Interestingly, people with little or no exposure to personality research seem to
readily accept that both genetic background and experiences are important inshaping personality. Parents often point to personality traits their children
“got from me, ”but few would deny that the way they raise their children also
plays a large role in what kind of adults the children become. Thus the ques-
tion is not which of these —genetics or environment —shapes our personalities
but rather to what extent and how our personalities are shaped by each.
So we might rephrase the question this way: To what degree was the
mold for your adult personality already cast by the time you were born?
Researchers now agree that relatively stable abilities and aptitudes, such as in-
telligence, appear to have a genetic component (Plomin & DeFries, 1998).This is not to say that a highly intelligent child cannot be born to relatively
unintelligent parents or that a child ’s environment plays no role in intellectual
development. But it does appear we are born with a potential for intelligence
that combines with environmental influences to determine adult intelligence le-
vels. Similarly, many psychological disorders appear to be affected by the genes
we inherited (Crabbe, 2002; DiLalla, Carey, Gottesman, & Bouchard, 1996;McGue & Christensen, 1997; Rhee & Waldman, 2002). Again, this does not
mean people are born to be schizophrenic or depressed. Rather, some people
are born with a higher susceptibility to these disorders than are others.
What about personality traits? Are people born to be aggressive or extra-
verted? There is now ample evidence that genetics influences these and otherpersonality traits. However, collecting evidence on this issue is not easy, and
many questions remain about how to interpret the data that are available.
Separating Environmental from Genetic Influences
Psychologists working on the environment –genetics question have a some-
what different task facing them than those working in other areas of person-
ality research. For technological and ethical reasons, it is not possible tomanipulate people ’s genes and observe the kind of adults they become.
Instead, researchers must rely on less direct means. Like detectives trying topiece together a picture of how we got to where we are, these researchers use
innovative and sometimes clever experimental procedures to track down the
roots of adult personalities. Each method has limitations and weaknesses,but data from a number of sources suggest a significant role for genetics in
the development of our personalities.
The most obvious source of information on this question is the similarity
of parents and children. Aggressive parents often have aggressive offspring;shy children often come from homes with shy parents. Similarly, we often
see brothers who are both outgoing or sisters who are both sensitive and car-
ing. Casual observers look at these relationships and often assume the chil-
dren inherited these traits from their parents. However, there is an obvious
alternative explanation for these similarities. Members of a family not only
share genes, they share living environments as well. Siblings ’personalities
may be similar because the parents raised them in the same basic manner.
Children of introverted parents might become introverted because of the
calm and quiet home they grow up in.252 CHAPTER 10 The Biological Approach