Saturday, February 23, 2008

The Bell Curve revisited: What science teaches us about heredity and environment

From The American Prospect, November 19, 2007. See
Excerpted by permission from The Sandbox Investment: The Preschool Movement and Kids-First Politics. Harvard University Press, Copyright © 2007 by David L. Kirp.
Nature, Nurture, and Destiny

The Bell Curve
revisited: What science teaches us about heredity and environment.
By David L. Kirp

In making the case for better early education programs, advocates rely heavily on bench science. Neuroscientists are summoned to demonstrate the palpable impact of severe deprivation in the first years of life -- recall the horrific accounts of the Romanian orphans -- and to show, with vivid MRI images, how early experience builds the scaffolding for everything that follows, as the brain incorporates early experience into its biological structure.

Mention genetics, however, and the advocates immediately change the subject. Those with an appreciation of history know that the American Eugenics Movement proposed sterilizing the "unfit" and that Hitler's Germany used the research for unspeakable purposes. When psychologist Richard Lerner wrote about the misuse of genetics, he pointedly titled his book Final Solution. And you don't have to be a history buff to recall that, in the mid-1990s, The Bell Curve became the bible of social conservatives with its conclusion that genetically-based IQ deficiencies of African Americans explain their disproportionate rates of poverty and incarceration, and that early education was a waste of money. Most recently, eminent scientist James Watson opined that he was "inherently gloomy about the prospect of Africa" because "all our social policies are based on the fact that their intelligence is the same as ours -- whereas all the testing says not really." Science must address questions of genetics and intelligence, he added, though the answers may be "cruel."

But as widespread denunciation of Watson's remarks suggests, liberals no longer have to fear genetics. Quite the contrary -- the "heredity versus environment" model, the intellectual underpinning of The Bell Curve, is itself wrong. A new generation of studies shows that genes and environment don't occupy separate spheres, that much of what is labeled "hereditary" becomes meaningful only in the context of experience. When it comes to explaining life outcomes it's not nature versus nurture but nature through nurture. What's more, in the topsy-turvy social world in which many poor kids grow up, it's almost all about nurture.

Such findings give added scientific heft to the preschool research that shows the effects of high-quality early education on an array of life outcomes. Those iconic studies demonstrate that early educational experiences can make a major difference. Genetics, no less than neuroscience, helps to explain why.

Environment 101

Over the years, studies of adopted children have found that their IQ scores are considerably closer to their biological parents' scores than to their adoptive parents' scores. That led geneticists to a logical conclusion: Intelligence is mainly inherited. But the newest research, looking at a range of other variables -- especially poverty -- has upended the conventional wisdom by showing the profound importance of the environment on later aptitude.

In one instance, experts tracked French youngsters from hardscrabble backgrounds -- abusive homes, impersonal institutions, multiple foster care placements and the like -- whose IQ scores averaged just 77, borderline retardation. Nine years after they were adopted, all of their scores had improved. Those adopted into affluent families jumped the most -- their progress was directly associated with their new socioeconomic status. The only, and crucial, difference among these children was the lives they'd led after being adopted.

Other research, notably by University of Virginia psychologist Eric Turkheimer, has focused on outcomes for twins, the gold standard in the field. Earlier research had shown that IQ differences were considerably smaller for identical than for fraternal twins, a finding consistent with the hereditarian view. But Turkheimer was the first researcher to focus on IQ differences between twins from poor and non-poor families. The key finding: Variations in IQ scores for twins from well-off families are mainly genetic, while heredity explains almost none of the IQ differences for twins in the poorest families. The impact of growing up poor overwhelms these children's genetic capacities.

Some of the most exciting work in the field of molecular genetics today aims at specifying the genes associated with diseases ranging from cancer to Alzheimer's, with the eventual hope of finding a cure. There is also an ongoing search for the "intelligence gene" or genes that can explain variations in intelligence, a hunt for the biological source of general intelligence. But that research, most scientists now believe, will confirm what the research on twins and adoptions has shown: The impact of heredity and environment on IQ is indelibly intertwined.

For years, molecular genetics focused on finding "candidate genes" -- the genes for a specific condition. There have been a few successes, Alzheimer's among them, and some spectacular failures, such as the supposed "manic depression gene" among the Amish. Identifying a gene is only the first step in establishing the pathway to any condition. Specifying that pathway means identifying the environmental influences on gene expression, the key process that determines the functional operation of genes.

Many scientists are now shifting gears. "Rather than trying to find the gene that causes a particular outcome," notes Thomas O'Connor, a psychologist at the University of Rochester Medical Center, who is studying the long-term impact of prenatal stress, "we said, 'let's think about how it's mediated through environmental risk.' Rather than, say, trying to link a serotonin transmitter directly to depression, it makes better sense to think about a genetic predisposition that's literally turned on or off by life risks."

