242 
What makes a person unique, and what 
makes a person different from other per -
sons? How do we develop into the persons 
we are? It is by now widely accepted that in -
dividual differences in personality, and the 
development thereof, can be explained by 
a combination of the genes that we inherit 
from our parents at conception and the ex -
periences we gain as we are exposed to (and 
seek out) different environments throughout 
our lives. The importance of genetic inheri -
tance (or “heritability”) of personality has 
been repeatedly demonstrated by behav -
ior geneticists (reviewed by Vukasovic & 
Bratko, 2015, see also, Krueger & Johnson, 
Chapter 9, this volume). But can we find this 
“heritability of personality” in our DNA? 
Are there genes that make a person more 
likely to develop a certain personality, and if 
so, which are these genes, and how do they 
influence our personalities?
In this chapter, I review the molecular ge -
netics studies that aim to localize genes asso -
ciated with personality. I show that impor -
tant progress has been made in recent years, 
although much scientific work remains to 
be done if we want to further increase our 
understanding of the complex molecular ge -
netics structure underlying personality. This 
chapter is organized as follows. I start with 
a brief introduction into personality theories 
and heritability studies on personality. Next, 
I introduce terminology about the human genome that is needed to understand molec -
ular genetics studies on personality. Then, 
I will review and discuss different types of 
molecular genetics studies on personality. 
Finally, I close by summarizing what we 
have learned about the molecular genetics of 
personality and discuss promising directions 
for future research.
Personality  can be defined as the complex 
and dynamic organization of psychophysi -
ological systems, residing within a person, 
that create patterns of behaviors, cognitions, 
and emotions that are characteristic for this 
person. These behaviors, cognitions, and 
emotions are unique to each individual and 
are thought to be relatively stable over time 
and across settings. Three theories of per -
sonality have been shown to be particularly 
important for molecular genetics research 
on personality. The personality theories 
of psychologists Hans and Sybil Eysenck 
(1985; Eysenck, 1967) and psychiatrist Rob -
ert Cloninger (1987; Cloninger, Svrakic, & 
Przybeck, 1993) assume that personality has 
a genetic, (neuro)biological basis, yet pro -
pose quite different higher-  order personal -
ity traits. Eysenck and Eysenck (1985) dis -
tinguished three dimensions of personality: 
neuroticism, extraversion  and psychoticism . 
Persons high in neuroticism are emotion -
ally reactive in response to external stim -
uli, which is hypothesized to be rooted in 
the functioning of the limbic brain system, CHAPTER 10
Molecular Genetics of  Personality
Marleen H. M. de Moor