Nature, Nurture

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• Chapter 3
• Nature, Nurture
• Human Diversity

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Behavior Genetics Predicting Individual
Differences
Behavior Geneticists study how heredity and
environment interact to influence psychological
characteristics.
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Genes Our Codes for Life
Chromosomes containing DNA (deoxyribonucleic
acid) are situated in the nucleus of a cell.
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Genes Our Codes for Life
Segments within DNA consist of genes that make
proteins to determine our development.
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Genome
Genome is the set of complete instructions for
making an organism, containing all the genes in
that organism. Thus, the human genome makes us
human, and the genome for drosophila makes it a
common house fly.
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Twin Biology
Studying the effects of heredity and environment
on two sets of twins, identical and fraternal,
has come in handy.
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Twins Studies
Behavior geneticists study identical and
fraternal twins to determine the role of genes in
behavior, personality, etc.
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Famous Ongoing Identical Twin Study

• University of Minnesota Twin Family Study
• Founded by Thomas Bouchard Currently led by
  David Lykken
• Basic Findings
• Identical Twins tend to share similar personality
  traits, levels of intelligence,
  likes/dislikes/fears, brainwaves and heartbeat
  patterns
• Identical twins separated at birth and raised
  separately also tend to show such similar traits
• Most Famous Example of subjects Jim Lewis and
  Jim Springer
• Both had been married twice
• Both had sons named James Alan/James Allan
• Both smoked the same brand of cigarettes and
  drank the same kind of beer
• Both worked as part-time sheriffs
• Both suffered stress-related migraines
• Both bit their fingernails
• Both built a circular bench around a tree in
  their front yards
• Both had dogs named toy
• Scored similarly on intelligence and personality
  tests
• Had similar speech patterns

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A Note of Caution about Separated Twins Studies

• Critics of separated twin studies note that such
  
• similarities
• can be found between strangers.
• can be a result of placement of separated twins
  into similar families
• are based on a few examples as opposed to a wide
  range of examples
• In response, the separated twin researchers point
  out that differences between fraternal twins are
  greater than identical twins.

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Adoption Studies

• Used to study the effects of nurture/environment
  
• on behavior, personality, etc.
• Basic findings
• Adoptees tend to have more similar personality
  traits to their birth parents than to their
  adoptive families
• Furthermore, siblings (biologically related or
  not) do not tend to show the same personality
  traits.
• But, children (adopted or not) tend to show
  similar attitudes, values, morals, political
  tendencies as do the parents who raised them
• Adopted children tend to be very well-adjusted
  people!

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Temperament Studies

• Temperament refers to a persons stable emotional
  reactivity and intensity.
• Identical twins express similar temperaments,
  suggesting heredity predisposes temperament.

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Heritability

• Heritability refers to the extent to which the
  differences among people are attributable to
  genes.
• In other words, if the environment is equal, then
  the results between two individuals would be more
  attributable to genetic factors (high
  heritability).
• Or, if the environment is vastly different, but
  the genetic factors similar, the results would be
  due to low heritability

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Group Differences
If genetic influences help explain individual
diversity in traits, can the same be said about
group differences?
Not necessarily. Individual differences in weight
and height are heritable and yet nutritional
influences have made westerners heavier and
taller than their ancestors were a century ago.
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Nature and Nurture
Some human traits are fixed, such as having two
eyes. However, most psychological traits can
change with environmental experience.
Genes provide choices for the organism to change
its form or traits when environmental variables
change. Therefore, genes are pliable or
self-regulating. In other words, genes react to
the environmental conditions.
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Gene-Environment Interaction
Genes can influence traits which affect
responses, and environment can affect gene
activity. Genes and environment interact.
A genetic predisposition that makes a child
restless and hyperactive evokes an angry response
from his parents. A stressful environment can
trigger genes to manufacture neurotransmitters
leading to depression.