The article tests theories that may explain why warfare frequency varies from society to society. The focus is on ecological problems, particularly different kinds of resource scarcity, but social and psychological theories are also tested with both bivariate and multivariate analyses. Because unpredictable disasters are such a strong predictor in nonstate societies, the authors theorize that war may mostly be caused by a fear of nature.

This study retests the data presented by Sillitoe (1977) in his study of the relationship between likelihood of warfare and population density in New Guinea. Contrary to Sillitoe, the author finds a strong and significant association between the two variables. The author also finds a significant relationship between the severity of food shortages and the frequency of warfare cross-culturally.

Using a cross-cultural sample of 91 societies, this paper draws on ecological theory to test if unpredictable environments will favor subsistence diversification. The general hypothesis is that societies with high climate unpredictability and resource stress would exhibit more subsistence diversity than societies in more stable climates. The authors examined four environmental and resource stress variables while controlling for temperature variance, subsistence activity, and phylogeny. Support was found for 2 of the 4 variables--chronic scarcity and environmental instability. In the discussion they suggest that more commonly observed events (e.g. annual hunger and climate unpredictability) may give people more motivation to change subsistence than rarer events (e.g. natural hazards and famine).

This study examines instances of group fission cross-culturally. Results suggest that internal political conflict and resource scarcity are the two most common causes of group fission. Results also suggest that group fission tends to occur along kin lines.

This article builds on previous cross-country and cross-state research into Tightness-Looseness (TL) theory, which proposes relationships between the incidence of ecological threat and cultural tightness, as well as tightness’ downstream effects on belief in a moralizing high god, inter-group contact and authoritarian leadership. To evaluate the generalizability of TL theory beyond complex cultures, the authors test these relationships among 86 nonindustrial societies from the ethnographic record. A structural equation model is presented of the results for nonindustrial societies; it is generally in accord with previous findings from more complex societies. Because the nonindustrial sample is more variable, they also look at relationships between societal complexity and kinship heterogeneity, aspects that vary in nonindustrial societies.

The authors of this study explore the relationship between climate variability and beliefs that high gods are associated with the weather. As predicted, they find significant correlations between these beliefs and dry climates. They then evaluate how these findings contribute to their previous understanding of resource stress and its association to beliefs in high gods.

This article tests a series of hypotheses differentiating internal warfare and external warfare. Results support the theory that internal warfare is a population control mechanism more common in patrilocal societies, whereas external warfare occurs between two societies, one of which recently migrated and adopted matrilocal residence. Based on these findings, the authors assert that internal warfare can be regulated while external warfare cannot.

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.

This study follows the theoretical construct of general cultural tightness and looseness (TL). Tightness is thought to be adaptive when facing socioecological threat, such as resource stress, since it involves a greater amount of cooperation. The study asks: "Why do some societies have relatively standardized or uniform clothing and adornment, whereas others have considerable variability across individuals?", which is connected to the broader question of why some societies show more within-group variation. The authors use a sample of 80 non-industrial societies from SCSS, to explore the relationship between general cultural tightness and standardization or synchrony in dress. The results support that tighter societies have more uniformity in dress and that resource stress is a predictor of synchrony. However, it is not supported that egalitarian societies have more synchrony, and that tightness is positively predicted by resource stress.

The author tests various hypotheses regarding cross-cultural occurrence of geophagy, the eating of earth. Nearly 500 years of references to geophagy were compiled into the Database on Human Geophagy, which was then used to examine biological justifications for this little-understood behavior.