The Nature-Nurture Debates Introducing Psychology 4/4/2019 The Nature-Nurture Debates Extreme biological position Personality traits, physical characteristics, etc. are all programmed or “hard-wired” Extreme environmental position All traits and characteristics are shaped by life experience So how do we study this??? ©2001 Prentice Hall

Introducing Psychology 4/4/2019 Twin-Study Method Comparison of pairs of identical and fraternal twins of the same sex Identical Twins Are genetic clones - genetically identical Share DNA, but not fingerprints Have identical brain wave patterns Occur once every 254 births Adoption Studies Comparison of twins and other siblings reared together with those separated by adoption ©2001 Prentice Hall

Twin and Adoption Studies Identical Versus Fraternal Twins

Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

Introducing Psychology Genetic influences 4/4/2019 Nature and Nurture Genetic influences Based on the Minnesota personality studies: When raised together, monozygotic twins are more similar than dizygotic twins. MZ Twins raised apart are almost as similar to each other as those living in the same home. Prepared by Michael J. Renner, Ph.D. These slides ©2001 Prentice Hall Psychology Publishing. ©2001 Prentice Hall

Where does this leave you? . Where does this leave you?

The Nature-Nurture Debates Introducing Psychology 4/4/2019 The Nature-Nurture Debates 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. ©2001 Prentice Hall

The Nature-Nurture Debates This study involved 672 twins who rated their attitudes on various issues and activities. The results show some influence of genetic factors.

The Nature-Nurture Debates Introducing Psychology 4/4/2019 The Nature-Nurture Debates Genetic differences typically account for less than 50 percent of the variation in personality. Environmental factors account for the rest of the variation. ©2001 Prentice Hall

The Nature-Nurture Debates A study of 5,542 three-year-olds found that Children with older brothers had higher masculinity scores Children with older sisters had higher femininity scores These results support the nurture hypothesis.

How do we study and quantify nature vs. nurture? Heritability A statistical estimate of the percentage of the variability of a trait within a group that is attributable to genetic factors.

Heritability Intelligence (50%) Height (90%) O 1 What does it mean when we say something is heritable? Intelligence (50%) Height (90%) O 1 100 % down to genes 100 % down to environment

So 50% with respect to intelligence means that genetic influence explains 50% of the observed variation among people w.r.t. intelligence In other words, we are looking at the extent to which difference among people are attributable to genes Heritability means…

Each value only refers to the particular population studied and its unique range of genetic and environmental factors The more an environment varies, the greater their opportunity to account for individual differences and the lower heritable estimates are likely to be Heritability estimates are controversial because they can be misapplied and because their application is limited

The Nature-Nurture Debates The Interplay of Nature and Nurture Introducing Psychology 4/4/2019 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. ©2001 Prentice Hall

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