 29. Narcissism in Contemporary Personality Psychology  633
for the different elements. Luo, Cai, and 
Song (2014) administered measures of both 
grandiosity and entitlement to 304 Chinese 
twin pairs. Grandiosity had a heritability of 
.23, with a nonshared environmental effect 
of .60. Interestingly, there was also a de -
tectable shared environmental effect (.17). 
Entitlement had a heritability of .35 and a 
nonshared environmental effect of .66. Con -
sistent with the idea that grandiosity and 
entitlement are separable dimensions, the 
vast majority of genetic and environmental 
influences on these attributes appeared to be 
independent. If replicable, this would mean 
that the different narcissistic attributes are 
distinct in terms of both their genetic and 
environmental influences.
Most of the genetically informed research 
about narcissism has been conducted with 
adults; however, a pattern of detectable ge -
netic influence seems to extend to childhood 
samples. Most notably Coolidge, Thede, and 
Jang (2001) reported a heritability of .66 for 
NPD in a sample of 112 twins with an aver -
age age of 8 years recruited by a university in 
the United States. Coolidge et al. used par -
ent report to assess NPD. The effect of the 
shared environment was not detectable in 
this small sample. If replicable, such a find -
ing may mean that many classic approaches 
to the development of narcissism that place 
the etiology squarely on parenting will need 
to be updated to account for both genetic 
factors and nonshared environmental fac -
tors (i.e., environmental factors that make 
children raised in the same household differ -
ent as opposed to similar). This likely means 
considering temperament-  by- parenting in -
teractions following Cramer (2011) and the 
dual-  pathway model in the NSM.
In summary, there is increasing interest 
in the developmental processes that produce 
narcissistic attributes. Parenting is often im -
plicated in developmental studies (although 
the effect sizes are modest), whereas behav -
ioral genetics research consistently points to 
substantial heritability and nonshared envi -
ronmental influences. Given this reality, we 
think it would be premature to conclude that 
parental overvaluation, hostility, or moni -
toring are promising targets for intervention 
(see e.g., the discussion in Brummelman et 
al., 2015). For example, if parents misin -
terpret a message to tone down their over -valuation and inadvertently increase their 
harshness, then simplistic parenting advice 
would backfire for reducing narcissism. 
More research is needed before recommen -
dations are offered to the public. Moreover, 
we believe that a focus on temperament-  by- 
parenting interactions is especially promis -
ing. The underlying theorizing of the NSM 
suggests that narcissistic entitlement might 
be an example of the concept of equifinal -
ity from developmental psychopathology 
(see, e.g., Masten, 2006). The idea is that 
entitlement is a common outcome produced 
by multiple pathways involving transactions 
between the developing individual and vari -
ous social contexts. These different path -
ways to entitlement might differ depending 
on whether individuals have high approach- 
related tendencies or avoidance- related ten -
dencies.
In addition to studying how parenting 
and temperamental attributes are implicated 
in the development of narcissism, research 
is needed to chart the developmental course 
of narcissism in adulthood. In line with this 
need, Wetzel, Grijalva, Robins, and Roberts 
(2020) recently evaluated the development 
of narcissism from ages of 18 to 41 using 
data from a longitudinal study based in Cal -
ifornia ( N = 486 at age 18; N = 237 at age 
41). They administered the NPI at both time 
points and found a latent correlation of .69 
for overall narcissism (i.e., this association 
was corrected for attenuation due to mea -
surement unreliability). They also looked at 
stability correlations for facets of narcissism 
and reported estimates of .67 for leader -
ship, .61 for vanity, and .85 for entitlement. 
Rank-order stability was therefore impres -
sive given the 23-year time interval. Mean-
level declines were observed with substantial 
overall declines in the NPI ( d = –0.79) and 
moderate to large declines in the facets (van -
ity: d = –0.46; leadership: d = –0.67; and 
entitlement: d = –0.82). These general find -
ings are consistent with existing literature 
on adult personality trait development with 
respect to rank-order consistency and mean-
level changes in the direction of greater ma -
turity (see Roberts & Nickel, Chapter 11, 
this volume).
In addition, Wetzel et al. (2019) evalu -
ated evidence for selection and socializa -
tion effects when considering associations 