1. 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

2. 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

3. Genes: Our Biological Blueprint
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)

4. Genes: Their Location and Composition
Nucleus
Chromosome
Gene
Cell
DNA

5. Genetics: Mendelian Theory

6. 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?

7. 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 ).
Gender
in psychology, the characteristics, whether biologically or socially influenced, by which people define male and female.

8. 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

9. 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)

10. Behavior Genetics Identical Twins Fraternal Twins
Same
sex only
Same or
opposite sex
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

11. 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

12. 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…

13. Comparison of correlations for MZA (apart) and MZT (reared together)
CHARACTERISTIC R(MZA) R(MZT)
Physiological
Brain wave activity
Blood Pressure
Heart Rate
Intelligence
Personality
Interests
Religiosity
Social Attitudes

14. Behavior Genetics Temperament Interaction
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

15. Environmental Influence

16. Environmental Influence
Two placental arrangements in identical twins

17. Environmental Influence
Experience affects brain development
Impoverished
environment
Rat brain
cell
Enriched

18. Environmental Influence
A trained brain (Myers’ text, p. 80)
Left (untrained) Right (trained)

19. 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

20. 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

21. 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

22. 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

23. The Nature and Nurture of Gender

24. 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

25. The Nature and Nurture of Gender
Two theories of gender typing