Political leanings may be etched in the genes

But study says party affiliation is linked to environment

Tuesday, June 21, 2005

By BENEDICT CAREY
THE NEW YORK TIMES

Political scientists have long held that people's upbringing and experience determine their political views. A child raised on peace protests and Bush-loathing generally tracks left as an adult, unless derailed by some powerful life experience. One reared on tax protests and a hatred of Kennedys usually lists to the right.

But on the basis of a new study, a team of political scientists is arguing that people's gut-level reaction to issues such as the death penalty, taxes and abortion is strongly influenced by genetic inheritance. The new research builds on a series of studies that indicate that people's general approach to social issues -- more conservative or more progressive -- is influenced by genes.

Environmental influences such as upbringing, the study suggests, play a more central role in party affiliation as a Democrat or Republican, much as they do in a person's affiliation with a sports team.

The report, which appears in the current issue of the American Political Science Review, the profession's premier journal, uses genetics to help answer several open questions in political science.

They include why some people defect from the party in which they were raised and why some political campaigns, like the 2004 presidential election, turn into verbal blood sport, though polls find little disparity in most Americans' views on specific issues such as gun control and affirmative action.

The study is the first on genetics to appear in the journal. "I thought, 'Here's something new and different by respected political scholars that many political scientists never saw before in their lives,' " said Lee Sigelman, editor of the journal and a professor of political science at George Washington University.

Sigelman said that in many fields the findings "would create nothing more than a large yawn," but that "in ours, maybe people will storm the barricades."

Geneticists who study behavior and personality have known for 30 years that genes play a large role in people's instinctive emotional responses to certain issues -- their social temperament.

It is not that opinions on specific issues are written into a person's DNA. Rather, genes prime people to respond cautiously or openly to the mores of a social group.

Only recently have researchers begun to examine how these predispositions, in combination with childhood and later life experiences, shape political behavior.

In the study, three political scientists -- John Hibbing of the University of Nebraska at Lincoln, John Alford of Rice University and Carolyn Funk of Virginia Commonwealth -- combed survey data from two large continuing studies, including more than 8,000 sets of twins.

From an extensive battery of surveys on personality traits, religious beliefs and other psychological factors, the researchers selected 28 questions most relevant to political behavior.

The researchers then compared dizygotic or fraternal twins, who, like any biological siblings, share 50 percent of their genes, with monozygotic, or identical, twins, who share 100 percent of their genes.

Calculating how often identical twins agree on an issue and subtracting the rate at which fraternal twins agree on the same item provides a rough measure of genes' influence on that attitude. A shared family environment for twins reared together is assumed.

On school prayer, for example, the identical twins' opinions correlated at a rate of 0.66, a measure of how often they agreed. The correlation rate for fraternal twins was 0.46. This translated into a 41 percent contribution from inheritance.

As found in previous studies, attitudes about issues such as school prayer, property taxes and the draft were among the most influenced by inheritance, the researchers found. Others like modern art and divorce were less so. And in the twins' overall score, derived from 28 questions, genes accounted for 53 percent of the differences.

But after correcting for the tendency of politically like-minded men and women to marry each other, the researchers also found the twins' self-identification as Republican or Democrat was far more dependent on environmental factors such as upbringing and life experience than was their social orientation, which the researchers call ideology. Inheritance accounted for 14 percent of the difference in party, the researchers found.

"We are measuring two separate things here, ideology and party affiliation," Hibbing, the senior author, said.

He added that his research team found the large difference in heritability between the two "very hard to believe," but that it held up.

The implications of this difference may be far-reaching, the authors argue. For years, political scientists tried in vain to learn how family dynamics such as closeness between parents and children or the importance of politics in a household influenced political ideology. But the study suggests that an inherited social orientation may overwhelm the more subtle effects of family dynamics.

A mismatch between an inherited social orientation and a given party may also explain why some people defect from a party. Many people who are genetically conservative may be brought up as Democrats, and some who are genetically more progressive may be raised as Republicans, the researchers say.

In tracking attitudes over the years, geneticists have found that social attitudes tend to stabilize in the late teens and early 20s, when young people begin to fend for themselves.

Some "mismatched" people stay loyal to their family's political party. But circumstances can override inherited bent. The draft may seem a good idea until your number is up.

The researchers are not optimistic about the future of bipartisan cooperation or national unity. Because men and women tend to seek mates with a similar ideology, they say, the two gene pools are becoming, if anything, more concentrated, not less.

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