This study explores ecological reasons that might explain why boys are mostly circumcised in tropical regions, particularly in Africa and the insular Pacific. The author postulates a long causal chain linking: 1) tropical climate to the growing of root and fruit crops; 2) the need to keep babies on mother's milk for as long as possible where the adult diet is lacking in protein; 3) a long post-partum sex taboo as a way to space births; 4) the practice of polygyny (and associated mother-child sleeping) in the face of a long sex taboo; 5) patrilocal residence; and 6) male initiation ceremonies which are believed to result from the combination of mother-child sleeping, the long poast-partum sex taboo and patrilocal residence.

This article focuses on the effect of environmental extremes and unpredictability on human behavior and reproductive strategies. Significant correlations were found between environmental extremes and unpredictability and several variables, including mobility, subsistence mode, and degree of polygyny.

This article focuses on ecological correlates of sexual division in the control of resources. The author tests several ecological theories put forth by others. Sex coalitions are examined in humans, and sexual dimorphism in resource acquisition and control is discussed.

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.

This article presents two evolutionary models that may explain relationships between war and socialization of children: the "environmentally contingent reproductive strategy" (ECRS) model put forward by Draper and Harpending (1982), and a model put forward by Carol and Melvin Ember. Results do not provide support for the hypotheses involving father-infant sleeping proximity derived from the ECRS model. The authors also find some inconsistencies with their own model.

The authors of this study integrate recent data with data on ancestral ethnic groups' exposure to the slave trade in order to examine the relationship between this historical exposure and children vaccination status against measles. They find evidence to support their hypothesis that children from mothers whose ancestors belonged to an ethnic group that exported slaves are less likely to be vaccinated against measles, theorizing that this correlation stems from distrust in medical and governmental institutions. Supporting this theory, they also find that groups historically exposed to the slave trade that have higher preference for traditional practices are even less likely to vaccinate their children against measles.

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 study seeks to examine the influence that UV radiation and climate might have on gender inequality, and tests two extant theories on why gender inequality exists -- the life-history theory (aligned with climate) and the cognitive performance theory (aligned with UV radiation). The model with UV radiation as the main predictor fits the data on gender inequality the best, and pathogen prevalence and the ACP1*B allele were also found to be associated with gender inequality. The model was found to be robust across continents and ancestry. The study also highlights the need for further research to better understand the complex interplay of these factors in different cultures.

This study examines husband-wife relationships, specifically rooming and sleeping arrangements, as they relate to variables such as infant care, subsistence, residence, and cultural complexity. Several hypotheses are tested and all are supported.

Dietary variation has been implicated in population-level heath outcomes such as adult height and infant health. Here the author investigates these relationships in a sample of 118 nonindustrial societies, providing a comparative and quantitative assessment of nutrition and health cross-culturally.