Steven Pinker, Johnstone Professor of Psychology at Harvard University and author of The Blank Slate: The Modern Denial of Human Nature, delivered the second of the 2003-2004 Bradley Lectures on October 7. Edited excerpts follow.

The dominant theory of human nature in modern intellectual life is based on three doctrines. First, the blank slate, or the belief that dogmas are formed by shared experiences rather than self-evident truths; second, the noble savage, or the respect for everything natural and a distrust of anything man-made; and third, the ghost in the machine, where freedom, dignity, and responsibility are often seen as incompatible with the biological understanding of the mind.

These ideas are being challenged by modern psychological and genetic sciences. Evolutionary psychology has undermined the blank slate by showing that a bedrock of universal ways of thinking, feeling, and behaving exists beneath the unquestioned fact of cross-cultural variation. The blank slate has been further attacked by neuroscience, which reveals that the brain is a diagram of the primate visual system, comprising some fifty distinct areas interconnected in precise ways and arranged by molecular cues during the course of embryonic development. The noble savage has been undermined by findings that heritable traits include antagonistic personalities, tendencies toward violent crime, and a lack of conscience.

The ghost in the machine has faced the most severe threats. Cognitive science shows that this formerly mysterious power called intelligence involves massively parallel, fuzzy, and analog computation, and that desires can be understood in cybernetic terms as mechanisms of control.

These modern forms of science are erroneously thought to threaten important moral values and encourage evils such as inequality, imperfectability, determinism, and nihilism, but these misconceptions can be clarified through a better understanding of what makes us tick and of our place in nature.

Common Fears

The fear of inequality derives from a mathematical fact that zero equals zero equals zero. As blank slates, we must be equal, but if the mind has any innate organization, then different races, sexes, or individuals could be biologically different, which would condone discrimination and oppression. However, we should not confuse the notion of fairness with the notion of sameness. Political equality does not require sameness but rather equal treatment as individuals with rights.

The fear of imperfectability dashes the dream of the purity of mankind by arguing that ignoble traits are innate and thus unchangeable. Attempts at social reform and human improvement are a waste of time: why try to make a world a better place if people are rotten to the core? However, ignoble motives do not automatically lead to ignoble behavior. The mind is not a blank slate but rather a complex system of parts that can apply the moral sense and knowledge of history to inhibit behavior. Moral progress does not require that the mind is free of selfish motives, only that it has other motives to counteract them.

The fear of determinism is the anxiety that if behavior is caused by a person's biology, he cannot be held responsible for his actions. When you want to hold people responsible for their actions, you impose contingencies on their behavior: reward, punishment, credit, and blame. So these contingencies are themselves causes of behavior by appealing to parts of the brain that can anticipate the consequences of behavior and inhibit it accordingly. We can keep this influence on the brain systems for inhibition, to hold people responsible, even as we come to understand the brain systems for temptation. Responsibility does not require that behavior is uncaused, only that it responds to contingencies of credit and blame.

The fear of nihilism is that biology strips life of meaning and purpose and that all the things we hold precious are mere figments of a brain pursuing selfish evolutionary strategies. Nihilism is based on a confusion of time scales, confusion of human time, years, and decades--how we want to live our lives today given the brains we have and the process that determines how and why our brain gives us those thoughts initially. Even if our genes are selfish, we are not necessarily selfish, and even if the process of evolution is amoral and without purpose, we are not necessarily amoral and without purpose. Meaning in life does not require that the processes that shape the brain have a purpose, only that the brain itself has a purpose.

Confronting Human Nature

Grounding values in a blank slate is a mistake because it makes our values hostages to fortune. This misdeed implies that empirical discoveries could make our values obsolete, and it conceals the downsides of denying human nature, including persecution of the successful; totalitarian social engineering; an exaggeration of environmental effects; a mystification of the bases of responsibility, democracy, and morality; and the devaluing of human life on Earth.