Today most psychologists readily embrace the notion that biology plays a
role in human personality, but students are often surprised to hear that thiswas not always the case. In truth, many psychologists came to accept this
conclusion rather reluctantly. Why the resistance? One reason is that the
“blank slate ”view of humankind has great appeal. If we accept that person-
ality is formed largely or exclusively by experiences, in theory we can mold
an individual into whatever kind of person we want. With enough knowledge
and resources, we could change the parts of personality that create problems.Low self-esteem, pessimism, neuroticism, and other personality traits could be
altered through therapy or avoided altogether with appropriate child rearing.
Accepting the role of biology in personality development usually means limit-ing these possibilities for change. Another reason some psychologists were
hesitant to accept the biological approach was a concern about inappropriate
and even offensive interpretations that come from placing too much emphasison biological determinants. In the past, some people have argued against so-
cial programs by maintaining that certain racial or gender differences are the
result of biological rather than cultural factors.
Of course, accepting a biological component to personality does not
mean that personality is fixed at birth. Those who resign themselves with
“That’ s the way men/women are” or“It’s just my nature ”are foolishly
ignoring the power of experience. But it would be equally foolish to ignore
the wealth of evidence indicating that biology has a hand in shaping personal-
ity. The most persuasive case for the biological approach can be found in the
growing amount of supportive research findings. We ’ll review some of those
findings in this chapter. As with research from other approaches to personal-
ity, the studies reported here are sometimes subject to criticisms and alternate
interpretations. However, taken together the data make it difficult to ignore
the importance of biological determinants of personality.
We begin by looking at research on the heritability of personality charac-
teristics. More specifically, we examine the methods researchers use to deter-mine how much of our personality is inherited from our parents. As you will
see, this research is not without its critics, and identifying the precise strengthof the genetic component remains elusive.
Next we ’ll review research generated from Hans Eysenck ’st h e o r yo fp e r s o n -
ality. Specifically, we ’ll look at some of the differences between extraverts and
introverts. This research suggests that your level of extraversion –introversion
affects a wide range of behavior, including how happy you are and where yousit in the library. We ’ll also examine one application of evolutionary personality
theory. According to this theory, men and women should differ in what they
look for in a romantic partner.
HERITABILITY OF PERSONALITY TRAITS
How much of your personality is the result of your genetic makeup, and how
much is the result of the environment you grew up in? This “nature –nurture ”
question is one of the oldest and most enduring issues in psychology.Heritability of Personality Traits 251