Ever since the rise of modern science, an almost impregnable wall separating it from religion, morality and human values has been raised to the heights. The “naturalistic fallacy,” sometimes rendered as the “is-ought problem”—the way something “is” does not mean that is the way it “ought” to be—has for centuries been piously parroted from its leading proponents, philosophers David Hume and G. E. Moore, as if pronouncing it closes the door to further scientific inquiry.

We should be skeptical of this divide. If morals and values should not be based on the way things are—reality—then on what should they be based? All moral values must ultimately be grounded in human nature, and in my book The Science of Good and Evil (Times Books, 2004), I build a scientific case for the evolutionary origins of the moral sentiments and for the ways in which science can inform moral decisions. As a species of social primates, we have evolved a deep sense of right and wrong to accentuate and reward reciprocity and cooperation and to attenuate and punish excessive selfishness and free riding. On the constitution of human nature are built the constitutions of human societies.

Grafted onto this evolutionary ethics is a new field called neuroethics, whose latest champion is the steely-eyed skeptic and cogent writer Sam Harris, a neuroscientist who in his book The Moral Landscape (Free Press, 2010) wields a sledgehammer to the is-ought wall. Harris’s is a first-principle argument, backed by copious empirical evidence woven through a tightly reasoned narrative. The first principle is the well-being of conscious creatures, from which we can build a science-based system of moral values by quantifying whether or not X increases or decreases well-being. For instance, Harris asks, Is it right or wrong to force women to dress in cloth bags and to douse their faces in acid for committing adultery? It doesn’t take rocket science— or religion, Harris astringently opines—to conclude that such “cultural values” decrease the well-being of the women so affected and thus are morally wrong.

These examples are the low-hanging fruit on the tree of the knowledge of good and evil, so it is easy for both science and religion to pluck the ripe ones and declare with confidence that such acts as, say, lying, adultery and stealing are wrong because they destroy trust in human relationships that depend on truth telling, fidelity and respect for property. It is when moral issues become weighted with political, economic and ideological baggage that the moral landscape begins to undulate.

Harris’s program of a science-based morality is a courageous one that I wholeheartedly endorse, but how do we resolve conflicts over such hotly contested issues as taxes? Harris’s moral landscape allows the possibility of many peaks and valleys— more than one right or wrong answer to moral dilemmas—so perhaps liberals, conservatives, libertarians, Tea partiers, Green partiers and others can coexist on different peaks. Live and let live I say, but what happens when the majority of residents on multiple moral peaks pass laws that force those in the minority on other peaks to help pay for their programs of social wellbeing for everyone? More scientific data are unlikely to eliminate the conflict.

I asked Harris about this potential problem. “‘Live and let live’ is often a wise strategy for minimizing human conflict,” he agreed. “But it only applies when the stakes are not very high or when the likely consequences of our behavior are unclear. To say that ‘more scientific data are unlikely to eliminate the conflict’ is simply to say that nothing will: because the only alternative is to argue without recourse to facts. I agree that we find ourselves in this situation from time to time, often on economic questions, but this says nothing about whether right answers to such questions exist.”

Agreed. Just because we cannot yet think of how science might resolve this or that moral conflict does not mean that the problem is an insoluble one. Science is the art of the soluble, and we should apply it where we can.

Humans are, by nature, tribal and never more so than in politics. In the culture wars we all know the tribal stereotypes of what liberals think of conservatives: Conservatives are a bunch of Hummer-driving, meat-eating, gun-toting, hard-drinking, Bible-thumping, black-and-white- thinking, fist-pounding, shoe-stomping, morally hypocritical blowhards. And what conservatives think of liberals: Liberals are a bunch of hybrid-driving, tofu-eating, tree-hugging, whale-saving, sandal-wearing, bottled-water-drinking, ACLU-supporting, flip-flopping, wishy-washy, namby-pamby bed wetters.

Like many other stereotypes, each of these contains an element of truth that reflects an emphasis on different moral values. Jonathan Haidt, who is a psychologist at the University of Virginia, explains such stereotypes in terms of his Moral Foundations Theory (see www.moralfoundations.org), which he developed “to understand why morality varies so much across cultures yet still shows so many similarities and recurrent themes.” Haidt proposes that the foundations of our sense of right and wrong rest within “five innate and universally available psychological systems” that might be summarized as follows:

1. Harm/care: Evolved mammalian attachment systems mean we can feel the pain of others, giving rise to the virtues of kindness, gentleness and nurturance.
2. Fairness/reciprocity: Evolved reciprocal altruism generates a sense of justice.
3. Ingroup/loyalty: Evolved in-group tribalism leads to patriotism.
4. Authority/respect: Evolved hierarchical social structures translate to respect for authority and tradition.
5. Purity/sanctity: Evolved emotion of disgust related to disease and contamination underlies our sense of bodily purity.

Over the years Haidt and his University of Virginia colleague Jesse Graham have surveyed the moral opinions of more than 110,000 people from dozens of countries and have found this consistent difference: self-reported liberals are high on 1 and 2 (harm/ care and fairness/reciprocity) but are low on 3, 4 and 5 (in-group loyalty, authority/respect and purity/sanctity), whereas self-reported conservatives are roughly equal on all five dimensions, although they place slightly less emphasis on 1 and 2 than liberals do. (Take the survey yourself at www.yourmorals.org.)

Instead of viewing the left and the right as either inherently correct or wrong, a more scientific approach is to recognize that liberals and conservatives emphasize different moral values. My favorite example of these differences is dramatized in the 1992 film A Few Good Men. In the courtroom ending, Jack Nicholson’s conservative marine Colonel Nathan R. Jessup is being cross-examined by Tom Cruise’s liberal navy Lieutenant Daniel Kaffee, who is defending two marines accused of accidentally killing a fellow soldier. Kaffee thinks that Jessup ordered a “code red,” an off-the-books command to rough up a disloyal marine trainee in need of discipline and that matters got tragically out of hand. Kaffee wants individual justice for his clients. Jessup wants freedom and security for the nation even at the cost of individual liberty, as he explains:

“Son, we live in a world that has walls. And those walls have to be guarded by men with guns…. You don’t want the truth because deep down, in places you don’t talk about at parties, you want me on that wall. You need me on that wall. We use words like honor, code, loyalty. We use these words as the backbone to a life spent defending something. You use ’em as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the blanket of the very freedom I provide, then questions the manner in which I provide it.”

Personally, I tend more toward the liberal emphasis on individual fairness, justice and liberty, and I worry that overemphasis on group loyalty will trigger our inner xenophobias. But evolutionary psychology reveals just how deep our tribal instincts are and why good fences make good neighbors. And I know that ever since 9/11, I am especially grateful to all the brave soldiers on those walls who have allowed us to sleep under a blanket of freedom.

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