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