In this chapter, we ’ll look at three ways psychol ogists have used biological
concepts to explain personality . First, we examine Hans Eysenck ’s description of
personality, which has been an influential model in personality research for sev-
eral decades. From the beginning, Eysenck maintained that the individual differ-
ences in personality he described are base d on physiological differences. Second,
we look at individual differences in gener al dispositions, called temperaments.
A strong case can be made that temperamen ts are based on biological differences.
Psychologists have been succ essful in identifying some of these temperamental
differences among very young children. Th ird, we examine an area of personality
research called evolutiona ry personality psychology. Psychologists using this ap-
proach borrow the concept of natural sele ction from biology to explain a large
number of human behaviors.
What each of these three theoretical perspectives makes clear is that a
complete understanding of human personality requires us to go beyond some
of the early boundaries of the discipline. It is no longer useful to think of our
personality as somehow separate from our physiological makeup.
HANS EYSENCK ’S THEORY OF PERSONALITY
Many years ago, when the conventional wisdom in psychology traced an
individual ’s personality to his or her experiences, a respected psychologist
argued that personality was, in fact, determined more by biological makeup
than by any actions or mistakes made by one ’s parents. Although Hans
Eysenck ’s (pronounced Eye-Zinc) theory of personality has always been
accorded respect within the field, his initial claims about such a large biologi-cal determinant of personality were met by many with a mix of skepticism
and tolerance. But today Eysenck ’s emphasis on biological aspects of indivi-
dual differences is increasingly compatible with the recognition of biology ’s
role in personality.
The Structure of Personality
Like Raymond Cattell and other psychologists described in Chapter 7,
Eysenck was concerned with discovering the underlying structure of personal-
ity. Also like these trait researchers, Eysenck employed factor analysis to iden-tify the basic number of what he called types, or supertraits. However, unlike
most of the trait researchers, Eysenck ’s conclusion after years of research was
that all traits can be subsumed within three basic personality dimensions. He
called these three dimensions extraversion –introversion, neuroticism, and
psychoticism.
Eysenck ’s research strategy begins by dividing the elements of personality
into various units that can be arranged hierarchically (Figure 9.1). The basic
structure in this scheme is the specific response level, which consists of spe-
cific behaviors. For example, if we watch a man spend the afternoon talking
and laughing with friends, we would be observing a specific response. If this
man spends many afternoons each week having a good time with friends, weHans Eysenck ’s Theory of Personality 223