Universality of Trait Structure 75traits—Alienation, Control, and Absorption—indicated that
the genetic influences were gender-specific. Jang, Livesley,
and Vernon (1998) reported some evidence for sex-limited
gene expression in 18 traits delineating personality disorder
measured by the DAPP. All dimensions except Submissive-
ness in males, and Cognitive Dysfunction, Compulsivity,
Conduct Problems, Suspiciousness, and Self-Harm in females
were significantly heritable. Sex-by-genotype analyses sug-
gested that the genetic influences underlying all but four
DAPP dimensions (Stimulus Seeking, Callousness, Rejection,
Insecure Attachment) were specific to each gender, whereas
environmental influences were the same in both genders
across all dimensions. Furthermore, the four higher-order di-
mensions derived from the 18 basic traits (Livesley et al.,
1998) were also heritable across sex, and genetic effects were
in common to both genders; the exception was Dissocial
Behavior, which was not heritable in females.
Such evidence of sex-limited effects challenges the as-
sumed universality of trait taxonomies. However, it could be
argued that the results based on the DAPP and MPQ are
atypical. The DAPP is a specialized scale designed primarily
to assess personality dysfunction. The scale does not cover
such areas of normal personality as Openness to Experience
(Jang & Livesley, 1999; Schroeder et al., 1992) because ab-
normal variants of Openness are not included in clinical
descriptions of personality disorder. The MPQ, unlike other
scales, routinely reveals nonadditive genetic effects due to
dominance (Waller & Shaver, 1994). This suggests that it
may assess content different from that tested by scales such
as the NEO-PI-R, which reveals genetic effects that are addi-
tive (e.g., Jang et al., 1998).
A more appropriate evaluation of the assumption of uni-
versality would be to examine sex-limited gene expression
on a major model of personality such as the five-factor
model. Evaluation of whether the same genes are present
across different samples is similar to the evaluation of cross-
cultural effects. Jang, Livesley, Riemann, and Angleitner
(in press) applied sex-limitation models to NEO-FFI data
obtained from the Canada and German twin samples de-
scribed earlier. Two general models were fit to the data. The
first specified additive genetic and nonshared environmental
influences for females and males and a male-specific genetic
factor. The second tested whether heritable influences com-
mon to males and females were the same across the two sam-
ples. Table 3.7 reports the intrapair twin correlations for each
zygosity group in each sample. The MZ male and MZ female
correlations exceed their respective DZ correlations, suggest-
ing the presence of heritable influences on each NEO-FFI
domain in each sample. Of particular interest is the com-
parison between the DZ opposite-sex correlations and the
same-sex DZ correlations. In both samples, the DZ opposite-
sex correlation for Conscientiousness was near zero, suggest-
ing the presence of differential gender effects. The final form
of the best-fitting model is presented in Table 3.8. The results
suggest that genetic and environmental influences common
to males and females influence four of the five FFM domains.
The exception was Conscientiousness, for which gender-
specific additive genetic influences operate. However, the
external events and experiences specific to each twin—
nonshared environmental influences—are common to males
and females. The results also suggest that the type and mag-
nitude of genetic and environmental influence were the same
across the two groups, supporting the notion that the five-
factor model as assessed by the NEO-FFI is applicable to
different cultures and genders.
This study has several limitations. The first is that the sam-
ple sizes are rather small in both samples, especially male DZ
twin pairs and opposite-sex pairs. The twin covariances asso-
ciated with these two zygosity types, especially the opposite-
sex pairs, are crucial for the validity of the analyses. The
availability of relatively few twin pairs calls into question
the stability of the correlations and thus the detection of sex-
limited genes—as was obtained for Conscientiousness. Sec-
ond, the study used the NEO-FFI, the short form of the
NEO-PI-R. The full scale might produce different results
because long versions of these scales sample domains moreTABLE 3.7 Intrapair Twin Correlations (Pearson’s r)
Canadian Sample German Sample
MZ DZ MZ DZ
NEO-FFI Domain M F M F M-F M F M F M-F
Neuroticism .41 .53 .22 .35 .13 .49 .52 .36 .20 .15
Extraversion .50 .49 .34 .30 .23 .57 .57 .34 .25 .17
Openness .63 .51 .28 .36 .20 .57 .50 .44 .26 .10
Agreeableness .50 .46 .14 .33 .26 .43 .42 .37 .10 .10
Conscientiousness .47 .50 .28 .38 .01 .57 .46 .40 .23 .05
Sample sizes (pairs) 102 165 61 129 73 104 425 38 163 68