DAVID LYKKEN: How is that some scientists, psychologists like Leon Kamin, biologists like Steven Rose, even the odd geneticist like Richard Lewontin, or the odd paleontologist like Stephen Gould, continue to believe with John Locke that the infant human mind is a tabula rasa. How can they suppose that baby brains are as alike as new Macintosh computers fresh from the factory; indeed, even more alike because the computers at least have operating systems and various ROMs already installed? How can anyone imagine that, sometime in the Pleistocene, evolution mysteriously stopped, but just for one sub-system of one mammalian genus, the nervous system of the genus homo?

Without postulating that we possess ancestral inclinations, slowly acquired over many millennia, how could one explain why children tend to shy away from snakes and spiders but not from guns or electric sockets, which are much more dangerous? When the Minnesota Twins won the World Series in 1987 and again in 1991, when "our boys" had defeated those invaders from the National League, why did nearly four million Minnesotans, most of whom had never seen a game, proudly think that something wonderful had happened? When the Gulf War ended and "our boys" had killed a lot of Iraqis so the Sultan of Kuwait could return from the RiviŽra to rebuild his palaces, the entire U.S. Congress stood, some on their seats or desks, to cheer President Bush for his accomplishment. Those senators and representatives were not play-acting to impress their constituents; they really felt proud (but why?).

Romantic love, which anthropologists once thought had been invented by French poets in the middle ages, is now known to have characterized virtually every traditional society of which we have records. The other great apes do not experience infatuation because they do not need to pair bond. The baby chimps cling to their mother's fur and she can provide for their care and sustenance without any help from the unknown father. But when our ancestors began producing those big-headed, altricial babies that needed several years of constant carrying and oversight, more than the mothers could manage on their own, some sort of attachment had to be invented to persuade the fathers to help out. It turns out that, over all known societies that permit divorce, the modal length of marriage for those couples who eventually split is just four years; the fast-setting superglue of romantic infatuation lasts just long enough for Junior to be sturdy on his feet.

Identical twins, whose tastes are remarkably similar in all other respects, are about as likely to be charmed by their cotwin's romantic choice as by some passing stranger of the same age and gender. The spouses of identical twins, infatuated with Twin A at the time they meet Twin B, are no more inclined to "fall for" Twin B, the clone of their beloved, than for the boy (or girl) across the street. Natural selection had millions of years in which to fashion pair bonding in eagles and wolves but it was a hurry-up job for the early hominids. My guess is that the mechanism used in our case was similar to that which produces imprinting in ducks and geese.

In their London debate, "The Two Steves" (Pinker and Rose) alluded briefly to why human parents love their babies. Pinker, a sensible evolutionary psychologist, thinks it is probably because those ancestral parents who were not somehow motivated to nurture their offspring were unlikely to have grandchildren and thus to become ancestors. I was never clear about what Rose thinks. But a more interesting question is why do Americans spend billions annually on dogs and cats and other pets? Assuming Pinker is correct, as assuredly he is, would natural selection continue fiddling with the machinery until parents felt nurturant about their own genetic offspring only? For some seals and sea birds that operate giant collective nurseries, where the young may wander off from their mothers, it appears that both mothers and offspring have evolved olfactory methods of identifying one another. But for most mammals, including the featherless bipeds, the danger of a parent "wasting" effort nurturing an unrelated baby was low enough so that a more precise targeting of maternal affection was unnecessary. The selection pressure favoring the more discriminating mothers was not great enough to produce a species change. Natural selection is parsimonious. It continues just long enough to fashion the ROM or module required to accomplish the necessary result in the environment of evolutionary adaptation.

A recent news report tells of a lost dog that had been fitted with a radio collar and was finally located in the den of a mother bear. Each time the dog started to emerge in response to his master's call, the bear gently drew him back again to his new home. My wife and I, like millions of others of our species, are more like the bears than we are like seals in this respect. In most jurisdictions, a person who kills a neighbor's dog or cat is treated by the law like someone who destroyed the neighbor's lawn mower. If law-makers understood evolutionary psychology (or human pet owners) better, the offense would be treated much more seriously. My bull terrier is to me much more like my adopted child, if I had one, than like my lawn mower.

