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

Dr. Lindon J. Eaves, a professor of human genetics and psychiatry at Virginia Commonwealth University, said the new research did not add much to this. Dr. Eaves was not involved in the study but allowed the researchers to analyze data from a study of twins that he is leading.

Still, he said the findings were plausible, "and the real significance here is that this paper brings genetics to the attention to a whole new field and gives it a new way of thinking about social, cultural and political questions."

In the study, three political scientists -- Dr. John Hibbing of the University of Nebraska, Dr. John R. Alford of Rice University and Dr. Carolyn L. 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 questions asked people "to please indicate whether or not you agree with each topic," or are uncertain on issues like property taxes, capitalism, unions and X-rated movies. Most of the twins had a mixture of conservative and progressive views. But over all, they leaned slightly one way or the other.

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.