Published: November 10, 2003
by: Jan Richter
Research
published this month is shedding new light on the
old nature/nurture argument. In a dramatic shift from
previous findings, this analysis finds that for families
at the very bottom of the socio-economic scale, environmental
factors have a much greater impact on the variations
in children’s IQ (Intelligence Quotient) than
genes.
For a piece of dense research couched in the language
of advanced statistics, Eric Turkheimer’s paper
in the November, 2003 issue of Psychological Science
is making quite a splash. That’s because the
main finding has such powerful policy implications.
Understanding the Research Findings
But reading Turkheimer’s report of his research
is not easy—it relies on new statistical methods
and computations that are difficult for the layman
to understand. So I decided to ask Turkheimer, a professor
of psychology at the University of Virginia, for a
tutorial. He and I met on a beautiful afternoon in
his office in mid-October, and talked for about an
hour.
I came away with a better understanding of why these findings are different from those of many previous studies. And why he’s confident his findings have serious policy implications for impoverished families.
Until now, “hard science” has been unable to demonstrate that home and community environments have much impact on variations in children’s IQ. Instead, genes have been found to account for most of the differences in IQ.
But what Turkheimer and his colleagues found was
that although the environmental impact on IQ is very
small when you look at families with incomes in the
moderate range, the reverse is the case when you look
at very low-income families.
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What's So Special
About IQ?
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How a Different Sample and Different Methods
Reveal Different Findings
One thing I wanted to know was why Turkheimer’s
results were so different from those of earlier studies.
On this, he made two points: first, that some earlier
studies had found similar results, but the findings
hadn’t been as clear; second, that the most
impoverished families were underrepresented in most
earlier studies.
“Our study found the phenomenon more definitively than anyone had ever found it before, using a better sample and better methods, but it wasn’t a bolt from the blue,” said Turkheimer.
Turkheimer explained that he had always accepted the view that genes play an important role in determining IQ. “What seemed troubling was the other side of that coin: that you couldn’t find an effect of family environment on IQ, or at best, at very best, you could find a small effect under ideal circumstances. And that just always seemed wrong,” he told me.
So when the opportunity arose to more closely investigate the relationship between IQ and environment among impoverished families, Turkheimer seized it.
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The National Collaborative Perinatal Project
database:
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Two things made the project possible: the public
release of a large, rich database including an unusually
large number of children from families of very low
socio-economic status; and advances in statistical
methods that use computers to carry out huge numbers
of computations very quickly.
Twin studies are the basis for much of the research
into the relative roles played by genes and the environment
in IQ. Research like Turkheimer’s relies on
the difference between fraternal twins, who are as
genetically similar as any siblings, and identical
twins, who share exactly the same genes.
For traits that are primarily determined by genes, identical twins will show no variation, but fraternal twins will. For traits that are determined by environment, identical twins and fraternal twins will show similar patterns of variation in the trait. For traits that reflect an interaction between genes and environment, identical twins will show somewhat less variation than fraternal twins. (Confused about twin studies? [1])
What Turkheimer found was dramatic: for the families
in the study at the very bottom of the socioeconomic
scale, shared family environment accounted for 60
percent of the variance in IQ; and the contribution
of genes was close to zero. (A third variable, non-shared
environment, which includes factors such as gender,
accounted for the remainder.)
As he looked at families further up the socio-economic
ladder, the effects of environment rapidly declined,
and genes took on an increasingly important role.
“The more poor families that you leave out (of
the sample), the more important the genes get…If
you leave out the bottom third of the sample, which
is what a typical twin study would do, you would completely
misrepresent what is going on,” said Turkheimer.
What the New Findings Mean for Parents and
Policies
Turkheimer believes his findings are helpful for clarifying
both public policy and decisions within individual
families.
For middle class families, he notes, “In the range where a lot of people spend their time…you know, ‘Should I hang the black and white mobile over my kids’ crib?’ kind of thing, it probably does not matter.”
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[2]
(:18)For very low-income families, on the other hand,
programs like Head Start and others that aim to provide
low-income children with better nutrition and health
care and richer experiences are “a good thing.”
But he cautions that “In the long run, what’s
going to help the most is getting kids out of that
state called poverty.”
What his research cannot do is identify the specific
environmental or family factors that contribute to
the variations in IQ among impoverished children.
Lead poisoning, poor nutrition, asthma, limited exposure
to varied experiences, stress, low-quality schooling
– there are plenty of potential contributors.
“My honest expectation is that it is not the
case that there is some major secret ingredient to
bad environments that is accounting for this,”
said Turkheimer. “What poverty is, is an accumulation
of a great many very small deprivations.”
“I would be very surprised if anyone ever did
research that showed, well, if your kids are raised
in poverty, if they get a good hot lunch every day,
then their IQ’s are going to be OK. Or if somebody
reads to them every day, or anything else like that,”
he added.
Turkheimer hopes that people will understand that
his findings do not mean that genes aren’t important
in IQ. “Too often, I think, people are attracted
to a polarized view. Genes ARE playing a role even
in the poorest of families, and across a broad range
of families they play a very important role, and it
would be foolish to close our eyes to that,”
said Turkheimer.
But understanding that there is a segment of our population
for whom family environment is much more important
than genes in determining IQ variation suggests that
changing environmental factors for these families
can change their children’s ability to learn.
In this study, as in IQ studies generally, higher socioeconomic status is associated with higher IQ scores.
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Turkheimer’s research has been drawing praise and vitriol on internet blogs from the left and right ever since the day a description of his research appeared in the Washington Post on September 2, 2003.
Turkheimer says he’s confident that his results
are sound, and will be replicated by other researchers.
“The most important thing to say is that it
is an extremely robust finding…I’ve analyzed
the data in a number of ways that are not repeated
in the paper…and you get the exact same result
no matter how you do it.”
If you ask him what he’d like people to understand
about his research, he’d say it gives us a different
picture than we had before about the relative role
of environment and genes on IQ differences among children.
It’s not that genes are not important, but,
for children living in deepest poverty, environment
accounts for more of the IQ differences than genetic
inheritance.
But if you pin him down—to one thing that would make a big difference—he will say that helping impoverished families improve their circumstances—getting them out of poverty and the conditions that typically accompany poverty—is critically important.
Resources:
The research referred to in this interview has been published in the November issue of Psychological Science, Vo,. 14, No. 6, under the title “Socioeconomic Status Modifies Heritability of IQ in Young Children,” Eric Turkheimer, Andreana Haley, Mary Waldron, Brian D’Onofrio, Irving I Gottesman.
The graphs were adapted from that article by Connect for Kids.
Jan Richter is the advocacy director for Connect for Kids.
http://www.connectforkids.org/node/516
Links:
[1] http://www.connectforkids.org//usr_doc/11_10_TurkheimerTwinStudies.htm
[2] http://stream.realimpact.net/rihurl.ram?file=realimpact/benton/c4k/Audio/turkheimer1.rm
[3] http://stream.realimpact.net/rihurl.ram?file=realimpact/benton/c4k/Audio/turkheimer2.rm
[4] http://www.connectforkids.org//resources3139/resources_show.htm?attrib_id=5016&doc_id=198202&parent=82335