Lecture Outline

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• Lecture Outline
• What is Development?
• Themes/Issues in Developmental Psychology
• Developmental Systems Theories

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• What is development?
• Development refers to systematic, successive
  changes in the individual that occur over time
  from conception to death

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• Themes/Issues in Developmental Psychology
• Is development due to nature (genes) or nurture
  (environment)?
• Genetic and environmental factors influence all
  aspects of development
• But still debate about the role of genetic and
  environmental factors in development
• Should we be asking How much? or How?

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• Family Studies
• Compare individuals with different degrees of
  genetic relatedness on a particular
  characteristic
• Exs twin studies, adoption studies

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• Twin Studies
• Compare identical twins to fraternal twins on a
  particular characteristic
• Identical twins share 100 of their genes and
  fraternal twins share 50 of their genes
• If identical twins are more similar than
  fraternal twins with respect to a particular
  characteristic, assumed that genes influence the
  characteristic

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• Concordance Rate
• The percentage of instances in which both twins
  show a trait when it is present in one twin
• Used for categorical traits (present/absent)
• Ex schizophrenia, depression
• If concordance rate is higher for identical than
  for fraternal twins, assumed that genetic factors
  influence the trait

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• Heritability Coefficient
• Estimates the extent to which individual
  differences in characteristics are due to genetic
  influence
• Used for continuous characteristics
• Ex IQ, personality traits
• Ranges from 0 to 1
• 1 H environmental influence

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• Important Points (Heritability Coefficients)
• Apply to populations (groups), not individuals
• Correct 50 of the variation in IQ in a
  specific population is due to genetic factors
• Incorrect 50 of my IQ is due to my genes

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• Heritability coefficients are specific to a
  particular population and cannot be generalized
• G E 1
• The more environments vary, the lower
  heritability estimates will be (and vice versa)
• Ex Heritability of IQ is higher in middle- and
  upper-class samples than in low-income samples
• Less variability in the environments of middle-
  and upper-class children

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• Characteristics that are heritable can also be
  modified by the environment
• Ex Height is highly heritable, but average
  height has increased across successive
  generations due largely to environmental factors
  such as improved nutrition

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• Criticisms of (Traditional) Behavior Genetics
• Does not explain how specific genetic and
  specific environmental factors affect development
• Assumes that effects of genes and environment are
  independent and additivei.e., that genetic and
  environmental influences can be separated
• Does not account for interactions between genetic
  and environmental factors very well
• Does not account for correlations between genes
  and environment very well

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• Childrens genes are correlated with the
  environments they experience
• Some researchers (e.g., Rowe, 1994 Scarr
  McCartney, 1983) argue that genetic factors drive
  development because they influence the
  environments that children experience or select
  for themselves

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• Developmental systems theorists argue
• Genetic and environmental factors are fused in
  development
• There are bidirectional influences between
  genetic/biological factors within the individual
  and all levels of the environment

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• Alternative Perspectives
• Genes may affect the environments that children
  experience and select for themselves
• But the expression of genes is also affected by
  the type of environment(s) available to a child
• Environmental influences can affect genetic
  activity

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• Developmental continuity and discontinuity

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• Continuous (Quantitative)
• Gradual, small, steady increases in
  skills/abilities

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• Discontinuous (Qualitative)
• Relatively abrupt changes (stages) that involve a
  re-organization of skills/abilities

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