Psychology2016

Theories of Personality 527

The results of the Minnesota twin study have revealed that identical twins are
more similar than fraternal twins or unrelated people in intelligence, leadership abilities,
the tendency to follow rules, and the tendency to uphold traditional cultural expecta-
tions (Bouchard, 1997; Finkel & McGue, 1997). They are also more alike with regard to
nurturance,* empathy,** assertiveness (Neale et al., 1986), and aggressiveness (Miles &
Carey, 1997). This similarity holds even if the twins are raised in separate environments.

ADOPTION STUDIES Another tool of behavioral geneticists is to study adopted chil-
dren and their adoptive and birth families. If studying genetically identical twins
raised in different environments can help investigators understand the genetic influ-
ences on personality, then studying unrelated people who are raised in the same environ-
ment should help investigators discover the influence of environment. By comparing
adopted children to their adoptive parents and siblings and, if possible, to their biolog-
ical parents who have not raised them, researchers can uncover some of the shared and
nonshared environmental and genetic influences on personality.
Adoption studies have confirmed what twin studies have shown: Genetic influ-
ences account for a great deal of personality development, regardless of shared or

*nurturance: affectionate care and attention.
**empathy: the ability to understand the feelings of others.

Figure 13.5 Personalities of Identical and Fraternal Twins
Identical and fraternal twins differ in the way they express the Big Five personality factors. In a recent study, data
from 696 twin pairs suggest identical twins have a correlation of about 45 percent for self-ratings across each of
the Big Five factor domains, whereas fraternal twins have a correlation of about 22 percent. These findings give
support to the idea that some aspects of personality are genetically based.
Based on: Kandler et al. (2010)

0.50

0.20

0.25

0.30

0.35

0.40

0.45

Corr

elation of scor

es

0.15

Neuroticism

0.10

0.05

0.00

Extraversio

n

Openness

Agreeableness

Conscientiousness

Averages across Big Five factor domains

Monozygotic Dizygotic

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