Another example of the parsimony of natural selection is our human xenophobia. We tend to distrust, fear, and dislike other humans who seem different than ourselves. This was adaptive in ancestral times when a stranger stepped out from behind a tree because that stranger might kill you, if you were a male, or to rape you or carry you off, if you were a female. A more selective mechanism would require both strangeness and threatening action to trigger our fear/dislike response. But just "stranger" turned out to be enough. Can this be why modern humans, both New Yorkers and the natives of Papua New Guinea, tend to paint and dress themselves in ways that immediately identify their group membership? And can this be one of the reasons why our contemporary Lockians want to believe in the tabula rasa mythology? "Let us not suppose that xenophobia is natural because then how could we hope to accomplish racial, religious, and social tolerance?" My three sons, white, non-theistic, Aryan types, are happily married to a Catholic, a Jew, and an African American, and have produced my ten beloved grandchildren. Reporting some early results of his celebrated study of twins who were separated in infancy and reared apart, my colleague, Tom Bouchard, pointed out that: "The genes sing a prehistoric song that must sometimes be resisted but which should never be ignored." Our xenophobia can be resisted, as my sons' example attests, but it should not be ignored, or we shall never be able to figure out what to do about Bosnia.

Another ancestral trait that we should not ignore is male sexual jealousy. One human sex difference that even Gloria Steinem cannot deny is that a woman knows that the baby she delivered is hers while her spouse cannot be certain it is his. (DNA data indicate, in fact, that about ten percent of human children could not have been produced by the mother's husband; for bluebirds, by comparison, the figure is about twenty percent.) The CEO of Natural Selection is aware of these facts and has endowed the males of our species with a suite of compensatory tendencies. David Buss has shown that, over many cultures, women are more disturbed by evidence that their mate has an affectionate relationship with another woman (an attachment that might lead him to invest his resources in her and her children) while men are much more concerned to learn that their mate has had sex with someone else. I once did some marriage counseling with a young "hippy" couple who were having problems. Their deeply held principles included opposition to the Vietnam War, support of environmental protections, legalization of psychoactive drugs, and free love. Their problem was that the young man was always grouchy and resentful. The solution to their problem was to accept the fact that most men cannot help feeling grouchy and resentful when their mate persists in having sex with other men. "Oh, Baby, I'm so sorry! I didn't think you cared!"

Another curious fact is that even some evolutionary psychologists, including Steve Pinker's mentors, John Tooby and Leda Cosmides, believe that the genetic differences between people, the very differences on which, during ancestral times, natural selection worked to make us what we are today, no longer exist. "Yes, we all come equipped with species-specific behavioral proclivities. Our infant brains are not just general-purpose computers waiting to be programmed by experience but, rather, they have modules that are preprogrammed to give us a head start at being human. But they are all alike at birth, except perhaps for bits of noisy artifact." Are these folks just being politic, just claiming only the minimum they need to pursue their own agenda while leaving the behavior geneticists to contend with the main armies of political correctness?

The denial of genetically based psychological differences is the kind of sophisticated error normally accessible only to persons having Ph.D. degrees. Even the be-doctored tend to give up radical environmentalism once they have a second child. In our twenty-five years of twin research at Minnesota, monozygotic twins, who share all their genes, have been found to be twice (or more than twice) as similar as dizygotic twins, who share on average half their polymorphic genes, on nearly every trait that we can measure reliably. The few exceptions include birth weight, years of education, romantic choice, and a few interests such as blood sports, gambling, and religious orientation. (Variation in general religiosity, on the other hand, is strongly genetic.) Moreover, monozygotic twins separated in infancy and reared apart, are as similar on most psychological traits as are MZ twins reared together. Middle-aged MZ twins, whether reared together or apart, correlate in IQ more than .70, and this is so whether IQ is estimated from the nonverbal Raven Matrices test administered and scored by computer, or from a standard IQ test individually administered by different examiners in separate rooms. IQ is not all there is to "intelligence" but it is very important. If your child's IQ is less than about 115, she is almost certain never to get through medical or law school.

One of the personality inventories that we use has a Well Being scale that measures current happiness. Like most psychological traits (even IQ), happiness varies from time to time due to the slings and arrows. When we measure Well Being in adult twins twice, ten years apart, the within-twin cross-time or retest correlation is only .55 (.02). But for MZ twins, the between-twin cross-time correlation (Twin A now vs Twin B then, etc.) is virtually the same, .54 (.03), suggesting that most of the happiness "set-point" or stable component is genetically determined. In contrast, the between-twin cross-time correlation for dizygotic (DZ) twins is only .05 (.07).

