Steven Pinker is Professor and Director of the Center for Cognitive Neuroscience of the Massachusetts Institute of Technology and author of *The Language Instinct*. This article is adapted from his forthcoming book *How the Mind Works* (Norton, October).
There is an old song by Tom Paxton, later made famous by Peter Paul, and Mary, in which an adult reminisces about a childhood toy:
A wonder to behold it was,
With many colors bright.
And the moment I laid eyes on it
It became my heart's delight.
It went ZIP! when it moved,
And POP! when it stopped,
and WHIRRR! when it stood still.
I never knew just what it was
and I guess I never will.
The whimsy of the song comes from the childlike pleasure in a complicated object with an inscrutable function. When we grow up, we demand to know what an artifact is designed to do. When we come across a contraption in an antique store, we ask what it is, and when we are told that it is a a cherry-pitter, the springs, hinges, and levers all suddenly make sense in a satisfying rush of insight.
This is called reverse-engineering. In forward-engineering, one designs a machine to do something; in reverse-engineering, one figures out what a machine was designed to do. Reverse-engineering is what the boffins at Sony do when a new product is announced by Panasonic. They bring one back to the lab and try to figure out what all the parts are for and how they combine to make the device work.
The human body is a complicated object, and since the seventeenth century, when William Harvey deduced that the valves in veins are there to make the blood circulate, we have understood the body by reverse-engineering it. The body is a wonderfully complex assembly of struts, springs, pulleys, hinges, sockets, tanks, pipes, pumps, and filters. Even today we can be delighted to learn what mysterious parts are for. Why do we have our wrinkled, asymmetrical ears? Because they filter sound waves coming from different directions in different ways. The sound shadow tells the brain whether the source of the sound is above or below, in front of or behind us.
The rationale for reverse-engineering living things comes, of course, from Charles Darwin. He showed how "organs of extreme perfection and complication, which justly excite our admiration" arise not from God's foresight but from natural selection operating over immense spans of time. Organisms vary, and in each generation the lucky variants that are better adapted to survival take up a larger proportion of the population. The complicated machinery of plants and animals thus appears to have been engineered to allow them to survive and reproduce.
The human mind is a product of the brain, another complex object shaped by natural selection, and we should be able to reverse-engineer it, too. And so we have for many parts of our psychology. Perception scientists have long realized that our sense of sight is not there to entertain us with pretty patterns and colors. It is contrived to grant us an awareness of the true forms and materials in the world. The selective advantage is obvious: animals that know where the food, the predators, and the cliffs are can put the food in their stomachs, keep themselves out of the stomachs of others, and stay on the right side of the clifftop. Many of our emotions are also products of natural engineering. Fear keeps us away from heights and dangerous animals; disgust deters us from eating bodily wastes, putrefying flesh, and other contaminants.
But reverse-engineering is possible only when you have an inkling of what the device was designed to accomplish. We don't understand the cherry-pitter until we catch on that it was designed as a machine for pitting cherries rather than as a paperweight or wrist-exerciser. The same is true in biological reverse-engineering. Through the 1950s, many biologists worried about why organisms seem to have body parts that did them no good. Why do bees have a barbed stinger that pulls the bee's body apart when dislodged? Why do mammals have mammary glands, which skim nutrients from the mother's blood and package it as milk for the benefit of another animal?
Today we know that these are pseudo-problems, which come from a faulty idea of what the bodies of organisms are for. The ultimate goal of a body is not to benefit the body or the species or the ecosystem, but to maximize the number of copies of the genes that made the body. Natural selection is about replicators, entities that keep a stable identity across many generations of copying. Replicators that enhance the probability of their own replication come to predominate -- crucially, regardless of whose body the replicated copies sit in. Genes for barbed stingers can predominate because copies of those genes sit in the body of the queen and are protected when the worker suicidally repels an invader. Genes for mammary glands can predominate because copies of those genes sit in the young bodies that are being nourished by the milk.
