Untangling Nature and Nurture Behavior Genetics: the study of the interaction of genes and environment on behavior

Heritability The percentage of trait variation in a group that can be attributed to genetic differences Depends on the population

Heritability Sara is very outgoing and agreeable Suzy is timid and non- conforming If this pair of IDENTICAL twins is my population, what percent of the personality differences is attributable to genetic differences between them? Thus, the heritability is 0%.

Heritability Joe and Hank are not related. At birth, both were placed in identical environments that were maintained identical until they were 10 years old. At 10, Joe is outgoing and friendly. At 10, Hank is withdrawn and shy. In this (very small) population, what is the heritability of their personality traits? In other words, what percentage of the difference is attributable to genes? 100%

How heritable is that trait? TraitPopulation Heritability Creativityadolescents25% Extraversionadults30-50% Autismgeneral90-95% Depressiongeneral40-55% Sleep qualitygeneral35% TV viewing3-5 year olds10-45% Religious beliefsgeneral0% Religious conservatism women40% Divorcegeneral55% Heightwomen92% The Stanton Peele Addiction Website

Identical Twins v.Fraternal Twins Same genes, Different genes, Same environmentSame environment Therefore, greater differences between the two groups indicate greater heritability (“Nature”). The trait might appear to have a large genetic component. Twin Studies

Criticism: 1)Do fraternal twins really have equally similar environments to identical twins? Differences in looks or inborn temperament may cause people to treat you differently. 2)Identical twins may share a placenta but fraternal twins do not. Thus, we can’t eliminate prenatal environments as the cause of the differences between the two groups.

Twin Studies Identical Twins Reared Together v.Identical Twins Reared ApartSame genes, Same environment Different environment Greater difference between these two groups indicates greater role of the environment (“nurture”).

Twin Studies Criticisms: 1)Adoption agencies try to place twins in similar families so the variation in environment may be small, and 2)There is a very limited sample.

Adoption Studies Is child more like adoptive parents… …or biological parents? Adoptive Parents - Nurture Biological Parents - Nature

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).

Your turn Analyze the behavior genetics research data to determine the role of nature and nurture in various traits.