Placentation Research - Meng Hu's Blog

CHAPTER 6
on Wechsler’s Vocabulary subtest (Rowe, Jacobson, & Van den
Oord, 1999). When categorized by parental education, the heritability
for the most highly educated families averaged 74%, versus
26% for the less well-educated families (Rowe et al., 1999).
In a twin study conducted in Russia, Grigorenko and Carter
(1996) evaluated the parenting styles of the mothers of identical
and fraternal twins and analyzed these relationships as a function
of the family’s social class. They found parenting styles to
differ for the two types of twins (e.g., mothers of identical twins
tended to infantilize identical twins more than did mothers of
fraternal twins, and to be more authoritarian). Parenting styles
also differed by social class. Grigorenko and Carter (1996) found
that Russian mothers with less education and lower occupational
status were more likely than their more educated, higher-status
counterparts to use authoritarian approaches, to view their children’s
behavior less positively, and to infantilize their twins’ behavior.
The styles associated with lower social classes also tended
to be associated with lower children’s IQs. These findings are especially
important because they challenge the basic assumption
that identical twins are raised in exactly the same way as fraternal
twins, and they remind us that heritability of IQ should not
be interpreted in a vacuum but ideally needs to be interpreted
within the context of social class and parenting styles.
Heritability and Ethnicity
Fischbein’s (1980) study included African Americans and Whites,
but his emphasis was on social class, and he administered only
one subtest (Vocabulary), not a complete IQ test, so we know little
about heritability for Whites versus African Americans. However,
heritability seems to be a function of ethnicity. Scarr and
Carter-Saltzman (1982, Figure 13.12) demonstrated substantial
differences among three ethnic groups in the relationships between
the cognitive scores obtained by children and their parents.
Correlations between children’s scores on cognitive tests
and their parents’ scores (average of fathers’ and mothers’ scores)
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