction, with possession of common language facilitating the creation of more complex political institutions.

The authors investigate the relationship between linguistic diversity and various environmental and spatial variables associated with biodiversity. Most of these variables predict linguistic diversity variably across different continents, and more so within Africa and extended Asia (Asia, the Pacific, and Australia) than within Europe and the Americas. This divide is theorized to be a result of differences in demography and impact of colonialism between the two global regions. However, two environmental factors, landscape roughness and density of river systems, are found to be significant predictors across all global regions. The authors suggest that, as in processes of speciation, rough terrain and watercourses both create physical barriers between which languages can develop in isolation while, in the case of river junctions, also providing transportation routes whereby hybrid languages can occasionally manifest.

The authors investigate environmental reasons for cross-cultural variation in the permissibility of cousin marriages. In particular, they test whether higher levels of pathogen prevalence and geographic isolation increase the likelihood that cousin marriage will be allowed. The authors' underlying theory is that cousin marriages provide protective homozygosity against some pathogens and provide more options when mate choices are limited.

This paper examines the relationship of productive variation in land between ethnic groups to determine if an increased range of producible goods will increase trade, thus decreasing language diversity between neighboring groups. The author initially found that high-variation in land production lessened the diversity of language between ethnic groups in that area. To further test this correlation, the author found that high-productive variation increased trade and exogamous marriage and decreased inter-ethnic conflict. Based on these findings, the author suggests that neighboring ethnic languages co-evolved through the economic benefit of inter-ethnic trade and social interaction.

By testing relationships between musical, geographic, genetic, and linguistic distance among nine indigenous groups in Taiwan, the researchers aim to quantitatively evaluate a developing theory of coevolution between these traits. An especially strong correlation between musical variability and genetic distance suggests that music may possess worldwide time depth, diversity, and universality equal to or greater than that of language, and could thus serve as a complementary marker for reconstruction of long-term population shifts.

This article examines possible environmental predictors of ethnic diversity around the world. Results suggest that global ethnic diversity is associated with latitude, habitat diversity, pathogen stress, and climate.

This exploratory study seeks to explain cassava production and processing in Africa by considering cultural, agronomic, and environmental data. After examining the descriptive results of the agricultural and social contexts of cassava use, the authors build upon Boserup's population density model (1965) to analyze their own hypothesized model of cassava's importance among the sampled societies.

The authors test the relationship between disease prevalence and three different personality traits, with the expectation that pathogen load will be negatively associated with degree of sociosexuality, extraversion, and openness to experience. This prediction is supported by all three tests, which they theorize is an example of cultural behaviors adapting to reduce vulnerability to environmental risks.

The authors contribute to a growing body of theory which posits cultural differences as a result of variable pathogen prevalence by testing the relationship between pathogen richness and various measures of conformity in a cross-regional sample. After controlling for confounds such as life expectancy, GDP, population density, arable land area, and agricultural labor force, the authors suggest that conformity is emphasized to varying degrees in response to the increased vulnerability to pathogens generally associated with deviation from normative social conduct.