TUESDAY, July 1 (HealthDay News) -- Heading to the polls on Nov. 4? If so, your genes may be driving you there, a new study suggests.

In fact, as much as 50 percent of whether you vote or not may be genetically determined, says a team at the University of California, San Diego. Genes may even be more important to your tendency to cast a ballot than family political history.

"Both nature and nurture play a role in voting," said lead author James H. Fowler, an associate professor of political science. "We expected genes would play a little bit of a role, but we were surprised how strong [a] role they played."

Previously, experts primarily focused on the environmental factors that pushed people to vote. "For a long time, they thought that parents and children have pretty much the same behavior when it comes to voting," Fowler said. "If they voted, it's likely you will go to the polls as well."

But, rather than transmitting ideas, "parents are transmitting genes," Fowler now believes.

He co-authored a report on the issue, published in July's The Journal of Politics.

In the study, Fowler and Ph.D. candidate Christopher T. Dawes drew on voter-turnout data in Los Angeles. They matched that data to a registry of identical and non-identical twins.

According to that analysis, 53 percent of the variation in voter turnout is due to differences in genes.

In fact, family upbringing appears to have little effect on how regularly offspring participate in elections. "The other half of the voting behavior was mostly attributable to the unshared environment between the two twins," Fowler said.

To try to replicate the findings more broadly across the country, Fowler and Dawes looked at nationwide voting patterns using the National Longitudinal Study of Adolescent Health, which ran from 1994 to 2002.

Using the genetic data in this study, Fowler and Dawes found that 72 percent of differences in voter turnout among identical twins can be accounted for by genes.

Genes also play a significant role in political participation, including giving money to a campaign, contacting a government official, running for office and attending political rallies, the two researchers found.

Fowler and Dawes also looked for specific genes involved in the decision to vote. They found that two genes that influence the brain's serotonin system, called MAOA and 5HTT, were also associated with a person's inclination to cast a ballot. The serotonin system helps regulates trust and social interaction, the experts noted.

In fact, they found that people with more efficient versions of those genes were about 10 percent more likely to vote.

"It's not just the gene that makes you vote, but it has an impact on how susceptible you are to different kinds of environments," Fowler said. "Depending upon what kind of environment you are in, it is going to activate those tendencies you might have to cause you to participate in politics or not."

To thoroughly understand politics, one has to include genetics, Fowler now believes.

"To study politics without genes is to miss half the story," he said. "To really get an understanding of what people are doing and why they are doing it, we need to integrate both nature and nurture into the study of politics," he said.

According to John T. Jost, a professor of psychology at New York University in New York City, this article is another in a growing list of studies suggesting that political orientation is partly heritable.

"In some ways, this conclusion is not so surprising, given that we have known for over 50 years that there are basic cognitive, motivational, and behavioral differences between leftists and rightists," Jost said.

"Unless one believes that basic psychological characteristics have no genetic antecedents whatsoever, one would have anticipated these results on the basis of the psychological literature," Jost said. "Still, it's quite important that these researchers appear to have identified specific gene combinations that are linked to political orientation," he said.

More information

There's more on how the brain works at Harvard's Whole Brain Atlas.