the nature and nurture of behavior. let’s start with genetics... gene a stretch of dna that...
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The Nature and Nurture of Behavior
Let’s start with genetics . . .
Gene A stretch of DNA that produces a specific protein,
which in turn forms building blocks of our bodies or drives the processes that allow us to live
DNA (deoxyribonucleic acid): molecule that contains genes
Human instruction manual: genes affect physical features, such as eye color and height, and behavior
Dogs are bred for genetic disposition/behavior One gene in fruit flies can be altered to produce courtship
behavior between two males
Genetics: Tour the Basics
Go to: http://learn.genetics.utah.edu/
Tour: “The Basics and Beyond”
The Human Genome Project
Genome: the complete instructions for making an organism
Project ran from 1990-2003 (completed 2 years ahead of schedule http://www.ornl.gov/sci/techresources/
Human_Genome/project/ What are some of the social and ethical
implications for genetic screening?
Darwin’s Natural Selection
Key is genetic fit with environment Mutation
Depending on environment, genetic makeup or organisms evolves throughout generations of offspring, producing changes in the dominant physical features and behavior of a group of organisms
Evolutionary Psychology
Using principles of natural selection, focuses on the evolution of behavior and the mind
Evolutionary psychologists study how natural selection favoured behavioural tendencies in order to explain commonalities in language learning, attention, perception, memory, sexual behaviour, reasoning and more.
Evolutionary Psychology
All organisms including humans are “gene-producing machines” with the basic motivation of perpetuating their own genetic pool.
Our genes predispose us to act in ways that enhance chances of surviving and spreading’ this motive underlies are behaviour
Evolutionary Psychology
Critics: Evolutionary psychologists make to
many hindsight explanations They underestimate the role of
culture
Evolutionary Theory: The Misunderstandings
Genetic Determinism – the idea that only genes control behaviour. In fact, human behaviour cannot occur without: Evolved adaptations Environmental influences
Evolutionary Theory: The Misunderstandings
That adaptive mechanisms are “optimally designed”– evolutionary psychologists recognize that the environment keeps changing, but evolution occurs slowly (humans are better designed for earlier environments)
Evolutionary Psychology
Mating behaviors One of the most studied areas in
evolutionary psychology Why do we find certain characteristics
attractive in a potential mate?
Sexuality
Task: Write down 5 or 6 attributes
that you look for in a mate
Handout 3-3
Comparison of Characteristics
Evolutionary Psychology – Gender Differences in Attraction
Women prefer economic resources & older partners
Men prefer physical attractiveness & younger partners
These differences may arise from the different social roles the genders have historically held or because of evolutionary factors These differences are more typically seen in
cultures with gender inequalities
The Coolidge Effect
What is it?
What would be the evolutionary explanation for the Coolidge effect?
Behavioral Genetics
Researches in this field study the contribution of heredity to individual differences in personality, mental ability, and other human characteristics
How much of the differences among people are due to their genes and how much are due to the environment? Genes cannot be described in isolation: they can
only be characterized in relation to the environments in which they operate
Nature vs. Nurture
No one argues in terms of nature or nurture today, but rather scientists understand that heredity and environment interact to produce not only our psychological traits but even our most physical traits (i.e. body weight)
Nature-Nurture: Body Weight
Previous belief: emotional disturbance, heaviness caused by over-eating
Now: set-point (the weight you stay at when you are not trying to gain or lose)
In U.S., half of adult population is overweight – obesity genes have not changed that fast.
Twin Studies
Identical twins: same egg, same genes, thus they develop from a single fertilized egg. May have separate placentas. Zygote splits (monozygotic)
Fraternal twins: different eggs, different genes, thus they develop from two fertilized eggs. They have separate placentas. Genetically no more similar than siblings. Two separate zygotes (dizygotic)
Identical Twins
More similar than fraternal twins in: Abilities Personality traits Interests Emotional stability Attitudes towards reading Playing sports Assisted suicide Divorce (5.5 times more likely compared to 1.6)
Identical Twins
Identical twins reported being treated alike. So is it experience or genes that are accounting for their similarities?
Separated Twins
More alike than fraternal twins raised together (MTS).
Identical twins share the same womb (that’s environmental) and crucial to brain development. While the IQ’s of identical twins are more similar, the IQ’s of fraternal twins are more similar than siblings even though they are genetically no more similar.