Groundbreaking recent research has shown specific instances in which variations in the environment determine actual "gene expression" -- that is, the form, or allele, the gene takes. In large-scale studies in New Zealand, psychologists Avsholom Caspi and Terrie Moffitt have demonstrated that MAO, the gene linked to aggressive and potentially violent behavior, is effectively deactivated when an individual grows up in a caring family. A relatively stress-free home life has the same benign effect on the 5-HTT gene, which helps regulate the brain's production of serotonin, a neurotransmitter likely linked to depression. Similarly, Finnish researchers have established that a child's environment can moderate the effect of the gene, DRD4, which is linked to thrill-seeking.
These studies offer genetic confirmation of earlier investigations that relied on clinical assessments to show that parents have a big influence in structuring children's worlds. And those early experiences have a powerful, long-lasting impact on children's resilience to many kinds of stress. "We're learning that it doesn't matter whether we're looking at gum disease, heart disease, cancer, depression, or risk-seeking," says Moffitt. "There's no straight genetic effect -- the vulnerability only emerges in circumstances of environmental risk."

Scientists have begun to trace these vulnerabilities back to the womb. "We're showing the persisting effects of stress in pregnancy on kids," says O'Connor. "We have been desperate to treat anxious, pregnant women, to see if making them less anxious will have an effect on the kid," he adds. "If responses to stress are tied to the immune function, psychological outcomes, maybe intelligence, then all bets are off. We could save the world by making moms less stressed in pregnancy."

In a series of animal experiments, Moshe Szyf and Michael Meaney at McGill University's Medical School have knocked another hole in genetic fatalism. Even when the structure of a gene isn't altered, the expression of individual genes can be permanently changed by changing the environment. Szyf and Meaney assigned rats born to anxious mothers, who didn't give their offspring adequate maternal licking, to high-licking rats. Not only did the nurturing behavior of these "foster" mothers change the pups' behavior -- they grew up to be calmer and smarter -- but the maternal grooming altered the mechanism in the baby rats' brains that regulates stress hormones. That alteration in brain chemistry persisted into adulthood: Even though there was no change in the underlying gene, the offspring of these well-raised rats were less anxious as well.

The IQ Gene?

Since the early 1990s, scientists have been on a quest for the gene -- or, more likely, the cluster of genes -- "for" IQ. So far they haven't been successful. Identifying a gene that significantly contributes to a well-defined disorder is hard enough, because of the interactions between nature and nurture described above. An even more sophisticated array of interactions makes the quest for an "intelligence gene" seem quixotic.

Even if a cluster of genes were found to be associated with IQ, the implications aren't obvious. This wouldn't show definitively that IQ is "real." After all, as Eric Turkheimer points out, "You could make up a concept, like being a good speller with big feet, and find genes that are associated with it." Complex social and biological concepts like intelligence don't allow for easy answers.

Robert Plomin, an internationally renowned molecular geneticist, and his research team at the University of London thought they had solved part of this puzzle in 1998 when they located a gene that was statistically associated with high SAT scores. That gene accounted for just 2 percent of the variance, though, and when the scientists redid the study in 2002 they couldn't replicate the result. To a thoughtful skeptic like Turkheimer, "Rooting around in the brain to find [a gene for intelligence] is a mistake." University of Sydney psychologist Dennis Garlick adds that even if such genes were found, "it is still a long road from identifying the genes responsible for intelligence to actually understanding what they do, and hence understanding how intelligence is inherited."

Genetics has traditionally been the redoubt of the hereditarians, but contemporary science is telling a different story. "I am skeptical that genetic work ever will provide an understanding of the basis of intelligence," says Sir Michael Rutter, professor of developmental psychopathology at the University of London. "It doesn't really matter whether the heritability of IQ is this particular figure or that one. Changing the environment can still make an enormous difference."

Appreciating how genes do their work is the heart of the matter, and this is where the infinitely intricate mechanisms of interplay between nature and nurture once again claim center stage. "Everything interacts with everything else," says Turkheimer. That conclusion unites cutting-edge research in genetics and neuroscience.

Across a wide array of disciplines in the natural and social sciences -- developmental and behavioral neuroscience, genetics, medicine, cognitive and developmental psychology, among them -- researchers are converging on a new understanding of human development, one that emphasizes the interplay of nature and nurture. The connections between neuroscience and molecular genetics are especially tantalizing.

Brain science focuses on the pathways of the brain, while molecular genetics looks at what's being transmitted along those pathways. "Of all the developments that have contributed to neuroscience in the past two decades," observes Nobel Prize-winning neurophysiologist Eric Kandel, "none has had a greater impact than the application of molecular genetics."

The hope is that this synthesis will reach beyond science, with its promise of elegant answers, to take account of the blooming complexities that real life introduces into the mix. That's the ultimate promise in this research -- relating findings in the laboratory to the processes of brain development over the course of a lifetime. When that day comes, the brain scientists and geneticists will be able to speak with specificity to parents and educators about the circumstances in which their young charges are most likely to thrive. Meanwhile, their findings bolster advocates' arguments -- no less than parents' intuitive sense -- that early education can have a profound impact on the future of a child.
Excerpted by permission from The Sandbox Investment: The Preschool Movement and Kids-First Politics. Harvard University Press, Copyright © 2007 by David L. Kirp.
David L. Kirp is a professor of Goldman School of Public Policy at the University of California, Berkeley, and a frequent contributor to the Prospect.

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