100 Biological Bases of Personality
disorder, and attention deficit and hyperactivity disorder in
children. MAO is low even in children of alcoholics and bipo-
lar disorders who have not yet manifested the disorders, sug-
gesting that it is a genetic risk marker for these disorders.
In a general normal population, low MAO was associated
with use of tobacco, alcohol, and illegal drugs, convictions for
crimes other than traffic offenses, and sociability in terms of
hours spent with friends (Coursey et al., 1979). A study of low-
MAO monkeys living in a natural environment showed that
they were more aggressive, dominant, sexually active, and so-
ciable than were high-MAO monkeys (Redmond, Murphy, &
Baulu, 1979). Monkeys with high MAO levels were social iso-
lates and passive. This study of another species suggests the
evolutionary advantage of sensation seeking as mediated by
MAO and possibly dopaminergic systems in the brain. Low
MAO, however, is also associated with impulsivity in labora-
tory tests (Klinteberg et al., 1991), as is sensation seeking
(Breen & Zuckerman, 1999; Thornquist & Zuckerman, 1995),
and impulsivity in risky situations could be a disadvantaged
trait that may lead to premature death. However, the advantage
in securing and dominating mates by intimidation of rivals
may have outweighed the evolutionary disadvantages of reck-
less behavior.
In the public mind testosterone is identified with sexual
drive and aggressiveness. However research shows that
testosterone (T) is associated with a broader range of traits
than these two. Androgens and T assayed from blood are cor-
related with sensation seeking (Daitzman & Zuckerman,
1980; Daitzman, Zuckerman, Sammelwitz, & Ganjam,
1978). Dabbs (2000) and Bogaert and Fisher (1995), using T
from saliva, found only nonsignificant tendencies in that di-
rection. A comparison of hypogonadal (low-T) and normal-T
men, all referred for complaints of erectile dysfunction,
showed that the low T-men were lower on sensation seeking
than were the normal-T men (O’Carroll, 1984).
Hormones
Testosterone and sensation seeking in young males are both
correlated with their sexual experience, in terms of the num-
ber of sex partners they have had (Bogaert & Fisher, 1995;
Dabbs, 2000; Daitzman & Zuckerman 1980). Testosterone
levels affect sexuality in women as well as men. Androgen
levels of married women were related to sexual responsivity,
frequency of intercourse, and sexual gratification (Persky
et al., 1982). As with MAO, we can see the evolutionary
advantage of the behavioral trait based on its biochemical
substrate. However, other correlates of T include sociability,
dominance, and activity, as well as inverse relationships to
socialization and self-control.
The high-T male tends to be assertive, impulsive, and
low in self-control, as well as high in sensation seeking.
There is much less work on T in women, but what data there
are suggest the same kind of personality correlates as in
men. Apart from aggression, high-T men were more likely
than others to misbehave in school as children, get into legal
difficulties as adults, use drugs and alcohol, and go AWOL
(absent without leave) while in the army (Dabbs, 2000). Fra-
ternities with high average T levels were generally disor-
derly and chaotic, and their members were described by an
observer as “crude and rude.” The high-T fraternities had
more parties, worse grades, and fewer community service
activities. Dabbs (2000) suggested that the total effect
among members is an outcome of an interaction between T
levels of its members and reinforcement of each other for
antisocial behavior. In this case, high T is clearly a predis-
posing factor for low socialization, which these authors
describe as “rambunctiousness.”
Testosterone levels reflect both trait and state moods. Al-
though reliability can be found in T levels taken at the same
time of day in the same setting, T levels can also be affected
by experiences in competition (Dabbs, 2000). Competitors
show increases in T when victorious and decreases when de-
feated. Even sports spectators show increases in T when their
team wins and decrease when their team loses.
High levels of cortisol are associated with prolonged
stress and depression. Ballenger et al. (1983) found that low
levels of CSF cortisol were associated with a P dimension
factor that included the P scale, the disinhibition subscale of
the Sensation Seeking Scale (SSS), the MMPI hypomania
scale, and lifetime number of sexual partners. Low levels of
cortisol have been found in prisoners who have a history of
psychopathic and violent behavior (Virkkunen, 1985). Low
cortisol was also associated with novelty seeking in veterans
with posttraumatic stress disorder (Wang, Mason, Charney,
& Yehuda, 1997). Low cortisol may indicate a low reactivity
to stress, which can be an advantage in some situations but
carries the dangers inherent in lack of control and impulsiv-
ity. Traits that may have been adaptive in the warrior societies
of the past may now confer a disadvantage in more socialized
civilizations.GeneticsTwin studies have found relatively high heritabilities (58%)
for sensation seeking whether based on twins raised together
(Fulker, Eysenck, & Zuckerman, 1980) or on twins separated
shortly after birth and raised in different families (Hur &
Bouchard, 1997). Heritability for Cloninger’s NS scale is
somewhat lower (40%) but typical of that found for other