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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 – – – – 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