General Occupational Themes and Basic Interest Scales of the
Strong Interest Inventory appear to stem from shared environmen-
tal effects (Betsworth et al., 1994).
5.Niche development as culmination of a gene-driven, culturally con-
strained trait development process.Our different social niches and out-
comes in adulthood—including careers—can also be conceptualized
as part of the trait development process, because they too are shaped
somewhat by our genotypes. These are represented in column 4 of
Figure 4.6. Behavioral geneticists often describe the personal events
and circumstances of our lives as our “extended phenotypes,” that is,
as factors seemingly outside ourselves but actually rooted partly in
our own genes. We know that these seemingly external factors have
a genetic component because, as noted before, many broad life out-
comes are moderately heritable. Moreover, multivariate genetic
analyses show that their heritable components overlap those for
general traits of personality or intelligence. For example, from one-
half to two-thirds of the heritable differences in education, occupa-
tion, and income level share the same genetic origins as intelligence
(Lichtenstein & Pedersen, 1997; Rowe, Vesterdal, & Rodgers,
1998), perhaps because phenotypic intelligence has such strong
effects on career attainment. (The outcomes’ genetic overlap with
other traits has not yet been assessed.) Because our environments
do not carry our genes, they correlate with our genotypes only be-
cause we select, create, and act on those environments.
An important difference between the development of life niches
and of general traits such as intelligence, however, is that general
traits develop relatively independently of cultural variation. In con-
trast, individual differences in life roles, activities, and niches—our
extended phenotypes—are less heritable, on average, because cul-
tures channel and constrain the use of even the most heritable traits.
Cultures limit our actions on the world around us. Depending on the
cultural era or ends in question, then, our genetic compass or gyro-
scope may have less influence and cultural forces more influence on
which activities we undertake and which niches we actually occupy.
Individual differences in level of education, occupation, and income,
122 CAREER CHOICE AND DEVELOPMENT