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Myers’ EXPLORING
PSYCHOLOGY
(7th Ed)
Chapter 3
The Nature and Nurture
Of Behavior
James A. McCubbin, PhD
Aneeq Ahmad, Ph.D.
(modified by Ray Hawkins, Ph.D.)
Worth Publishers
Genes: Our Biological
Blueprint
 To what extent are we shaped by our heredity
(nature) and by our life history (of our nurture)?
 Chromosomes
 threadlike structures made of DNA that contain the
genes
 DNA (deoxyribonucleic acid)
 complex molecule containing the genetic information
that makes up the chromosomes
 has two strands-forming a “double helix”- held
together by bonds between pairs of nucleotides
Genes: Our Biological
Blueprint
 Genes
 biochemical units of heredity that make up
the chromosomes
 a segment of DNA capable of synthesizing a
protein
 Each human is estimated to have about
30,000 genes. We are 99.9 similar in our
DNA
 Human traits are influenced by gene
complexes---many genes acting in concert
(e.g., intelligence)
Genes: Their Location and
Composition
Nucleus
Cell
Chromosome
Gene
DNA
Genetics: Mendelian Theory
Evolutionary Psychology
 Natural Selection
 the principle that, among the range of inherited trait
variations, those that lead to increase reproduction and
survival will most likely be passed on to succeeding
generations
 Mutation: a random error in gene replication that leads
to genetic damage
 Of our .10% genetic differences, 6% are differences
among races, 8% are differences within a race, and
over 85% are individual variations within local groups.
Why are we so much alike?
Evolutionary Psychology
 Evolutionary Psychology
 the study of the evolution of behavior and the
mind, using the principles of natural selection
 Example: breeding “friendly” foxes (Belyaev &
Trutt) (Myers’ text, p. 74-75).
 Gender
 in psychology, the characteristics, whether
biologically or socially influenced, by which
people define male and female.
Evolutionary Psychology
 Men preferred attractive physical features
suggesting youth and health
 Women preferred resources and social status
 Critique: “post hoc ergo propter hoc” /
backward reasoning. Wood & Eagly (2002)
found that in cultures with gender equality
these gender differences in mate preferences
are much smaller (Myers text, p. 78).
Film
Behavior Genetics
 Behavior Genetics
 study of the relative power and limits of
genetic and environmental influences on
behavior
 Environment
 every nongenetic influence, from prenatal
nutrition to the people and things around us
(shared and non-shared environmental
effects) (Cohen, 1999, Stranger in the Nest)
Behavior Genetics
Identical
twins
Fraternal
twins
 Identical Twins
 develop from a single
fertilized egg that splits in
two, creating two
genetically identical
organisms
 Fraternal Twins
Same
sex only
Same or
opposite sex
 develop from separate eggs
 genetically no closer than
brothers and sisters, but
they share the fetal
environment
On Twins…
Monozygotic twins = start as 1 fertilized
egg (zygote), then split into 2 identical
embryos
Fraternal twins- only as genetically similar as
non-twins (dizygotic)
MZ adopted into separate homes
Often raised without knowledge of twin
In different, contrasting environments
Example Study (from
Niederhoffer, 2004 lecture)
56 sets of MZA (reared apart)
From 8 countries
Intensive psychological and physiological tests
and measurements
Nearly 50 hours of testing
Life history, psychiatric interview, checklists of
household belongings, family environment scale,
intelligence, personality, etc.
IF environment = responsible for individual
differences, MZT from same environment should
be more similar than MZA…
Comparison of correlations for MZA
(apart) and MZT (reared together)
CHARACTERISTIC
R(MZA)
Physiological
Brain wave activity
Blood Pressure
Heart Rate
Intelligence
Personality
Interests
Religiosity
Social Attitudes
.80
.64
.49
.78
.50
.40
.49
.34
R(MZT)
.81
.70
.54
.76
.49
.49
.51
.28
Behavior Genetics
 Temperament
 a person’s characteristic emotional reactivity and
intensity
 Bokhorst et al. (2004) attachment security and
temperament.
 Suomi video, “Bringing up Monkey”
 Interaction
Film
 the effect of one factor (such as the environment)
depends on another factor (such as heredity)(e.g.,
aggressive child may be yelled at by the teacher)
Environmental Influence
Environmental
Influence
 Two placental arrangements in identical
twins
Environmental
Influence
 Experience affects brain development
Impoverished
environment
Rat brain
cell
Enriched
environment
Rat brain
cell
Environmental
Influence
 A trained brain (Myers’ text, p. 80)
 Left (untrained)
Right (trained)
Environmental
Influence
 Peer Influences on development may exceed parental influences
(Harris, 1998, Myers’, p. 81)
 Culture
 the enduring behaviors, ideas, attitudes, and traditions shared by
a large group of people and transmitted from one generation to
the next
 Norm
 an understood rule for accepted and expected behavior---these
may differ cross-culturally. Personal Space: the buffer zone we
like to maintain around our bodies
 Culture and Child Rearing
 Example: Westernized cultures’ emphasis on individualism, in
contrast to collectivism
 Developmental similarities across groups
 In surface ways we may differ, but as members of one species
we are subject to psychological forces which are generally similar
The Nature and
Nurture of Gender
 X Chromosome
 the sex chromosome found in both men and
women
 females have two; males have one
 an X chromosome from each parent produces
a female child
 Y Chromosome
 the sex chromosome found only in men
 when paired with an X chromosome from the
mother, it produces a male child
The Nature and
Nurture of Gender
 Testosterone
 the most important of the male sex hormones
 both males and females have it
 additional testosterone in males stimulates
 growth of male sex organs in the fetus
 development of male sex characteristics during
puberty
 The Nurture of Gender: Gender Roles
 A role is a set of expectations (norms) about a social
position
 defining how those in the position ought to behave
The Nature and
Nurture of Gender
 Gender Role
 a set of expected behaviors for males and females
 biology and evolution may predispose gender roles,
but cultural factors and individual differences are
also influential (e.g., Spence & Helmreich, EPAQ
scales).
 Gender Identity
 one’s sense of being male or female
 Gender-Typing
 the acquisition of a traditional masculine or feminine
role
The Nature and
Nurture of Gender
The Nature and
Nurture of Gender
 Social Learning Theory
 theory that we learn social behavior by
observing and imitating and by being
rewarded or punished
 Gender Schema Theory
 theory that children learn from their cultures
a concept of what it means to be male and
female and that they adjust their behavior
accordingly
The Nature and
Nurture of Gender
 Two theories of gender typing