When nasty breeds nice: threats of violence amplify agreeableness at national, individual, and situational levels.

Humans have perennially faced threats of violence from other humans and have developed functional strategies for surviving those threats. Five studies examined the relation between threats of violence and agreeableness at the level of nations, individuals, and situations. People living in countries with higher military spending (Study 1) and those who chronically perceive threats from others (Study 2) were more agreeable. However, this threat-linked agreeableness was selective (Studies 3-5). Participants primed with threat were more agreeable and willing to help familiar others but were less agreeable and willing to help unfamiliar others. Additionally, people from large families, for whom affiliation may be a salient response to threat, were more likely than people from small families to shift in agreeableness. Returning to the national level, military spending was associated with increased trust in ingroup members but decreased trust in outgroups. Together, these findings demonstrate that agreeableness is selectively modulated by threats of violence.