Why are we getting smarter?

[archerships]

A fascinating paper….

Heritability Estimates vs. Large Environmental Effects:
The IQ Paradox Resolved

Psychological Review, Vol. 108, No. 2 (April 2001)

William Dickens, Senior Fellow, Economic Studies, and
James R. Flynn, University of Otago

(Note: this is a synopsis of an article in Psychological
Review, vol. 108, no. 2, April 2001.)

Darwin's Origin of Species sparked the modern debate about
genes versus environment in explaining differences between
human individuals and groups. Ever since, the pendulum of
scientific opinion has swung back and forth with consensus
always out of reach. For the last 15 years, psychologists
have been plagued by a paradox that suggests that
environment is both feeble and overwhelmingly potent.

The paradox emerged from a debate about race. US whites
outscore US blacks on IQ tests by 15 points. Does that gap
have environmental causes or is it partially due to genes?
In 1973, Arthur Jensen constructed a model that applied
kinship data to group differences in IQ. Evidence from
kinship studies showed identical twins separated at birth
and raised in different homes grow up with very similar
IQs. The fact that they have identical genes provides an
obvious explanation. Jensen argued that fully 75 percent
of IQ variance between individuals was due to genetic
differences (a value which sits in the middle of the range
recently endorsed by a select committee of the American
Psychological Association for adult IQ). Jensen's model
showed that a purely environmental explanation of the
black/white IQ gap meant that the environment of the
average US black must be as unfavorable for the
development of IQ as the lowest one percent of white
environments measured in terms of their effects on
IQ. That simply did not seem possible.
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Jensen's model seemed to preclude a purely environmental
explanation for any large IQ gap between groups. Then, in
1987, Flynn showed that in nation after nation, the
current generation outscores the last generation by some 9
to 20 IQ points. The gains are greatest on those tests
often called the best measures of intelligence. Their size
and speed dictate an environmental explanation. Flynn
applied Jensen's model. An environmental explanation meant
putting the current generation within the top one-tenth of
one percent of the last generation in terms of
environmental quality. What was known to be true was shown
to be impossible.

How could solid evidence show both that environment was so
feeble (kinship studies) and yet so potent (IQ gains over
time)?

Dickens has proposed a model that we believe solves the
paradox. It assumes that people who have an advantage for
a particular trait will become matched with superior
environments for that trait; and that genes can derive a
great advantage from this because genetic differences are
persistent. A genetic advantage remains with you
throughout life, while environmental differences tend to
come and go, unless sustained by the steady pressure of
genes.

Take those born with genes that make them a bit taller and
quicker than average. When they start school, they are
likely to be a bit better at basketball. The advantage may
be modest but then reciprocal causation between the talent
advantage and environment kicks in. Because you are better
at basketball, you are likely to enjoy it more and play it
more than someone who is bit slow or short or
overweight. That makes you better still. Your genetic
advantage is upgrading your environment, the amount of
time you play and practice, and your enhanced environment
in turn upgrades your skill. You are more likely to be
picked for your school team and to get professional
coaching.

Thanks to genes capitalizing on the powerful multiplying
effects of the feedback between talent and environment, a
modest genetic advantage has turned into a huge
performance advantage. Just as small genetic differences
match people with very different environments, so
identical genes tend to produce very similar
environments-even when children are raised in separate
homes.

In other words, kinship studies of basketball, no matter
whether they involved people with identical genes or
different genes, would underestimate the potency of
environmental factors. Playing, practicing, being on a
team, coaching, all of these would be credited to
genes-simply because differences in them tend to accompany
genetic differences between individuals. Genes might seem
to account for as much as 75 percent of variance across
individuals in basketball performance. If someone showed
that the present generation was far more skilled at
basketball than the last (as indeed they are), Jensen's
math would prove that it was impossible. It would show
that those aspects of environment that are not correlated
with genes (which is all that environment gets credit for
in kinship studies) were very feeble. So feeble that the
present generation would have to be within the top one
percent of the last in terms of quality of environment for
basketball.

The cognitive ability differences measured by IQ tests may
have the same dynamics. People whose genes send them into
life with a small advantage for these abilities start with
a modest performance advantage. Then genes begin to drive
the powerful engine of reciprocal causation between
ability and environment. You begin by being a bit better
at school and are encouraged by this, while others who are
a bit 'slow' get discouraged. You study more, which
upgrades your cognitive performance, earn praise for your
grades, start haunting the library, get into a top
stream. Another child finds that sport is his or her
strong suit, does the minimum, does not read for pleasure,
and gets into a lower stream. Both of you may go to the
same school but the environments you make for yourselves
within that school will be radically different. The modest
initial cognitive advantage conferred by genes becomes
enormously multiplied.

Once again, just as different genes are matched with very
different environments, so identical genes will be matched
with very similar environments. You and your separated
identical twin will get very similar scores on IQ tests at
adulthood. Using Jensen's model, genes will get credit for
all of the potent environmental influences you both
share. And environment will appear so feeble that it could
not possibly account for the huge IQ advantage your
children enjoy over yourself. Our model shows why this is
a mistake. It shows that kinship studies hide or 'mask'
the potency of environmental influences on IQ. Therefore,
they do not really demonstrate the impossibility of an
environmental explanation of massive gains over time.

