Chapter 15 Buss: Evolutionary Theory of Personality 449revealed that 70 of the teens met criteria for alcohol abuse and 66 for alcohol
dependency. Results showed that, for both boys and girls, those with difficult
temperaments were most likely to abuse alcohol. The relationship held even when
they statistically held age constant—that is, the relationship holds at all ages from
12 to 18. In short, these findings paint a portrait of the adolescent with alcohol
abuse as someone who has the temperament qualities of troubled mood, sleep,
distractibility, regularity of eating and routine, and is low in activity level.
Genetics and Personality
Partly due to how genetics was taught in high-school biology, a common assumption
many people have is that there is a simple and nearly one-to-one correspondence
between genes and traits. Recall how you learned to calculate the probability that
offspring would inherit a trait if its parents were either dominant or recessive car-
riers of that trait. There are simple categorical traits (e.g., eye color) that get
transmitted by one gene. But all complex psychological traits that are expressed
on a continuum from low to high get transmitted by many, many genes. More
technically, simple categorical traits are “monogenically” (single gene) transmitted,
whereas traits that range from a little to a lot (e.g., aggression, height, weight,
anxiety) are “polygenically transmitted” (Ebstein, 2006; Evans et al., 2007). Sim-
ply put, monogenic transmission happens when single genes produce single traits
(phenotypes), and polygenic transmission occurs when many genes interact to
create a single characteristic (Rutter, 2006). This distinction is very important in
understanding a fundamental idea in modern genetics, namely our genome is the
starting point, not the end point, for how our genes are expressed (our phenotype).
There is no “smart” gene, “shy” gene, or “aggressive” gene. Many, many (dozens
and maybe more) genes are responsible for personality traits.
When studying behavioral genetics, researchers use two major methods to
examine the relationship among genetics, behavior, and personality. With the first
method, the quantitative trait loci (QTL) approach, they look for the location of
specific bits of DNA on genes that might be associated with particular behaviors. In
this sense, it is a search for “genetic markers” of behavior. The traits are quantitative
because they are markers for behaviors that are expressed on a broad continuum,
from very little to very much. For example, anxiety is a quantitative trait because
some people are not at all anxious, most people are average, and a few are very
anxious. The QTL method uncovers the location on particular genes that is associated
with high or low levels of a trait. These locations are also known as “markers.”
QTL research points to genetic markers for several basic personality traits, such
as novelty- or thrill seeking, impulsivity, and neuroticism/anxiety (Benjamin et al.,
1996; Dina et al., 2005; Hamer & Copeland, 1998; Lesch et al., 1996; Plomin &
Caspi, 1999; Retz et al., 2010; Rutter, 2006). Consider the case of thrill seeking, a
trait that entails risk taking. People with this trait may seek out highly exciting activi-
ties like bungee jumping, mountain climbing, or scuba diving. Thrill-seeking activities
create a “rush” of excitement—a positive feeling that may be related to the release
of dopamine, a neurotransmitter associated with physiological arousal. Given the
possible connection between dopamine and thrill seeking, one theory suggests that
people who are deficient in dopamine will tend to seek out exciting situations as a