temporarily in childhood) or in personality. This fact is illustrated
by biological siblings who are no more alike phenotypically by ado-
lescence in these respects than their genetic similarity (50 percent,
on the average) would predict. It is also shown by adoptive siblings
who are phenotypically no more alike than strangers by adoles-
cence. In fact, while adoptees losetheir early similarity in IQ with
adoptive relatives as they age (a similarity that could have arisen
only from living in the same home), they become moresimilar to
the genetic relatives they have never met. Surprisingly, it is only the
environments that siblings do notshare that permanently affect
their general mental abilities and personality traits. Behavioral
geneticists have therefore concluded that “[e]nvironmental influ-
ences largely operate in a nonshared manner, making children
growing up in the same family different from one another” (Plomin
et al., 2001, p. 304). Researchers have yet to identify specifically
what those nonshared factors are, but some suggest that they are
random and thus uncontrollable. It should be noted, however, that
manynarrowerskills and behaviors might be subject to shared envi-
ronmental effects. This has been shown true of vocational interests,
for example, as will be discussed shortly.
8.Polygenic nature of complex heritable attributes. Finally, be-
havioral geneticists believe that, with the exception of certain
single-gene disabilities, individual differences in complex traits and
behaviors arise from the cumulative action of many genes. Having
shown that all complex traits yet studied are substantially heri-
table, researchers are now looking for the genes involved.
In short, socialization theory is false. We are not passive lumps of
clay merely to be molded by chance or others’ artifice; we are active
agents in our own creation. We help to create our own environments
and experiences—and hence our selves—based on our genetic ten-
dencies. To the extent that our most central, stable traits are perma-
nently shaped by nongenetic forces, those forces are not the ones that
even behavioral geneticists had once assumed. Namely, they are not
114 CAREER CHOICE AND DEVELOPMENT