Feist−Feist: Theories of
Personality, Seventh
EditionIV. Dispositional Theories 14. Eysenck, McCrae, and
Costa’s Trait and Factor
Theories(^434) © The McGraw−Hill
Companies, 2009
going from biological bases to basic tendencies. Such a claim is based mostly on the
robust findings from behavioral genetics that the five dimensions of personality can
be almost exclusively explained (about 50% each) by two factors, namely genetics
and non-shared environment (Hamer & Copeland, 1998; Loehlin, 1992; Plomin &
Caspi, 1999). Genetic influence is demonstrated by what behavioral geneticists refer
to as heritability coefficients and comes out of the research on adoption studies and
twin studies. Heritability addresses the question of what is the difference in the cor-
relation on a given personality trait between individuals who are genetically identi-
cal (identical twins) and those who share only about 50% of their genes (all other
siblings). If genes played no role in shaping traits, no differences would be found in
correlations between people who vary in their degree of genetic similarity. Identical
and fraternal twins would be just as similar or just as different. Evidence indicates
that identical twins, even if reared in different environments, show greater similarity
in personality than other siblings. And in the case of most personality traits, the de-
gree of similarity suggests that about 50% of the variability in personality is due to
heritability or genetics. Most of the remaining 50% is explained by nonshared expe-
riences of siblings of varying ages; that is, siblings usually have different experi-
ences, friends, and teachers. For instance, parents change their own parenting be-
haviors with time and experience. Thus, a child born three or four years after another
is being raised in a somewhat different environment.
Third, the development postulate assumes that traits develop and change
through childhood, but in adolescence their development slows, and by early to
mid-adulthood (roughly age 30), change in personality nearly stops altogether (Costa
& McCrae, 1994; Costa, McCrae, & Arenberg, 1980).
McCrae and Costa (2003) speculated that there may be some evolutionary
and adaptive reasons for these changes: When people are young and establishing
their relationships and careers, high E, O, and even N would be beneficial. As
people mature and become settled, these traits are no longer as adaptive as they were
earlier. Moreover, increases in agreeableness and conscientiousness might be help-
ful as people age. In our section on research, we discuss stability of traits during
adulthood.
Finally, the structurepostulate states that traits are organized hierarchically
from narrow and specific to broad and general, just as Eysenck (1990) had sug-
gested. This postulate grows out of McCrae and Costa’s long-held position that the
number of personality dimensions is five and only five. This number is more than the
three hypothesized by Eysenck and considerably fewer than 35 found by Cattell.
With the structure postulate, McCrae and Costa and other five-factor theorists con-
verge on five as the answer to the long-standing debate among factor theorists.
Postulates for Characteristic Adaptations
The postulate concerning characteristic adaptations states that, over time, people
adapt to their environment “by acquiring patterns of thoughts, feelings, and behav-
iors that are consistent with their personality traits and earlier adaptations” (McCrae
& Costa, 2003, p. 190). In other words, traits affect the way we adapt to the changes
in our environment. Moreover, our basic tendencies result in our seeking and select-
ing particular environments that match our dispositions. For instance, an extraverted
428 Part IV Dispositional Theories