In February 2008, Jonathan Haidt gave a TED Talk on the psychological differences between liberals and conservatives. The talk made Haidt America’s most well-known moral psychologist. Haidt would go on to found Heterodox Academy, an organization dedicated to promoting view point diversity at universities.

While Haidt is better known for his work promoting intellectual diversity and his remarkably blunt critique of the campus left, his 2012 book, The Righteous Mind, provides much-needed background on the science informing his positions. The Righteous Mind explores human morality from an evolutionary-psychology perspective; the book is less “Conservatives are from Mars, liberals are from Venus,” and more “Sociobology: the new synthesis.”

When Haidt began graduate school, moral psychology was dominated by what Haidt refers to as “the moral rationalists.” These were scholars such as Lawrence Kohlberg, Jean Piaget, and Elliot Turiel.

The rationalists believed that one’s morality develops in much the same way that one’s understanding of the physical world develops. Most of us had some idea that gravity existed prior to taking a physics class. Through our experience with the physical world we deduced underlying principles of the physical world, even if we couldn’t define them in the precise terms of a scientist.

In the rationalist account, children discover morality in much the same manner. By interacting with other children we learn that our relations with others are governed by abstract rules. At a certain stage, we learn to distinguish between immutable moral principles and mere social conventions: recess is at 1 P.M., because the principal says so; hurting other children is wrong, regardless of what the principal or the teacher says.

While Haidt was indoctrinated into the rationalist paradigm, intuition told him something didn’t make sense. His childhood experiences were rather different from Kohlberg’s. In Haidt’s recollection, he and his sisters reasoned opportunistically, attempting to gain the upper hand on each other, rather than trying to discover the truth.

When psychologists examined other cultures, moral rationalism began to crumble. The moral rationalists put a great deal of emphasis on harm and fairness as the basis of morality, but people in non-Western countries seemed to have a broader set of moral concerns. What Kohlberg saw as the final stages of an individual’s moral development seemed to be the norms of a particular culture and not the inevitable endpoint of reason.

In a series of brilliant experiments, Haidt and others demonstrated that judgment precedes reasoning. In other words, we make judgments and then employ our reasoning to justify these judgments, or as Haidt puts it, “intuitions come first, strategic reasoning second.”

In The Righteous Mind, Haidt attempts to describe our moral intuitions, to catalogue the things we intuitively care about with regard to moral judgment. Haidt defines five “moral foundations:” harm, fairness, loyalty, authority, and sanctity. Haidt tentatively proposes a sixth moral foundation, liberty/oppression, which he describes as a sort of innate sensitivity toward tyranny.

In Haidt’s retelling, our minds are preloaded to care about certain things. When we see another person suffering, we respond viscerally and automatically. However, we are not just sensitive toward the suffering of others, we also care about fairness, authority, sanctity, and liberty. If you cringe when you witness children disrespecting their parents, your authority foundation has been activated.

According to Haidt, most of us share the same five or six moral foundations, but we care about them to varying degrees. Conservatives utilize all of the foundations equally when making judgments. However, liberals tend to emphasize the first two much more strongly. For Haidt, this partially explains why our politics are so polarized.

In the final section of his book, Haidt attempts to solve a core dilemma of evolutionary psychology: why are humans altruistic?

From the simplest Darwinian perspective, the most successful strategy would be pure selfishness. On an individual level, it seems that the selfish would outcompete the altruistic, and altruistic genes would be washed out of the gene pool.

However, if we move up from the level of the individual to the level of the group, altruism is very beneficial. Cooperative groups outcompete selfish individuals for resources. Once people began living in groups, cooperation became more important, and more cooperative groups out-competed less cooperative groups. This was, according to Haidt, the origin of human morality.

Jonathan Haidt does a thorough job of debunking the naive moral rationalism of psychologists such as Lawrence Kohlberg. Haidt offers a plausible explanation for the emergence of human morality; group level selection favored more cohesive groups of people, and this selected for altruistic genes. Haidt’s moral foundation theory, along with his description of the differences between liberals and conservatives, is promising, but it needs to be tested by other researchers.

While I found The Righteous Mind persuasive, I worry that Haidt has given short shrift to moral rationalism. His book details how easily human intuitions can be manipulated by researchers; given this, shouldn’t we be cautious about trusting our intuitions? Also, the people we admire most really do appear to be acting from a sort of Kantian motive of duty, defying group pressure in order to do what’s right.

Haidt’s book suggests two very different readings. One could conclude that everyone else is irrational, driven by gut feelings and immune to reason. One could also conclude that everyone, including oneself, employs reason to justify their beliefs; therefore, one should be humble about one’s beliefs. If readers adopt the second interpretation, Haidt’s book will be a success.