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.

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 authors test the relationship between linguistic diversity and parasite richness, theorizing that anti-pathogen behaviors, such as the favoring of contact with a limited range of similar, nearby populations carrying the same suite of parasites and pathogens, will be selected for due to variability in immunobiological makeup between groups. As a result, cultural and gene pool isolation will be likely to further divide local parasite-host groups, generating language diversity as well as population divergence and new evolutionary forms among the parasites themselves. A significant positive correlation is found, which the authors suggest has important implications for future research regarding cross-cultural transmission and interaction.

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.

Population size is generally assumed to play a pivotal role in the evolution of languages and cultures, but the expected patterns and potential mechanisms of change are unsettled. Theoretical models are limited by this uncertainty because they require making prior assumptions about language evolution. Using a sample of 20 Polynesian languages, authors test the effect of population size on the gain, loss, and total change of basic vocabulary words.

The author investigates whether geographic factors--namely high elevation or 1500 m+ above sea level (reduced atmospheric pressure)-- impact the production, use, and ubiquity of ejective phonemes in eight non-contiguous language clusters. It is suggested that increased use of ejective phonemes has a physiological benefit: the reduction of water vapor loss via exhaled air. Evidence is presented in support of the hypothesized geographic-phonetic linkage.

This study investigates the relationship between historical utilization of the plow and modern sex ratios. The authors argue that in societies without the plow subsistence is generally egalitarian with both men and women contributing. However, the use of the plow requires more physical strength which, they argue, leads to a preference for boys and, thus, men. Therefore, in cultures that use the plow, this is reflected in male-biased sex ratios which are negotiated by way of practices like sex-selective abortions, infanticide, and/or differential access to resources based on sex.

The researchers examine Boserup's (1970) theory that variation in traditional agricultural practices shape gender roles by examining the relationship between historical plough use and contemporary fertility rates and preferential attitudes towards fertility. Contrary to expectation, tests show a negative relationship between plough use and both of these variables. The authors theorize that since children are less capable of performing the intensive labor required by plough agriculture compared to hoe agriculture, adoption of the plough deincentivized increased fertility and reduced its value among agriculturalists.

There is considerable variation both within and across societies in attitudes towards female employment outside of the household. In some societies, the dominant belief is that women should have equal opportunity to work outside the home, while in others women are strongly discouraged from working outside of the domestic sphere. Here the authors use pre-industrial ethnographic data and contemporary observations of gender inequality to test the hypothesis that cultural attitudes regarding the appropriateness of women working outside of the household are rooted in the ancestral adoption of plough cultivation. Contemporary measures of gender inequality assess variation across countries, ethnic groups, and individuals.

The authors of this article evaluate how the legacies of early statehood (i.e., precolonial centralized ethnic groups) in Africa continue to impact democratic governance. They find a positive relationship between early states and support for autocratic rule, especially in former British colonies that were highly centralized prior to colonization. They suggest that the transmission of political and cultural norms play an important role in the support for autocracies.