The particular gene accounts for only about 10% of the genetic variance. But now that the human genome has been defined, many of the other genes contributing to this and other personality traits may soon be discovered.
Genes, however, do not directly make traits. They make proteins that shape our nervous systems. Between a gene and a behavior stand, among other things, the structure and function of the brain and the biochemistry of neurotransmitter systems.
The greatest risk-takers are young males in their adolescent years—a fact reflected in their high rates of auto accidents, binge drinking, drug use and pathological gambling. The military has always preferred younger men for soldiers, not only because of their physical strength but for their willingness to risk their lives in combat.
Young men of this age are also at their peak on sensation-seeking. And, not surprisingly, they are at their peak in levels of the sex hormone testosterone. Testosterone correlates particularly with the disinhibitory types of sensation-seeking—those associated with drinking, drugs, sex and antisocial behavior. It is also associated with normal traits like dominance, sociability and activity. As testosterone levels drop, men's aggressive, antisocial tendencies begin to mellow. Sensation-seeking scores of men aged 50 to 59 are half those of males aged 16 to 19.
Women also have testosterone, but less of it. Still, the hormone is linked to behaviors in women similar to those in men, such as assertiveness, aggression and sexual arousal.
Another biological correlate of sensation-seeking is the enzyme monoamine oxidase (MAO), active in the brain. Monoamine oxidase functions as a regulator, keeping neurotransmitters in balance. It could also contribute to the gender and age differences in sensation-seeking and risk-taking.
A form of monoamine oxidase called type B is particularly related to sensation-seeking—and to regulation of dopamine. The link between MAO and dopamine is notable in light of the fact that the dopamine-4 receptor gene has been connected to sensation-seeking, and another dopamine receptor, D2, has been connected with substance abuse, a particular form of risk-taking behavior.
The enzyme monoamine oxidase is low in high-sensation-seekers, implying a lack of regulation. What is more, levels of MAO are known to be higher in women than in men, and MAO levels in brain and in the blood rise with age. Further evidence that MAO is involved in sensation-seeking is that low MAO levels are also found in forms of psychopathology characterized by impulsive tendencies to seek immediate rewards without regard for consequences.
Sensation-seekers who are drug users have found a direct pathway to activate the brain's pleasure centers. Others seek the same arousal through exciting stimuli and experiences. Risk is not a necessary requirement for sensation-seeking, although it does intensify the thrill for a high sensation-seeker.
Although risk-taking has negative aspects and can even prove fatal, it is a positive force as well. Without risky experiences, humanity would stagnate; there would be little impetus for discovery. Risk-taking was obviously adaptive in earlier hominids. The trait persists—but there is little left to explore. What is more, work is anything but exciting for many people.
Modern life, with its protected cultures and curtailment of war, has not wiped out the need for excitement. Some people find it through other people, in relationships and sex. Others need more of a thrill, and go hang-gliding or bungee-jumping, although the most common everyday outlet for sensation-seeking is reckless driving. My work has shown that people have basic need for excitement—and one way or another, they will fulfill it.
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