[Paleopsych] Oscar: Nature or nurture?

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Nature or nurture?

    By Christine Parker Martin (Foreign Affairs '92)
    Posted 2/17/05

    Think back ... way back ...to grade school, when you were given a
    Styrofoam cup, potting soil and a bean. You took care to deposit your
    bean in the rich soil and tenderly watered it. Then, names were picked
    from a hat to decide which cups would get a spot on the windowsill,
    relegating the others to a shelf inside a cupboard. You might remember
    the outcome of this simple biology experiment, particularly if your
    bean plant resided in the dark cupboard.

    As with bean plants, the development of human traits involves both
    nature (genes) and nurture (environment). Psychology professor Eric
    Turkheimer demonstrated this phenomenon as it applies to IQ in a
    landmark twin study published last year in Psychological Science.
    Turkheimer's findings diverge from earlier nature/nurture IQ studies,
    which suggested genes are nearly all-important in determining
    differences in human intelligence and consequently led to heated
    debate as to whether publicly funded childhood assistance programs
    like Head Start can make a difference.

    "We found that for the poorest twins, IQ seemed to be determined
    almost exclusively by their socioeconomic status, which is to say
    their impoverished environment. Yet, for the best-off families, genes
    are the most important factor to determining IQ, with environment
    playing a much less important role," Turkheimer explained.

    Turkheimer's findings may seem intuitive. After all, the bean plant
    devoid of light not surprisingly emerges stunted. And the toy industry
    is capitalizing on this idea with best-selling enrichment products
    like Baby Einstein(TM) videos and black, white and red mobiles.
    Moreover, who hasn't heard such anecdotal evidence as the inner-city
    kid who beat all odds and wound up at Harvard thanks to a teacher who
    provided nurturing, stability and motivation?

    Yet, earlier nature/nurture IQ studies repeatedly demonstrated that
    people's genes--not environment--account for variability in individual
    IQ. And Turkheimer acknowledges, too, the undeniable importance of
    genes to human traits, including IQ. "We often joke in behavior
    genetics that everybody is an environmentalist until they have their
    second child," he said.

    But the research as it stood didn't satisfy Turkheimer, who felt
    previous studies told "too simple a story" because lower-income and
    impoverished families were typically, yet unintentionally,
    underrepresented in such studies. Said Turkheimer: "I'm a clinical
    psychologist, and I've seen and tested people raised in poverty whom I
    knew from observation had suppressed IQs because of their poverty."

    Turkheimer's study differed from previous twin IQ studies in two
    important ways. First, he identified a data source comprised of over
    600 twin pairs, of which a substantial proportion represented families
    living near or below the poverty level. Second, Turkheimer relied on
    fairly recent statistical advances that made it possible to determine
    the importance of genes as a function of socioeconomic status.

    The study results show that in the most impoverished families,
    hereditability of IQ is essentially zero, with environment accounting
    for almost 60 percent of the differences in IQ among individuals. The
    impact of environment declines as socioeconomic level improves,
    playing a nominal role in the most affluent families, for which
    virtually all variability in IQ is attributed to genes.

    The study suggests that specific minimal environmental conditions are
    necessary for a person's genetic potential to be expressed.
    Socioeconomic status is a complex variable, and Turkheimer doesn't
    identify these factors, such as prenatal care, nutrition, income or
    parental involvement, for example, or suggest their relative
    importance to the results. "I think it's the accumulation of many,
    many small things that together make poverty, rather than any one
    thing that matters most," he speculated.

    Turkheimer recently replicated the study using a different twin
    sample, a necessary step before he or others can begin to try to
    understand the phenomenon in detail and look at such questions as
    "What kinds of intelligence and abilities, aside from IQ, are
    particularly sensitive to environment?" and, conversely, "What kinds
    of environmental differences are particularly important to
    intelligence and abilities?"

    Yet even without all the answers, Turkheimer is satisfied that his
    study now provides a theoretical framework in which it would be
    reasonable to expect that programs like Head Start might work. Noted
    Turkheimer: "It suggests that if you're going to work with people's
    environment to try and increase IQ, then the place to invest your
    money is in taking people in really bad environments and making them
    OK, rather than taking people in pretty good environments and making
    it better."

    Christine Parker Martin (Foreign Affairs '92) is a freelance writer
    who lives in Charlottesville with her husband and their son and

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