1 Nature and Nurture What is the difference between behavior genetics molecular genetics and evolutionary psychology? What do we mean by nature and nurture?

2 Behavior Genetics: Predicting Individual Differences Behavior Geneticists study our differences and weigh the relative effects of heredity and environment

3 Behavior Genetics: Types of Research  Minnesota Twin Studies - Monozygotic (mz) and dizygotic (dz) twins separated at birth  Adoption studies Comparisons of adopted children and their biological and adoptive parents  Temperament studies findings. Role of heredity, predispositions and stability

4 Minnesota Twin Studies Studying the effects of heredity and environment on two sets of twins, identical and fraternal, has been valuable

5 MZ Twin Studies Identical Twins Reared Together v. Identical Twins Reared Apart Same genes,Same genes Same environment Different environment Greater difference between these two groups indicates greater role of the environment (“nurture”)

6 Separated MZ Twins and Similarities A number of studies compared identical twins raised separately from birth, or close thereafter, and found numerous similarities. Exploring the Traits of TwinsExploring the Traits of Twins NG Twins Separated Twins Personality, Intelligence Abilities, Attitudes Interests, Fears Brain Waves, Heart Rate

Twin Studies Criticisms: 1)Adoption agencies try to place twins in similar families so the variation in environment may be small, and 2)There is a very limited sample

8 Heritability (Coefficient) The percentage of trait variation within a group that can be attributed to genetic differences (v. environmental). For example, assume you all were raised in identical, enriched environments – all differences in I.Q. are then due to genetic difference (100% heritability) Determined by comparing MZ twins separated at birth. Remember, heritability estimates are NOT measures of the importance of genes in the production of a trait (e.g., I inherit 65% of my intelligence from…)

9 Group Differences If genetic influences help explain individual diversity in traits, can the same be said about group differences? No. Individual differences in weight and height are heritable (within a group), but nutritional influences have made westerners heavier and taller than their ancestors were a century ago, or others in the developing world. The notion of maximal expression

Adoption Studies Is child more like adoptive parents… …or biological parents?

Adoption Studies Note: Two related siblings that grow up in the same family are strikingly different in personality (as I’m sure many of you can attest to).

12 Temperament Studies Temperament refers to a person’s stable emotional reactivity and intensity. Identical twins research and that of Jerome Kagan (reactivity studies) suggest that temperament is fixed or stable, and under some genetic influence. Environmentalists vehemently disagree Kagan The TemperamentalistThe Temperamentalist

13 Nature and Nurture Dynamic While some traits are fixed (ear lobes, tongue curl, PTC) most behavioral traits are modified by or under the influence of environmental experience. Our previous understanding of Nature versus Nurture turned out to be a false dichotomy Genes can influence traits which affect responses. And so, environment can affect gene activity. In such circumstances genes are allowed to be expressed (e.g., a genetic predisposition to restlessness evokes an angry response from a parent which, in turn, results in fuller expression of the genetic tendency. Related notion of maximal expression

14 Role of Environment What do we mean by environment? Prenatal experiences, early childhood experience, parental and peer influence, culture… –Early experience – Rosenzweig’s and Greenough’s enriched environment studies, issue of developmental plasticity, synaptic pruning, and epigenetics research –Peer influence over parental? Judith Harris –Cultural influences, e.g., collective v. individualistic societies, cross-cultural research notes similarities and variations across culture

15 Prenatal Environment Identical twins who share the same placenta are more alike than those who do not, suggesting prenatal influences on psychological traits

16 Experience and Brain Development Early postnatal experiences affect brain development. Rosenzweig et al., showed that rats raised in enriched environments developed thicker cortices than those in impoverished environments. Subsequent work by Greenough

17 The Role of Parenting? Peer Influence? While biological inputs are significant, parenting does have a considerable effect on both biologically related and unrelated children Parenting Influences children’s Attitudes, Values Manners, Beliefs Faith, Politics

18 Peers are influential in such areas as learning to cooperate with others, gaining popularity, and developing interactions Judith Rich Harris’ Do Parents Matter?Do Parents Matter? The Role of Peer Influence

19 Cultural Influences on Behavior Cultures differ. Each culture develops norms – rules for accepted and expected behavior. Men holding hands in Saudi Arabia is the norm. Norms are behavioral expectations; what is allowed to be by the group

20 Epigenetics and Gene Expression Epigenetics refers to changes in gene expression caused by environmental factors, not by changes in the underlying DNA sequence. Changes may remain for the remainder of the cell's life and may last for multiple generations. However, there is no change in the underlying DNA sequence of the organism, instead, environmental factors cause the organism's genes to behave (or "express themselves") differently ScienceNow Epigenetics BBC Article

21 Reflections on Nature and Nurture: Bio-PsychoSocial Influences

22 Molecular Genetics: Promises and Perils Molecular geneticists are currently seeking to identify genes that put people at risk for specific disorders This raises ethical issues involving choices to abort or even alter genes related to genetic predispositions - Mental illness, Addiction? Criminality? Homosexuality?

23 Evolutionary Psychology Evolutionary psychology studies why we as humans are alike. In particular, it studies the evolution of behavior and mind using principles of natural selection

24 Human Sexuality Gender Differences in Sexuality Question (summarized)MaleFemale Casual sex60%35% Sex for affection25%48% Think about sex everyday54%19%

25 Evolutionary Psychology  Critiquing the Evolutionary Perspective  The central premise is impossible to prove. Predictive power is null.  It’s hindsight bias, reductionist and dangerous. Potential justification for harmful behaviors and attitudes  EPs respond  EP does not imply genetic determinism, in fact adaptation is premised in environmental influence  EP instructs us to change our destructive evolutionary behaviors