We all like to think that our political views are shaped by our personal experiences and by deep reflection on the great issues of the day. Yet research suggests that they may also be influenced by our biology.

An experiment in the United States has revealed that a person’s political leanings tend to correspond remarkably closely with physiological traits, indicating that nature, as well as nurture, could play a defining role.

The positions people take on a range of “hot button” issues in US politics, including Iraq, gun control, the death penalty and abortion rights, can be predicted accurately from the way their bodies respond to frightening stimuli, scientists say.

While the results do not prove that biology moulds liberal or conservative beliefs, they suggest that it could be an important factor. A likely explanation is that genetic differences in brain activity may affect bodily responses and political outlooks.

The findings, from a team led by Douglas Oxley, of the University of Nebraska, are consistent with previous studies, which found that political beliefs are highly heritable.

Identical twins, who share all their genes, are more likely to have similar views on current affairs and social issues than fraternal twins, who share a similar upbringing but only a proportion of their DNA.

A strong role for biology may explain why people change their core beliefs so rarely.

In the study, the scientists recruited 46 volunteers living in Lincoln, Nebraska, all of whom had strong political beliefs. They were asked for their opinions on a wide variety of controversial issues. All the questions concerned social or international issues, rather than economic matters.

The participants were then given two laboratory tests, to establish their physiological responses to frightening or unexpected stimuli. In the first test, they viewed 33 images, three of which were distressing or threatening: a large spider on the face of a frightened person; a dazed person with a bloody face; and maggots in an open wound. The scientists measured the electrical conductance of the skin, a standard measure of distress and arousal.

In the second test, the volunteers were subjected to a loud, unexpected noise, with scientists measuring the involuntary blinking that followed. A strong startle response is indicative of heightened fear and arousal. The results, which are published in the journal Science, revealed significant differences in both responses, which corresponded with people’s political views. Those with “markedly lower physical sensitivity to sudden noises and threatening visual images” tended to support liberal positions, while those with strong responses tended to be more conservative.

This would fit with the hypothesis that people who have more fearful responses to perceived threats are more likely to be conservative, while those who have weaker responses develop more liberal views.

The scientists considered it likely that “physiological responses to generic threats and political attitudes on policies related to protecting the social order may both derive from a common source”. This was unlikely to be indoctrination by parents and peer-groups, they said, because involuntary reflexes could be altered only with systematic training, which usually involves punishment. More probable was that political outlook and startle responses were affected by differences in brain activity, possibly in the amygdala region, which processes emotions such as fear and disgust. “Amygdala activity is also crucial in shaping responses to socially threatening images, and may be connected to political predispositions,” they said.

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