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Chapter 4

CHAPTER 4 Psych 211

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Chris Burris

CHAPTER 4: PSYCH 211 – JANUARY 26, 2012 CHAPTER 4: BIOLOGY AND BEHAVIOR 1. Heritability and behavioral Genetics 2. Facultative Adaptation and Learning MEDIA REPORTS  E.g.: study shows that IQ is 67% a matter of genetics  What do these headlines mean? BEHAVIORAL GENETICS  What are the effects of genetic and environmental factors on behavior and development?  Claim: all behavioral traits are heritable e.g.: TV watching – does this mean that there’s a gene for watching? NO! 2 premises: 1. To extent that genetics is important: genotypic similarity --=> phenotypic similarity - People who are genetically similar have similar traits 2. To the extent that the environment is important: similar environment  phenotypic similarity - People who grew up In the same environment has the same traits - E.g.: performance of the kids are clustered in day cares; kids in one day care fail severely or in one day care where kids get high scores How do you do a behavioral genetic study? Look at some trait – e.g.: smart, sociable, aggressive, psychotic, height Family Study Look at correlations between: o Individual and close relatives o Individual and more distant relatives - Which correlations are higher? - This examples a genetic factor - Problem: families may share or differ in environments Adaption Study Look at correlations between: o Adopted person and adopted family (e.g.: parents, siblings) o Adopted person and biological family (e.g.: parents, siblings) - Which correlations are higher? Twin Studies: Look at correlations between o MZ twins o DZ twins - If MZ twins show stronger correlations, importance of genetics Adoption twin study: Compare: o Correlations between twins reared apart o Correlations between twins reared together - MZ twins reared together have high correlation (.86) - DZ twins reared together got lower correlation (.60) - Siblings reared apart have very low correlation (0.24) - MZ twins reared apart has pretty high correlation (0.76) – even higher than DZ twins together reared HERITABILITY  Statistical estimate of proportion of variance on a given trait among individuals in a given population that is attributable to genetic differences  E.g.: the country club example - race - High heritability score – score is accounted by genetics; Low heritability score – accounted by environment - Heritability score of speed is high – variance depends in genes - If they share the same environment the variance is probable due to genes and vice versa  E.g.: Race of 12 cloned individuals - Their population has none in terms of genetics - Their heritability score is low Limitations: 1. Heritability score applies to particular group in particular environment at particular time. e.g.: height in rich country vs. country with disparity - It cannot be generalized – low external validity - you can’t just have a single heritability score, it depends a lot on where you’re talking abt 2. Heritability does not inform about % contributions to individual, jus
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