So when we ask questions like "Who or what is supposed to benefit from an adaptation?" and "What is a design in living things a design *for*?" the theory of natural selection provides the answer: the long-term stable replicators, genes. This has become a commonplace in biology, summed up in Samuel Butler's famous quip that a hen is an egg's way of making another egg, in Richard Dawkins' book title *The Selfish Gene*, and in Stephen Jay Gould's remark that reproductive success "cannot be the passage of one's body into the next generation -- for, truly, you can't take it with you in this sense above all!"
What difference does this make to reverse-engineering the mind? For many parts of the mind, not much. We can understand vision and fear with a vague sense that they benefit the perceiver and fearer. But when it comes to our social lives, where our actions often do not benefit ourselves, it makes a big difference who or what we take to be the ultimate beneficiary. Mammary glands were demystified only when we realized that they benefit genes for making the mammary glands -- not the copies in the mother, but the copies likely to be found in the milk-drinker. In the same way, kind acts towards our children and other relatives can be demystified when we realize that they benefit copies of the genes that build a brain that inclines a person toward kind acts towards relatives -- not the copies in the kind actor, but the copies likely to be found in the beneficiaries. We nurture our children and favor our relatives because doing so has a good chance of helping copies of the genes for nurturance and nepotism inside the children and the relatives.
In the case of altruistic behavior toward *non*relatives, a different explanation is needed, but it still hinges on an ultimate benefit to the genes for the altruistic behavior. People tend to be nice to those who are nice to them. Genes for trading favors with other favor-traders can prosper for the same reason that the partners in an economic trade can prosper: both parties are better off if what they gain is worth more to them than what they give up.
The theory that human social behavior is a product of natural engineering for gene propagation came to be known in the 1970s as sociobiology, and was summed up by saying that the brain is a fitness-maximizer, or that people strive to spread their genes. It offered a realization of Darwin's famous prediction in *The Origin of Species* that "psychology will be based on a new foundation," fully integrated into our understanding of the natural world.
But there was one problem with the theory. When we look at human behavior around us, we discover that the brain-as-fitness-maximizer theory is obviously, crashingly, stunningly wrong. Much of human behavior is a recipe for genetic suicide, not propagation.
People use contraception. They adopt children who are unrelated to them. They take vows of celibacy. They watch pornography when they could be seeking a mate. They forgo food to buy heroin. In India, some people sell their blood to buy movie tickets. In our culture, people postpone childbearing to climb the corporate ladder and eat themselves into an early grave.
What are we to make of this Darwinian madness? One response is to look for subtle ways in which behavior really might aid fitness. Perhaps celibate people have more time to raise large broods of nieces and nephews and thereby propagate more copies of their genes than they would if they had their own children. Perhaps priests and executives in childless households made up for their lack of legitimate offspring by having many clandestine affairs. But these explanations feel strained, and less sympathetic observers have come to different conclusions: human behavior has nothing to do with biology and follows arbitrary cultural norms instead.
To anyone with a scientific curiosity, it would be disappointing if human behavior had to be permanently walled off from our understanding of the natural world. The founders of a new approach called evolutionary psychology have argued that it needn't be. The anthropologist Donald Symons, and the husband-and-wife team of John Tooby, another anthropologist, and Leda Cosmides, a psychologist have shown that when you think it through, you find that the gene-centered theory of evolution does *not* predict that people are fitness-maximizers or gene-propagators.
First, natural selection is not a puppetmaster that pulls the strings of behavior directly. The target of selection, the genes buried in eggs and sperm, are unable to control behavior either, because obviously they are in no position to see the world or to move the muscles. Naturally selected genes can only design the *generator* of behavior: the package of neural information-processing and goal-pursuing mechanisms called the mind.
That is why it is wrong to say that the point of human striving is to spread our genes. With the exception of the fertility doctor who artificially inseminated patients with his own semen, the donors to the sperm bank for Nobel Prize winners, and other kooks, *no* human being (or animal) strives to spread his or her genes. The metaphor of the selfish gene must be taken seriously: people don't selfishly spread their genes; genes selfishly spread themselves. They do it by the way they build our brains. By making us enjoy life, health, sex, friends, and children, the genes buy a lottery ticket for representation in the next generation, with odds that were favorable in the environment in which we evolved (because healthy, long-lived, loving parents did tend, on average, to send more genes into the next generation). Our goals are subgoals of the ultimate goal of the genes, replicating themselves. But the two are different. Resist the temptation to think of the goals of our genes as our deepest, truest, most hidden, motives. Genes are a play within a play, not the interior monologue of the players. As far as *we* are concerned, our goals, conscious or unconscious, are not about genes at all, but about health and lovers and children and friends.
