Born this way? Nature, nurture, narratives, and the making of our political personalities.

• Author: Haidt, Jonathan
• Position: Cover story

As A NATION, we've made great strides overcoming our differences. North vs. South, Catholic vs. Protestant, black vs. white. These divisions once brought forth extraordinary animosity. Even male vs. female had its day in the sun, for those of us old enough to remember the absurd 1973 tennis match between Bobby Riggs and Billie Jean King. Those differences have not disappeared, but the urgency and rancor has faded.

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There is one difference, however, that is widening into a chasm and threatening to split the nation into two dysfunctional halves: left vs. right. Voters themselves have spread out only a bit in the last 10 years: Gallup reports a decline in the number of people calling themselves centrists or moderates (from 40 percent in 2000 to 36 percent in 2011), a slight rise in the number of conservatives (from 38 percent to 41 percent), and a slight rise in the number of liberals (from 19 percent to 21 percent).

But the political class, the political parties, and the media have completely changed their game since the 1980s. Politics used to be hardball: very competitive, but at the end of the day, Ronald Reagan and Tip O'Neill could meet for a drink and a private conversation. Congressmen and senators had the sense that they all belonged to a grand institution. They had enough in common, and enough friends across the aisle, that they could work together on solving the nation's biggest challenges, from facing down the Soviets to dismantling Jim Crow.

Not any more. Now it's cage-match wrestling, and there is a lot more blood. As long-serving former congressman Rep. Jim Cooper (D-Tenn.) put it in September, "This is not a collegial body any more. It is more like gang behavior. Members walk into the chamber full of hatred."

What is going on here? Part of the answer will come from historians who can trace out the events of recent decades and their effects on our political institutions. But part of the answer must come from psychology. In the last 10 years we psychologists have discovered a great deal about the origins of ideology and why ideology makes it so hard for people to understand, respect, and accept each other. This research partly confirms what Gilbert and Sullivan said in the light opera Iolanthe: "Nature always does contrive / That every boy and every gal / That's born into the world alive / Is either a little Liberal / Or else a little Conservative!" But the story is more interesting than that.

(A note about political diversity: People don't come in just two types. Unfortunately, most research on political psychology has used the left-right dimension with American samples, so in many cases that's all we have to go on. But I should also note that this one dimension is still quite useful. Most people in the United States and in Europe can place themselves somewhere along it--though usually somewhere near the middle. And it is the principal axis of the American culture war and of congressional voting, so even if relatively few people fit perfectly into the extreme types I'm going to describe, understanding the psychology of liberalism and conservatism is vital for understanding a problem that threatens the entire nation.)

What Is Ideology?

Here's a simple definition of ideology: "a set of beliefs about the proper order of society and how it can be achieved." And here's the most basic of all ideological questions: Should we preserve the present order or change it?

Political theorists since Marx had long assumed that people chose ideologies to further their self-interest. The rich and powerful want to preserve and conserve; the peasants and workers want to change things (or at least they would if their consciousness could be raised and they could see their self-interest properly, said the Marxists). But while social class may once have been a good predictor of ideology, that link has been largely broken in modern times, when the rich go both ways (industrialists mostly right, tech billionaires mostly left), and so do the poor (rural poor mostly right, urban poor mostly left). And when political scientists looked into it, they found that self-interest does a remarkably poor job of predicting political attitudes.

So for most of the late 20th century, political scientists embraced blank-slate theories in which people soaked up the ideology of their parents or the TV programs they watched. Some political scientists even said that most people were so confused about political issues that they had no real ideology at all.

But then came the studies of twins. In the 1980s, when scientists began analyzing large databases that allowed them to compare identical twins (who share all of the same genes, plus, usually, their prenatal and childhood environments) to same-sex fraternal twins (who share half of their genes, plus their prenatal and childhood environments), they found that the identical twins were more similar on just about everything. What's more, identical twins reared in separate households (because of adoption) usually turn out to be very similar, whereas unrelated children reared together (because of adoption) rarely turn out similar to each other, or to their adoptive parents; they tend to be more similar to their genetic parents. Genes contribute, somehow, to just about every aspect of our personalities.

We're not just talking about IQ, mental illness, and basic personality traits such as shyness. We're talking about the degree to which you like jazz, spicy foods, and abstract art; your likelihood of getting a divorce or dying in a car crash; your religiosity; and your political orientation as an adult. Whether you end up on the right or the left of the political spectrum turns out to be just as heritable as most other traits: Genetics explains between one-third and one-half of the variability among people in their political attitudes. Being raised in a liberal or conservative household accounts for much less.

How can that be? How can there be a genetic basis for attitudes about nuclear power, progressive taxation, and foreign aid when these issues emerged only in the last century or two? And how can there be a genetic basis for ideology when people sometimes change their political parties as adults?

Innate does not mean "hard-wired" or unmalleable. To say that a trait or ability is innate just means it was "organized in advance of experience" The genes guide the construction of the brain in the uterus, but that's only the first draft, so to speak. The draft gets revised by childhood experiences. To understand the origins of ideology you have to take a developmental perspective, starting with the genes and ending with an adult voting for a particular candidate or joining a political protest. There are three major steps in the process.

Step 1: Genes Make...