526 CHAPTER 13
Personality: Genetics and Culture
What about genetics? How much of our personality is inherited?When was the last time you were around a lot of family members other than your
own? Was it a reunion? Or maybe when meeting your significant other’s family for
the first time? Did you notice any commonalities in the way different family mem-
bers interacted, spoke, or behaved? This section will explore the “nature” side of per-
sonality, or the degree that some of our personality is linked to our parents and close
relations.The Biology of Personality: Behavioral Genetics
13.12 Explain how twin studies and adoption studies are used in the field
of behavioral genetics.
The field of behavioral genetics is devoted to the study of just how much of an indi-
vidual’s personality is due to inherited traits. Animal breeders have known for a long
time that selective breeding of certain animals with specific desirable traits can produce
changes not only in size, fur color, and other physical characteristics but also in the tem-
perament of the animals (Isabel, 2003; Trut, 1999). As stated earlier in this chapter, tem-
perament consists of the characteristics with which each person is born and is, therefore,
determined by biology to a great degree. If the temperaments of animals can be influ-
enced by manipulating patterns of genetic inheritance, then it is only one small step to
assume that at least those personality characteristics related to temperament in human
beings may also be influenced by heredity.
Animal breeders have an advantage over those who are studying the influence
of genes in human behavior. Those who breed animals can control the mating of cer-
tain animals and the conditions under which those animals are raised. Human research
cannot ethically or practically develop that degree of control and so must fall back on
the accidental “experiments” of nature and opportunity, studies of twins and adopted
persons.TWIN STUDIES The difference between monozygotic (identical) and dizygotic
( fraternal) twins was discussed in Chapter Eight. to Learning Objective 8.4. As
discussed previously, identical twins share 100 percent of their genetic material, hav-
ing come from one fertilized egg originally, whereas fraternal twins share only about
50 percent of their genetic material, as any other pair of siblings would. By comparing
identical twins to fraternal twins, especially when twins can be found who were not
raised in the samve environment, researchers can begin to find evidence of possible
genetic influences on various traits, including personality. (See Figure 13. 5 .)
Many people have heard the story of the “Jim” twins, James Arthur Springer and
James Edward Lewis, identical twins separated just after birth. At age 39, Springer and
Lewis were the first set of twins studied by University of Minnesota psychologist Thomas
Bouchard, who examined the differences and similarities between identical and fraternal
twins raised apart from each other (Bouchard et al., 1990).
The two Jims were remarkably similar. They shared interests in mechanical drawing
and carpentry, they smoked and drank the same amount, and they even both divorced
women named Linda before marrying women named Betty. It is easy to attribute these
similarities to their shared genetics. But Springer and Lewis were both raised in Ohio by
parents from relatively similar socioeconomic backgrounds—how much of their similar-
ity to each other might be due to those conditions?behavioral genetics
field of study devoted to discovering
the genetic bases for personality
characteristics.
James Edward Lewis, and James Arthur
Springer, otherwise known as the “Jim”
twins, pictured here with Lewis’s adoptive
mother. Although separated shortly after birth
and reunited at age 39, they exhibited many
similarities in personality and personal habits.
Although genetics may explain some of these
similarities, what other factors might also be
at work?