424 Part V Biological/Evolutionary Theories
Grossarth-Maticek, Eysenck, and Vetter replicated this study in Heidelberg, Germany,
and found very similar results.
As Eysenck (1996) pointed out, these and other studies on the relationship
between personality and disease do not prove that psychological factors cause cancer
and heart disease. Rather, these diseases are caused by an interaction of many factors.
For cardiovascular disease, these factors include family history, age, gender, ethnic
background, hypertension, unfavorable ratio of total cholesterol to high-density lipopro-
tein (HDL), smoking, diet, inactive lifestyle, and several personality factors. For cancer,
the risks include smoking, diet, alcohol, sexual practices, family history, ethnic back-
ground, and personality factors (Brannon & Feist, 2007). Eysenck (1996) contended
that cigarette smoking alone does not cause cancer or CVD, but when it is combined
with stress and personality factors, it helps contribute to death from these two diseases.
For example, Eysenck and his associates (Marusic, Gudjonsson, Eysenck, & Starc,
1999) developed a complex biopsychosocial model for heart disease that included 11
biological and 7 psychosocial factors. Their research with men in the Republic of
Slovenia supported the hypothesis that personality factors interact with a variety of
biological factors to contribute to heart disease. One such interaction was for smoking,
neuroticism, and emotional reactivity; that is, high P scorers who smoke and who react
to stress with anger, hostility, and aggression increase their risk for heart disease.Related Research
Eysenck developed the Eysenck Personality Questionnaire (EPQ) and its offshoots
(Eysenck, 1959; Eysenck & Eysenck, 1964, 1968, 1975, 1993). The EPQ has been
used in conjunction with neurophysiological and genetic measures to assess the
biological basis of personality.The Biological Basis of Extraversion
One of the major thrusts of Eysenck’s theory is that personality dimensions are
not arbitrary creations of culture but, rather, result from the basic genetic and
neurophysiological makeup of the human species. If there were a biological basis
to personality, two key assumptions should hold true. First, neurophysiological
differences should exist between people high on one end of a dimension (for
instance, introversion) and those high on the other end of that dimension (for
instance, extraverts). Second, the basic personality dimensions should be universal
and not limited to a given culture.
The first domain to test Eysenck’s biological model of personality is in neu-
rophysiology. If, as Eysenck proposed, introverts have lower thresholds of arousal
than do extraverts, then they should be more reactive (that is, sensitive) to sensory
stimulation. One way to test this idea is to present both groups with varying inten-
sities of stimulation and measure their physiological reactivity. If Eysenck’s theory
is to be supported, then introverts should be more reactive than extraverts.
Over the past 30 years, a substantial amount of research has explored cognitive,
behavioral, and physiological measures of reactivity in relation to extraversion-
introversion (Beauducel, Brocke, & Leue, 2006; Eysenck, 1990; Stelmack, 1990,
1997). In general, Eysenck’s assumption that introverts are more reactive (have lower