Biological differences between liberals and conservative are not confined to the high powered computing organ that fills the space between our ears. They also can be found in the more mundane aspects of our physiology. Take sweat. Sweat, or at least the process that produces wet pits, clammy palms, and attendant social awkwardness, provides interesting insights into our psychology, including our political psychology. Indeed, psychophysiologists have been fascinated with the whole phenomenon for decades and have devoted considerable time and energy to understanding the process of perspiration.

An obvious reason for all this interest is the organ where sweat happens: the skin. Neuroscience might be the glamour field for investigating the biological basis of social attitudes and behavior but skin is also a sensory and processing organ, and a big one at that. Of the 78 organs in the human body, skin is by far the largest, accounting for 20 to 25 pounds of a person’s total body weight. By way of comparison, a typical brain weighs in at a comparative paltry 3 pounds or so. Importantly, skin is not just a prophylactic barrier to keep germs out of your body, nor is it just a nice soft sheath that wraps you in a socially presentable package. It is also an information processing organ that is responsive to a variety of signals originating within and outside our bodies. Those signals can be picked up by measuring changes in the electrical properties of skin, which have long been known to fluctuate based on internal psychological states (these fluctuations are generically known as electrodermal activity, or EDA). This is why EDA has been a central part of polygraph (lie detector) protocols for decades. Moreover, compared to electrical activity in the brain, measuring the skin’s electrical properties is easy, cheap and can be done with an extremely high degree of accuracy.

True, this accuracy has not provided a foolproof way to figure out if a given individual is speaking gospel or telling tall tales. Polygraphs, after all, can be beaten by the guilty and damn an innocent as a liar. Yet there is no doubt that EDA can tell us something important about general patterns of (autonomic) nervous system activity. We know this because, unlike some of the mysterious processes of the brain, scientists have a pretty good grasp on what makes us sweat. Sweating is the result of the skin responding to signals coming from the sympathetic nervous system (SNS), the part of nervous system that quickly and without conscious input    prepares the body for action. Part of this preparation entails opening sweat glands. When the SNS activates these glands, moisture is drawn to the surface of the skin, sort of like racks of teeny straws sucking up fluid.  A hot room or the thought of a hot date can both induce sweat, but only the former involves ambient temperature. The latter is an example of the SNS responding to an internal psychological rather than an external environmental state. It is responses to those internal signals that most interest us, and we can investigate the topic pretty effectively because one type of sweat gland, the eccrine gland, is particularly sensitive to SNS signals generated by internal psychological states. Eccrine glands are densely concentrated in the palms of our hands, and the key thing to remember is that when the SNS perks up because of an internal psychological state like fear or arousal, thousands of those little straws in and around our palms start sucking moisture toward the surface of the skin.

Bunny Rabbit

Non-threatening Image

SNS activity can be inferred by the electrical properties of the skin. Just as the most efficient way to get an electric current from one end of a bathtub to the other is to fill it with water, skin in the vicinity of open eccrine glands will conduct electricity faster than skin with less moisture. Those little straws can be thought of as a dense array of electrical resistors controlled by the SNS; as moisture moves up and down inside them they regulate how efficiently the skin can conduct an electrical current. That fluctuation in conductance or resistance (EDA) directly measures SNS activation or deactivation. This well-understood phenomenon makes EDA a simple and direct means of measuring SNS activation. Run a (very) small electrical current between two sensors on the fingertips or the palm and measure changes in that current. If the current spikes in response to a particular stimulus, it is safe to conclude that the stimulus is jacking up the subject’s SNS. If the current drops, the SNS is gearing down.


Threatening Image

The SNS is often referred to as the body’s “fight or flight” system. This is accurate as far as it goes. Still, fight or flight is an incomplete description of what the SNS does. The SNS perks up when we need to pay attention or think hard. It mobilizes resources that we might need when we have to take any sort of action, be it action in response to a snake slithering toward us,  tackling a tenth-grade algebra problem, or anticipating a reunion with a loved one.

At this point you might be thinking thanks for reminding me to get some anti-perspirant, but what does this have to do with your politics?  Well, if political orientations are biologically based, stable individual-level differences in SNS activation seem like good place to look for them, and indeed a number of studies have found that SNS activation correlates with particular sets of political attitudes and behaviors. One of these studies was conducted by our lab back in 2008. We brought in about 50 adults and showed them several images on a computer screen—everything from babies and cute bunnies to animals of a more threatening nature. We were interested in the individual level differences in EDA response to threatening versus non-threatening images. What we found was that the pattern of EDA response to these images was systematically correlated with a particular set of policy positions. We termed these “socially protective policies” because that is exactly what they seemed to reflect: policies designed to protect the interest of the participant as well as the participant’s social group from threats. These issues included the death penalty, immigration, foreign aid, and gun control.

Graph of Results

Liberal vs. Conservative EDA Response to Threatening Images

We found that individuals with conservative positions on socially protective policies stands (the blue bars in the graph below) demonstrated significant SNS activation in response to threatening images, compared with a modest deactivation in response to non-threatening images.  This pattern contrasted strongly with that found for individuals with liberal positions on socially protective policies (the red bars in the graph below).  Liberals showed essentially no SNS activation in response to the threatening images.  It’s not that those with liberal positions on these issues were unaware of the threat – when asked, they rated the threatening images as more threatening than the neutral images - they just didn’t have the same somatic experience of threat that the conservatives had.  We think that this supports the notion that individual-level differences in physiology predispose people to the adoption of particular political attitudes. In this particular case, people who were more physiologically responsive to threat stimuli were more susceptible to arguments in favor of policies aimed at reducing, or at least addressing, threats to the social status quo. It seems to us that this is exactly what conservatives are referring to when they say that liberals ‘just don’t get it’ on topics like meeting with foreign dictators that are enemies of the US.  If liberals really perceived this then the palm of the hand they extend to those enemies shouldn’t be quite so dry.


Adapted from Predisposed: Liberals, Conservatives, and the Biology of Political Differences, Routledge Books, Sept 2013.

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