The answer, according to Talhelm, Haidt and their colleagues: “liberals and conservatives in the same country think as if they were from different cultures.”

These researchers argue that liberals share a propensity for analytic thinking and have

a stronger preference for deep thought and a rejection of simple solutions. Liberals are more tolerant of ambiguity and uncertainty, and they have less of a need for order, structure and closure.

Analytic thinking, in this view, “emphasizes slicing up the world and analyzing objects individually, divorced from context — much like scientific analysis requires thinkers to separate complex phenomena into separate parts.” Talhelm elaborated in a phone conversation: The analytic thinking typical of liberals is “more conscious, more focused on the rules of logic.”

Conversely, these researchers define holistic thinking – which they consider more typical of conservatives — as “seeing scenes as a whole and seeing people as a product of situations.” Talhelm described this style of thought as “more automatic, caught up in emotions, and in some ways less adherent to the rules of logic.”

Talhelm wrote me in an email that “analytic thinkers tend to do better in engineering, and they hold more patents for inventions. But holistic/intuitive thinkers tend to do better in more social fields, such as early childhood education and marketing.” One study in the 1960s, he said, “found that analytic thinkers were more likely to have long hair (for men) and short skirts (women).”

In their 2014 paper, Talhelm and his co-authors

hypothesize that liberals think more analytically because liberal culture is more individualistic, with looser social bonds, more emphasis on self-expression, and a priority on individual identities over group identities.

Conservatives, in this analysis, are more dedicated to their communities and to the idea of community than liberals. Conservatism, they write,

is often associated with rural areas, where people are enmeshed in tight-knit communities and are more likely to know the people they see walking on the street. Conservatism is also associated with interconnected groups, such as churches, fraternities, and the military.

Talhelm and his colleagues suggest a different interpretation for the words “individualism,” which traditionally is associated with conservatism, and “collectivism,” which is often linked to liberalism:

Collectivism is not generalized sharing with “other people.” Collectivism is a system of tight social ties and responsibilities, but less trust and weaker ties toward strangers — a stronger in-group/out-group distinction. Conservatives care deeply about close others, but they may dislike welfare programs because those programs serve strangers or even people from out-groups.

Liberal individualism focuses on the self and personal fulfillment. As Talhelm put it:

If you see the world as all individuals, then welfare recipients are individuals too, just like you. Indeed analytic thinkers are more likely to agree with statements about universalism — “all people are equal”; “an African life is worth as much as an American life.”

Looking at the issue of partisan conflict in historical terms, Keith T. Poole, a political scientist at the University of Georgia, explained via email that polarization was very high before the Civil War, and again in the 1880s and 1890s “at the height of industrial capitalism” when the parties split over “gold vs. silver, taxes, tariffs, labor organization and inflation.” Starting in the 1960s, when race came to the forefront, Poole wrote, other issues involving nothing to do with economics — gun control, gay rights, sexual issues — began to be drawn into the “liberal” vs. “conservative” dimension. Now almost every issue from foreign policy to taxes to lifestyle issues has been drawn into the left vs. right alignment.

The work of Iyengar, Talhelm and Haidt adds a new layer to the study of polarization. In seminal work, scholars like Nolan McCarty, Jacob Hacker and Paul Pierson, political scientists at Princeton, Yale and Berkeley, respectively, have stressed the key role of external factors in deepening our political schism, including inequality, the nationalization of politics, immigration and the fast approaching moment when whites will no longer be in the majority.

David Leege, political scientist emeritus at Notre Dame, provided further insight into the economic forces exacerbating polarization:

the pool of under-employed and unemployed semi-skilled labor and their former managers, accountants, etc. have been ripped from the productive (assembly-line) and social institutions (organized labor, health care, ethnic and industrial bars) that ordered their lives and assured a meaningful place in their communities. For the persons who worked hard and more or less lived by the rules, there is no longer the pride of breadwinning and self-sufficiency brought to home or church or neighborhood interactions. These people are setups for polarizing political appeals.

Iyengar, Talhelm and Haidt do not reject the importance of these external factors. But they do argue that the depth of our polarization reflects ingrained personal, cognitive and psychosocial traits — traits that are, in Iyengar’s word, “primal.”

This is not an easy problem for politicians to solve. Republican and Democratic leaders are struggling to moderate their parties’ most extreme ideological positioning. But if polarization reflects primal aspects of the human condition, particularly when we are under stress, it isn’t going anywhere. However much they might want to pitch themselves toward the center, politicians will feel the need to tap into the energy, not to mention the primary votes, that ideological purity provides. It is this contradiction between purity and pragmatism that will shape the political landscape for the foreseeable future.