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

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

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?”

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

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

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

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

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

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

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

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

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

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

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

Developmental continuity and discontinuity

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

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