 9. Behavioral Genetics and Personality  223
interpreted in much the same way as observ -
able correlations (e.g., a genetic correlation 
of 1.0 means that the genetic influences on 
the two variables are entirely overlapping). 
Series of these correlations can be subjected 
to multivariate factor analyses of the same 
sort that are used to parse the observed 
structure of personality.
Although the Big Five have been influen -
tial constructs in behavioral genetics person -
ality studies, an even broader hierarchical 
structure integrates various structural mod -
els involving two, three, four, and five “big 
traits” (Krueger & Markon, 2014; Markon, 
Krueger, & Watson, 2005). Working with 
normal-  range personality traits, when two 
“higher-  order” or broader factors are con -
sidered, extraversion and openness from the 
Big Five combine to form a broader factor 
of “plasticity,” and agreeableness, conscien -
tiousness, and lack of neuroticism combine 
to form a broader factor of “stability” (De -
Young, 2006; Hirsh, De  Young, & Peterson, 
2009; Digman, 1997).
If three higher-  order factors are modeled, 
neuroticism breaks off from the broader sta -
bility factor, resulting in factors that reflect 
negative emotionality (neuroticism), positive 
emotionality (extraversion and openness), 
and disinhibition (disagreeableness and 
unconscientiousness). Primary personality 
traits that delineate the Big Three at the ob -
served level show this same Big Three struc -
ture at the genetic level (Krueger, 2000). The 
observed four-trait model consists essen -
tially of the Big Five without openness, and 
this model has been influential in research 
linking personality and psychopathology 
(D. Watson, Clark, & Harkness, 1994), and 
related research on dimensional approaches 
to classifying personality pathology (Wi -
diger, Simonsen, Krueger, Livesley, & Ver -
heul, 2005). Factor analyses of genetic cor -
relations among scales delineating primary 
dimensions of personality pathology reveal 
essentially these same Big Four dimensions 
(Livesley, Jang, & Vernon, 1998). Finally, 
genetic correlations among scales designed 
to delineate the Big Five at the observed level 
reveal the Big Five at the genetic level as well 
(McCrae, Jang, Livesley, Riemann, & An -
gleitner, 2001; Yamagata et al., 2006).
This hierarchical perspective on genetic– 
observed correspondence in personality structure is consistent with behavioral ge -
netics research examining genetic and envi -
ronmental influences on traits more specific 
than the Big Five. Jang, McCrae, Angleitner, 
Riemann, and Livesley (1998) examined the 
heritability of variance in facets of the Big 
Five that remained after the common Big 
Five variance was removed, and found non -
trivial residual heritabilities. We (Johnson 
& Krueger, 2004) examined the extent to 
which genetic influences on specific adjec -
tives that delineate the Big Five are tightly 
clustered within each Big Five domain. We 
found evidence that genetic influences on 
extraversion and neuroticism were relatively 
tightly clustered, whereas genetic influences 
on conscientiousness, agreeableness, and 
openness were relatively diffuse. Indeed, 
there may even be specific genetic influences 
on very fine-  grained “nuances,” or traits 
below the level of specific personality facets 
(Mottus, Kandler, Bleidorn, Riemann, & 
McCrae, 2017). Taken together, these stud -
ies suggest that genetic influences on person -
ality are not organized around any specific 
model of personality, such as the Big Five. 
Rather, they suggest that genetic influences 
are organized much like observed individual 
differences, no matter how they are parsed 
at the observed level.
A potentially provocative implication of 
this body of work is that genetic influences 
may operate differently at different levels 
of the personality hierarchy. If true, the 
idea of genes “for” broad phenotypic traits 
may not map nature well in all cases. For 
example, genes involved in building brain 
systems that regulate emotion may contrib -
ute to the broad traits of extraversion and 
neuroticism (Eid, Riemann, Angleitner, & 
Borkenau, 2003; Smillie, De  Young, & Hall, 
2015) relatively coherently, as we (Johnson 
& Krueger, 2004) observed, yet there may 
be other genetic factors that influence more 
specific, narrow individual differences at 
levels beneath these very broad traits, such 
as characteristic responses to more specific 
stimuli. For example, sociability may have 
genetic influences at least partly distinguish -
able from achievement striving, within the 
broader domain of positive emotionality. Ul -
timately, better understanding of the brain 
systems that underlie personality could help 
to refine theories about how specific genetic 