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.

Is grammatical complexity shaped by sociodemographic and sociolinguistic factors? The previously accepted "linguistic niche hypothesis" claims that with an increased number of nonnative speakers in a social group (high exotericity), grammatic complexity decreases; on the other hand, grammatical complexity increases amongst isolated linguistic communities (low exotericity). Through the use of spatiophylogenetic modelling of 1314 languages, the authors of this study do not find adequate evidence to support the linguistic niche hypothesis. Instead, they suggest that linguistic complexity is better predicted by phylogeny and geographic contiguity.

Is grammatical complexity shaped by sociodemographic and sociolinguistic factors? The previously accepted "linguistic niche hypothesis" claims that with an increased number of nonnative speakers in a social group (high exotericity), grammatic complexity decreases; on the other hand, grammatical complexity increases amongst isolated linguistic communities (low exotericity). Through the use of spatiophylogenetic modelling of 1314 languages, the authors of this study do not find adequate evidence to support the linguistic niche hypothesis. Instead, they suggest that linguistic complexity is better predicted by phylogeny and geographic contiguity.

The authors compare language phylogenies and spatial distributions with folktale frequencies of Indo-European peoples in order to reconstruct their cultural transmission. A stronger association is found between folktale frequency and language phylogeny than has been proposed in earlier literature studies, indicating that vertical transmission is more influential on folktale distribution than horizontal transmission through spatial proximity. Finally, the frequencies of certain folktales appear to trace the ancestral divergences of Indo-European languages to a much deeper level than previously though, suggesting that folktales are representative of broader features of culture, rather than recent literary inventions.

Inter-group variation is greater in humans than in any other animal, and scholars continue to debate the cause of this diversity. Two competing explanatory models of human variation emphasize either (1) ecological differences and "evoked" culture or (2) population-level effects of cultural transmission. The former emphasizes mechanisms that operate within a single generation, while the latter emphasizes cumulative cultural history operating over many generations. To test these competing models, the authors measured the relative power of ecological variables as compared to culture history to predict behavioral variation in 172 western North American tribes. Culture history is subdivided into culture phylogeny (based on language phylogeny) and spatial distance.

Inter-group variation is greater in humans than in any other animal, and scholars continue to debate the cause of this diversity. Two competing explanatory models of human variation emphasize either (1) ecological differences and "evoked" culture or (2) population-level effects of cultural transmission. The former emphasizes mechanisms that operate within a single generation, while the latter emphasizes cumulative cultural history operating over many generations. To test these competing models, the authors measured the relative power of ecological variables as compared to culture history to predict behavioral variation in 172 western North American tribes. Culture history is subdivided into culture phylogeny (based on language phylogeny) and spatial distance.

The article discusses the role of gender in within-society variation in cooperative behavior, and whether gender differences in cooperation emerge similarly across diverse societies. The authors use cross-cultural datasets of 4- to 15-year-old children's preferences for equality in experimental tasks measuring prosociality and fairness to investigate these questions. They find that gender has little impact on the development of prosociality and fairness within the datasets, and there is not much evidence for substantial societal variation in gender differences. The authors discuss the implications of these findings for understanding the nature and origin of gender differences in cooperation and for future research.

In order to investigate cross-cultural variation in systems of conversational turn-taking (who speaks and when), the researchers analyze the association of various contextual, verbal, and non-verbal factors with mean response time. Despite some variation in response time between languages, each of the explanatory variables is found to have significant impact on response time independent of language. A further test on subjective perception of ideal response time suggests that although similar factors act on response patterns cross-culturally (in support of a 'universal systems' theory), speakers are hypersensitive to even minor cultural variations in response time.

Using HRAF's ethnographic reports from 11 immigrant groups to North America (1959-1989), the author asks: what social structural factors account for these patterns of language loss and retention? While focusing on the second and third generations, this study assesses the impact of residence, religion, school, festivals, homeland, marriage, and labor on language retention. The author suggests that residential closeness and the continued practice of religious rituals from the country of origin are the main factors influencing mother tongue maintenance into the third generation, while participation in community festivals is a marginal predictor.

The authors examine musical diversity in India using cantometric data from 32 Indian societies with the goal of better understanding how music varies between and within cultures. They find very minor musical differences between language families, greater diversity between societies but within language families, and the most variation within societies.