Another reason that human nature doesn't rule out social progress is that many features of human nature have free parameters. This has long been recognized in the case of language, where some languages use the mirror-image of the phrase order patterns found in English but otherwise work by the same logic. Our moral sense may also have a free parameter as well. People in all cultures have an ability to respect and sympathize with other people. The question is, with which other people? The default setting of our moral sense may be to sympathize only with members of our clan or village. Over the course of history, a knob or a slider has been adjusted so that a larger and larger portion of humanity is admitted into the circle of people whose interests we consider as comparable to our own. From the village or clan the moral circle has been expanded to the tribe, the nation, and most recently to all of humanity, as in the Universal Declaration of Human Rights. It's an idea that came from the philosopher Peter Singer in his book The Expanding Circle. It's an example of how we can enjoy social improvement and moral progress even if we are fitted with certain faculties, as long as those faculties can respond to inputs. In the case of the moral sense the relevant inputs may be a cosmopolitan awareness of history and the narratives of other peoples, which allow us to project ourselves into the experiences of people who might otherwise be treated as obstacles or enemies.

The third fear is a fear of determinism: that we will no longer be able to hold people responsible for their behavior because they can they can always blame it on their brain or their genes or their evolutionary history—the evolutionary-urge or killer-gene defense. The fear is misplaced for two reasons. One is that the silliest excuses for bad behavior have in fact invoked the environment, rather than biology, anyway—such as the abuse excuse that got the Menendez brothers off the hook in their first trial, the "black rage" defense that was used to try to exonerate the Long Island Railroad gunman, the "pornography made me to it" defense that some rapists have tried. If there's a threat to responsibility it doesn't come from biological determinism but from any determinism, including childhood upbringing, mass media, social conditioning, and so on.

But none of these should be taken seriously in the first place. Even if there are parts of the brain that compel people to do things for various reasons, there are other parts of the brain that respond to the legal and social contingencies that we call "holding someone responsible for their behavior." For example, if I rob a liquor store, I'll get thrown in jail, or if I cheat on my spouse my friends and relatives and neighbors will think that I'm a boorish cad and will refuse to have anything to do with me. By holding people responsible for their actions we are implementing contingencies that can affect parts of the brain and can lead people to inhibit what they would otherwise do. There's no reason that we should give up that lever on people's behavior—namely, the inhibition systems of the brain—just because we're coming to understand more about the temptation systems.

The final fear is the fear of nihilism. If it can be shown that all of our motives and values are products of the physiology of the brain, which in turn was shaped by the forces of evolution, then they would in some sense be shams, without objective reality. I wouldn't really be loving my child; all I would be doing is selfishly propagating my genes. Flowers and butterflies and works of art are not truly beautiful; my brain just evolved to give me a pleasant sensation when a certain pattern of light hits my retina. The fear is that biology will debunk all that we hold sacred.

This fear is based on a confusion between two very different ways to explain behavior. What biologists call a "proximate" explanation refers to what is meaningful to me given the brain that I have. An "ultimate" explanation refers to the evolutionary processes that gave me a brain with the ability to have those thoughts and feelings. Yes, evolution (the ultimate explanation for our minds) is a short-sighted selfish process in which genes are selected for their ability to maximize the number of copies of themselves. But that doesn't mean that we are selfish and short sighted, at least not all the time. There's nothing that prevents the selfish, amoral process of natural selection evolution from evolving a big-brained social organism with a complex moral sense. There's an old saying that people who appreciate legislation and sausages should not see them being made. That's a bit like human values—knowing how they were made can be misleading if you don't think carefully about the process. Selfish genes don't necessarily build a selfish organization.

EDGE: So if intellectuals are afraid of human nature, what do they believe instead? What are some of the indications that we are in denial? What are some of the prevalent myths?

PINKER: I think that there is a quasi-religious theory of human nature that is prevalent among pundits and intellectuals, which includes both empirical assumptions about how the mind works and a set of values that people hang on those assumptions. The theory is has three parts.

One is the doctrine of "the blank slate": that we have no inherent talents or temperaments, because the mind is shaped completely by the environment—parenting, culture, and society.

The second is "the noble savage": that evil motives are not inherent to people but come from corrupting social institutions.

The third is "the ghost in the machine", that the most important part of us is somehow independent of our biology, so that our ability to have experiences and make choices can't be explained by our physiological makeup and evolutionary history.

These three idea ideas are increasingly being challenged by the sciences of the mind, brain, genes, and evolution, but they are held as much for their moral and political uplift as for any empirical rationale. People think that these doctrines are preferable on moral grounds and that the alternative is a forbidden territory that we should avoid at all costs.

EDGE: How has the empirical work in the sciences undermined these beliefs?

PINKER: The blank slate has been undermined by a number of discoveries. One of them is a simple logical point that no matter how important learning and culture and socialization are, they don't happen by magic. There has to be innate circuitry that does the learning, that creates the culture, that acquires the culture, and that responds to socialization. Once you try to specify what those learning mechanisms are, you're forced to posit a great deal of innate structure to the mind.

It's also been undermined by behavioral genetics, which has found that at least half of the variation in personality and intelligence in a society comes from differences in the genes. The most dramatic demonstration of this fact is that that identical twins who were separated at birth have fantastic similarities in their talents and tastes.

The Blank Slate has also undermined by evolutionary psychology and anthropology. For example, despite the undeniable variation among cultures, we now know that there is a vast set of universal traits that are common to all of the world's 6,000 cultures. Also, evolutionary psychology has shown that many of our motives make no sense in terms of our day-to-day efforts to enhance our physical and psychological well-being, but they can be explained in terms of the mechanism of natural selection operating in the environment in which we evolved.

A relatively uncontroversial example is our tastes for sugar and fat, which were adaptive in an environment in which those nutrients were in short supply but don't do anyone any good in a modern environment in which they are cheap and available anywhere. A more controversial example may be the universal thirst for revenge, which was one's only defense in a world in which one couldn't dial 911 to get the police to show up if one's interests were threatened. A belligerent stance was one's only deterrent against other people whose interests were in conflict with one's own. Another one is our taste for attractive marriage partners. As wise people have pointed out for millennia, this makes no sense in terms of how happy or compatible the couple will be. The curve of your date's nose, or the shape of her chin, doesn't predict how well one you're going to get along with her for the rest of your life. But evolutionary psychology has show that the physical features of beauty are cues to health and fertility. Our fatal weakness for attractive partners can be explained in terms of our evolutionary history, not our personal calculations of well-being.