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Even the impressive data from personality assessments are clouded by the reunion of
many of the separated twins some years before they were tested. Moreover, when adoption
TEACH 1.1-3 agencies are involved, separated twins tend to be placed in similar homes. Despite these
criticisms, the striking twin-study results helped shift scientific thinking toward a greater
Teaching Tip appreciation of genetic influences.
You may have students in class who Biological Versus Adoptive Relatives
have been adopted. Be sensitive to For behavior geneticists, nature’s second real-life study — adoption — creates two groups:
their possible feelings and visible genetic relatives (biological parents and siblings) and environmental relatives (adoptive par-
reactions as you discuss research ents and siblings). For personality or any other given trait, we can therefore ask whether
concerning the impact of nature adopted children are more like their biological parents, who contributed their genes, or their
adoptive parents, who contributed their home environment. And while sharing that home
and nurture on the development of environment, do adopted siblings come to share traits?
adopted children. Some students The stunning finding from studies of hundreds of adoptive families is that, apart from
in your class may know, for exam- identical twins, people who grow up together — whether biologically related or not — do
not much resemble one another in personality (McGue & Bouchard, 1998; Plomin, 2011;
ple, that their biological parents had Rowe, 1990). On personality traits such as extraversion and agreeableness, for example,
substance abuse problems or other people who have been adopted are more similar to their biological parents than to their
psychological issues. This knowledge caregiving adoptive parents.
The finding is important enough to bear repeating: The normal range of environments
may cause concern over whether they shared by a family’s children has little discernible impact on their personalities. Two adopted chil-
will face similar challenges. Emphasize dren raised in the same home are no more likely to share personality traits with each other
than with the child down the block.
that although a trait may be heritable, Heredity shapes other primates’ personalities, too. For example, macaque monkeys
it doesn’t necessarily mean that the raised by foster mothers exhibit social behaviors that resemble those of their biological,
Worth Publishers.
trait will manifest itself. rather than foster, mothers (Maestripieri, 2003).
Why are children in the same family so different? Why does a shared family environment
have so little effect on children’s personalities? Is it because each sibling experiences unique
TEACH 1.1-3 peer influences and life events? Because sibling relationships ricochet off each other, ampli-
fying their differences? Because siblings — despite sharing half their genes — have very
Discussion Prompt different combinations of genes and may evoke very different kinds of parenting? Such
questions fuel behavior geneticists’ curiosity.
In her book The Nurture Assumption, & Worth Publishers. Not for redistribution.
The genetic leash may limit the family environment’s influence on personality, but it
Judith Rich Harris proposed that does not mean that adoptive parenting is a fruitless venture. One study followed more than
parents do not have as much influence 3000 Swedish children with at least one biological parent who had depression. Compared
on the development of their children to their not-adopted siblings, those raised by an adoptive family were about 20 percent less
likely to develop depression (Kendler et al., 2020a). As an adoptive parent, I [ND] especially
as people generally believe. In his find it heartening to know that parents do influence their children’s attitudes, values, man-
book The Blank Slate: The Modern ners, politics, education, and faith (Gould et al., 2019; Kandler & Riemann, 2013). This was
Denial of Human Nature, Steven dramatically illustrated during World War II by separated identical twins Jack Yufe, a Jew,
and Oskar Stöhr, a member of Germany’s Hitler Youth. After later reuniting, Oskar mused
Pinker also argues that infants are Bedford, Freeman &
to Jack: “If we had been switched, I would have been the Jew, and you would have been the
born not blank, but rather come Nazi” (Segal, 2005, p. 70). Parenting — and the cultural environments in which parents raise
their children — matters!
Distributed by Bedford, Freeman
equipped with a structure that Tim Clayton/Corbis/Getty Images Moreover, child neglect and abuse and even parental divorce are rare in adoptive
influences how they behave and think. homes. (Adoptive parents are carefully screened; biological parents are not.) One study
Have students consider the following: looked at the parenting of siblings being raised apart — some with their biological mother,
that your genes had the greatest Copyright © risk of psychological disorder, most adopted children thrive, especially when adopted as
some with an adoptive mother (Natsuaki et al., 2019). Compared with the biological moth-
• How much of your behavior would Adoption matters Olympic gold ers, the adoptive mothers used gentler parenting, gave more guidance, and experienced less
medal gymnast Simone Biles benefited
depression. It is not surprising, then, that studies have shown that, despite a slightly greater
from one of the biggest gifts of love:
you attribute to biology? How
adoption.
much to environment? Why?
• How would you feel if you knew 14 Unit 1 Biological Bases of Behavior
influence on your behavior? Why? 03_myersAPpsychology4e_28116_ch01_002_163.indd 14 15/12/23 9:21 AM
14 Unit 1 Biological Bases of Behavior
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