The disgusted mind: investigating the effects of parasite stress on social behaviour and beliefs

The parasite-stress theory of values and sociality offers a compelling evolutionary explanation as to why and how there is such wide variation and diversity of cultures and their underlying value and belief systems. Its authors propose that temporal and geographical variation in parasite stress in the ecological environment imposes causal effects on human behaviour by activating the behavioural immune system and motivating assortative sociality, i.e. philopatry, ethnocentrism, xenophobia, and religiosity. High parasite stress levels motivate strong assortative sociality thereby causing group isolation from which values and beliefs then arise and evolve independently and differently from outside groups, resulting in distinct cultural systems. There is an expanding body of correlational evidence to support this theory but critics argue that we should be cautious about attributing causal mechanisms. The main aim of this thesis was to provide some initial experimental tests of the parasite-stress theory. Four studies were conducted in this endeavour. The first study generated a new cross-culturally validated four-factor disgust image set to be employed in the subsequent studies as visual parasite stress. The next study tested whether variation in parasite stress could generate variation in the value given to physical attractiveness as a phenotypic indicator of genetic quality. The third study tested whether variation in parasite stress could lead individuals to diverge in their preferences for assortative versus prosocial rule systems in the formation of a hypothetical new society. Whereas, the final study tested whether variation in parasite stress could generate variation in the expression of assortative social behaviours. Results were mixed. The third study provided support for the parasite-stress theory, while the second and fourth studies did not. However, as these studies did support the evolutionary theory on which the parasite-stress theory is founded, the findings may be products of design issues. The parasite-stress theory is still valid and ripe for experimental investigation