Jon Haidt: University of Virginia Department of Psychology

Morality has long been thought to come from outside – from God, society, or parents – into children, who are empty vessels. In contrast, an “externalization” model is presented in which four cognitive/affective modules generate intuitions about social events. The modules respond to issues of harm/suffering, reciprocity/fairness, hierarchy/duty, and purity/piety. (This theory draws heavily on the works of A. Fiske and R. Shweder.) The modules were created by natural selection, but they co-evolved with cultural learning. Cultures create variable sets of virtues that are grounded in and constrained by the four modules. The case of the purity module is worked out in detail, including experimental demonstrations that flashes of irrelevant disgust (triggered by hypnosis, or by working at a dirty desk) make moral judgments more severe.
http://www.bec.ucla.edu/papers/Haidt_1-31-05.pdf