Heredity and EnvironmentHeredity and Environment

Michael Hoerger

IntroductionIntroduction

• Long-standing debate: nature vs. nurture (heredity vs. environment, genetic diathesis vs. stress)

• Opinions fluctuate over time (multicontextual)

• What is the current zeitgeist?– Alcoholism, ADHD, schizophrenia, IQ,

personality traits, athletic and music ability

HeritabilityHeritability

• Definition: extent that observed differences on a trait or behavior are due to genes

• Psychologists and behavior genetics researchers attempt to estimate heritability using the heritability coefficient, h2

hh22

• Ranges from 0 to 1

• Higher h2 = genes estimated to account for more variation in a trait (genes are more important)

• Compares MZ twins to DZ twins, using complex calculations

• Only a very rough estimate, depends on the particular sample, time period, context

“Many traits, such as leadership, political skills, ideology, and moral strength, run in families. Look at the Bush family, the Kennedys, the Roosevelts. We are the product of good genes.”

““Runs in families” = Heritable?Runs in families” = Heritable?

Sorry, Mr. PresidentSorry, Mr. President

• If a trait runs in families, it could be due to…– Genes– Social learning (modeling)– Operant conditioning (rewards)– Sociocultural variables (SES)– Chance

Heritable = Unchangeable?Heritable = Unchangeable?

“Once a schizophrenic always a schizophrenic”

“Alcoholism is a disease you must battle your entire life”

Sorry, Dr. MeehlSorry, Dr. Meehl

• Some heritable traits are difficult to change

• Others change across generations (height)

• Some highly heritable conditions are easily modified:– Vision– Mental retardation due to Phenylketonuria

(PKU)

Heritable = Drug Treatment?Heritable = Drug Treatment?

“If a condition is heritable, treat it with drugs”

“If a condition responds to drugs, it is probably heritable.”

Sorry, Dr. BergerSorry, Dr. Berger

• Heritable conditions may respond just fine to social and behavioral interventions– Anxiety treatments– Bedwetting

• Heritability is not closely linked to the type of treatment that works

hh22 is a Constant? is a Constant?

“IQ, personality traits, criminality, and psychological disorders are all highly heritable, with h2 > .50!”

Sorry, Mr. MurraySorry, Mr. Murray

• h2 is only an estimate, depending on the…– Sample studied (e.g. Americans)– Historical context (time)– Location studied (place)

• h2 varies substantially by group, time, and place– Schizophrenia, depression, liberalism,

conscientiousness

Schizo-gene?Schizo-gene?

“A new study has finally found the gene for schizophrenia!”

Sorry, News MediaSorry, News Media

• There is no schizo-gene, or depression gene, or leadership gene

• Most psychological traits are complex, depending on…– Multiple genes interacting– Numerous environmental effects

In SummaryIn Summary

• Remember the Gould video!– Dangerous + harmful to label problems as

heritable and unchangeable when they are not

• Currently fashionable to make this mistake– Misunderstand heritability, ignore importance

of environment

Michael Hoerger

To cite this lecture:

• Hoerger, M. (2007, January 17). Heredity and Environment. Presented at a PSY 220 lecture at Central Michigan University.