What is the origin of individual differences in ideology and personality? According to the parasite stress hypothesis, the structure of a society and the values of individuals within it are both influenced by the prevalence of infectious disease within the society's geographical region. High levels of infection threat are associated with more ethnocentric and collectivist social structures and greater adherence to social norms, as well as with socially conservative political ideology and less open but more conscientious personalities. Here we use (...) an agent-based model to explore a specific opportunities-parasites trade-off hypothesis, according to which utility-maximizing agents place themselves at an optimal point on a trade-off between the gains that may be achieved through accessing the resources of geographically or socially distant out-group members through openness to out-group interaction, and the losses arising due to consequently increased risks of exotic infection to which immunity has not been developed. We examine the evolution of cooperation and the formation of social groups within social networks, and we show that the groups that spontaneously form exhibit greater local rather than global cooperative networks when levels of infection are high. It is suggested that the OPTO model offers a first step toward understanding the specific mechanisms through which environmental conditions may influence cognition, ideology, personality, and social organization. (shrink)

Can ownership status influence probability judgements under condition of uncertainty? In three experiments, we presented our participants with a recording of a real horse race. We endowed half of our sample with a wager on a single horse to win the race, and the other half with money to spend to acquire the same wager. Across three large studies, we found the endowment effect – owners demanded significantly more for the wager than buyers were willing to pay to acquire it. (...) However, we also found that probability estimates of each horse winning the race did not differ between owners and non-owners of the betting slip. Our results demonstrate that distorted perception of probability is unlikely to be a mechanism explaining the endowment effect. (shrink)