Understanding Psychology (10th Ed)

456 Chapter 
13 
Personality
easily upset, and diffi cult to soothe. Temperament is quite consistent, with signifi -
cant stability from infancy well into adolescence (Wachs et al., 2004; Kagan et al., 
2007; Evans & Rothbart, 2007, 2009). 
Some researchers contend that specifi c genes are related to personality. For 
example, people with a longer dopamine-4 receptor gene are more likely to be 
thrill-seekers than those without such a gene. These thrill-seekers tend to be extro-
verted, impulsive, quick-tempered, and always in search of excitement and novel 
situations. Furthermore, the structure of their brains may refl ect their thrill-seeking 
tendencies (see Neuroscience in Your Life, Figure 5; Robins, 2005; Golimbet et al., 2007; 
Ray et al., 2009). 
Does the identifi cation of specifi c genes linked to personality, coupled with the 
existence of temperaments from the time of birth, mean that we are destined to 
have certain types of personalities? Hardly. First, it is unlikely that any single gene 
is linked to a specifi c trait. For instance, the dopamine-4 receptor accounts for only 
around 10% of the variation in novelty seeking between different individuals. 
The rest of the variation is attributable to other genes and environmental factors 
(Keltikangas-Järvinen et al., 2004; Lahti et al., 2005). 
More important, genes interact with the environment. As we see in discussions 
of the heritability of intelligence and the nature–nurture issue, it is impossible to 
completely divorce genetic factors from environmental factors. Although studies of 
identical twins raised in different environments are helpful, they are not defi nitive 
because it is impossible to assess and control environmental factors fully. Further-
more, estimates of the infl uence of genetics are just that—estimates—and apply to 
groups, not individuals. Consequently, fi ndings such as those shown in Figure 4 must 
be regarded as approximations. 
Finally, even if more genes are found to be linked to specifi c personality charac-
teristics, genes still cannot be viewed as the sole cause of personality. For one thing, 
genetically determined characteristics may not be expressed if they are not “turned 
on” by particular environmental experiences. Furthermore, behaviors produced by 
genes may help to create a specifi c environment. For instance, a cheerful, smiley baby 
may lead her parents to smile more and be more responsive, thereby creating a 
supportive, pleasant environment. In contrast, the parents of a cranky, fussy baby 
Infants are born with particular temperaments—dispositions that are consistent throughout 
childhood.
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