Once you separate the goals of our minds from the metaphorical goals of our genes, many problems for a naturalistic understanding of human behavior evaporate. If altruism, according to biologists, is just helping kin or exchanging favors, both of which serve the interests of one's genes, wouldn't that make altruism just some kind of hypocrisy? Not at all. Just as blueprints don't necessarily specify blue buildings, selfish genes don't necessarily specify selfish organisms. Sometimes the most selfish thing a gene can do is to build a selfless brain -- for example, one that gives rise to a loving parent or a loyal friend.
Take another example. Recently a major newsmagazine ran a cover story entitled, "Adultery: Is it in Our Genes?" A skeptic wrote in to say that since adulterers take steps to prevent pregnancy, adultery has nothing to do with a strategy for spreading genes. Ah, but whose strategy we are talking about? Sexual desire is *not* people's strategy to propagate their genes; it's people's strategy to attain the pleasures of sex, and the pleasures of sex are the genes' strategy to propagate themselves. When the genes don't get propagated, it's because we are smarter than they are.
But if a desire for sex serves the interests of the genes, are we condemned us to an endless soap-opera of marital treachery? Again, not if you remember that human behavior is the product of a complex brain with many components, which can be thought of as distinct circuits, modules, organs, or even little agents, as in Marvin Minsky's metaphor of The Society of Mind. Perhaps there is a component for sexual desire that serves the long-term interests of the genes by making more children, but there are, just as surely, other components that serve the interests of the genes in other ways. Among them are a desire for a trusting spouse (who will help bring up the copies of one's genes inside the children), and a desire not to see one's own body -- genes included -- come to an early end at the hands of a jealous rival.
There is a second reason that behavior should not and does not maximize fitness. Natural selection operates over thousands of generations. For ninety-nine percent of human existence, people lived as foragers in small nomadic bands. Our brains are adapted to that long-vanished way of life, not to brand-new agricultural and industrial civilizations. They are not wired to cope with anonymous crowds, written language, modern medicine, formal social institutions, high technology, and other newcomers to the human experience.
Since the modern mind is adapted to the Stone Age, not the computer age, there is no need to strain for adaptive explanations for everything we do, such as pornography, drugs, movies, contraception, careerism, and junk food. Before there was photography, it was adaptive to receive visual images of attractive members of the opposite sex, because those images arose only from light reflecting off fertile bodies. Before opiates came in syringes, they were synthesized in the brain as natural analgesics. Before there were movies, it was adaptive to witness people's emotional struggles, because the only struggles you could witness were among people you had to psych out every day. Before there was effective contraception, children were difficult to postpone, and status and wealth could be converted into more children and healthier ones. Before there was a sugar bowl, salt shaker, and butter dish on every table, and when lean years were never far away, one could never get too much sweet, salty, and fatty food.
And, to come full circle, right now you and I are co-opting yet another part of our minds for an evolutionarily novel activity. Our ancestors evolved faculties of intuitive engineering and intuitive science to master tools and make sense of their immediate physical surroundings. We are using them today to make sense of understand the universe, life, and our own minds.
Reverse-engineering our minds -- figuring out what they are "designed" to accomplish -- could be the fulfilment of the ancient injunction to know ourselves, but only if we keep track of who is designed to accomplish what. People don't have the goal of propagating their genes; people have the goal of pursuing satisfying thoughts and feelings. Our genes have the metaphorical goal of building a complex brain in which the satisying thoughts and feelings were linked to acts that tended to propagate those genes in the ancient environment in which we evolved. With that in mind, we might make better sense of the mysterious ways in which we humans pop, zip, and whir.