Chapter 7 Thinking and Intelligence 249et al., 2009). (You might review pages 57–59 to
refresh your memory about heritability.)
Behavioral-genetic studies show that the kind
of intelligence that produces high IQ scores is
partly heritable, at least in the middle-class sam-
ples usually studied. For children and adolescents,
heritability estimates average around .40 or .50;
that is, genetic differences explain about half of
the variance in IQ scores (Chipuer, Rovine, &
Plomin, 1990; Devlin, Daniels, & Roeder, 1997;
Plomin, 1989). For adults, most estimates are
even higher—in the .60 to .80 range (Bouchard,
1995; McClearn et al., 1997; McGue et al., 1993).
These estimates show that the genetic contribu-
tion becomes relatively larger and the environ-
mental one relatively smaller with age.
In studies of twins, the scores of identical
twins are always much more highly correlated
than those of fraternal twins, a difference that
reflects the influence of genes. In fact, the scores
of identical twins reared apart are more highly
correlated than those of fraternal twins reared
together, as you can see in Figure 7.5. In adoption
studies, the scores of adopted children are more
highly correlated with those of their birth parents
than with those of their biologically unrelated
adoptive parents; the higher the birth parents’
scores, the higher the child’s score is likely to be.
As adopted children grow into adolescence, the
correlation between their IQ scores and those
of their biologically unrelated family members
diminishes, and in adulthood, the correlation falls
to zero (Bouchard, 1997b; Scarr, 1993; Scarr &
Weinberg, 1994). This does not mean that adop-
tion has no positive effects; as a group, adoptedRecite & Review
Recite: Out loud, say how the cognitive approach to intelligence differs from the psychometric
approach, and what you know about working memory, metacognition, Sternberg’s triarchic theory,
and emotional intelligence.
Review: Next, reread this material.Now take this Quick Quiz:
- What goals do cognitive theories of intelligence have that psychometric theories do not?
- Logan understands the material in his statistics class, but on tests he spends the entire period
on the most difficult problems and never even gets to the problems he can solve easily. Which
ingredient of intelligence does he need to improve? - Tracy does not have an unusually high IQ, but at work she is quickly promoted because she
knows how to set priorities, communicate with management, and make others feel valued.
Tracy has __ knowledge about how to succeed on the job.
Answers:
Study and Review at MyPsychLabto understand people’s strategies for solving problems and use this information to improve mental performance 1.tacit 3. metacognition2.You are about to learn...
• the extent to which intelligence may be
heritable.
• a common error in the argument that one group
is genetically smarter than another.
• how the environment nurtures or thwarts mental
ability.
• the role of motivation and hard work in
intellectual performance.
the Origins
of Intelligence
“Intelligence,” as we have seen, can mean many
things. But however we define or measure it, clearly
some people think and behave more intelligently
than others. What accounts for these differences?
Genes and Individual Differences
LO 7.15
Behavioral geneticists approach this question by
doing heritability studies, focusing mainly on g,
the kind of intelligence measured by IQ tests.
Heritability is the proportion of the total variance
in a trait within a group that is attributable to
genetic variation within the group (see Chapter 2).
This proportion can have a maximum value of 1.0,
which means that the trait is completely heritable—
although most traits, including even height, are not
perfectly heritable; genes interact constantly with
the environment throughout our lives (Johnson
heritability A statistical
estimate of the proportion
of the total variance in
some trait that is attrib-
utable to genetic differ-
ences among individuals
within a group.