Download Heredity and Environment

Heredity and Environment
Michael Hoerger
Introduction
• 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
Heritability
• 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
h2
• 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
“Runs in families” = Heritable?
“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.”
Sorry, 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?
“Once a schizophrenic
always a schizophrenic”
“Alcoholism is a
disease you must
battle your entire life”
Sorry, 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?
“If a condition is heritable,
treat it with drugs”
“If a condition responds to
drugs, it is probably
heritable.”
Sorry, 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
h2 is a Constant?
“IQ, personality traits,
criminality, and
psychological disorders
are all highly heritable,
with h2 > .50!”
Sorry, 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?
“A new study has
finally found the gene
for schizophrenia!”
Sorry, 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 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.