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Chapter 3
Nature,
Nurture, and
Human
Diversity
Chapter Overview
Behavior Genetics
Evolutionary Psychology
Parents and Peers
_________________
Gender Development
Reflections on Nature and
Nurture
Behavior Genetics and Evolutionary
Psychology
GENES:
The Building Blocks of
Heredity and
Development
Genes are
parts of DNA
molecules,
which are
found in
chromosomes
in the nuclei of
cells.
Video
DNA
(Deoxyribonucleic Acid)
Chromosomes are made of DNA,
which are made of genes.
Chromosome:
threadlike structure
made largely of DNA
molecules
DNA:
a spiraling, complex
molecule containing
genes
}
Chromosomes and Inheritance
 The human genome
includes 46 chromosomes
in 23 sets matched sets;
each chromosome has
the same gene locations.
 This includes the X and Y
chromosomes, not a
matched set in males,
who are missing some
genes on the Y.
 We received half a set of
chromosomes from each
biological parent.
How Genes Work
 Genes are not blueprints;
they are molecules.
 These molecules have
the ability to direct the
assembly
____________________
__________________
 This genetic protein
assembly can be turned
on and off by the
environment, or by other
genes.
 Any trait we see is a
result of the complex
interactions of many
genes and countless
other molecules.
Evolutionary Psychology:
Understanding Human Nature
Some topics:
 Natural selection and
adaptation
 Evolutionary success may help
explain similarities
 An evolutionary explanation
of human sexuality
__________________
_____________is the
study of how
evolutionary
principles help explain
the origin and
function of the human
mind, traits, and
behaviors.
Can we may now learn something
about evolution by studying the
the ways in which humans are
alike?
Video
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Evolutionary Psychology:
Natural Selection: How it Works
Begin with a
species’ genome,
which contains a
variety of
versions of genes
that shape traits.
Conditions make it
difficult for
individuals with
some traits (some
versions of those
genes) to survive
long enough to
reproduce.
Other individuals
thus have their
traits and genes
“selected” to
spread in the
population.
Evolutionary
Psychology
Evolutionary
Psychology
 __________________
 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
 Only the Strong Survive???
 __________________
 Mutation
 a random error in gene replication that leads to
genetic damage
Evolutionary
Psychology
Evolutionary
Psychology
 ______________
 Charles Darwin
 Galapagos Islands
 Finch’s (Beak Size)
 Impact on biology
 Recent trends in Evolutionary
Psychology
Evolutionary
Misconceptions
Evolutionary
Psychology-Myth
vs Reality
• Man comes from monkeys?
Skull Evolution
Take Anthropology….
Primate Similarities…What about behavior?
Primate Cooperation Video
___________________
The Domesticated Silver Foxes
 Dmitri Balyaev and
Lyudmila Trut spent
40 years selecting
the most gentle,
friendly, and tame
foxes from a fox
population, and
having those
reproduce.
 As a result, they
were able to shape
avoidant and
aggressive creatures
into social ones, just
as wolves were once
shaped into dogs.
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Evolutionary Psychology’s Explanation of
Biologically Driven Phobias
 Why do people so
easily acquire a phobia
of snakes, more easily
than a phobia of cars?
 An evolutionary
psychologist would
note that snakes are
often poisonous…
…so, those who more
readily learned to fear
them were more likely
to survive and
reproduce.
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Evolution
Evolutionary
Psychology
Evolutionary
Psychology
Evolutionary
Psychology
_______________________
 the study of the evolution of behavior and the
mind, using the principles of natural selection
 The “Why” of behavior
 In what ways could our current behaviors have been
advantageous to our ancestors?




Fears-Snakes and Heights
Agression- Violent Species
Sexual Behaviors
What else??
Evolutionary
Psychology
Evolutionary
Psychology
 Ask the Class
 In one study __percent of adult video
customers were male.
 Most romance novel readers are female.
 Men __% Women __% “If 2 people really like
each other its ok for them to have sex even if
they have known each other a very short
time.”
Evolutionary
Psychology
Evolutionary
Psychology
 Poll the Class
 More women mention affection as a reason
for having first sexual intercourse,
 Think about sex multiple times per day. Men
__% and Women ___%
 More likely to attribute friendliness to sexual
interest.
 More likely to initiate sexual activity.
Evolutionary
Psychology
Evolutionary
Psychology
 Men preferred __________________
suggesting youth and health
 Women preferred ___________________
How Many Babies Could You Have??
• Women- are fertile ages 13 through 50
–
–
–
–
About 1.25 per year
For about 37 years
Which equals about…..
46 children in a lifetime….at most!
• Men- are fertile ages 13 through death
–
–
–
–
–
About how many a day? Be realistic!! Maybe 5!
365 days a year
for about 67 years
Who has a calculator??.............
122,275 children in a lifetime….Whoa!!!
___________________:
Predicting Individual Differences
More ways of exploring the
origins of the biology of
behavior:
1. Understanding genes
2. Twin and adoption
studies
3. Gene/environment
interactions
4. Evolutionary
Psychology
Behavior geneticists
study how heredity
and environment
contribute to
human differences.
Fraternal and Identical Twins
Fraternal “twins” from separate eggs
are not any more genetically alike than
other siblings.
Identical twin: Same sex only
Fraternal twin: Same or opposite sex
Twin and
Adoption Studies
To assess the
impact of nature
and nurture, how
do we examine
how genes make a
difference within
the same
environment?
 study traits of
siblings vs.
identical twins
 see if the
siblings vary
more than
twins
___________________Twins
Studies of twins in adulthood show
that identical twins are more alike than
fraternal twins in:
 personality traits such as
extraversion (sociability) and
neuroticism (emotional instability).
 behaviors/outcomes such as the
rate of divorce.
 abilities such as overall Intelligence
test scores.
Twin and
Adoption Studies
How do we find
out how the same
genes express
themselves in
different
environments?
We can study the
traits of identical
twins as they grow
up, or if they were
raised separately
(e.g., the
Minnesota Twin
Family Study).
Studies of Identical Twins Raised Apart
Similarities found in
identical twins despite
being raised in different
homes:
 personality, styles of
thinking and relating
 abilities/intelligence
test scores
 attitudes
 interests, tastes
 specific fears
 brain waves, heart
rate
Critiques of Twin Studies
1. In the more recent years of the
Minnesota Twin Family Study, twins
have known about each other and
may influence each other to be
more similar.
2. Coincidences happen; some
randomly chosen pairs of people will
have similar traits.
3. Environments may be similar;
adoptive families tend to be more
similar than randomly selected
families in education, income, and
values.
BUT none of these factors explains,
better than the genetic explanation,
why fraternal twins have more
differences than identical twins.
Searching for Parenting Effects:
Biological vs. Adoptive Relatives
Studies have been performed with adopted children for
whom the biological relatives are known.
Findings: Adopted children seem to be more similar to
their genetic relatives than their environmental/nurture
relatives.
Given the evidence of genetic impact
on how a person turns out,
does parenting/nurture
make any difference?
Does the home environment have any
impact?
Parenting Does Matter
Despite the strong impact of
____________ on personality,
___________has an influence
on:
 religious beliefs
 ___________
 manners
 attitudes
 politics
 habits