Myers’ EXPLORING PSYCHOLOGY (7th Ed)

Chapter 3

The Nature and NurtureOf BehaviorJames 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 Chromosome Gene

Cell 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 develop from a single

fertilized egg that splits in two, creating two genetically identical organisms

Fraternal Twins develop from separate

eggs genetically no closer

than brothers and sisters, but they share the fetal environment

Identicaltwins

Fraternaltwins

Samesex only

Same oropposite sex

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 countriesIntensive 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) R(MZT)

PhysiologicalBrain wave activity .80 .81Blood Pressure .64 .70Heart Rate .49 .54

Intelligence .78 .76Personality .50 .49Interests .40 .49Religiosity .49 .51Social Attitudes .34 .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 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)

Film

Environmental Influence

Environmental Influence

Two placental arrangements in identical twins

Environmental Influence

Experience affects brain development

Impoverishedenvironment

Rat braincell

Rat braincell

Enrichedenvironment

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