The difference between liberals and conservatives may be explained by psychological and biological predispositions, a new article published in the Cambridge Journal explains.

Political scientists John Hibbing and Kevin Smith from the University of Nebraska-Lincoln, and John Alford from Rice University, in “Differences in negativity bias underlie variations in political ideology” argue that political bias is not always a conscious choice, or even a product of our upbringing. They claim that genetics and physiology play a large role in which way a person leans politically.

The scientists conducted experiments in which subjects were shown both positive and negative images or asked to judge facial expressions. Some of the negative images included spiders, burning houses, and infected wounds. The subjects’ reactions were monitored, including by an eye-tracking device recording involuntary responses. The scientists found that people who self-identified as conservative tended to react faster and spend more time focused on the negative images than those who self-identified as liberal.

“It is not surprising,” said the authors, “that those attuned to the negative in life might take steps to avoid it, perhaps by refraining from taking chances with the unknown, by following instructions, and by sticking to the tried and true.”

“[N]ot only do political positions favoring defense spending, roadblocks to immigration, and harsh treatment of criminals seem naturally to mesh with heightened response to threatening stimuli but those fostering conforming unity (school children reciting the pledge of allegiance), traditional lifestyles (opposition to gay marriage), enforced personal responsibility (opposition to welfare programs and government provided healthcare), longstanding sources of authority (Biblical inerrancy; literal, unchanging interpretations of the Constitution), and clarity and closure (abstinence-only sex education; signed pledges to never raise taxes; aversion to compromise) do, as well. Heightened response to the general category of negative stimuli fits comfortably with a great many of the typical tenets of political conservatism.”

The authors conclude,

“Thus, it is reasonable to hypothesize that individuals who are physiologically and psychologically responsive to negative stimuli will tend to endorse public policies that minimize tangible threats by giving prominence to past, traditional solutions, by limiting human discretion (or endorsing institutions, such as the free market, that do not require generosity, discretion, and altruism), by being protective, by promoting ingroups relative to out-groups, and by embracing strong, unifying policies and authority figures.”

Read the authors’ full report at the Cambridge Journal.