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As a story of creation, the Book of Genesis long, long ago crumbled under the weight of science, notably Darwin's theory of natural selection. But Genesis isn't just about the beginning of the human race. It is also about the beginning of evil--about how and why sin and suffering entered human experience and stayed there. And here the verdict of science is more ambiguous. In some ways, the Bible's account of evil actually draws strength from the very Darwinism that undermined its account of history.

This doesn't mean that paleontologists have found hominid bones with "Adam" stamped on them along with evidence that Adam disobeyed God, thus condemning the rest of us to lives of toil and hardship. But it does mean that this biblical story line, as transmuted by later thinkers into religious doctrine, has produced some ideas that resonate with modern Darwinian theory. In particular, the Christian doctrine of original sin makes more sense as evolutionary psychologists learn more about why people do bad things.

The doctrine of original sin says that at birth we all inherit Adam's sinfulness. This is partly a claim about blame--it holds us accountable for Adam's sin even before we've done anything wrong--but it is also a claim about human nature; it says we are inclined to do wrong, that we have a hereditary dark side. As St. Augustine put it in the 5th century A.D.: After Adam sinned, our "soiled" and "corrupt" nature was "already present in the seed from which we were to spring."

As scientifically minded nitpickers have noted, there is a flaw here. The idea that Adam's choice of cuisine somehow affected biological inheritance involves the generally discredited Lamarckian notion that acquired traits get transmitted genetically. Still, a more generic version of Augustine's assertion--that sin results from biological drives passed through the human lineage ever since its origin--makes scientific sense.

By Darwinian lights, the classic sins, such as gluttony, lust, greed and envy, are the unchecked expression of impulses that arose by natural selection. During evolution, individuals with strong innate yearnings for food, sex and material goods did a better job of surviving and reproducing than individuals less drawn to these things. So we inherited genes conducive to such yearnings. In the same manner, anger (another of the deadly sins) became a naturally engrained tool of survival, aimed, for example, at those who would take our food or our mates.

In the essentially pre-technological context of human evolution, impulses such as gluttony, greed, even lust, were often blunted by scarcity. Only amid the material abundance that came with agriculture and grew thereafter could self-indulgence regularly reach grotesque levels. (Sodom and Gomorrah lay in the fertile plains. Their residents sinned amid plenty while Abraham herded his flock in rustic innocence on dryer terrain.) Similarly, anger acquired a new layer of evil with the invention of knives and spears, to say nothing of guns.

The biological roots of sin are not by themselves a news flash from the frontiers of science. More than a century ago, Thomas Huxley, Darwin's popularizer, lamented the fact that evolution has given all children "the instinct of unlimited self-assertion"--"their dose of original sin." But the past few decades have brought a deeper Darwinian understanding of human nature, and some of its pioneers believe Huxley underestimated our badness.

But first the good news. Evolutionary psychologists say our "moral sentiments" do, as Darwin speculated, have an innate basis. Such impulses as compassion, empathy, generosity, gratitude and remorse are genetically based. Strange as it may sound, these impulses, with their checks on raw selfishness, helped our ancestors survive and pass their genes to future generations.

Now the bad news. Contrary to a misconception that flourished in Darwin's day, these impulses did not give this boost to genetic proliferation mainly by furthering the overall "welfare of society"--and certainly not by furthering the "welfare of the species." As a result, humans don't naturally deploy our "moral" impulses diffusely--showering love and compassion on any needy Homo sapiens in the vicinity. We tend to reserve major doses of kindness either for close kin (the result of an evolutionary dynamic known as "kin selection") or for non-kin who show signs of someday returning the favor (a result of the evolution of "reciprocal altruism"). This finickiness gives our "moral" sentiments a naturally seamy underside. Beneath familial love, for example, is malice toward our relatives' rivals. Remember the woman in Texas who plotted to kill the mother of her daughter's rival for a cheerleading slot? Fortunately, she's an extreme example. But she's an example, nonetheless--as any father or mother, on honest reflection, will admit.

The grimness of this new Darwinian worldview has been stressed by the biologist George Williams, whose 1966 book Adaptation and Natural Selection laid its theoretical foundations. Rather like the World War II physicists who were horrified by the weapon they had invented, Williams blanches at the view of human nature and of natural selection that he helped usher in. "Mother Nature," he says, "is a wicked old witch."

