less genetically heritable—perhaps insignificantly so, as environ-
mental influences accumulate with age. This expectation is shown
in the top panel of Figure 4.5 by the successively thicker arrows
from “experience” to “traits” but a waning influence for genes with
advancing age.
Research Disproving Socialization Theory
Although most social scientists still favor socialization theory for
explaining the differences among us, behavioral genetic research has
nonetheless decisively disproved it. The theory’s Achilles heel is that
it rests on correlations between relatives without regard to their
genetic relatedness. However, no conclusions whatsoever can be
drawn about environmental effects from correlations between chil-
dren and the biological parents or siblings with whom they live,
because those correlations reflect some unclear mix of genetic and
nongenetic influences on the children. The two sorts of influence
can be disentangled only by studying pairs of family members that
reflect different degrees of environmental and genetic relatedness,
for instance, identical twins raised apart (they share 100 percent of
their genes but 0 percent of their family environments, meaning that
any similarity between them is owing to genes) and adopted children
raised together (they are no more genetically alike than strangers but
100 percent alike in family environment, meaning that any similar-
ity is owing to shared environments). The following seven replicated
findings from genetically sensitive family studies (primarily from
families of working class or higher in Western countries) suffice to
illustrate that socialization theory is false (for reviews, see Bouchard,
1998; Plomin, DeFries, McClearn, & McGuffin, 2001; Wachs, 1992;
in the context of vocational interest theory, see Gottfredson, 1999,
and Betsworth & Fouad, 1997). The sixth and seventh findings have
shocked even behavioral geneticists.
1.Heritability of highly general traits. Individual differences in all
broad psychological traits studied so far (mental abilities and dis-
110 CAREER CHOICE AND DEVELOPMENT