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 Why and 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 smart than others Nature Nurture Problem them that way Methodological Problems Are people different because they re born that way or their environment makes Most of the time parents raise their own biological children thus providing them with 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 traits Francis Galton and the Beginnings of Behavior Genetics Galton child prodigy was born Feb 16 1822 from a wealthy family and is the Half 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 men had more eminent relatives Limitations Families provide environments as well as genetics obviously people from wealthier families would be more eminent proposed twin and adoption studies 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 different environmentally 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 same sex and 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 DZ Twinning Placental membranes that begin to form day 4 MZ pairs are either monochrionic 75 or dichrionic 25 All DZ twins are dichorionic 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 Mean arithmetic avg Variance differences around a mean measure of a spread of a distribution Analysis of Variance correlation Variance and Twins Sources of Variance MZ Twins share all their genes and their family environment A C DZ Twins share half their genes and their family A C 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 C Shared Environment How much of our difference comes from being raised in E Nonshared Environment How much people vary AFTER considering genes Always about Differences separate families and families everything else Eugenics and the Nazis Charles Davenport Eugenics Record O ce Biological Lab Experimental Evolution Basic studies of eye color and stature Moved on to personality and intelligence Harry Laughlin Established Eugenics Record o ce 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 Law Animal 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 restricted environments seriously interferes with the development of behavior Lessons from Reading Dog breeds differ in trainability but there doesn t seem to be anything xed like intelligence among dog breeds Some breeds are better at responding to humans at active things at resisting emotionality and some are more less prone to ghting Adoption 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 biological parents or adoptive parents Group Differences Differences in average outcome in adopted children compared 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 bio mothers or siblings nurture Iqs of chldren are better predicted by their bio parents rather than adoptive parents nature Quiz 2 The 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 Summary 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 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 Three Laws of Behavior Genetics Three Laws of BG We aren t depressed because of experiences we re depressed because of genes Everything is heritable Families contribute a relatively small portion of the variability in genetically Most variability in human behavior cannot be predicted from genes or informed studies environment Most complex behaviors are more genetic than we thought Problems A lot of statistical assumptions made for twin studies to work BG ignores the real environment Partitions variance doesn t identify causes Leads to reductionist reactionary or racist conclusions First law complications Everything is heritable Heritability of X doesn t mean there s a gene for X Many