Implications of the behavioural immune system for social behaviour and human health in the modern world

Social insect colonies have evolved collective immune defences against parasites. These 'social immune systems' result from the cooperation of the individual group members to combat the increased risk of disease transmission that arises from sociality and group living. In this review we illustrate the pathways that parasites can take to infect a social insect colony and use these pathways as a framework to predict colony defence mechanisms and present the existing evidence. We find that the collective defences can be both prophylactic and activated on demand and consist of behavioural, physiological and organisational adaptations of the colony that prevent parasite entrance, establishment and spread. We discuss the regulation of collective immunity, which requires complex integration of information about both the parasites and the internal status of the insect colony. Our review concludes with an examination of the evolution of social immunity, which is based on the consequences of selection at both the individual and the colony level.

A reconceptualization of stigma is presented that changes the emphasis from the devaluation of an individual's identity to the process by which individuals who satisfy certain criteria come to be excluded from various kinds of social interactions. The authors propose that phenomena currently placed under the general rubric of stigma involve a set of distinct psychological systems designed by natural selection to solve specific problems associated with sociality. In particular, the authors suggest that human beings possess cognitive adaptations designed to cause them to avoid poor social exchange partners, join cooperative groups (for purposes of between-group competition and exploitation), and avoid contact with those who are differentially likely to carry communicable pathogens. The evolutionary view contributes to the current conceptualization of stigma by providing an account of the ultimate function of stigmatization and helping to explain its consensual nature.

Many researchers have claimed that the emotion of disgust functions to protect us from disease. Although there have been several discussions of this hypothesis, none have yet reviewed the evidence in its entirety. The authors derive 14 hypotheses from a disease-avoidance account and evaluate the evidence for each, drawing upon research on pathogen avoidance in animals and empirical research on disgust. In all but 1 case, the evidence favors a disease-avoidance account. It is suggested that disgust is evoked by objects/people that possess particular types of prepared features that connote disease. Such simple disgust are directly disease related, are acquired during childhood, and are able to contaminate other objects/people. The complex disgust, which emerge later in development, may be mediated by several emotions. In these cases, violations of societal norms that may subserve a disease-avoidance function, notably relating to food and sex, act as reminders of simple disgust elicitors and thus generate disgust and motivate compliance. The authors find strong support for a disease-avoidance account and suggest that it offers a way to bridge the divide between concrete and ideational accounts of disgust. (c) 2009 APA, all rights reserved.