Happiness is one of the interesting traits that I call "emergenic." Although they have strong genetic roots, hence the strong MZ correlations, the negligible similarity of DZ twins indicates that these traits do not tend to run in families. Metrical traits that do run in families, traits like stature, reflect the additive combination of polygenic effects(the lengths of the head, neck, torso, upper and lower leg add up to body height. Emergenic traits seem to involve configural rather than additive combinations of the polygene effects, so that small gene changes can produce large changes in the trait. Because each parent contributes just half of her or his genes to each child, and because siblings share on average just half of their polymorphic genes, first-degree relatives are unlikely to share all of the genes involved in an emergenic configuration.

Facial beauty seems to be an emergenic trait as is the distinctive quality of the singing or speaking voice. MZ twins can usually fool even family members by impersonating their cotwins on the telephone; DZ twins very seldom can do this. Music majors at my university, including those specializing in voice, commonly have musical parents, but the voice major seldom have parents who sing. The racing ability of the legendary stallion, Secretariat, seems to have been emergenic. Mated with only the most promising mares, he produced more than 400 foals, only one of them(Risen Star) was a winner and even he could not have run with dad.

Were it not for ideological prejudice, any rational person looking at the evidence would agree that human aptitudes, personality traits, many interests and personal idiosyncrasies, even some social attitudes, owe from 30 to 70 percent of their variation across people to the genetic differences between people. The ideological barrier seems to involve the conviction that accepting these facts means accepting biological determinism, social Darwinism, racism, and other evils. I myself fall prey to this mistake from time to time. In the paper reporting our happiness data, for example, noting that the happiness set-point is largely genetic while the events that move us temporarily above or below our set-points are largely fortuitous, I wrote: "Perhaps trying to be happier is like trying to be taller." To make up for this error, I have had to write a book (Happiness: Its Nature and Nurture) explaining why trying to be happier is both feasible and fun.

The actual mechanism by which the genes affect the mind is still what Pinker (and Noam Chomsky) would call a mystery rather than a mere problem. We do not have a clue about how the brain module that permits humans but not chimps to acquire language is actually fashioned by the genetic enzyme factory. In the comparatively simple brain of a chicken there is a gizmo that produces an alarm reaction when the silhouette of a flying hawk passes overhead, but not when it is passed backwards so that it looks more like a flying chicken. We cannot locate that gizmo or describe its construction. We do not know which genes in the chicken DNA mutated eons ago to bring about this adaptive response and we clearly have no idea at all as to how these genes manage to fabricate this gizmo in every modern chicken's brain. Yet the existence of the gizmo cannot be doubted.

In the case of most human psychological traits, however, an important part of the mechanism is less mysterious. We know that, to an important extent, the genes affect the human mind indirectly by influencing the kinds of experiences we have, the way in which other people react to us, and especially by influencing the kinds of environments we seek out and the ways in which we react to our experiences. For genetic reasons, some babies are fretful and unresponsive while others tend to smile and coo. These different behaviors elicit different parenting responses. A genetically venturesome toddler climbs on things, falls off, explores, knocks things over, and has physical and social experiences that his more sedentary sibling seldom has. A naturally bright, inquisitive youngster notices and thinks about things, reads more, asks more questions, and elicits better answers than does a child whose mental processes are slower and less intrinsically rewarding. A little boy who is at the low end of the normal distribution of genetic fearfulness is less easily intimidated by the punishment on which both parents and peers tend to rely in trying to modify that boy's behavior. Many parents of such children give up the battle and the child remains unsocialized, a kind of psychopath. More skillful and persistent parents emphasize reward instead of punishment, work to instill pride rather than guilt. A fearless child left to himself is likely to become a leader of the gang, delinquent, then criminal, but with skillful parenting that same boy can grow to be the kind of man we like to have around when danger threatens. I think that the hero and the psychopath are twigs on the same genetic branch.