Perhaps the most disturbing aspect of our nature is our natural blindness to it. According to some evolutionary psychologists, we are "designed" by natural selection to conceal selfish motives from ourselves--indeed, to unconsciously build elaborate moral rationales for our selfish behavior. Thus do wars routinely feature two sides convinced that they are in the right.

Even at the level of pettier sins--lust, greed--we are naturally good at making our actions seem just. How many spouses are lured into infidelity, even desertion, by the conviction that they married the "wrong" person the first time around or that this person has "changed"? These often delusional rationales are (to put it a bit metaphorically) our genes "trying" to get us to do the kinds of things--infidelity, betrayal--that during evolution helped propel them into the next generation. Hence the human dimension of our animal behavior: it feels so rational and right. Lots of animals are violent, treacherous and nasty, but only one convinces itself that God approves.

Which brings us back to Eden. Adam and Eve eat from the tree of knowledge because they have pretensions of divinity. "Your eyes will be opened," the serpent promises, "and you will be like God, knowing good and evil." Thus the original sin is often described as a kind of hubris--"the pride which sprang from [our] likeness to God," as one scholar put it. By the lights of evolutionary psychology, an essential human weakness is indeed a tendency to be seduced by our seemingly godlike rationality into thinking we can readily know good and evil; our downfall is a lack of philosophical humility, a smug assumption that our "moral" intuitions can be trusted as a guide to true morality. The effects have ranged from homicide to genocide.

Certainly, as even Williams stresses, our moral sentiments have lots of upside, including a heartening plasticity. They can be deployed less self-servingly than they were "designed" to be deployed. Darwin himself often felt pangs of concern about the plight of slaves, even though there were none in England to reciprocate his empathy. And consider the flush of compassion we feel upon witnessing, via TV, famine that is a hemisphere away. When moved by such images to donate money or canned goods--the rough opposite of greed and gluttony--we are in some Darwinian sense "misusing" our equipment of reciprocal altruism; the equipment is being "fooled" by electronic technology into (unconsciously) thinking that the victims of famine are right next door and might someday reciprocate. But that doesn't diminish the act. Our capacity to thus distort biological purpose, to prevail over our selfish heritage, is a deep source of hope and a glimmer of true goodness.

Still, to prevail comprehensively--to frustrate all or even most of the subtle selfishness built into us--takes massive, ongoing effort and painful self-knowledge. The difficulty of the exercise lends a kind of credence to what some Christians see as the upshot of their doctrine of original sin: that people are born in need of a salvation gained through repentance. To put it in secular terms: so deeply hidden from natural introspection is our badness that moral reform requires a solid jolt of enlightenment, sharp and persistent awareness of our inherent baseness.

Moral reform may or may not come as Christians prefer--in the course of accepting Jesus as savior. But certainly Jesus said some things that could lead even an agnostic toward it. He asked us to doubt the moral basis of all hatreds--even of our enemies--and to doubt our frequent feelings of moral superiority, our illusion of clarity. ("You hypocrite, first take the log out of your own eye; and then you will see clearly to take the speck out of your brother's eye.") Other religions also preach universal love and harsh self-scrutiny. Buddha said, "The fault of others is easily perceived, but that of one's self is difficult to perceive."

There remains one basic, unbridgeable divergence between religious doctrine and Darwinism: according to Genesis, nature is in essence benign. In the beginning, there were no thorns, and snakes spent their time not biting people but chatting with them. Only when man fell to temptation did the natural world receive a coating of evil. But according to Darwinism, the evil in nature lies at its very roots, instilled by its creator, natural selection. After all, natural selection is chronic competition untrammeled by moral rules. Heedless selfishness and wanton predation are traits likely to endure. If these things are sins, then the roots of sin lie at the origin--not just of humankind but of life.

Yet this dark, Darwinian view of nature has its saving grace. True, it doesn't let us imagine some idyllic time when nature was benign and the human heart pristine--a time when, as Augustine believed, human flesh had not yet been corrupted by raw desire and self-absorption. On the contrary, our distant evolutionary past was a time when desire was even rawer than now, and self-absorption less nuanced.

Still, there's something hopeful about a hideous past. Though our great intelligence and our elaborate "moral" sentiments were created solely for the purpose of genetic proliferation and not for true edification, they now interact in strange and unpredicted ways, and the occasional burst of moral progress breaks through. People like Jesus and Buddha come along and say radical things that somehow stick in the world's consciousness. And the most animal of institutions--such as slavery--do seem slowly to die out. Who knows where this could lead? Personally, I'd rather see Eden on the horizon--however dimly and elusively--than in the rearview mirror.