Nature vs. Nurture: Understanding Individual Differences

1. Chapter 3 Nature, Nurture & Human Diversity

2. Behavior Genetics: Predicting Individual Differences Behavior Geneticists study how heredity and environment interact to influence psychological characteristics.

3. Genes: Our Codes for Life ChromosomescontainingDNA (deoxyribonucleic acid) are situated in the nucleus of a cell.

4. Genes: Our Codes for Life Segments within DNA consist of genes that make proteins to determine our development.

5. Genome Genome is the set of complete instructions for making an organism, containing all the genes in that organism. Thus, the human genome makes us human, and the genome for drosophila makes it a common house fly.

6. Twin Biology Studying the effects of heredity and environment on two sets of twins, identical and fraternal, has come in handy.

7. Twins Studies Behavior geneticists’ study identical and fraternal twins to determine the role of genes in behavior, personality, etc.

8. Famous Ongoing Identical Twin Study: • University of Minnesota Twin Family Study • Founded by Thomas Bouchard & Currently led by David Lykken • Basic Findings: • Identical Twins tend to share similar personality traits, levels of intelligence, likes/dislikes/fears, brainwaves and heartbeat patterns • Identical twins separated at birth and raised separately also tend to show such similar traits • Most Famous Example of subjects: Jim Lewis and Jim Springer • Both had been married twice • Both had sons named James Alan/James Allan • Both smoked the same brand of cigarettes and drank the same kind of beer • Both worked as part-time sheriffs • Both suffered stress-related migraines • Both bit their fingernails • Both built a circular bench around a tree in their front yards • Both had dogs named “toy” • Scored similarly on intelligence and personality tests • Had similar speech patterns

9. A Note of Caution about Separated Twins Studies: • Critics of separated twin studies note that such similarities • can be found between strangers. • can be a result of placement of separated twins into similar families • are based on a few examples as opposed to a wide range of examples • In response, the separated twin researchers point out that differences between fraternal twins are greater than identical twins.

10. Adoption Studies • Used to study the effects of nurture/environment on behavior, personality, etc. • Basic findings: • Adoptees tend to have more similar personality traits to their birth parents than to their adoptive families • Furthermore, siblings (biologically related or not) do not tend to show the same personality traits. • But, children (adopted or not) tend to show similar attitudes, values, morals, political tendencies as do the parents who raised them • Adopted children tend to be very well-adjusted people!

11. Temperament Studies • Temperament refers to a person’s stable emotional reactivity and intensity. • Identical twins express similar temperaments, suggesting heredity predisposes temperament.

12. Heritability • Heritability refers to the extent to which the differences among people are attributable to genes. • In other words, if the environment is equal, then the results between two individuals would be more attributable to genetic factors (high heritability). • Or, if the environment is vastly different, but the genetic factors similar, the results would be due to low heritability

13. Group Differences If genetic influences help explain individual diversity in traits, can the same be said about group differences? Not necessarily. Individual differences in weight and height are heritable and yet nutritional influences have made westerners heavier and taller than their ancestors were a century ago.

14. Nature and Nurture Some human traits are fixed, such as having two eyes. However, most psychological traits can change with environmental experience. Genes provide choices for the organism to change its form or traits when environmental variables change. Therefore, genes are pliable or self-regulating. In other words, genes react to the environmental conditions.

15. Gene-Environment Interaction Genes can influence traits which affect responses, and environment can affect gene activity. Genes and environment interact. A genetic predisposition that makes a child restless and hyperactive evokes an angry response from his parents. A stressful environment can trigger genes to manufacture neurotransmitters leading to depression.