Nature-Nurture Debate - Quiz 1● Behavior Genetics○ Study of how human behavior is influenced by genes○ Intellectual problems of human existence (Free wll + Mind body problem)● Species Typical is why humans in general are the way they are○ Why do we have two ears and one nose? Why are humans social beings? Whyand how are people intelligent?● Individual differences is about why humans differ from each other○ Why can people hear better than others? Why are some people more social/smartthan others?● Nature-Nurture Problem○ Are people different because they’re born that way or their environment makesthem that way?● Methodological Problems○ Most of the time, parents raise their own biological children thus providing themwith both genes and environment○ A lot of BG involves finding ways around this problem● Genetic Architecture○ There isn’t a gene for anything, yet most human traits are in some sense “genetic”○ Single gene disorders vs polygenic traitsFrancis Galton and the Beginnings of Behavior Genetics● Galton (child prodigy) was born Feb 16, 1822 from a wealthy family and is theHalf-cousin of Charles Darwin● Produced anthropological studies, founder of psychometrics, created first weather map,first person to undertake systematic study of fingerprints, influenced by origins of species(about evolution, not genetics)● Historiometry- searched through biographical studies to count whether “eminent” menhad more eminent relatives○ Limitations: Families provide environments as well as genetics, obviously peoplefrom wealthier families would be more eminent, proposed twin and adoptionstudies● Eugenics- Developed largely by Francis Galton as a method of improving the human race(racist, so largely abandoned after WW2)○ Popular amongst Liberals?Twin Studies● Galton assumed twins were similar genetically, and studies how they become differentenvironmentally (used twins in a different way they usually used today)● Two kinds of twins○ MZ, (monozygotic) genetically identical○ DZ, (dizygotic) ordinary siblings, 50% identical● Weingberg method○ Probability says that DZ twins should be ½ same sex and ½ opposite sex○ Twice the number of opposite sex twins should be total of DZ○ Rest are MZ○ Not perfectly correct (occasional op-sex MZ, mistakes about who is MZ and DZ)● Chorion○ Placental membranes that begin to form day 4○ MZ pairs are either monochrionic (75%) or dichrionic (25%)○ All DZ twins are dichorionic● DZ Twinning○ Only animals that produces MZ twins is the armadillo○ Rates of DZ twinning was declining, but is now increasing○ Rate varies with sunlight and runs in families● Analysis of Variance○ Mean- arithmetic avg○ Variance- differences around a mean, measure of a spread of a distribution(correlation)● Variance and Twins○ MZ Twins - share all their genes and their family environment (A + C)○ DZ Twins- share half their genes and their family ½ (A + C)● Sources of Variance○ A- Variability coming from additive effect of genes○ C- Variability coming from being raised in the same family○ E- Individual variability, random variability● ACE○ A=Heritability (ex. Proportion of height differences that comes from gender-Always about Differences)○ C= Shared Environment (How much of our difference comes from being raised inseparate families?)○ E= Nonshared Environment (How much people vary AFTER considering genesand families- everything else)Eugenics and the Nazis● Charles Davenport○ Eugenics Record Office, Biological Lab, Experimental Evolution○ Basic studies of eye color and stature○ Moved on to personality and intelligence● Harry Laughlin○ Established Eugenics Record office in Cold Spring Harbor○ Developed model sterilization law○ Nazi sympathizer● Laws against inter-racial marriage in 28 states (Virginia Racial Integrety Act 1924)○ Ex. Loving vs Virginia, Moved to VA, had to leave the state for 25 years● Carrie Buck○ 17 yr old from Charlottesville○ First person to be picked for sterilization under Virginia law○ Judge ruled she should be sterilized● First Nazi eugenics law was modeled on American LawAnimal Behavior Genetics● Inbred Strains○ No MZ twins for most animals○ Brothers and sisters mated together for at least 20 generations○ Average differences between strains are genetic○ Differences with strains environmental● It’s important that environmental conditions are controlled, however, restrictedenvironments seriously interferes with the development of behavior● Lessons from Reading○ Dog breeds differ in trainability, but there doesn’t seem to be anything fixed like“intelligence” among dog breeds○ Some breeds are better at responding to humans, at active things, at resistingemotionality, and some are more/less prone to fightingAdoption Studies● The most direct way to separate genetic and environmental influences on an outcome● Two Aspects of Adoption Studies○ Individual difference- what is a better predictor of child’s outcomes, biologicalparents or adoptive parents○ Group Differences= Differences in average outcome in adopted childrencompared to biological parents or non-adopted siblings● Summary of Adoption Studies on Intelligence○ Children from low income to high income environments have higher IQs than biomothers or siblings (nurture?)○ Iqs of chldren are better predicted by their bio parents rather than adoptive parents(nature)Quiz 2The Heydey of Twin Studies● Psychology After The War○ Psychoanalysis + Behaviorism● Cyril Burt○ Studied with Pearson and Spearman○ May have faked some of his data● Raymond Cattell○ Racist and anti-semite○ Invented a religion● Proband Method○ Hard to do “population” twin studies with traits that are rare○ Look for gay man w/ twins, ask if they’re gay and are they MZ or DZ● Summary○ MZ Twins are always more similar than DZ Twins○ Biological Parents are more predictive of adoptive kids than adoptive parents○ Pretty much everything seems to have substantial heritability○ Family effects are very difficult to find● Nature won the Nature-Nurture Debate● Psychoanalytic Explanations Are Wrong○ We aren’t depressed because of experiences, we’re depressed because of genesThree Laws of Behavior Genetics● Three Laws of BG○ Everything is heritable○ Families contribute a relatively small portion of the variability in geneticallyinformed