Genes v. Environment

Predispositions  Genes do not determine how we look or act, they predispose us It’s a possibility

Who Studies This Conflict?  Behavior Genetics Focus on the extent to which heredity accounts for individual differences in behavior and thinking Look at the effects of hereditary and environment  Evolutionary Psychology

Heritability  Extent to which the differences among people are attributable to genes  “inherit” “capable”  Can never say what percentage of an individual’s personality/intelligences is inherited  Heritability refers to the extent to which differences among people are attributable to genes  If we held constant environment, the heritability of a trait would increase

Study Techniques  Want to tease apart the influence of environment and heredity  Twin Studies Identical Twins: formed from one fertilized egg that splits in two; genetically identical ○ Reared apart and together Fraternal Twins: formed from separate fertilized eggs; are not more alike than ordinary siblings ○ Reared apart and together  A person whose identical twin has Alzheimer’s has a 60% risk of developing it; 30% if a fraternal twin  What about behavior? If you have a fraternal twin who has divorced the odds of you divorcing go up 1.6 times. If you have an identical twin – 5.5 times Researchers have concluded that people’s differing divorce risks are 50% genetic  Adoption Studies

Results  The story of Jim and Jim  Identical twins (regardless of environment) have similar Personalities Intelligence levels Abilities Attitudes Interests Fears Brain waves Heart Rate Temperaments (emotional reactivity and sensitivity)  Identical twins raised together had more personality similarities than identical twins raised apart  Criticisms Many similarities can be found between strangers

Results cont  Adopted children’s personalities are more similar to their biological parents Two adopted children reared in the same home are no more likely to share personality traits with each other than the child down the block  So does parenting matter?  Adopted children share similar with their adoptive parents regarding: Attitudes Values Manners Beliefs Faith Politics  Keep in mind, adoptive parents go through screening processes and child abuse, neglect, and divorce are rare in adoptive homes (meaning, adoptive homes have similar environments)

Why do children in the same family have such different personalities?  Unique peer experiences?  Because sibling relationships ricochet off each other, amplifying their differences?  Despite sharing half their genes, siblings have different combinations of genes an may evoke different kind of parenting?

Interaction  Some traits are fixed (we all have two eyes)  Most traits are liable to change with environmental experience  Genes can influence traits which affect responses, which affects environment A genetic predisposition makes a child restless and hyperactive  angry response from parents  stressful environment triggers genes to manufacture neurotransmitters leading to depression  Genes and environment work together  Genes do not act as a blueprint resulting in the same result no matter the context, instead they react to the environment Example: A particular gene will, in response to environmental stresses, help release a neurotransmitter involved in depression (gene doesn’t cause depression, but is part of the recipe)