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Chapter 4
Nature/Nurture
Evolution
Behavior-Genetics
The Nature of
Behavior and Mental
Processes
Chromosomes
Hormones
Brain Structures/Chemicals
Genes: Our Biological Blueprint

Chromosomes

23 Pair
 Contain genetic material

DNA (deoxyribonucleic acid)

Building blocks of the chromosomes
 has two strands-forming a “double helix”

Genes

segment of DNA capable of synthesizing a
protein
Gender and Nature

23rd Chromosome = Sex
X
from egg
 X or Y from sperm
 XX = Female
 XY = Male
Testosterone (androgen) Levels/Testes
 Estrogen Levels/Ovaries
 Brain Development
 Identity

Cognitive Differences
No differences for most cognitive
abilities
 Verbal, reading, and writing— females
consistently score higher
 Spatial skills —males outscore females
on mentally rotating objects, females
score better on remembering locations
of objects
 Math Skills— males score slightly better
than females

The Role of Hormones
Hormones are chemicals that control bodily
responses such as emotions, growth, and sexuality.
The sex hormones are estrogen and androgen.
 Males have more androgen.
 Females have more estrogen.
 Hormones play a lesser role in human
development and behavior than they do in
animals.
The Nurture of
Behavior and Mental
Processes
Social Learning Theory
Parenting
Peers
Culture
Norms
The Nurture of Gender

Gender Role


Gender Identity


a set of expected behaviors for males and
females
one’s sense of being male or female
Gender-typing

the acquisition of a traditional masculine or
feminine role
Gender Role Stereotypes


The beliefs and expectations people hold
about the typical characteristics, preferences,
and behaviors of men and women
“I’m Glad I’m a Boy, I’m Glad I’m a Girl”
Gender Role Development





Between ages 2-3 years, children can identify
themselves and other children as boys or
girls.
The concept of gender or sex, however is
based more on outward characteristics such
as clothing.
Toddler girls tend to play more with dolls and
ask for help more than boys
Toddler boys tend to play more with trucks
and wagons, and tend to play more actively
After age 3 years we see consistent gender
differences in preferred toys and activities
The 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 Nurture of Gender

Two theories of gender typing
David(Brenda) Reimer


What, if any, aspects
of David’s
development
support the nature
theory of gender?
What aspects
support the nurture
theory?
Personality Differences
No significant differences between men
and women on most characteristics
 Women tend to be more nurturant than
men (very broad)
 Men tend to be more assertive than
women (very broad)

Male/Female Differences
The only activity that is clearly defined along
gender lines is reproduction. All other activities are
shared by both sexes to different degrees.
Nurturance: Women generally
show more empathy, but males
can also be nurturing. No one
has proven the existence of
strong maternal instinct in
humans.
Aggression: Males are
aggressive in more situations
than females. Females do show
aggression in some situations,
however.
Physical activity: Boys start
out more physically active.
By adulthood, differences in
activity levels between
genders have disappeared.
Mathematical Ability
Studies are not clear and have not as yet
conclusively shown that males are innately
better at math.
 Males do better than females on the SAT math
section, but study findings have not been
consistent.
 Teachers and parents have higher expectations
for males.
 Females may avoid difficult areas such as math.
Verbal Ability
Includes not just speaking but also word problems,
reading and writing. Generally, girls do better than
males until early adolescence.
Evolutionary Psychology

Evolutionary Psychology


the study of the evolution of behavior
and the mind, using the principles of
natural selection
Gender

in psychology, the characteristics,
whether biologically or socially
influenced, by which people define male
and female
Evolutionary Psychology


Natural Selection
Mutations

random errors in gene replication that lead to a
change in the sequence of nucleotides
 the source of all genetic diversity

Maximizing Fitness

Maximizing the fitness of your gene pool by
selecting a mate with healthy genes and thus
increasing your chances of producing healthy
offspring.
Evolutionary Psychology

Critiquing the Evolutionary Explanation

Evolutionary psychologists make too many
hindsight explanations.
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
Behavior Genetics
Identical
twins
Fraternal
twins

Identical (monozygotic) Twins


Fraternal (dizygotic) Twins


Same
sex only
Same or
opposite sex
develop from a single
fertilized egg that splits in
two, creating two genetically
identical organisms
develop from separate eggs
genetically no closer than
brothers and sisters, but they
share the fetal environment
Behavior Genetics

Temperament


a person’s characteristic emotional
reactivity and intensity
Heritability


the proportion of variation among
individuals that we can attribute to genes
may vary, depending on the range of
populations and environments studied
Behavior Genetics

Interaction


the dependence of the effect of one
factor (such as environment) on another
factor (such as heredity)
Molecular Genetics

the subfield of biology that studies the
molecular structure and function of
genes
Environmental Influence

Experience affects brain development
Impoverished
environment
Rat brain
cell
Enriched
environment
Rat brain
cell