Researchers sampled 48 societies cross-culturally to study the genetic survival of male homosexual preference, which is argued to be deleterious in nature due to its fertility costs. The researchers test for a sexually antagonistic factor that would produce a pleotropic advantage, such as male homosexual preference increasing the reproduction of sisters. Utilizing theoretical models, researchers assert that the survival of male homosexual preference is a result of the positive association between social stratification and discriminate female hypergyny due to selection for attractiveness in females.

The second and third parts of this book classify the economic systems of foraging and agricultural societies in the SCCS based on correlations between their institutions of property an distribution. These economic types are then examined for relationships with other social, political, demographic, and environmental factors in order to draw tentative conclusions regarding the origins of the Agricultural and Industrial Revolutions. The fourth part of the book uses cross-national data to examine similar associations in industrial/service economies, and is not included here.

The "equi-complexity hypothesis" suggests that there is an equal complexity across languages, meaning that there are constant trade-offs between different domains. Using phylogenetic modelling in a sample of 244 languages, this study follows a diachronic perspective to explore if there is an inversed coevolution within the grammatical coding of nominal and verbal domains. The results show that while there appears to be a coevolutionary relationship between some features of these two domains, there is no evidence to support the idea that all languages maintain an overall equilibrium of grammatical complexity. Rather, the correlation nominal and verbal domains vary between lineages. Austronesian languages do not show a coevolution between the domains. Sino-Tibetan languages seem to have a positive correlation while Indo-European languages appear to have a negative correlation, meaning that this inverse coevolution can be lineage specific.

This chapter examines the relationship between male parental behavior and influences of species, ecological and social factors. The authors first present a cross-phylogenetic perspective on paternal differences between species, then offer two quantitative studies: a comparative study of non-western human societies that correlates father-infant proximity with socioecological factors and another about father-infant proximity among the !Kung.

The researchers develop and compare two evolutionary models to evaluate the association between social stratification and female genital modification(FGMo) in a cross-cultural African sample, theorizing that social hierarchy creates competition for high-value males in which FGMo acts as a costly demonstration of paternity certainty. Although the null model outperforms the stratification model when applied to empirical data, an association between FGMo and stratification is found in the expected direction. The authors suggest that while stratification may be an important factor in the de novo origins of FGMo, spread and persistence of the practice subsequently become more heavily dependent on other selective forces.

Researchers tested the popular identity fusion theory, which states that while maintaining one’s own individual identity, a deep affinity with one’s group can contribute to sacrifice for that group, in conjunction with their own hypotheses, using a behavior economic experiment. The experiment looked at whether after rolling a die to determine which cup a coin was placed into, participants actually followed the rules, or favored themselves (by putting the coin into their own cups at a disproportionate rate). The findings state that while on average, the individual participants did indeed favor themselves, those with higher ingroup fusion were more likely to sacrifice coins to other members of their ‘ingroup.' The experiments were conducted in 8 culturally diverse field sites.

This paper seeks to understand how the conflict resolution strategies of indigenous and non-indigenous groups differ in their efficacy. The authors suggest that indigenous methods of conflict resolution are more effective than non-indigenous methods by demonstrating that subjects from the Outline of Cultural Materials (OCM) associated with indigenous conflict management (ICM) will co-occur less frequently with OCM terms related to conflict than subjects related to non-ICM. They tested this by selecting OCM subjects that they felt best represented ICM, non-ICM, and instances of conflict and using chi-square tests to show how often these subjects co-occurred. They subsequently split up the "conflict" variable into four forms of conflict in order to show whether any of these forms might be more frequently found associated with ICM or non-ICM subjects. The results showed that conflict subjects were more likely to co-occur with non-ICM subjects, and that sociocultural/interpersonal conflicts were more likely to be associated with ICM subjects, whereas political conflicts were more likely to be associated with non-ICM subjects.

This article tests four hypotheses regarding scarification, which is described as 1) a rite of passage, 2) a hardening/trauma procedure, 3) a nonadaptive sexually selected character, or 4) an adaptive pathogen driven sexually selected character. Only the third hypothesis is supported in a worldwide sample, suggesting that scarification is associated with polygyny. The other three are each supported in different regional subsamples—principally the first hypothesis (supported in Africa, the Insular Pacific, and South America).

The research examines daily food sharing norms of 73 preindustrial societies from the Standard Cross-Cultural Sample. Multilevel regression models reveal that hunting and less predictable environments are not indicative of everyday food sharing, but offer support for many other predictions. Animal husbandry, external trade, daily labor sharing, and the presence of food storage are all predictive of daily food sharing practices whereas sharing is less common amongst large and stratified societies. These results align with evolutionary theories for food sharing practices.

The author analyzes 76 societies synchronically, positing that the evil eye belief functions as a useful heuristic and prosocial/cohesive element in weakly-institutionalized societies with significant wealth inequality; in particular, the evil eye belief is found to be more prevalent in agro-pastoral societies where material wealth is vulnerable and plays a dominant role in subsistence economy.