1. The Nature-Nurture Debates The Pursuit of Heritability Nature-Nurture Debate –The debate over the extent to which human behavior is determined by genetics and the environment. Heritability –A statistical estimate of the percentage of the variability of a trait within a group that is attributable to genetic factors.

2. The Nature-Nurture Debates The Pursuit of Heritability Family Studies –Studies that estimate genetic influences through similarities of family members who vary in their degree genetic relatedness Twin-Study Method –A method of testing nature and nurture by comparing pairs of identical and fraternal twins of the same sex Adoption Studies –A method of testing nature and nurture by comparing twins and other siblings reared together with those separated by adoption

3. The Nature-Nurture Debates Genetic Influences Other studies of twins and adoptees show: –Genetic factors account for some differences in intelligence, verbal and spatial abilities, criminality, vocational interests, and aggressiveness. –There is a genetic component to psychological disorders, such as alcoholism, depression, and schizophrenia. –And, there is evidence for a genetic link to people’s attitudes toward issues and activities.

4. The Nature-Nurture Debates Environmental Influences The studies of twins and adoptees also support the importance of environmental influences. –Genetic differences typically account for less than 50 percent of the variation in personality. –Environmental factors account for the rest of the variation. –Nonshared environments play a vital role in a person’s development and may be equally, or more, significant compared to shared environments.

5. The Nature-Nurture Debates The Interplay of Nature and Nurture Genetic and environmental influences are not independent. –Identical twins receive more similar treatment from their parents compared to fraternal twins. People’s genetic makeup influences how they are treated by others, the environments in which they live, and the way they perceive and recall the details of that environment.