The model's next task it to suggest just how environment
performs its demanding role. Social forces affecting the
whole of society can provide something that an
individual's life experiences normally do not. They
provide environmental influences that are just as
persistent over time as the individual's genetic
endowment, and that are not at the mercy of genes. After
all, the present generation has no advantage in genetic
quality over the last, indeed, it is often argued that the
reverse is true due to the lower fertility of the more
highly educated. So between generations, the mask slips
and environmental forces stand out in bold
relief. Relatively small environmental differences between
generations gain enormous potency just as small genetic
differences between individuals did: They seize control of
the powerful reciprocal causation that exists between
cognitive ability and environment.

No one knows for certain what environmental trends caused
massive IQ gains but we can suggest a scenario consistent
with their history. There is indirect evidence that
massive gains in the cognitive abilities IQ tests measure
began in Britain as far back as those born in 1872. They
probably began with the industrial revolution and were
there waiting for IQ tests to be invented to measure
them. The industrial revolution upgraded years and quality
of schooling, nutrition, disease control, all things that
could have had a profound influence in raising IQ, at
least up to about 1950.

After 1950, in nations like the US and Britain, IQ gains
show a new and peculiar pattern. The are missing or small
on the kind of IQ tests closest to school-taught material
like reading and arithmetic. They are huge on tests that
emphasize on-the-spot problem-solving, like seeing what
verbal abstractions have in common, or finding the missing
piece of a Matrices pattern, or making a pattern out of
blocks, or arranging pictures to tell a story.

Perhaps the industrial revolution stopped demanding
progress in the basics and started demanding that people
take abstract problem-solving more seriously. Post-World
War Two affluence may be the key. It brought a dilution of
the pragmatic depression psychology, smaller families in
which children's whys were taken more seriously, work
roles in which people were expected to take more
initiative, more energy for making leisure more
cognitively demanding, whether devoted to chess or bridge
or video games or simply to conversation in which people
were expected to take ideas and logic seriously.

We call these products of the industrial revolution that
may have set massive IQ gains rolling 'triggers'. The
model itself does not specify ultimate causes and we
suggest those listed very tentatively. What the model does
do is demonstrate the potency triggers would gain from
seizing control of reciprocal causation between cognitive
ability and environment. The most dramatic tool at their
disposal is the 'social multiplier'. This posits that when
something raises the average performance of society, that
rise becomes a powerful cause in its own right, and raises
the average performance further, and raises it further,
until the original rise is greatly multiplied.

The most potent facet of our environment is other
people. When something, perhaps the popularity basketball
got from television, triggered greater participation in
basketball, the average performance rose as individuals
played more and got better. Initially, a few people learn
to shoot with either hand, then others imitate them. The
rise in average performance feeds back into a new
challenge for each individual. Those who want to excel
have to learn to pass with either hand and this spreads
and raises the average performance once again. In other
words, every rise in individual performance raises the
group average, which forces everyone to raise their
individual performance a notch higher, which raises the
group average a notch higher, and so on. Even a modest
environmental trigger of enhanced performance can become
potent by seizing control of the social multiplier-and
cause huge performance gains in a relatively short time.

The same kind of reciprocal causation explains IQ
gains. Environmental triggers raise the cognitive demands
of work, family interaction, leisure, and everyday
conversation. Those who respond by upgrading their
cognitive performance raise the average cognitive
performance. Then the rising average affects your
employer, family, and friends and they demand or expect
more, and you (and many others) rise to meet their
expectations, so the average cognitive performance jumps
once again, and so on, and so on. The model quantifies
this process and shows that quite plausible initial
environmental changes would be enough to explain huge IQ
gains-gains of 20 points over a single generation.

The model has a third task. It offers an explanation for a
whole range of other phenomena that have proved
baffling. Why people's genes seem to count more for IQ as
they age. Why enrichment programs boost IQ a lot at the
start, then little more, and then see their effects fade
away after children leave the program. Why cross-racial
adoptions do not raise the IQs of black adoptees to the
white average. Why certain methodologies produce nonsense
results, such as showing that group IQ differences known
to be environmental in origin have a genetic component.
And to return to the race and IQ debate, it shows that
environment could explain racial IQ differences just as it
explains IQ differences between generations.

Finally, the model has an overriding purpose. In
principle, it applies to the dynamics of any human ability
where there is positive feedback between that ability and
environment. We hope it will reconcile social scientists
who have divided themselves, sometimes with bitterness,
between hereditarians who think genes dominant and
environmentalists who think culture dominant. They are
both right: It all depends on whether genetic differences
or environmental factors seize control of potent processes
like the social multiplier. We hope that our model will
allow them all, from the psychologists inspired by Sir
Cyril Burt to the anthropologists inspired by Franz Boas,
to find common ground, and work together to advance our
understanding of human intelligence and other important
traits.
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