In this article the researcher conducted five different studies on in-group or "we-group" vs out-group or "they-group" discrimination practices. Two previous hypotheses are re-examined, the pathogen stress hypothesis and the rice-wheat hypothesis, in order to explain heightened ingroup-outgroup differentiation, before turning to overarching geographical hypothesis. Each of the five studies look at a different group of societies cross-culturally, ending in an index of intergroup discrimination by individuals across 222 countries in study 5. All five studies conclude that differentiation between us and them varies based on geographical location and more specifically, along latitude.

In this article the researcher conducted five different studies on in-group or "we-group" vs out-group or "they-group" discrimination practices. Two previous hypotheses are re-examined, the pathogen stress hypothesis and the rice-wheat hypothesis, in order to explain heightened ingroup-outgroup differentiation, before turning to overarching geographical hypothesis. Each of the five studies look at a different group of societies cross-culturally, ending in an index of intergroup discrimination by individuals across 222 countries in study 5. All five studies conclude that differentiation between us and them varies based on geographical location and more specifically, along latitude.

This study, primarily a review on the evolution of the human diet, also includes a small study on the distribution of meat-eating and its relationship with climate and cultural factors, namely subsistence type. The authors find that societies with subsistence strategies that prioritize fishing, hunting, or pastoralism also tend to consume more animal products, whereas those that focus on agriculture have more plant-based diets. The authors argue that these small-scale societies have a healthier approach to diet than industrialized societies regardless of their subsistence type or meat consumption.

The researchers test the relationship between toolkit complexity and diversity as defined by Oswalt (1973) and environmental and demographic variables. Neither population size nor risk of resource failure predict toolkit characteristics among all groups in the sample. However, population size is significantly positively correlated with toolkit diversity and complexity among food-producers, whereas environmental factors indicating risk of resource failure are significantly positively correlated among hunter-gatherers. This leads the researchers to suggest that food-producers' effectiveness at niche construction is a result of their large population size, which thus has a larger effect on toolkit composition than does environmental risk relative to hunter-gatherers.

The present study examines the effect of social status on stature sexual dimorphism and whether food security acts as a mediator for this relationship. In societies where females have high social status and can exercise mate choice, there is lower stature sexual dimorphism. Food security enhances these results. Conversely, there is greater stature sexual dimorphism in societies where females have low social status and cannot exercise mate choice, especially if there is food insecurity.

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.

Authors investigate the prevalence of male homosexual preference (MHP) cross-culturally. They employ four models to test the link between level of social stratification and the probability of observing male homosexual preference (MHP). Authors believe that this link supports the hypergyny hypothesis, which proposes that increased social stratification allows for some sort of factor that improves functional female fertility, perhaps through marriage to men of higher social classes. This would thereby allow more access to resources and consequently the ability to support a greater number of more reproductively-successful offspring. Authors do not make a causal link, however; rather, social stratification may be associated with a yet-undetermined pleiotropic factor that is somehow positive despite its cost on functional male fertility.

This study, primarily a review on the evolution of the human diet, also includes a small study on the distribution of meat-eating and its relationship with climate and cultural factors, namely subsistence type. The authors find that societies with subsistence strategies that prioritize fishing, hunting, or pastoralism also tend to consume more animal products, whereas those that focus on agriculture have more plant-based diets. The authors argue that these small-scale societies have a healthier approach to diet than industrialized societies regardless of their subsistence type or meat consumption.

The 'obstetrical dilemma' postulates that human females evolved a pelvis shape that was a compromise between the needs of bipedal locomotion and the need for a wider pelvic opening. The implication is that the female pelvis should be similar across the world. Researchers examine the size and shape of the birth canal of female individuals in the Goldman and Human Origin datasets. Contrary to the 'obstetrical dilemma,' the findings reveal that there is indeed significant geographical variation in size and shape of the female birth canal. Neutral evolutionary processes, particularly genetic drift, were suggested to be influential in female canal shape whereas the predicted effects of climate on canal diversity were only minimal.

A model for the development of counting systems is tested. The hypothesis presented predicts that unpredictable climate conditions result in inconsistent food supply which leads to the need for food storage and, thus, a system to account for the stored food. Results strongly support this hypothesis.