For most of human history, researchers believed that social factors alone shaped people's political preferences, attitudes and behavior. But starting in the 1970s, researchers began to identify genetic influences, and that line of research has boomed over the last decade. The result has been a paradigm shift, say political scientists Peter K. Hatemi, PhD, of Pennsylvania State University, and Rose McDermott, PhD, of Brown University, who review the literature in a 2012 paper in the journal Trends in Genetics.

By now, says Hatemi, it's clear that genetic factors play a substantial role in people's political differences. While there is no gene for liberalism, conservativism or any other political trait, he says, a burgeoning number of studies have found that genetic factors interact with environmental and psychological ones to shape everything from whether you turn out to vote to how you feel about such issues as immigration and the death penalty.

Research with twins has been especially helpful in providing that evidence. Hatemi points as an example to one of his own studies, which found that both identical and fraternal twins have similar ideological orientations — until they leave home. After that, only the identical twins maintain their similar viewpoints, while the viewpoints of fraternal twins start diverging.

"Socialization is king when you're at home," says Hatemi. "It's only when children leave home that all these divergences happen."

While such findings have met with some resistance among political scientists and other social science disciplines, psychology is much more open to the idea, says Hatemi. While political science is still debating whether this work is important, he says, "psychology has moved beyond that stage to asking, ‘How does it work? What's the process?'"

John T. Jost, PhD, a psychology professor at New York University, is among the psychologists asking such questions.

The integration of genetics and the social and behavioral sciences "is under way and has the capacity to revolutionize the study of political attitudes and behaviors, among other domains of research," says Jost. Work in the area "is important and groundbreaking, even if it will take years for us to sort out the precise role of genetics in political outcomes," he adds.

—Rebecca A. Clay