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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 additive—i.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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• Children’s 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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