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 article explores differences between "tight" cultures ("have many strong norms and low tolerance of deviant behavior") and "loose" cultures ("have weak social norms and high tolerance of deviant behavior"). The tightness-looseness measure manifests in a myriad of macro and micro phenomena, from governance and religiosity to individual psychological processes. This study investigates these phenomena in modern nations rather than traditional societies. Potential ecological, historical, and socio-political predictors of tightness-looseness are also examined.