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.
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 like 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 that the twins’ self-identification as Republican or Democrat was far more dependent on environmental factors like 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.
Here is the nasty clincher:
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.
Here is the full story.