Transcript Nature and Nurture

Nature and Nurture
What makes us both similar and
different from each other?
Similarities
• All humans are virtually identical
– 99.9% of your genes are shared by ALL
humans (we are all ~twins)
– Shared biology and behavioral characteristics
• Language, form social groups, metabolize
food, brain structure
• What produced this unique human
constellation?
Differences
• Individual Differences abound
– Tiger Woods, Einstein, Ted Bundy, you and
your siblings
• 3 Billion nucleotide string in human DNA
(ATCG)
– Humans differ on .1% or 3,000,000 proteins
What makes us similar and
different from each other?
• Similarity due to species evolution (99.9%)
– Evolutionary Psychology
• Differences due to genes (.1%) and their
interactions with the environment
– Behavioral Genetics
Evolutionary Psychology
• Attempts to understand universals in human
behavioral characteristics
• Animal research & natural selection for
physical and behavioral characteristics
– Snakes and vibration, size, coloring (rattler)
– Wolves and loyalty
– Sharks and smell, teeth
Evolutionary Psychology
• Characteristic facilitate survival selected for
– Genes that produce sharper teeth or loyalty
passed on to next generation
– Over long expanse of time these features
became part of that species
• Selected characteristics dependent on
adaptational challenges
– Differed across species and environment)
Evolutionary Psychology
• Human evolution though to occur similarly
• All modern humans’ ancestors faced similar
adaptational challenges
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Social groups
Sensory abilities (vision and audition restricted)
Bodies and brains
Creativity, learning, flexible problem solving,
abstract thought, self-awareness
– Even how we respond to...
Evolutionary Psychology
Evolutionary Psychology
• Physical structures, behavioral tendencies,
cognitive abilities due to natural selection
• Human evolution has endowed us with
capacity to learn and adapt to change
– Does not doom us to preprogrammed,
instinctual behavior
– Allows us to continue to learn and develop
Evolutionary Psychology
• Passive influence
– Hardwired to have certain characteristics
because those who did in the past put more
genes into human gene pool
– No will/awareness need be invoked
Evolutionary Psychology
• Person with Trait B reproduces more
• Trait B becomes more common in
population
Evolutionary Psychology
• Gender differences in sexuality
– Males:
• Use more pornography
• Initiate sex more
• Think about/have sex more often
• Interpret friendliness as sexual come-on
Evolutionary Psychology
• How would you respond if an average looking
stranger of the opposite sex said to you,
– “I have been noticing you around campus and I find
you to be very attractive. Would you go to bed with
me tonight?” ?
• 75% of males said yes / 0% females said yes
• Why all these differences in sexuality?
Evolutionary Psychology
• Early humans developed sex strategy that met
their unique reproductive challenges
– Males can father *infinite* number of children w/
little parental investment but no paternity certainty
– Females - can have only few children (1/yr) w/
large parental investment & paternal certainty
Evolutionary Psychology
• Both want to maximize reproduction
– Males desire sex with many anonymous
partners who exhibit signs of health/fertility
– Females desire sex with fewer partners who
exhibit loyalty and resources
• Women pair wisely and men pair widely
Evolutionary Psychology
• Survey of mate preferences in 37 countries
supports these predictions
– Males prefer youthful, healthy, fertile beauty
– Females prefer mature, dominant, affluent,
resourceful, loyal men (dads > cads)
Problems with Evolutionary
Psychology
• Post-hoc (IV after DV)
• Circular logic
–Social because it aided
survival
–How do you know?
–Because we are still social
• Distal not proximal IV
• Environment also key
• Reinforces sex stereotypes
• Weak predictor
–Gender differences in mate
preference small compared to
universal desire for kind,
honest, intelligent mates
Evolutionary Psychology Summary
• Explains human characteristics through
principles of natural selection and evolution
• Argues that our shared characteristics are
due to a common genetic make-up produced
through eons of natural selection of genes
that maximized survival
• Although not problem free, Evol Psych
provides a unifying theory that offers many
testable hypotheses
Behavioral Genetics
• Attempts to understand basis for individual
differences
– Genes and environment
Behavioral Genetics
• Methods to tease these 2 apart
Identical
twins
Fraternal
twins
Same
sex only
Same or
opposite sex
–Twin studies
•Confounds environment
–Twin separation studies
•Separates genes and environment
–Adoption studies
•Compares biological w/ adoptives
Behavioral Genetics
• Results
– Consistently results show that identical twins
and biological relatives are more alike than
fraternal twins or adoptive relatives (even when
separated at birth!)
Behavioral Genetics
• Genes account for
~50% of variability
–Intelligence
–Personality
–Sexual orientation
–Mental illness
–Divorce & career choice
Behavioral Genetics
• Genes are key but they do not work in isolation
• Genetics provide framework but complex
interactions between genes & environment
determine what we feel, think and do
– Genes provide system of roads and interactions
with environment determine where you go
– Genes provide range and environment determines
position
Behavioral Genetics
• Identical twins
• Sue & Lori
• Whose IQ will be highest?
• PKU
• Recessive gene unable to metabolize amino acid
• Produces retardation ONLY if child injects this
acid often found in diet soda
Behavioral Genetics
• Genes passively impact environment &
environment responds to genes
– Cranky baby
– Non-common family environments
• Siblings reared together are often unique
• Genes also actively impact environment
– Would you rather read or go to a party?
Molecular Genetics
• Attempts to understand which genes
produce which characteristics
• Human Genome Project
– Genetic counseling
– Selection for certain characteristics in babies
– Gattaca - will there be genetic discrimination?
Behavioral Genetics - Summary
• Explains individual differences through
genetic variation among people and
interactions with environment
• Argues that about 50% of the differences
due to genes and interactions with
environment
• Implications for society
Environmental Influences - the
other 50%
• Parenting/rearing
– Weak influence on behavior
– Shared environ accounts for < 10% of
personality
– Parents are less to blame than thought
• Prenatal
– Very important influence on behavior
– Placenta placement, nutrition, hormones
Environmental Influences - the
other 50%
• Experience (early and late)
– Early helps shape brain connections
– Enriched environment increases brain weight
by 7% and neuron connections by 20%
– Similar effects among elderly rats (Greenough)
– Throughout lifespan experience changes brain
• Culture, peers & ender (see text)
Nature & Nurture Summary
• Nature AND nurture are key influences
• Genes dictate overall plan and accounts for
most similarities
• Experience directs the details and interacts
with genes to account for most differences
Nature & Nurture - the lighter
side