Thus, genetic effects on human psychology are often distal in the causal chain while the proximal causes are environmental, just as those reactionary Lockians have always claimed. A better formula than Nature versus Nurture would be Nature via Nurture. But, distal or not, the genetic influences are strong and most of us develop along a path determined mainly by our personal genetic steersmen. It is often possible to intervene but it is seldom easy. A genetically timid child, for example, can be desensitized by carefully calibrated exposures to increasingly stressful situations. Meanwhile, a genetically venturesome child, a boy like General Chuck Yeager for example, is doing the same thing much faster on his own, climbing higher, taking greater risks, learning to fly, becoming a fighter pilot, then an ace, then a test pilot, and finally breaking the sound barrier.

In her soon-to-be-published book, The Nurture Assumption, Judy Harris argues that parents' contribution to what will be their children's adult personality, interests, and attitudes, is substantially completed when sperm meets egg. The experiences that will interact with the genome to determine that child's adult future occur mainly outside the home, with the peer group. One reason young adults feel slightly uncomfortable going home at Thanksgiving, Harris suggests, is that as children they learned one way of behaving at home and another way outside with their peers and it was the latter suite of habits and values that developed into their adult personas. Back home for a visit, they find themselves again wearing the parent-approved personality, a disguise they had discarded as children whenever they left the house and which they had thought was gone forever when they reached adulthood. This radical doctrine (to which I cannot do justice here, of course) dumps much of developmental psychology into the recycle bin and it is bound to dismay all parents except those whose children haven't turned out very well.

Yet Harris's arguments are so cogent and compelling that I, for one, have been forced to reassess. She says, in effect, that if we plotted the success of children's socialization on the Y-axis, and the skill of the parents on the X-axis, then the function relating the two variables would be a horizontal line. Harris has convinced me that the curve really is flat(that parents really are fungible(in the broad middle range between, say, the 10 percent and the 90 percent points on the X-axis distribution of parental competence. (Harris points out that this 80 percent approval rating is better than Clinton's!) But I think (although I cannot prove) that the curve rises on the far right, that there are some super-parents who really do make a lasting difference, the parents who succeed in socializing the really difficult children, for example. And I am confident that the bottom ten percent, the immature, abusive, unsocialized, or simply incompetent parents (which include a large proportion of the rising tide of impoverished and overburdened single mothers) are responsible for the epidemic of crime and other social pathology that has been accelerating in this country since the 1960s.

In spite of small declines each year since 1993, the rate of violent crime in the U.S. is presently 300 percent higher than it was in 1960. The recent dip is due largely to the fact that there are now 1.3 million Americans in state or federal prisons, compared to about 180,000 in 1965. Because the average inmate will privately admit to some 12 crimes committed in the year prior to his last arrest, imprisoning an extra million men is bound to yield a small but significant decrease in the crime rate. But it is an expensive and an inadequate solution. The place to fight crime is in the cradle. My own proposal would be parental licensure along the lines suggested by child psychiatrist, Jack Westman, in his 1994 book with that title.

Once again, evolutionary psychology and behavior genetics can provide guidance. Traditional societies, in which children are reared much as our ancestors were, experience very little intramural crime. The few outlaws in those communities tend to be people whose innate temperaments made them extraordinarily difficult to socialize, people we would now call psychopaths. We were designed by natural selection to be able to develop a conscience, feelings of empathy and altruism, to become responsible and to carry our share of the load in the group effort for survival. Like our language instinct, these socialization proclivities require to be elicited, shaped, and reinforced beginning in early childhood. In the extended-family milieu of our hunter-gatherer ancestors, with the help of numerous adults and the older children, we can suppose that this process was usually successful. When a modern young couple, inexperienced and untrained, attempt this most demanding of human responsibilities on their own, we can expect the failure rate to be higher. When a single mother, often immature and poorly socialized herself and usually in straightened circumstances, takes on this responsibility, the failure rate is very high indeed. In the U.S., more than two-thirds of(incarcerated delinquents, teenage mothers, high school dropouts, teenage runaways, juvenile murderers(were reared without fathers.

Evolutionary psychology does not tell us that crime is biologically determined but, rather, the opposite. Behavior geneticists have never located any "crime genes" although they have identified heritable traits of temperament that make some children hard to socialize. Regarding this greatest social problem of our time, these two lines of research dictate a message, not of fatalism, but of hope. Those 1.3 million men now languishing in American prisons began as innocent babes, some of them difficult, most of them average, almost all of whom could have been fashioned into taxpaying citizens, friends, and neighbors, had they been luckier in the circumstances of their growing up.