Authors examine suicidality within small-scale non-industrial societies. They use ethnographic data to test two models: deCatanzaro's inclusive fitness model and the bargaining model (suicide attempts as a costly signal of need). Limited support is found for deCatanzaro's inclusive fitness model while strong support is found for the bargaining model. Support for deCatanzaro's inclusive fitness model increased with increasing latitude; authors suggest that in climactically-harsher environments, in which elderly or infirm individuals may impose a higher burden on kin, completed suicide occurs more because it might increase inclusive fitness. Fit of and support for each model were differentially age-dependent.

Researchers coded 473 texts from 53 cultures on suicidal behavior in the Probability Sample Files looking for evidence to support a new theoretical framework called the Costly Apology Model (signaling "I am genuinely remorseful for my actions, and you can trust that I will not do it again," (7)) to explain suicidal behavior that occurs after someone violates one or more social norms. This is theorized to be distinct behavior from the Bargaining Model (signaling "My fitness is genuinely being threatened, and I need your support." (7)) which could explain suicidal behavior after someone suffers harm from another, and from the Inclusive Fitness Model, where suicide occurs as a fitness behavior when an individual cannot reproduce or has a high cost to the fitness of their kin. .

This study seeks to better understand different forms of leadership across non-WEIRD (Western, Educated, Industrialized, Rich, and Democratic) societies, and tests evolutionary theories regarding the qualities of leaders, their functions, and the costs and benefits they incur and provide as a part of their leadership. The authors assess the various aspects of leaders and leadership by coding 109 dimensions of leadership as represented in eHRAF World Cultures, using the Probability Sample Files, comprised on 60 cultures. By assessing the prevalence of each of these dimensions in the various cultures under consideration, the authors were able to ascertain some largely universal characteristics of leaders: that they 1) were judged intelligent and knowledgeable; 2) resolved conflicts; and 3) received material and social benefits. They also found that other dimensions varied by considerably group context (e.g., kin group leaders tended to be older), subsistence strategy (e.g., hunter-gatherer leaders tend to lack coercive authority), and gender (e.g., female leaders are more associated with family contexts). Further analyses showed that followers and leaders both benefited from leadership, and that shamans constitute a new brand of leader that both utilizes prestige and dominance in order to effectively rule.