Implications for Personality Structure 71models of personality positing links between specific geneti-
cally based neurotransmitter systems and specific personality
traits. They also suggest a different conception of the trait
hierarchies from that assumed by many trait taxonomies.
Hierarchical Structure
Factor analyses of genetic correlations and the modeling
studies cited in the previous section identified general genetic
factors that account for trait covariation. The model-fitting
analyses also confirmed conclusions based on regression
analyses that lower-order traits are not merely components of
higher-order traits, but rather are distinct etiological entities.
It appears that each basic or facet trait is influenced by general
and specific genetic factors. Genetic dimensions that affect
multiple traits appear to influence each trait directly rather
than indirectly through a higher-order phenotypic entity. This
raises questions about the basis for the hierarchy consistently
identified by factor analytic studies and the conceptual status
of higher-order constructs like neuroticism and extraversion
and their role in theories of individual differences.
Although the facets delineating each of the five-factor do-
mains covary due to shared genetic effects, it is not necessary
to invoke a higher-order latent construct to explain this
covariation. This raises the possibility that higher-order con-
structs such as neuroticism merely represent the pleiotropic
action of genes. If this is the case, neuroticism and other
higher-order domains are not entities that are distinct from
the specific traits that delineate them. They are not traits in
Allport’s sense of distinct phenotypic entities with an under-
lying biology, but rather heuristic devices that represent clus-
ters of traits that covary because of a common genetic effect.
This is consistent with the conception of domains as lexical
categories (Saucier & Goldberg, 1996). Nevertheless, facet
traits defining domains such as neuroticism and extraversion
overlap sufficiently to justify grouping them into an overall
global measure.
The model of trait structure implied by these findings dif-
fers from that of traditional trait theories. With traditional
models in which lower-order traits are nested within a few
higher-order factors, it follows that any statement about the
higher-order factor applies to all subordinate traits. This is
not the case with the model proposed because each basic trait
has its own specific etiology. A second difference is that tra-
ditional hierarchical models seem to assume that trait tax-
onomies are similar to any classification based on set theory
principles. At each level in the hierarchy, categories are as-
sumed to be exhaustive and exclusive (Simpson, 1961).
Exhaustivenessmeans that trait categories exist to classify all
subordinate traits, whereas exclusivenessrefers to the princi-
ple that each subordinate feature can be classified into only
one superordinate trait. Considerable effort has been ex-
pended in attempts to delineate a structure with these proper-
ties. Indeed, this is the reason for debate on number andTABLE 3.5 Illustrative Scales: Multivariate Genetic Analyses of the DAPP-DQ Facet Scales
A1 A2 A3 E1 E2 A C E
^2 = 52 .45,df=54,p=. 53
Rejection
Rigid Cognitive Style — — — .43 — .38 — .56
Judgmental .13 — — .46 — .34 — .57
Interpersonal Hostility .46 — — .31 — .34 — .51
Dominance .53 — — — — .40 — .61
^2 = 90 .63,df=84,p=. 22
Restricted Expression
Self-Disclosure .55 .30 — .12 .49 .33 — .49
Affective Expression .31 .58 — .21 .56 — — .45
Angry Affects .24 .38 — .75 — .49 — —
Positive Affects .40 .51 — — .46 .33 — .52
Self-Reliance .55 .15 — .17 .50 .23 — .59
^2 = 154 .48,df=166,p=. 73
Callousness
Contemptuousness .36 .27 .42 .28 .15 .44 — .57
Egocentrism .28 .36 .28 .46 .21 .47 — .48
Exploitation .26 .54 .43 .35 .18 — — .51
Irresponsibility .40 .33 .23 .22 .23 .40 — .65
Lack of Empathy .53 .20 .16 .33 .23 .26 — .65
Remorselessness .42 .16 .34 — .76 .32 — —
Sadism .36 — .66 .27 .14 .40 — .65