[Paleopsych] Oscar: Nature or nurture?
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Sun Apr 24 20:11:20 UTC 2005
Nature or nurture?
By Christine Parker Martin (Foreign Affairs '92)
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
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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