Adoption Studies
Why are children in the same family so different? Genes? Peer influence? Birth order? Life events?
Adoption studies Compared adopted kids with biological
and adopted parents
Adoption Studies
Findings? People who grow up together,
whether biologically related to not, do not much resemble each other in personality
Adopted children have traits more like there biological parents than there adoptive parents
Adoption Studies
So does adoptive parenting matter?
Attitudes, values , manners, faith, politics as identical as identical twins.
In adoptive homes, less neglect, abuse, divorce.
They score higher than biological parents on IQ tests.
Fewer problems than the children of mothers who changed their mind about adoption.
Temperament Studies
Examining how emotionally excitable an infant is ‘Easy’ babies are cheerful, relaxed & predictable ‘Difficult’ babies are more irritable, intense &
unpredictable Temperament is mostly stable and mostly based
on heredity Earlier temperament predicts later temperament and
behavior Identical twins have more similar temperaments than
fraternal twins
Assignment
Handout 3-5 Find someone you don’t know at
lunch today and complete the questionnaire.
Be prepared to discuss your findings.
Nature vs. nurture?
The environment has very little effect on personality development But that doesn’t mean that your parents
don’t effect you at all Their influence can be seen in your attitudes,
values, manners, religion, and politics
Most behaviors/traits are an interaction of your genes and the environment
Environmental Influence
Should we really blame the parents? NO in the environmental sense and YES in the
genetic sense Experience and brain development
Use it or lose it, especially early on Peer influence
Parents are necessary for early childhood survival – peers are necessary for lifelong survival
Peers are who we play with, work with, and eventually mate with
Environmental Influence
Genetic differences account for about half of our person-person differences in personality. What accounts for the rest? Parental nurture? Prenatal nutrition? Early stimulation? Peer influences? Culture?
Parental Influence
Recall, shared environmental influences account for less than 10% of children’s personality differences
What matters is how parents respond to a child’s genetically influenced characteristics (the “relationship-code” as termed by Reiss). The aggressive, fearless and impulsive boy
(criminal or astronaut?)
Parental Influence
Recall, shared environmental influences account for less than 10% of children’s personality differences
What matters is how parents respond to a child’s genetically influenced characteristics (the “relationship-code” as termed by Reiss). The aggressive, fearless and impulsive boy
(criminal or astronaut?)
Pre-natal Influence
Embryos receive different nutrition and varying exposure to toxic agents
Shared placentas (2/3 of identical twins) do not translate into equal blood supply. One twin can be “greedy” or be better positioned.
Early research is indicated that twins in separate placentas are less similar than twins in the same placenta
Experience & Brain Development
Studies with rats in impoverished environments.
Studies with string musicians show larger and more complex neurons.
Critical period for learning language.
What has been the most important influence in your life?
Peer Influence
As the child ages, parental influence decreases and peer influence takes over. Preschoolers will eat food with friends they
don’t eat at home Immigrant children lose parent culture if
placed with a peer group of nonimmigrants Teens who smoke have friends who smoke
Selection Effect: we seek out peers with similar attitudes and interests
Check out:
http://home.att.net/~xchar/tna/
For information on peer influence
Peer Influence
Cultural Influence
Culture The behaviors, ideas, attitudes, and traditions
shared by a large group of people Norms: the rules for accepted and expected
behavior (based on group membership) Regardless of the cultural norms of a group,
most are very successful at raising children One important consideration is that while
there are significant cultural differences present, we are still more alike than we are different
Gender – Biologically Speaking
Until the 7th week of pregnancy, all babies are female It’s the activation of testosterone in a fetus
that has the XY pair of chromosomes that triggers male organ production
In the fourth & fifth months, different brain patterns develop due to different levels of testosterone and ovarian hormones
Gender – Socially Speaking
Gender roles The expectations about how men and
women behave In nomadic cultures, there is minimal
gender role occurrence Boys and girls experience the same upbringing
In agricultural societies (of which ours originated), there are strict gender role structures in place
Most of our gender identity is acquired through social learning
Gender Roles
What pressure (if any) do you feel to conform to gender roles?
Conclusion
“To what extent to biology and society determine gender roles?”
Make some point form notes on the following video to discuss next class (watching this video at school is best). Go to the Annenberg site on the blog
and watch “#17 Sex and Gender” or “youtube” it.