There are a series of papers out right now which show the positive relationship between political conservatism and reflexive disgust responses. Instead of summarizing the research myself I will point you to Observations of a Nerd, who does a really good job. The only caution I would add is that the post has a rather disgusting illustration of a toilet, so it seems possible that the author is skewing the readership toward liberals who are more likely to be able to overcome their revulsion!
In any case, as with most psychological models this is a complex one with many shades of gray. For example, it seems likely that human aversion to the odor of rotting meat and bodily waste is reflexive and innate in a very deep sense. There doesn’t need to be a very suble adaptive explanation for this since the risks of consuming bad meat are rather high (I have read that the majority of the mild illneses experience in our lives are probably due to food poisoning!). On the other hand aversions to specific foods, such as taboos against consumption of certain types of meat, are learned behaviors which tend to crystalize during one’s pre-teen years. Though an aversion to dog or pig meat is not hardwired, proximately the way people respond to these is not learned, but rather a co-option of innate disgust responses which are primed by cultural norms toward specific stimuli.
There is human variation in this. We all know that some people are picky eaters while others are adventurous. This generalizes to many aspects of life in terms of openness to the novel and new. Not surprisingly one of the most significant correlates of political liberalism within the population is openness to the novel and new. Psychologist Jonathan Haidt has constructed a model to explain the emergence of political worldviews out of lower level moral dispositions, and naturally these moral dispositions themselves probably emerge from even lower psychological biases.
What is the moral, so to speak, of these research projects? One implication is that much political talk (though not all) about the axioms which drive our orientations are simply plausible stories which our conscious pre-frontal cortex generates as a “reasonable” facade on top of deeper emotionally driven commitments. The model that politics derives from explicit principles, as opposed to intuitive dispositions, naturally results in attempts of reasoned “dialogue.” But talking may ultimately be as futile as a discussion about why two individuals differ in their preference for the taste of watermelon.
