That these two systems are distinct is especially apparent in autism, a developmental disorder whose dominant feature is a lack of social understanding. Children with autism typically show impairments in communication (about a third do not speak at all), in imagination (they tend not to engage in imaginative play), and most of all in socialization. They do not seem to enjoy the company of others; they don't hug; they are hard to reach out to. In the most extreme cases children with autism see people as nothing more than objects—objects that move in unpredictable ways and make unexpected noises and are therefore frightening. Their understanding of other minds is impaired, though their understanding of material objects is fully intact.
At this point the religion-as-accident theory says nothing about supernatural beliefs. Babies have two systems that work in a cold-bloodedly rational way to help them anticipate and understand—and, when they get older, to manipulate—physical and social entities. In other words, both these systems are biological adaptations that give human beings a badly needed head start in dealing with objects and people. But these systems go awry in two important ways that are the foundations of religion. First, we perceive the world of objects as essentially separate from the world of minds, making it possible for us to envision soulless bodies and bodiless souls. This helps explain why we believe in gods and an afterlife. Second, as we will see, our system of social understanding overshoots, inferring goals and desires where none exist. This makes us animists and creationists.
For those of us who are not autistic, the separateness of these two mechanisms, one for understanding the physical world and one for understanding the social world, gives rise to a duality of experience. We experience the world of material things as separate from the world of goals and desires. The biggest consequence has to do with the way we think of ourselves and others. We are dualists; it seems intuitively obvious that a physical body and a conscious entity—a mind or soul—are genuinely distinct. We don't feel that we are our bodies. Rather, we feel that we occupy them, we possess them, we own them.
This duality is immediately apparent in our imaginative life. Because we see people as separate from their bodies, we easily understand situations in which people's bodies are radically changed while their personhood stays intact. Kafka envisioned a man transformed into a gigantic insect; Homer described the plight of men transformed into pigs; in Shrek 2 an ogre is transformed into a human being, and a donkey into a steed; in Star Trek a scheming villain forcibly occupies Captain Kirk's body so as to take command of the Enterprise; in The Tale of the Body Thief, Anne Rice tells of a vampire and a human being who agree to trade bodies for a day; and in 13 Going on 30 a teenager wakes up as thirty-year-old Jennifer Garner. We don't think of these events as real, of course, but they are fully understandable; it makes intuitive sense to us that people can be separated from their bodies, and similar transformations show up in religions around the world.
This notion of an immaterial soul potentially separable from the body clashes starkly with the scientific view. For psychologists and neuroscientists, the brain is the source of mental life; our consciousness, emotions, and will are the products of neural processes. As the claim is sometimes put, The mind is what the brain does. I don't want to overstate the consensus here; there is no accepted theory as to precisely how this happens, and some scholars are skeptical that we will ever develop such a theory. But no scientist takes seriously Cartesian dualism, which posits that thinking need not involve the brain. There is just too much evidence against it.
Still, it feels right, even to those who have never had religious training, and even to young children. This became particularly clear to me one night when I was arguing with my six-year-old son, Max. I was telling him that he had to go to bed, and he said, "You can make me go to bed, but you can't make me go to sleep. It's my brain!" This piqued my interest, so I began to ask him questions about what the brain does and does not do. His answers showed an interesting split. He insisted that the brain was involved in perception—in seeing, hearing, tasting, and smelling—and he was adamant that it was responsible for thinking. But, he said, the brain was not essential for dreaming, for feeling sad, or for loving his brother. "That's what I do," Max said, "though my brain might help me out."
Max is not unusual. Children in our culture are taught that the brain is involved in thinking, but they interpret this in a narrow sense, as referring to conscious problem solving, academic rumination. They do not see the brain as the source of conscious experience; they do not identify it with their selves. They appear to think of it as a cognitive prosthesis—there is Max the person, and then there is his brain, which he uses to solve problems just as he might use a computer. In this commonsense conception the brain is, as Steven Pinker puts it, "a pocket PC for the soul."
If bodies and souls are thought of as separate, there can be bodies without souls. A corpse is seen as a body that used to have a soul. Most things—chairs, cups, trees—never had souls; they never had will or consciousness. At least some nonhuman animals are seen in the same way, as what Descartes described as "beast-machines," or complex automata. Some artificial creatures, such as industrial robots, Haitian zombies, and Jewish golems, are also seen as soulless beings, lacking free will or moral feeling.
Then there are souls without bodies. Most people I know believe in a God who created the universe, performs miracles, and listens to prayers. He is omnipotent and omniscient, possessing infinite kindness, justice, and mercy. But he does not in any literal sense have a body. Some people also believe in lesser noncorporeal beings that can temporarily take physical form or occupy human beings or animals: examples include angels, ghosts, poltergeists, succubi, dybbuks, and the demons that Jesus so frequently expelled from people's bodies.
This belief system opens the possibility that we ourselves can survive the death of our bodies. Most people believe that when the body is destroyed, the soul lives on. It might ascend to heaven, descend to hell, go off into some sort of parallel world, or occupy some other body, human or animal. Indeed, the belief that the world teems with ancestor spirits—the souls of people who have been liberated from their bodies through death—is common across cultures. We can imagine our bodies being destroyed, our brains ceasing to function, our bones turning to dust, but it is harder—some would say impossible—to imagine the end of our very existence. The notion of a soul without a body makes sense to us.
Others have argued that rather than believing in an afterlife because we are dualists, we are dualists because we want to believe in an afterlife. This was Freud's position. He speculated that the "doctrine of the soul" emerged as a solution to the problem of death: if souls exist, then conscious experience need not come to an end. Or perhaps the motivation for belief in an afterlife is cultural: we believe it because religious authorities tell us that it is so, possibly because it serves the interests of powerful leaders to control the masses through the carrot of heaven and the stick of hell. But there is reason to favor the religion-as-accident theory.
In a significant study the psychologists Jesse Bering, of the University of Arkansas, and David Bjorklund, of Florida Atlantic University, told young children a story about an alligator and a mouse, complete with a series of pictures, that ended in tragedy: "Uh oh! Mr. Alligator sees Brown Mouse and is coming to get him!" [The children were shown a picture of the alligator eating the mouse.] "Well, it looks like Brown Mouse got eaten by Mr. Alligator. Brown Mouse is not alive anymore."
The experimenters asked the children a set of questions about the mouse's biological functioning—such as "Now that the mouse is no longer alive, will he ever need to go to the bathroom? Do his ears still work? Does his brain still work?"—and about the mouse's mental functioning, such as "Now that the mouse is no longer alive, is he still hungry? Is he thinking about the alligator? Does he still want to go home?"