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
OBJECTIVE 2| Describe the type of questions that interest behavior geneticists.

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
OBJECTIVE 4| Explain how identical and fraternal twins differ, and ways that behavior geneticists use twin studies to understand the effects of environment.

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.
A History of Twin Studies
Nancy Segal
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate

7. Twin Studies Criticisms:
Adoption agencies try to place twins in similar families so the variation in environment may be small, and
There is a very limited sample
A Second Look

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

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

11. 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 Temperamentalist
OBJECTIVE 6| Discuss how the relative stability of our temperament illustrates the influence of heredity on development.

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
OBJECTIVE 15| Describe some of the conditions that can affect development before birth.

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
OBJECTIVE 16| Describe how experience can modify the brain.

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

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
OBJECTIVE 20| Describe some ways that culture differ.

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
OBJECTIVE 30| Describe the biopsychosocial perspective on development.

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
OBJECTIVE 10| Describe the areas of psychology that interests evolutionary psychologists

24. Question (summarized)
Human Sexuality
Gender Differences in Sexuality
Question (summarized)
Male
Female
Casual sex
60%
35%
Sex for affection
25%
48%
Think about sex everyday
54%
19%
OBJECTIVE 12| Identify gender differences in sexuality.

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