As several previous posts on this blog, and a giant pile of research from various fields, shows, it isn't that simple. There are all kinds of ways that our beliefs and preferences are sensitive things that don't seem like they should be relevant. In philosopher-speak we often have 'non-epistemic' reasons.
This paper suggests that political affiliation may be related in some way to what in the title is called physiological traits. You might more plainly say 'biology'. This isn't a crazy hypothesis at all. Risk aversion, aggression, and all kinds of other strategic dispositions are related to physiology. And the mixture of strategies in a population, as well as the connections between strategies and other properties of the individual are among the targets for natural selection. So there could well be interesting patterns here.
Douglas R. Oxley and a team of others, in a commendably interdisciplinary team of political scientists, psychologists and others, took on one aspect of the question about political attitudes and physiology. Here's the abstract:
Although political views have been thought to arise largely from individuals' experiences, recent research suggests that they may have a biological basis. We present evidence that variations in political attitudes correlate with physiological traits. In a group of 46 adult participants with strong political beliefs, individuals with measurably lower physical sensitivities to sudden noises and threatening visual images were more likely to support foreign aid, liberal immigration policies, pacifism, and gun control, whereas individuals displaying measurably higher physiological reactions to those same stimuli were more likely to favor defense spending, capital punishment, patriotism, and the Iraq War. Thus, the degree to which individuals are physiologically responsive to threat appears to indicate the degree to which they advocate policies that protect the existing social structure from both external (outgroup) and internal (norm-violator) threats.
First a telephone survey identified individuals with strongly held political beliefs. These individuals then visited the lab and completed a survey including demographic information, and measures of specific political beliefs and personality traits. About two months later each individual made a second visit, during which the physiological measurements were made. The two measurements were skin conductance, and "orbicularis oculi startle blink electromyogram (EMG) response".
This study didn't attempt to study political beliefs in general. Subjects were asked about their level of support for 28 policies or political acts, and 18 were identified as "those most likely to be held by individuals particularly concerned with protecting the interests of the participantsí group, defined as the United States in mid-2007, from threats." (So the list included military expenditure, opposition to foreign aid, etc.) The authors don't endorse the view that any of these positions actually have the protective consequences, merely that "given the common frames of the modern American policy, those most concerned about social protection will tend to be attracted to the particular policy positions listed."
The subjects were divided into two groups for the purposes of the skin conductance response test - those above, and those below, the group median score for concern to protect the social group. Skin conductance was measured during a picture viewing session, where 3 out of 33 pictures were of threatening images "(a very large spider on the face of a frightened person, a dazed individual with a bloody face, and an open wound with maggots in it)". Here are the results:
So there's a significant difference in skin conductance response for threatening images, associated with degree of support for measures aimed at protecting the individual's own social group. (This effect stood up to a further regression analysis controlling for gender, age, income, and education.)
The other physiological measure was the startle blink EMG response. This response habituates, but there are inter-individual differences in the hardness of the blink, which is regarded as indicating a higher level of fear. Subjects wore headphones while looking at a computer screen with a single point they were supposed to focus on. During the staring session each participant was subjected seven times to the threatening stimulus of an unexpected burst of loud white noise. Here are the results (with the same division into groups) in a series of overlapping three event clusters of stimuli, to show habituation:
A different way of looking at the eye blink data ignores the habituation, and presents mean blink amplitude for all seven threatening stimuli, again with the same group division:
So there you go. This is impressive and interesting stuff. And the authors are clear that there is very much that we don't know about the result and what explains it:
Our data [...] do not permit firm conclusions concerning the specific causal processes at work. Particular physiological responses to threat could cause the adoption of certain political attitudes, or the holding of particular political attitudes could cause people to respond in a certain physiological way to environmental threats, but neither of these seems probable. More likely is that physiological responses to generic threats and political attitudes on policies related to protecting the social order may both derive from a common source. Parents could both socialize their children to hold certain political attitudes and condition them to respond in a certain way to threatening stimuli, but conditioning involuntary reflex responses takes immediate and sustained reinforcement and punishment, and it is unlikely that this conditioning varies systematically across political beliefs.
That seems about right. Behavioural genetics in other species suggests that fearfulness, or behaviours associated with it, have some heritable component. And there's independent evidence of various kinds for heritable components of personality (leading to the result I blogged a while ago showing a relationship between iris characteristics and personality). It's an empirical question how much variation in the physiological responses studied is genetic, but we know how to find that out. It will also be interesting to see what sorts of environmental and developmental contingencies (early malnutrition? season of birth? birth order?) bear on the development of the physiological traits.
Needless to say this paper generated some twitchy responses. On a crude reading (not that of the authors) it says conservatives are cowards. But that's not really what it says at all. People who have stronger startle responses tend to support more protective policies, sure, but the authors were careful to say their classification of political views was narrower than "conservative vs. liberal". I couldn't find serious write ups from a quick search, though, so no links. If you know of any substantial coverage, let me know, and I'll add links.
Finally, there's a related paper in Nature Neuroscience that anyone who has read this far might find interesting. The authors (David Amodio and colleagues) claim to show that "greater liberalism was associated with stronger conflict-related anterior cingulate activity, suggesting greater neurocognitive sensitivity to cues for altering a habitual response pattern." (Quoted from the abstract.)
D. R. Oxley, K. B. Smith, J. R. Alford, M. V. Hibbing, J. L. Miller, M. Scalora, P. K. Hatemi, J. R. Hibbing (2008). Political Attitudes Vary with Physiological Traits Science, 321 (5896), 1667-1670 DOI: 10.1126/science.1157627