UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Shared Human Nature Behavior Genetics In all cultures, we start fearing strangers at about 8 months We are uniquely similar as a human race Genes = Nature Environments = Nurture Both genes and environment play a part in shaping us Behavior Genetics is the study of the relative power and limits of nature and nurture on behavior

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Genes Genes Each human has 46 chromosomes 23 from mother’s egg 23 from father’s sperm Chromosomes are found within a cell’s nucleus DNA is found within each chromosome Genes are found within each strand of DNA Genes may be active (“turned on”) or inactive (“turned off”). Environmental events are responsible for “turning on” genes. Our DNA sequence is 96% the same as a chimpanzee. Our observable traits such as height are influenced by our genes.

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Twin & Adoption Studies Twin & Adoption Studies Identical Twins – develop from a single fertilized egg that splits in two (identical genes) May not always have the same number of copies of those genes 1 in 3 sets develop in separate placentas Fraternal Twins – develop from separate fertilized eggs (no more genetically similar than any other sibling) In virtually all ways, identical twins are more similar than fraternal twins Shared experiences Divorce rates Genes more than shared experiences account for differences in identical twins

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Twins University of Minnesota Study Separated identical twins Jim Lewis and Jim Springer had amazingly similar life experiences without having contact with one another for 38 years When measuring personality, intelligence, heart rate, and brain waves, their results were as those of the same person tested twice! U of MN researcher Bouchard studied 80 pairs of identical twins that were raised apart Found similarities in personality, abilities, attitudes, interests, fears “…the plural of anecdote is not data…”

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Biological vs Adoptive Relatives Biological vs Adoptive Relatives Key question: Are adopted children more like their biological parents or their adoptive parents? In the area of personality, they are closer to biological parents Environments shared by children have NO discernible impact on personality Parenting has less influence on personality, but a greater influence on: Attitudes Values Manners Faith/Religious Views Political Views

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Adoptions Temperament & Heredity Adoptive parents are carefully screened; natural parents are NOT 7/8 adopted children feel a close bond to adoptive parents Big Picture: children benefit from adoption Many times adopted children outperform their biological parents (stability, intelligence) Temperament = emotional reactivity and intensity Irritable, intense, unpredictable Cheerful, relaxed, predictable Temperament persists over the long haul, although some change is possible Heredity predisposes temperament differences

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Temperament & Heredity Heritability “Our biologically rooted temperament helps form our enduring personality.” Heritability – the extent to which variation among individuals can be attributed to their differing genes. We can never say what % of an individual’s intelligence or personality is actually inherited. The key here is “differences among people”

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Group Differences Nature and Nurture Individual differences in height and weight are highly heritable. Differences in males vs females or in people of varying ethnicities cannot be easily explained through heritability. Humans have an enormous adaptive capacity. Genes are self-regulating The same gene that makes the African butterfly green in the summer, makes it brown in the fall Humans with very similar genes may have very different experiences, therefore the genes may be expressed differently.

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Nature and Nurture Nature and Nurture Eating disorders are primarily a Western cultural phenomenon Not found in most other cultures Definitely a product of both nature and nurture “Heredity deals the cards; environment plays the hand.”

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Gene-Environment Interaction Gene-Environment Interaction Baby who is attractive, sociable, and easy-going may attract more affectionate and stimulating care. This in turn may lead the individual to be a warmer and more outgoing person, more often seeking activities and friends. Children experience being parented based on their own qualities. We should start thinking “nature via nurture”.

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Molecular Genetics Molecular Genetics Goal Find genes that influence human traits Explore mechanisms that control gene expression Procedure Seek out families that have had a disorder across several generations Draw blood from both affected and healthy family members Examine DNA to look for differences and hopefully identify genes on which to focus their attention

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Ethical Considerations Evolutionary Psych Might early testing of embryonic qualities lead to discrimination? Boys valued in China Some famous Americans were troubled people Individuals may parent differently knowing their child is labeled “at risk” Organisms varied offspring compete for survival Biological and behavioral variations increase reproductive and survival chances Offspring that survive are more likely to pass their genes on to next generation Over time, population characteristics change

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Natural Selection & Adaptation Evolutionary Success Dmitry Belyaev – Russian scientist who studied possibility of domesticating foxes Carefully selected the most tame, docile foxes Over 30 generations of mating, the desired traits prevailed “Our shared human traits were shaped by natural selection acting over the course of human evolution.” -Steven Pinker -no more than 5% of genetic differences among humans arise from population group differences; 95% comes within groups

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Evolutionary Success Evolutionary Success Women’s experience of nausea during the first 3 critical months of pregnancy serves as a protective mechanism for developing embryo. Certain bitter, strong tasting foods may be poisonous to the developing baby. Sweet and fats once helped our ancestors survive famines Today famine is not a concern in Western cultures, and those same traits lead to obesity and other disease

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Human Sexuality Mating Preferences In almost every human culture, men exhibit a stronger sex drive than women Men more often than women attribute a woman’s friendliness to sexual interest Helps to explain sexual harassment and date rape Women’s approach to sex is usually more relational, and men’s more recreational Men usually find women attractive if they have a youthful appearance (evolutionary explanation = able to reproduce)

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Mating Preferences Mating Preferences Men prefer youth and health in seeking a partner Women prefer resources and social status in seeking a partner Young, middle-aged, and older men prefer women in their child-bearing years Women of all ages prefer men who seem dominant, mature, bold, and affluent (support and protection)

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Critiquing Evolutionary Perspective Parents & Peers The sexes, having faced similar adaptive problems, are far more alike than different Evolutionary perspective usually works from a hindsight explanation, which makes it look more correct than it may be. Rosenweig & Krech study on rats: Rats living in an enriched environment developed a heavier and thicker brain cortex. (Brain weights and number of synapses both increased). Those living in impoverished environments had thinner cortices.

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Parents & Peers Parents & Peers Stimulation by touch or massage help infants develop faster neurologically and gain weight faster. Neural pathways are broadened or pruned, depending on their early usage. In early childhood, excess neural connections are available – good time to learn another language. Some language must be mastered by adolescence, or no language may be mastered. (critical period)

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Parents & Peers Parenting In early years especially, the brain operates by the principle: Use it or Lose it! Are children easily wounded by normal parental mistakes? “Two children in the same family (are on average) as different from one another as are pairs of children selected randomly from the population.” – Plomin & Daniels (behavior geneticists) Children are NOT easily sculpted by parental nurture

UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY Peer Influence Peer Influence Especially during childhood and adolescence, we seek to fit into groups. Children get more of their culture from peers than from parents (adapt to peers characteristics). Children seek out friends with similar interests/habits as their own. Parents influence: Education, discipline, responsibility, orderliness, charitableness, and ways of interacting with authority. Peers influence: Cooperation, popularity, and ways of interacting with peers.