66 Genetic Basis of Personality Structure
factor. Factor analysis of the ratings yielded the familiar five
factors. Some researchers concluded from such studies that
trait structure merely reflects the effects of semantic biases on
person perceptions (Shweder, 1975). Ratings of strangers
must contain bias due to implicit personality theory because
they cannot be influenced by the true personalities of the tar-
gets. It is also likely that self-reports and ratings of well-
known targets incorporate a similar bias. For example, two
observers may agree that a person is sociable but disagree on
the extent of his or her sociability. The observer assigned a
higher rating for sociability is also likely to assign a higher
rating for cheerfulness and talkativeness. Thus, part of the co-
variance of these traits may be attributable to systematic bi-
ases in person perception that lead to correlated errors in
individual judgments. If this is the case, similarities in struc-
ture between genetic covariance and nonshared environmen-
tal covariance could reflect the biasing effects of implicit
personality theory on the latter.
To test for this bias, self-report twin data were supple-
mented with cross-observer correlations on the NEO-PI-R.
This allowed the computation of two matrices of nonshared
environmental covariance. The first estimated the covariance
due to implicit personality theory bias alone. Factorial analy-
sis of this matrix yielded the familiar five factors. Comparison
with normative structure yielded congruence coefficients of
.81, .45, .81, .89, and .85 for Neuroticism, Extraversion,
Openness, Agreeableness, and Conscientiousness, respec-
tively. The second matrix of nonshared environmental covari-
ance estimated was free from systematic bias. Factor analysis
of this “unbiased” matrix with targeted rotations to the nor-
mative NEO-PI-R factors produced low congruence coeffi-
cients at .53, .68, .22, .61, and .80 for Neuroticism,
Extraversion, Openness, Agreeableness, and Conscientious-
ness, respectively. Subsequent factor analysis of this matrix
yielded two factors. The first resembled a broad form of Con-
scientiousness with salient loading of the facets Activity,
Order, Dutifulness, Achievement Striving, Self-Discipline,
and (low) Impulsiveness. The second factor was defined by
the facets Warmth, Gregariousness, Positive Emotions, Open-
ness to Feelings, Altruism, and Tender-Mindedness. This
combination of Extraversion and Agreeableness facets resem-
bles the Love axis of the Interpersonal Circumplex (Wiggins,
1979). The other interpersonal axis—Dominance—does not
appear to be influenced by the nonshared environment. As-
sertiveness did not load on either factor.
These results suggest that when the conventional estimates
of nonshared environmental covariances are decomposed
into implicit personality theory bias and true nonshared ef-
fects, much of the resemblance to the five-factor structure
appears attributable to bias. Overall, these studies point to the
conclusion that genetic factors are largely responsible for the
observed pattern of trait covariation.THE HIERARCHICAL STRUCTURE
OF PERSONALITYBeyond problems with the content of personality taxono-
mies, there are also uncertainties about the nature of the pro-
posed hierarchical structure of traits and the relationship
between higher- and lower-order traits. Factor analytic stud-
ies provide consistent evidence that specific traits are orga-
nized into more global entities. Lexical studies also show that
natural language reflects this structure. Substantial agreement
exists among individuals in judgments of trait breadth
(Hampson et al., 1986). Despite this evidence, the nature and
origins of the hierarchy are unclear. This is clearly a problem
that requires explanation.
Fundamental differences exist among models on the way
the personality hierarchy is conceptualized. The lexical ap-
proach seems to consider the higher-order domains to be
lexical categories that impose structure on personality de-
scriptors by organizing them into clusters that are not neces-
sarily discrete or equally important (Saucier & Goldberg,
1996). The lexical structure “provides a framework for de-
scription, but not necessarily for explanation” (Saucier &
Goldberg, 1996, p. 24–25). Saucier and Goldberg also as-
serted that “as a representation of phenotypes based on nat-
ural language, the Big Five structure is indifferent and thus
complementary to genotypic representations of causes, moti-
vations, and internal personality dynamics”(p. 42). The
higher-order terms do not appear, therefore, to have any sig-
nificance beyond that of description.
Traits psychologists, including other five-factor theorists,
make different assumptions. For Allport (1961), a trait is “a
neuropsychic structure” (p. 347) and therefore an explana-
tory concept. Eysenck also adopted this approach: Traits have
heritable biological basis. Similarly, the five-factor model
assumes that traits are “endogenous basic tendencies” with
a substantial heritable component (McCrae & Costa, 1996,
p. 72). For Eysenck and Costa and for McCrae, traits are
explanatory as well as descriptive. In contrast to the lexical
approach, the five-factor model assumes that domains are
equally important and equal in breadth.
Assumptions that trait theories make about the psycho-
biological basis for the higher-order domains initially cre-
ated uncertainty about the status of the lower-order traits.
Most research effort has been directed toward understanding
higher-order factors and little attention has been paid to
parsing these domains into more specific components. Until