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.

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 present study examines the relationship between pathogen prevalence and the domestic living-organization of 186 societies from the Standard Cross-Cultural Sample (SCCS). The measurement for pathogen stress consists of ten diseases described by Low (1991) and Caden and Steele (2013). These are dengue, typhus, plague, filariae, schistosomes, leishmanias, trypanosomes, malaria, leprosy, and spirochetes; the transmission for these diseases was contagious and/or mobile. The measurement for the living organization came from the 'Household Form' variable by Murdock and White (1969). The seven categories of household form variable were then re-coded into two variables. The first is modular, which includes single-family and family homestead. The second is communal and includes large communal structure, multifamily household, husband rotates, individuals, married, and husband separate. The findings offer support for the evolutionary hypothesis that modular living is adaptive because it may reduce pathogen stress. Specifically, pathogen stress is influential in the way people live.

In order to evaluate an adaptive justification for restriction of ritualized physical contact, the authors test association between three manifestations of physical interaction and prevalence of pathogens cross-culturally. Their expectation, supported by two of the three tested hypotheses, is that higher pathogen prevalence will lead to customs of restricted physical contact. Both cultural and biological evolution are suggested to be influential in selecting for physically intimate behaviors.

Researchers investigated further into why and how humans speak so many languages across the globe, and why they are spread out unevenly. Using two different path analyses, a Stationary Path analysis and a GWPath, researchers tested the effect of eight different factors on language diversity. Out of the eight variables (river density, topographic complexity, ecoregion richness, temperature and precipitation constancy, climate change velocity, population density, and carrying capacity with group size limits), population density, carrying capacity with group size limit, and ecoregion richness had the strongest direct effects. Overall, the study revealed the role of multiple different mechanisms in shaping language richness patterns. The GWPath showed that not only does the most important predictor of language diversity vary over space, but predictors can also vary in the direction of their effects in different regions. They conclude that there is no universal predictor of language richness.